A base-catalyzed protocol is reported for the construction of 1,3-thiazolidine-2-thione scaffolds bearing quaternary carbon centers from carbon disulfide and α-tertiary propargylamines. The reaction proceeds using low catalyst loading, under ambient temperatures, and in the absence of solvent. Various α-tertiary propargylamines have been employed, affording a series of previously unreported thiazolidine-2-thione compounds and avoiding purification via column chromatography in certain cases. We also describe a one-pot strategy for the synthesis of the same products through a KA2 coupling-CS2 incorporation approach. The reaction mechanism and substituent-dependent catalytic behavior were studied through a combination of detailed experimental and computational studies.

The aminolysis reaction between MN’’2 (N’’ = N(SiMe3)2; M = Fe, Co, Ni) and the neutral pro-ligand 6,6'-(1,4-phenylenebis(propane-2,2-diyl))bis(2,4-di-tert-butylphenol) (LH2) affords the low coordinate, isomorphous, monomeric bis-aryloxide complexes (2-M) (M =...

The synthesis and characterisation of two square planar {PdNO}10 pincer complexes of the form [Pd(pincer)(NO)]+ (pincer = 2,6-(tBu2PCH2)2C5H3N, 1; 2,6-(tBu2PO)2C5H3N, 2) are reported. These complexes are readily isolated by phosphine substitution of T-shaped [Pd(PtBu3)2(NO)]+ 3 in THF and the bent nitrosyl coordination mode observed in 3 is retained, as evidenced by X-ray diffraction (∠PdNO ∼ 120°), IR spectroscopy and analysis of isotopically enriched samples by 15N NMR spectroscopy. Effective oxidation states of Pd0/NO+ are calculated for 1–3 and nitrosyl coordination is principally attributed to metal-centred σ-bonding, with supplementary π-backbonding. Computational analysis, however, indicates that the Pd−NO bonds in 1 and 2 have greater PdI/NO• character and σ-bonding is more prominent than in 3. These differences in bonding are manifested experimentally in more red-shifted nitrosyl stretching frequencies and the propensity of 1 and 2 to react with dichloromethane to afford palladium(II) chloride derivatives.

We report on the preparation, crystal structure and spectral properties of the novel trimethylsulfonium tin tribromide, [(CH3)3S]SnBr3. The compound was synthesized by the solid-state reaction of (CH3)3SBr and SnBr2 in evacuated pyrex tubes at 150 °C. Single-crystal X-ray diffraction (SCXRD) studies at −173.15 °C show that it forms a 0D network of isolated pyramids of [SnBr3]− and (CH3)3S+ units in an orthorhombic structure (space group P212121, No. 19, a = 9.4508(8) Å, b = 14.1691(12) Å, c = 15.4409(14) Å)). Powder X-ray diffraction (PXRD) and Le bail profile fit analysis reveals that [(CH3)3S]SnBr3 adopts at room temperature a different crystal structure with space group (Pmmm, No. 47). Moreover, the oxidation of the compound occurs gradually in ambient air, towards the formation of [(CH3)3S)]2SnBr6 (space group Pa-3, No. 205). Multi-temperature Raman spectroscopy reveals that a fully reversible structural phase transition occurs for [(CH3)3S]SnBr3 between −36 and −56 °C, as evidenced by the changes in the vibrational modes of the [SnBr3]− ions. A direct band gap of 3.38 eV at RT is determined via UV–vis diffuse reflectance spectroscopy. Photoluminescence spectroscopy at −196.15 °C and 25 °C shows a weak luminescence signal with an emission maximum at ca. 460 nm for both temperatures.

Thuwalamides A–E (1, 3, 5, 6 and 8), previously undescribed polychlorinated amides, along with ten previously reported related compounds (2, 4, 7 and 9–15), were isolated from the organic extract of the marine sponge Lamellodysidea herbacea (Keller), collected off the village of Thuwal in the Red Sea at Saudi Arabia. The structures of the isolated compounds have been determined through extensive analysis of their NMR and MS data, while their absolute stereochemistry was unequivocally established via single crystal X-ray diffraction. Additionally, the absolute stereochemistry of the previously reported compounds 2 and 4, whose configuration was not determined, has also been established using single-crystal X-ray crystallographic analysis. The antibacterial activity of compounds 1–15 was evaluated against Escherichia coli and Staphylococcus aureus. Among them, compound 14 displayed activity against S. aureus comparable to vancomycin that was used as a positive control with a MIC value of 4 μg/mL.

The pincer complexes [NiIIBr(CNC)]Br (4), [CrIIIBr3(CNC)] (5 a) and [CrIIIBr2.3Cl0.7(CNC)] (5 b), where CNC=3,3′-(pyridine-2,6-diyl)bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br2 and [NiIIBr2(PPh3)2] or from [CrII{N(SiMe3)2}2(THF)2] and (CHNCH)Br2 by aminolysis, respectively. The tetrahedrally distorted square planar (τ4≅0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone. Computational methods highlighted the dependence of the coordination geometry and the singlet-triplet energy difference on the size of the N-substituent of the tetrahydropyrimidine wingtips and contrasted it to the situation in 5-membered imidazolin-2-ylidene pincer analogues. The octahedral CrIII metal center in 5 a and 5 b is presumably formed after one electron oxidation from CH2Cl2. 4/MAO and 5 a/MAO were catalysts of moderate activity for the oligomerization and polymerization of ethylene, respectively. The analogous (CH^N^CH)Br2 precursor, where (CH^N^CH)=3,3′-(pyridine-2,6-diylbis(methylene))bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-1-ium), was also prepared, however its coordination chemistry was not studied due to the inherent instability of the resulting free C^N^C ligand.

Carbene-metal-amide (CMA) complexes of gold, silver, and copper have been studied extensively for their photochemical/photocatalytic properties and as potential (pre-)catalysts in organic synthesis. Herein, the design, synthesis, and characterization of five bench-stable Au-, Ag-, and Cu-NHC complexes bearing the benzotriazolyl anion as an amide donor, are reported. All complexes are synthesized in a facile and straightforward manner, using mild conditions. The catalytic activity of the Ag and Cu complexes was studied in propargylamide cycloisomerization and carbonyl hydrosilylation reactions. Both CMA-catalyzed transformations proceed under mild conditions and are highly efficient for a range of propargylamides and carbonyl compounds, respectively, affording the desired corresponding products in good to excellent yields.

The synthesis of thiazolines, thiazolidines, and thiazolidinones has been extensively studied, due to their biological activity related to neurodegenerative diseases, such as Parkinson’s and Alzheimer’s, as well as their antiparasitic and antihypertensive properties. The closely related thiazolidin-2-imines have been studied less, and efficient strategies for synthesizing them, mainly based on the reaction of propargylamines with isothiocyanates, have been explored less. The use of one-pot approaches, providing modular, straightforward, and sustainable access to these compounds, has also received very little attention. Herein, we report a novel, one-pot, multicomponent, copper-catalyzed reaction among primary amines, ketones, terminal alkynes, and isothiocyanates, toward thiazolidin-2-imines bearing quaternary carbon centers on the five-membered ring, in good to excellent yields. Density functional theory calculations, combined with experimental mechanistic findings, suggest that the copper(I)-catalyzed reaction between the in situ-formed propargylamines and isothiocyanates proceeds with a lower energy barrier in the pathway leading to the S-cyclized product, compared to that of the N-cyclized one, toward the chemo- and regioselective formation of 5-exo-dig S-cyclized thiazolidin-2-imines.

The synthesis, isolation, and characterisation of well-defined low-valent actinide complexes are reviewed with a main focus on compounds featuring uranium and thorium metal centres in formal oxidation states ≤ +3. The importance of the ligand environment in enabling access to these highly reactive species, as well as its influence on ground state electronic configurations and their reactivity, are emphasised. Furthermore, we highlight cyclic voltammetry (C.V.) studies as a more widely used method that can guide the synthesis of these highly reducing species.

Organometallic complexes of the formula [Ru(N^N)(p-cymene)Cl][X] (N^N = bidentate polypyridyl ligands, p-cymene = 1-methyl-4-(1-methylethyl)-benzene, X = counter anion), are currently studied as possible candidates for the potential treatment of cancer. Searching for new organometallic compounds with good to moderate cytotoxic activities, a series of mononuclear water-soluble ruthenium(II)–arene complexes incorporating substituted pyridine–quinoline ligands, with pending -CH2OH, -CO2H and -CO2Me groups in the 4-position of quinoline ring, were synthesized, for the first time, to study their possible effect to modulate the activity of the ruthenium p-cymene complexes. These include the [Ru(η6-p-cymene)(pqhyme)Cl][X] (X = Cl− (1-Cl), PF6− (1-PF6), pqhyme = 4-hydroxymethyl-2-(pyridin-2-yl)quinoline), [Ru(η6-p-cymene)(pqca)Cl][Cl] ((2-Cl), pqca = 4-carboxy-2-(pyridin-2-yl)quinoline), and [Ru(η6-p-cymene)(pqcame)Cl][X] (X = Cl− (3-Cl), PF6− (3-PF6), pqcame = 4-carboxymethyl-2-(pyridin-2-yl)quinoline) complexes, respectively. Identification of the complexes was based on multinuclear NMR and ATR-IR spectroscopic methods, elemental analysis, conductivity measurements, UV–Vis spectroscopic, and ESI-HRMS techniques. The solid-state structures of 1-PF6 and 3-PF6 have been elucidated by single-crystal X-ray diffraction revealing a three-legged piano stool geometry. This is the first time that the in vitro cytotoxic activities of these complexes are studied. These were conducted in HEK293T (human embryonic kidney cells) and HeLa cells (cervical cancer cells) via the MTT assay. The results show poor in vitro anticancer activities for the HeLa cancer cell lines and 3-Cl proved to be the most potent (IC50 > 80 μΜ). In both cell lines, the cytotoxicity of the ligand precursor pqhyme is significantly higher than that of cisplatin.

Organometallic ruthenium complexes with p-cymene = 1-methyl-4-(1-methylethyl)-benzene and N^N = bidentate polypyridyl ligands constitute interesting candidates with biological and catalytic properties. Towards this aim, we have synthesized four ruthenium(II)–arene complexes of the type [Ru(η6-p-cymene)(N^N)Cl][X] (N^N = Br-Qpy = 6-bromo-4-phenyl-2-pyridin-2-yl-quinoline, X = Cl− (1a); PF6− (1b); N^N = OH-Ph-Qpy = 4-(4-phenyl-2-(pyridin-2-yl)quinolin-6-yl)phenol, X = Cl− (2a); PF6− (2b)). This is the first report of ruthenium(II) p-cymene complexes incorporating substituted pyridine–quinoline ligands, with –Br and –C6H4OH groups in the 6-position of quinoline. We also refer to the cytotoxicity of the ligands and their possible effect of modulating the activity of the ruthenium(II) complexes. These were characterized by a combination of spectroscopic methods (ATR-IR, UV–Vis, multinuclear NMR), elemental analysis, and conductivity measurements. The solid-state structure of 2b, determined by single-crystal X-ray diffraction, reveals a three-legged piano-stool geometry. The in vitro cytotoxic activities of the new complexes were evaluated in HEK293T (human embryonic kidney cells) and in HeLa cells (cervical cancer cells), via the MTT assay. Poor in vitro anticancer activities were observed for the HeLa cancer cell line, with 2a being the most potent (IC50 = 75 μΜ). The cytotoxicity of Br-Qpy in HEK293T is comparable to that of cisplatin. Both complexes 1a and 1b successfully catalyze the transfer hydrogenation of benzophenone to benzhydrol by 2-propanol at 82 °C. The catalytic performance of 1a in the ratio of S:Cat:B = 400:1:40 (S = substrate, Cat = catalyst, B = base = KOiPr) leads to a conversion of 94%, within 3 h of reaction. Presumably, catalytic transformation takes place via ruthenium(II) hydride species being the active catalyst.

The synthesis and characterization of a homologous series of T-shaped {MNO}10 nitrosyl complexes of the form [M(PR3)2(NO)]+ (M = Pd, Pt; R = tBu, Ad) are reported. These diamagnetic nitrosyls are obtained from monovalent or zerovalent precursors by treatment with NO and NO+, respectively, and are notable for distinctly bent M-NO angles of ∼123° in the solid state. Adoption of this coordination mode in solution is also supported by the analysis of isotopically enriched samples by 15N NMR spectroscopy. Effective oxidation states of M0/NO+ are calculated, and metal-nitrosyl bonding has been interrogated using DFT-based energy decomposition analysis techniques. While a linear nitrosyl coordination mode was found to be electronically preferred, the M-NO and P-M-P angles are inversely correlated to the extent that binding in this manner is prevented by steric repulsion between the bulky ancillary phosphine ligands.

Despite the unique position of gold catalysis in contemporary organic synthesis, this area of research is notorious for requiring activators and/or additives that enable catalysis by generating cationic forms of gold catalysts. Cycloisomerization reactions occupy a significant portion of the gold-catalyzed reaction space, while they represent a diverse family of reactions that are frequently utilized in synthesis. Herein, hexafluoroisopropanol (HFIP) is shown to be a uniquely simple tool for gold-catalyzed cycloisomerizations, rendering the use of external activators obsolete and leading to highly active catalytic systems with ppm levels of catalyst loading in certain cases. HFIP assumes a dual role as a solvent and an activator, operating via the dynamic activation of the Au-Cl bond through hydrogen bonding, which initiates the catalytic cycle. This special mode of catalysis can enable efficient and scalable cyclization reactions of propargylamides and ynoic acids with simple [AuCl(L)] complexes. A thorough screening of ancillary ligands and counter anions has been performed, establishing this methodology as an alternative to elaborate ligand/catalyst design and to the use of activators. Additionally, this concept is applied in C-C bond-forming cycloisomerization reactions leading to 2H-chromenes and to the design of catalytic systems for sequential or one-pot transformations leading to activated ketoesters, a functionalized N-heterocyclic carbene (NHC) precursor salt, and a compound bearing the bioactive indole core, among others. Importantly, through mechanistic investigations, including a “snapshot” of the species of interest in the solid state, we were able to unambiguously detect the key H-bonding interaction between HFIP and the gold catalyst, shedding light on the intermolecular mode of activation that enables catalysis. In the cases examined herein, HFIP is not only an excellent solvent but also a potent activator and a valuable synthetic handle when incorporated into functional groups of products.

The chemical investigation of the organic extract of the red alga Laurencia majuscula collected from Hurghada reef in the Red Sea resulted in the isolation of five C15 acetogenins, including four tricyclic ones of the maneonene type (1–4) and a 5-membered one (5), 15 sesquiterpenes, including seven lauranes (6–12), one cuparane (13), one seco-laurane (14), one snyderane (15), two chamigranes (16, 17), two rearranged chamigranes (18, 19) and one aristolane (20), as well as a tricyclic diterpene (21) and a chlorinated fatty acid derivative (22). Among them, compounds 1–3, 5, 7, 8, 10, 11 and 14 are new natural products. The structures and the relative configurations of the isolated natural products have been established based on extensive analysis of their NMR and MS data, while the absolute configuration of maneonenes F (1) and G (2) was determined on the basis of single-crystal X-ray diffraction analysis. The anti-inflammatory activity of compounds 1, 2, 4–8, 10, 12–16, 18 and 20–22 was evaluated by measuring suppression of nitric oxide (NO) release in TLR4-activated RAW 264.7 macrophages in culture. All compounds, except 6, exhibited significant anti-inflammatory activity. Among them, metabolites 1, 4 and 18 did not exhibit any cytostatic activity at the tested concentrations. The most prominent anti-inflammatory activity, accompanied by absence of cytostatic activity at the same concentration, was exerted by compounds 5 and 18, with IC50 values of 3.69 μM and 3.55 μΜ, respectively.

Reaction of the syn-bimetallic complex [Ti2(µ:η5,η5-Pn††)2] (1) (Pn†† = 1,4-(SiiPr3)2-C8H4) with 1,3-trans-butadiene in toluene results in the clean formation of the 1:1 adduct [Ti2(µ:η5,η5-Pn††)2(μ: η2,η2-s-trans-C4H6)] (2) featuring an essentially planar butadiene ligand. Complex (2) represents the first example of a bimetallic early transition metal complex where a coordinated butadiene adopts such a conformation. When (1) is reacted with propene an unexpected “tuck-over” alkene π-complex (3) is formed with co-current loss of propane. Complex (3) features a coordinated η2,η1 vinylic (H2C = CMe)-SiiPr2-Pn† moiety as a result of C–H activation of one of the isopropyl substituents of the SiiPr3 groups on the Pn†† supporting ligand. One of the hydrogens of this secondary vinylic moiety is significantly shifted upfield in the 1H NMR spectrum of (3) and a single crystal XRD study shows an interaction between this hydrogen and one of the Ti centres. Preliminary kinetic studies of the formation of (3) show a slightly negative entropy of activation and 1st order consumption of (1) both of which suggest the involvement of a Ti-H(iPr) agostic interaction during the cyclometallation reaction.

Cyclobutadienyl complexes of the f-elements are a relatively new yet poorly understood class of sandwich and half-sandwich organometallic compounds. We now describe cyclobutadienyl transfer reactions of the magnesium reagent [(η4-Cb'''')Mg(THF)3] (1), where Cb'''' is tetrakis(trimethylsilyl)cyclobutadienyl, toward thorium(IV) and uranium(IV) tetrachlorides. The 1:1 stoichiometric reactions between 1 and AnCl4proceed with intact transfer of Cb'''' to give the half-sandwich complexes [(η4-Cb'''')AnCl(μ-Cl)3Mg(THF)3] (An = Th, 2; An = U, 3). Using a 2:1 reaction stoichiometry produces [Mg2Cl3(THF)6][(η4-Cb'''')An(η3-C4H(SiMe3)3-κ-(CH2SiMe2)(Cl)] (An = Th, [Mg2Cl3(THF)6][4]; An = U [Mg2Cl3(THF)6][5]), in which one Cb'''' ligand has undergone cyclometalation of a trimethylsilyl group, resulting in the formation of an An-C σ-bond, protonation of the four-membered ring, and an η3-allylic interaction with the actinide. Complex solution-phase dynamics are observed with multinuclear nuclear magnetic resonance spectroscopy for both sandwich complexes. A computational analysis of the reaction mechanism leading to the formation of 4 and 5 indicates that the cyclobutadienyl ligands undergo C-H activation across the actinide center. copy; 2022 American Chemical Society.

A series of hybrid uranocenes consisting of uranium(iv) sandwiched between cyclobutadienyl (Cb) and cyclo-octatetraenyl (COT) ligands has been synthesized, structurally characterized and studied computationally. The dimetallic species [(η4-Cb′′′′)(η8-COT)U(μ:η2:η8-COT)U(THF)(η4-Cb′′′′)] (1) forms concomitantly with, and can be separated from, monometallic [(η4-Cb′′′′)U(THF)(η8-COT)] (2) (Cb′′′′ = 1,2,3,4-tetrakis(trimethylsilyl)cyclobutadienyl, COT = cyclo-octatetraenyl). In toluene solution at room temperature,1dissociates into2and the unsolvated uranocene [(η4-Cb′′′′)U(η8-COT)] (3). By applying a high vacuum, both1and2can be converted directly into3. Using bulky silyl substituents on the COT ligand allowed isolation of base-free [(η4-Cb′′′′)U{η8-1,4-(iPr3Si)2C8H6}] (4), with compounds3and4being new members of the bis(annulene) family of actinocenes and the first to contain a cyclobutadienyl ligand. Computational studies show that the bonding in the hybrid uranocenes3and4has non-negligible covalency. New insight into actinocene bonding is provided by the complementary interactions of the different ligands with uranium, whereby the 6d orbitals interact most strongly with the cyclobutadienyl ligand and the 5f orbitals do so with the COT ligands. The redox-neutral activation of diethyl ether by [(η4-Cb′′′′)U(η8-C8H8)] is also described and represents a uranium-cyclobutadienyl cooperative process, potentially forming the basis of further small-molecule activation chemistry.

The reaction of the uranium(III) complex [U(η8-Pn††)(η5-Cp*)] (1) (Pn†† = C8H4(1,4-SiiPr3)2, Cp∗ = C5Me5) with ethene at atmospheric pressure produces the ethene-bridged diuranium complex [{(η8-Pn††)(η5-Cp*)U}2(μ-η2:η2-C2H4)] (2). A computational analysis of 2 revealed that coordination of ethene to uranium reduces the carbon-carbon bond order from 2 to a value consistent with a single bond, with a concomitant change in the formal uranium oxidation state from +3 in 1 to +4 in 2. Furthermore, the uranium-ethene bonding in 2 is of the δtype, with the dominant uranium contribution being from f-d hybrid orbitals. Complex 2 reacts with hydrogen to produce ethane and reform 1, leading to the discovery that complex 1 also catalyzes the hydrogenation of ethene under ambient conditions.

Reduction of the uranium(III) metallocene [(η 5 ‐C 5 i Pr 5 ) 2 UI] ( 1 ) with potassium graphite produces the “second‐generation” uranocene [(η 5 ‐C 5 i Pr 5 ) 2 U] ( 2 ), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground‐state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f 3 6d 1 . Appreciable covalent contributions to the metal‐ligand bonds were determined from a computational study of 2 , including participation from the uranium 5f and 6d orbitals. Whereas three unpaired electrons in 2 occupy orbitals with essentially pure 5f character, the fourth electron resides in an orbital defined by strong 7s‐6d mixing.

The 1:1 reactions of uranium(iv) tetrakis(borohydride) with the sodium and potassium salts of the cyclobutadienyl anion [C4(SiMe3)4]2- (Cb′′′′) produce the half-sandwich complexes [Na(12-crown-4)2][U(η4-Cb′′′′)(BH4)3] and [U(η4-Cb′′′′)(μ-BH4)3{K(THF)2}]2. In the 1:2 reaction of U(BH4)4 with Na2Cb′′′′, formation of [U(η4-Cb′′′′)(η3-C4H(SiMe3)3-κ-(CH2SiMe2)(BH4))]- reveals that a Cb′′′′ ligand undergoes an intramolecular deprotonation, resulting in an allyl/tuck-in bonding mode. A computational study reveals that the uranium-Cb′′′′ bonding has an appreciable covalent component with contributions from the uranium 5f and 6d orbitals.

The activation of C3O2 by the U(iii) complex [U(η5-Cp′)3] (Cp′ = C5H4SiMe3) is described. The reaction results in the reductive coupling of three C3O2 units to form a tetranuclear complex with a central cyclobutane-1,3-dione ring, with concomitant loss of CO. Careful control of reaction conditions has allowed the trapping of an intermediate, a dimeric bridging ketene complex, which undergoes insertion of C3O2 to form the final product.

The reaction of the bis(pentalene)dititanium complex Ti2(μ:η5,η5-Pn†)2 (Pn† = C8H4(1,4-SiiPr3)2) (1) with the N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene results in intramolecular C-H activation of an isopropyl substituent to form a tucked-in hydride (3). Whilst pyridine will also effect this cyclometallation reaction to form (5), the pyridine analogue of (3), the bases 1,2,4,5-tetramethyl-imidazole, 2,6-lutidine, DABCO or trimethylphosphine are ineffective. The reaction of (1) with 2,6-dichloro-pyridine affords crystallographically characterised (6) which is the product of oxidative addition of one of the C-Cl bonds in 2,6-dichloro-pyridine across the Ti-Ti double bond in (1). The tucked-in hydride (3) reacts with hydrogen to afford a dihydride complex (4) in which the tuck-in process has been reversed; detailed experimental and computational studies on this reaction using D2, HD or H2/D2 support a mechanism for the formation of (4) which does not involve σ-bond metathesis of H2 with the tucked-in C-H bond in (3). The reaction of (3) with tBuCCH yields the corresponding acetylide hydrido complex (7), where deuteration studies show that again the reaction does not proceed via σ-bond metathesis. Finally, treatment of (3) with HCl affords the chloro-derivative (9) [(NHC)Ti(μ-H)Ti{(μ,η5:η5)Pn†}2Cl], whereas protonation with [NEt3H]BPh4 yielded a cationic hydride (10) featuring an agostic interaction between a Ti centre and an iPr Me group.

The mixed sandwich U(III) complex {U[η8-C8H6(1,4-Si(iPr)3)2](Cp*)(THF)} reacts with the organic azides RN3 (R = SiMe3, 1-Ad, BMes2) to afford the corresponding, structurally characterised U(V) imido complexes {U[η8-C8H6(1,4-Si(iPr)3)2](Cp*)(NR)}. In the case of R = SiMe3, the reducing power of the U(III) complex leads to reductive coupling as a parallel minor reaction pathway, forming R-R and the U(IV) azide-bridged complex{[U]}2(μ-N3)2, along with the expected [U] = NR complex. All three [U] = NR complexes show a quasi-reversible one electron reduction between −1.6 and −1.75 V, and for R = SiMe3, chemical reduction using K/Hg affords the anionic U(IV) complex K+{U[η8-C8H6(1,4-Si(iPr)3)2](Cp*) = NSiMe3}-. The molecular structure of the latter shows an extended structure in the solid state in which the K counter cations are successively sandwiched between the Cp* ligand of one [U] anion and the COTtips2 ligand of the next.

The synthesis and characterisation of a new anionic flexible scorpionate ligand, methyl(bis-7-azaindolyl)borohydride [MeBai]- is reported herein. The ligand was coordinated to a series of group nine transition metal centres forming the complexes, [Ir(MeBai)(COD)] (1), [Rh(MeBai)(COD)] (2), [Rh(MeBai)(CODMe)] (2-Me) and [Rh(MeBai)(NBD)] (3), where COD = 1,5-cyclooctadiene, CODMe = 3-methyl-1,5-cyclooctadiene and NBD = 2,5-norbornadiene. In all cases, the boron based ligand was found to bind to the metal centres via a κ3-N,N,H coordination mode. The ligand and complexes were fully characterised by spectroscopic and analytical methods. The structures of the ligand and three of the complexes were confirmed by X-ray crystallography. The potential for migration of the "hydride" or "methyl" units from boron to the metal centre was also explored. During these studies an unusual transformation, involving the oxidation of the rhodium centre, was observed in complex 2. In this case, the η4-COD unit transformed into a η1,η3-C8H12 unit where the ring was bound via one sigma bond and one allyl unit. This is the first time such a transformation has been observed at a rhodium centre.

A series of uranium(III) mixed sandwich complexes with sterically demanding CpR ligands, of the type [U(COTTIPS2)(CpR)] (CpR = CptBu (C5H4tBu), CptBu2 (C5H3tBu2-1,3), CptBu3 (C5H2tBu3-1,2,4), CpTIPS2 (C5H3(SiiPr3)2-1,3), CpMe4Bz (C5Me4CH2Ph), IndMe6 (C9HMe6) and IndMe7 (C9Me7), and COTTIPS2 = C8H6(SiiPr3)2-1,4), have been synthesised and their X-ray crystal structures determined. The reactivity of these complexes with CO and CO2 is reported, including the squarate complex [U(COTTIPS2)(IndMe6)]2(μ-C4O4), IR data on the long-lived carbonyl complex [U(COTTIPS2)(IndMe7)(CO)] and the carbonate complex [U(COTTIPS2)(CptBu)]2(μ-η1:η2-CO3). The Solid-G algorithm has been to assess the steric properties of these and previously reported mixed-sandwich complexes in the solid state and correlate these properties with the observed reactivity.

The reaction of the syn-bimetallic bis(pentalene)dititanium complex Ti2(μ:η5,η5-Pn†)2 (Pn† = C8H4(1,4-SiiPr3)2) 1 with carbon suboxide (OCCCO, C3O2) results in trimerisation of the latter and formation of the structurally characterised complex [{Ti2(μ:η5,η5-Pn†)2}{μ-C9O6}]. The trimeric bridging C9O6 unit in the latter contains a 4-pyrone core, a key feature of both the hexamer and octamer of carbon suboxide which are formed in the body from trace amounts of C3O2 and are, for example, potent inhibitors of Na+/K+-ATP-ase. The mechanism of this reaction has been studied in detail by DFT computational studies, which also suggest that the reaction proceeds via the initial formation of a mono-adduct of 1 with C3O2. Indeed, the carefully controlled reaction of 1 with C3O2 affords [Ti2(μ:η5,η5-Pn†)2 (η2-C3O2)], as the first structurally authenticated complex of carbon suboxide.

The reaction of the bis(pentalene)dititanium complex Ti2(μ:η5,η5-Pn)2 (Pn = C8H4(1,4-SiiPr3)2) with the N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene results in intramolecular C-H activation of one of the iPr methyl groups of a Pn ligand and formation of a "tucked-in" bridging hydride complex. The "tuck-in" process is reversed by the addition of hydrogen, which yields a dihydride featuring terminal and bridging hydrides.

A family of benzotriazole based coordination compounds, obtained in two steps and good yields from commercially available materials, formulated as [CuII(L1)2(MeCN)2]·2ClO4·MeCN (1), [CuII(L1)(NO3)2]·MeCN (2), [ZnII(L1)2(H2O)2]·2ClO4·2MeCN (3), [CuII(L1)2Cl2]2 (4), [CuII5(L1)2Cl10] (5), [CuII2(L1)4Br2]·4MeCN·CuII2Br6 (6), [CuII(L1)2(MeCN)2]·2BF4 (7), [CuII(L1)2(CF3SO3)2] (8), [ZnII(L1)2(MeCN)2]·2CF3SO3 (9), [CuII2(L2)4(H2O)2]·4CF3SO3·4Me2CO (10), and [CuII2(L3)4(CF3SO3)2]·2CF3SO3·Me2CO (11), are reported. These air-stable compounds were tested as homogeneous catalysts for the A3 coupling synthesis of propargylamine derivatives from aldehyde, amine, and alkyne under a noninert atmosphere. Fine tuning of the catalyst resulted in a one-dimensional (1D) coordination polymer (CP) (8) with excellent catalytic activity in a wide range of substrates, avoiding any issues that would inhibit its performance.

A ferrocene containing o-aminoanilide, N1-(2-aminophenyl)-N8-ferrocenyloctanediamide (2b, Pojamide) displayed nanomolar potency vs HDAC3. In comparison to RGFP966, a potent and selective HDAC3 inhibitor, Pojamide displayed superior activity in HCT116 colorectal cancer cell invasion assays; however, TCH106 and romidepsin, potent HDAC1 inhibitors, outperformed Pojamide in cellular proliferation and colony formation assays. Together, these data suggest that HDAC1,3 inhibition is desirable to achieve maximum anticancer benefits. Additionally, we explored Pojamide-induced redox pharmacology. Indeed, treating HCT116 cells with Pojamide, SNP (sodium nitroprusside), and glutathione (GSH) led to greatly enhanced cytotoxicity and DNA damage, attributed to activation to an Fe(III) species.

The synthesis and molecular structures of a U(v) neutral terminal oxo complex and a U(v) sodium uranium nitride contact ion pair are described. The synthesis of the former is achieved by the use of tBuNCO as a mild oxygen transfer reagent, whilst that of the latter is via the reduction of NaN3. Both mono-uranium complexes are stabilised by the presence of bulky silyl substituents on the ligand framework that facilitate a 2e- oxidation of a single U(iii) centre. In contrast, when steric hindrance around the metal centre is reduced by the use of less bulky silyl groups, the products are di-uranium, U(iv) bridging oxo and (anionic) nitride complexes, resulting from 1e- oxidations of two U(iii) centres. SQUID magnetometry supports the formal oxidation states of the reported complexes. Electrochemical studies show that the U(v) terminal oxo complex can be reduced and the [U(iv)O]- anion was accessed via reduction with K/Hg, and structurally characterised. Both the nitride complexes display complex electrochemical behaviour but each exhibits a quasi-reversible oxidation at ca. -1.6 V vs. Fc+/0.

A range of iron(II) complexes incorporating the silylated pentalene ligands (Pn†H = 1,4-{SiiPr3}2C8H5and Pn† = 1,4-{SiiPr3}2C8H4) have been investigated as model molecules/building blocks for metallocene-based polymers. Six complexes have been synthesised and extensively characterised by a range of techniques, including by cyclic voltammetry and X-ray diffraction studies. Amongst these compounds are the homobimetallic [Cp∗Fe]2(μ-Pn†) which is a fused analogue of biferrocene, and the 3d/4s heterobimetallic [Cp∗Fe(η5-Pn†)][K] which forms an organometallic polymer in the solid state. DFT calculations on model mono-Fe(η5-Pn) compounds reveal the charge densities on the uncoordinated carbon atoms of the pentalene ligand, and hence the potential for incorporating these units into heteronuclear bimetallic complexes is assessed.

The novel platinum (II) dimethyl complexes Pt(κ2-L1)Me2 and Pt(κ2-L1)Me2 (1), Pt(κ2-L2a)Me2 (2a) and Pt(κ2-L2b)Me2 (2b) bearing the functionalised N-heterocyclic carbenes (NHCs), L1 = 1-(2-diphenylphosphinoethyl)-3-(2,6-diisopropyl-phenyl)-imidazol-2-ylidene, L2a = 1-(2-pyridyl)-3-(2,6-diisopropyl-phenyl)-imidazol-2-ylidene, L2b = 1-(2-(3-picolinyl))-3-(2, 6-diisopropyl-phenyl)-imidazol-2-ylidene, react with the acid [H(Et2O)2+B(ArF)4-], ArF = 3, 5-(CF3)2C6H3, in the presence of various neutral donors (Dn) to give the salts [{Pt(κ2-L)(Me)(Dn)}+{B(ArF)4}-], where Dn occupies specifically the site trans to the P and the CNHC donor atoms of the coordinated ligands L1 and L2a, L2b, respectively. Spectroscopic data give evidence that the same selectivity prevails when other acids are employed. Activation of the Cl-CH2Cl bond by 2b led to [Pt(κ2-L2b)(Me)Cl], while reaction of CH3I with the dimethyl complexes led to isolable [Pt(κ2-L)Me3I] species.

The synthesis and molecular structures of a range of uranium(iii) mixed sandwich complexes of the type [U(η8-C8H 6(1,4-SiMe3)2)(η5-Cp Me)4R] (R = Me, Et, iPr, tBu) and their reactivity towards CO2 are reported. The nature of the R group on the cyclopentadienyl ring in the former has a significant effect on the outcome of CO2 activation: when R = Me, the products are the bridging oxo complex {U[η8-C8H6(1,4-SiMe 3)2](η5-CpMe5)} 2(μ-O) and the bridging oxalate complex {U[η8- C8H6(1,4-SiMe3)2](η5- CpMe5)}2(μ-η2: η2-C2O4); for R = Et or iPr, bridging carbonate {U[η8-C8H6(1,4-SiMe 3)2](η5-CpMeR4)} 2(μ-η1:η2-CO3) and bridging oxalate complexes {U[η8-C8H 6(1,4-SiMe3)2](η5-Cp MeR4)}2(μ-η2: η2-C2O4) are formed in both cases; and when R = tBu the sole product is the bridging carbonate complex {U[η8-C8H6(1,4-SiMe3) 2](η5-CpMetBu4)} 2(μ-η1:η2-CO3). Electrochemical studies on both the uranium(iii) complexes and the dimeric uranium(iv) CO2 reduction products have been carried out and all exhibit quasi reversible redox processes; in particular, the similarities in the U(iii)/U(iv) redox couples suggest that the selectivity in the outcome of CO2 reductive activation by these complexes is steric in origin rather than electronic. The latter conclusion is supported by a detailed computational DFT study on the potential mechanistic pathways for reduction of CO2 by this system. © 2014 the Partner Organisations.

The novel bimetallic bis(pentalene) complex Ti2(μ:η5,η5-Pn†)2 (Pn† = C8H4(SiiPr3-1,4)2) has been synthesised and structurally characterised. Structural data show a Ti-Ti distance of 2.399(2) å, consistent with a strong metal-metal interaction, which DFT calculations best describe as a double bond with σ and π components. © 2013 The Royal Society of Chemistry.

The facile two-electron reduction of the phosphaalkyne tBuC=P by the U III cyclopentadienyl-pentalene mixed-sandwich complex [U(η5-C5Me5){η8-C 8H4(SiiPr3)2}] is reported. A single-crystal X-ray structural analysis of the diuranium(IV) product [(U{η5-C5Me5}{η8-C 8H4(SiiPr3)2})2(μ- tBuCP)] shows that it contains a slightly unsymmetrical, bridging μ-η2:η1- ligated phosphaalkene dianion. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The reactions of [Ir(κ3N,N,H-Tai)(COD)] and [Ir(κ3N,N,H-PhBai)(COD)] (where Tai = HB(azaindolyl)3 and PhBai = Ph(H)B(azaindolyl) 2) with carbon monoxide result in the formation of Z-type iridium-borane complexes supported by 7-azaindole units. Analysis of the reaction mixtures involving the former complex revealed the formation of a single species in solution, [Ir(η1-C8H 13){κ3N,N,B-B(azaindolyl)3}(CO) 2], as confirmed by NMR spectroscopy. In the case of the PhBai complex, a mixture of species was observed. A postulated mechanism for the formation of the new complexes has been provided, supported by computational studies. Computational studies have also focused on the reaction step involving the migration of hydrogen from boron (in the borohydride group) to the iridium center. These investigations have demonstrated a small energy barrier for the hydrogen migration step (ΔG298 = 10.3 kcal mol-1). Additionally, deuterium labeling of the borohydride units in Tai and PhBai confirmed the final position of the former borohydride hydrogen atom in the resulting complexes. The importance of the "third azaindolyl" unit within these transformations and the difference in reactivity between the two ligands are discussed. The selective coordination properties of this family of metallaboratrane complexes have also been investigated and are discussed herein. © 2013 American Chemical Society.

The selectivity of the mixed-sandwich U(III) complexes of the type [U(η-C8H6{SiiR3-1,4} 2)(η-CpR′)] (R = Me, iPr; R′ = Me4H, Me5, Me4iPr, Me 4SiMe3, Me4Et) toward the reductive coupling of CO to form uranium-bound oxocarbons has been explored. In this context, the new U(III) mixed-sandwich complexes [U(η-C8H6{Si iPr3-1,4}2)(η-CpMe4TMS)], [U(η-C8H6{SiiPr3-1,4} 2)(η-CpMe4iPr)], [U(η-C8H 6{SiiPr3-1,4}2)(η-Cp Me4Et)], [U(η-C8H6{SiMe3-1,4} 2)(η-Cp*)], and [U(η-C8H 6{SiMe3-1,4}2)(η-CpMe4TMS)] have been prepared and structurally characterized. The reactivity toward CO is dominated by the "global" sterics around the uranium center, while selectivity for oxocarbon formation is largely regulated by the steric bulk of the CpR′ ligand. Accordingly, with excess CO [U(η-C 8H6{SiiPr3-1,4}2)(η- CpMe4TMS)] and [U(η-C8H6{Si iPr3-1,4}2)(η-CpMe4iPr)] show no reactivity, [U(η-C8H6{SiMe3-1,4} 2)(η-CpMe4TMS)] is completely selective for the formation of the ynediolate complex [U(η-C8H 6{SiMe3-1,4}2)(η-CpMe4TMS)] 2(μ-η1:η1-13C 2O2), [U(η-C8H6{SiiPr 3-1,4}2)(η-Cp*)] affords only the deltate complex [U(η-C8H6{SiiPr3-1,4} 2)(η-Cp*)]2(μ-η2: η2-C3O3), and [U(η-C8H 6{SiiPr3-1,4}2)(η-CpMe4H)] gives solely the squarate complex [U(η-C8H6{SiiPr 3-1,4}2)(η-CpMe4H)]2(μ- η2:η2-C4O4). Additionally, the squarate moiety has been removed from the uranium center in the last complex by reaction with Me3SiCl to afford the TMS ester of squaric acid, C4O2(OTMS)2. © 2012 American Chemical Society.

Two novel boron-based flexible scorpionate ligands based on 7-azaindole, Li[HB(azaindolyl)2(1-naphthyl)] and Li[HB(azaindolyl) 2(mesityl)] {Li[NaphthBai] and Li[MesBai] respectively}, have been prepared (mesityl = 2,4,6-trimethylphenyl). These salts have been isolated in two forms, either as dimeric structures which contain bridging hydride interactions with the lithium centres or as crystalline material containing mono nuclear bis-acetonitrile solvates. The newly formed ligands have been utilised to prepare a range of group nine transition metal complexes with the general formula [M(COD){κ3-NNH-HB (azaindolyl)2(Ar)}] (where M = rhodium, iridium; Ar = 1-naphthyl, mesityl; COD = 1,5-cyclooctadiene) and [Rh(NBD){κ3-NNH-HB (azaindolyl)2(Ar)}] (where NBD = 2,5-norbornadiene; Ar = 1-naphthyl, mesityl). These new complexes have been compared to the previously reported compounds which contain the related scorpionate ligands Li[HB(azaindolyl) 2(phenyl)] and K[HB(azaindolyl)3] {Li[PhBai] and K[Tai] respectively}. Structural characterisation of the complexes [Rh(COD){κ3-NNH-HB (azaindolyl)2(mesityl)}], [Ir(COD){κ3-NNH-HB (azaindolyl)2(mesityl)}] and [Rh(NBD){κ3-NNH-HB (azaindolyl)2(naphthyl)}] confirm the expected κ3-NNH coordination mode for these new ligands. Spectroscopic analysis suggests strong interactions of the B-H functional group with the metal centres in all cases. © 2011 The Royal Society of Chemistry.

The addition of H2 across a transition metal-borane bond is reported for the first time providing a mechanism for recharging borane functional groups to borohydride. © 2010 The Royal Society of Chemistry.

The complexes [Ru(Tai)H(PPh3)2] (4) [Tai = HB(7-azaindolyl)3] and [Ru(ArBai)H(PPh3) 2] [ArBai = Ar(H)B(7-azaindolyl)2; Ar = phenyl (5), mesityl (6) and 2-naphthyl (7)] have been prepared and fully characterised. Structural characterisation of complexes 4, 5 and 7 confirmed the expected κ3-NNH coordination mode of the azaindolyl-based ligands. In all complexes, the borohydride unit is located trans to the hydrido ligand, and the two triphenylphosphane ligands occupy sites trans to the two nitrogen donors. The strong Ru⋯H-B interaction means that the third substituent at the boron atom is held in close proximity to the ruthenium centre. In the case of complex 7, rotation of the naphthyl group about the boron centre is hindered by the triphenylphosphane substituents. The synthesis of a number of ruthenium hydride complexes containing azaindole-based scorpionate ligands is reportedherein. The scorpionate ligands bind to the metal centre with κ3-NNH coordination modes. The strong borohydride⋯metal interaction pulls the additional substituent at the boron atom towards the bulky triphenylphosphane ligands. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The complexes [Ru(Tai)Cl{=C(H)Ph}(PCy3)] (4) and [Ru( PhBai)Cl{=C(H)Ph}(PCy3)] (5) [where Tai = HB(7-azaindolyl)3 and PhBai = Ph(H)B(7-azaindolyl) 2] have been prepared and structurally characterised. The borohydride unit is located in the coordination site trans to the chloride ligand in both complexes. The degree of interaction between the borohydride group and the metal centre was found to be significantly large in both cases. Thermolysis reactions involving complex 4 led to a dehydrogenation reaction forming [Ru(Tai)Cl{PCy2(η2-C6H9)}] (6) where the benzylidene group acts as a hydrogen acceptor. © The Royal Society of Chemistry 2011.

The ensemble of forces that stabilize protein structure and facilitate biological function are intimately linked with the ubiquitous aqueous environment of living systems. As a consequence, biomolecular activity is highly sensitive to the interplay of solventĝ€"protein interactions, and deviation from the native conditions, for example by exposure to increased thermal energy or severe dehydration, results in denaturation and subsequent loss of function. Although certain enzymes can be extracted into non-aqueous solvents without significant loss of activity, there are no known examples of solvent-less (molten) liquids of functional metalloproteins. Here we describe the synthesis and properties of room-temperature solvent-free myoglobin liquids with near-native structure and reversible dioxygen binding ability equivalent to the haem protein under physiological conditions. The realization of room-temperature solvent-free myoglobin liquids with retained function presents novel challenges to existing theories on the role of solvent molecules in structural biology, and should offer new opportunities in protein-based nanoscience and bionanotechnology. © 2010 Macmillan Publishers Limited. All rights reserved.

The reaction of [Ru(η6-p-cymene)Cl2]2 with 2.0 mol equivalents of C(CH2SMe)4, C(CH 2SeMe)4, 1,2,4,5-C6H2(CH 2SMe)4 or 1,2,4,5-C6H2(CH 2SeMe)4 (L4) and [NH4][PF 6] in ethanol solution forms the [RuCl(η6-p-cymene) {κ2-L4}][PF6] complexes. Similar Os(II) complexes are obtained starting with [Os(η6-p-cymene)Cl 2]2. Treatment of [RuCl(η6-p-cymene) {κ2-L4}][PF6] with a further 0.5 mol equivalents of [Ru(η6-p-cymene)Cl2]2 or reaction of [Ru(η6-p-cymene)Cl2]2 directly with 1.0 mol equivalent of L4 forms the homobimetalllic [{RuCl(η6-p-cymene)}2{κ2κ ′2-L4}][PF6]2. Reaction of [OsCl(η6-p-cymene)-{κ2-C(CH2SeMe) 4}][PF6] with [Ru(η6-p-cymene)Cl 2]2 or [PtCl2(MeCN)2] affords the heterobimetallic [{OsCl(η6-p-cymene)}{RuCl(η6-p- cymene)}{κ2κ′2-C(CH2SeMe) 4}][PF6]2 and [{OsCl(η6-p- cymene)}{PtCl2}{κ2κ′2- C(CH2SeMe)4}][PF6] respectively. The complexes have been characterised by multinuclear NMR and IR spectroscopy and X-ray crystallography. The synthesis and properties of homomonometallic and homo-and hetero- bimetallic complexes based upon tetrathio-or tetraselenoether ligands with {(arene)MCl]+ units are described, and crystal structures reported for representative examples. © 2010 Elsevier B.V.

The first structurally characterised zerovalent platinum complex to contain a tridentate pincer-type coordination mode (κ3-SBS) is presented, raising further questions concerning the geometries and trans influence of Z-type ligands. © The Royal Society of Chemistry 2010.

A new boron-based flexible scorpionate ligand based upon 7-azaindole, Li[Ph(H)B(azaindolyl)2] (Li[phBai]), has been prepared. This ligand, together with the previously reported ligand K[HB(azaindolyl) 3] (K[Tai]), have been used to prepare a range of monovalent group 9 transition-metal complexes. The complexes [M(COD){K3N,N,H-Ph(H) B(azaindolyl)2}] (where M = rhodium, iridium and COD = 1,5-cyclooctadiene) and [Rh(NBD){K3N,N,H-HB(R)(azaindolyl) 2}] (where NBD = 2,5-norbornadiene and R = Ph, azaindolyl) have been prepared. Structural characterization of [M(COD){K3NNH-Ph(H) B(azaindolyl)2}] (where M = rhodium, iridium) and [Rh(NBD){k 3N, N, H-HB(azaindolyl)3}] reveal strong interactions of the B-H functional group with the metal centers, particularly in the case of [Ir(COD){K3N,N,H-Ph(H)B(azaindolyl)2}]. The complex [Rh(NBD){K3N,N,H-HB(azaindolyl)3}] undergoes a further reaction, resulting from hydride migration from boron to the norbornadiene group. Subsequent rearrangement results in the formation of the rhodium-nortricyclyl complex [Rh(nortricyclyl){k4 N,N,-B,N-B(azaindolyl)3}], providing the first nitrogen-based metallaboratrane complex to contain the tetradentate (K4N,N,B,N) coordination mode. © 2009 American Chemical Society.

The reaction of Ir(COD)(Tai) [where Tai = {HB(7-azaindoyl) 3}-] with carbon monoxide results, via a sequence of hydride migration and insertion steps, in the formation of the first complexes to contain a metal-to-boron dative interaction supported by 7-azaindole units. © The Royal Society of Chemistry 2009.

A range of complexes of the binucleating tetrathio- and tetraseleno-ether ligands, 1,2,4,5-C6H2(CH2EMe)4 (E = S, L3 or Se, L4) or C(CH2EMe)4 (E = S, L5 or Se, L6) and of bidentate analogues 1,2-C6H2(CH2EMe)2 (E = S, L1 or Se = L2) with molybdenum and tungsten carbonyls and manganese carbonyl chloride have been prepared, and characterised by IR and multinuclear NMR (1H, 13C{1H}, 77Se, 55Mn, 95Mo) spectroscopy and mass spectrometry. Crystal structures are reported for [Mo(CO)4(L2)], [Mo(CO)4(L3)], [Mo(CO)4(μ-L3)Mo(CO)4], [Mo(CO)4(L4)], [Mn(CO)3Cl(μ-L3)Mn(CO)3Cl], [Mo(CO)4(μ-L5)Mo(CO)4], [Mn(CO)3Cl(L5)] and two forms (containing meso and DL diastereoisomers) of [W(CO)4(L5)]. © 2009 Elsevier B.V. All rights reserved.

Rhodium and iridium complexes of flexible scorpionate ligands based on azaindole were synthesised in good yields. The complexes were characterised in solution and in the solid state. Structural characterisation revealed a B-H-metal interaction, which is retained in solution. Given the greater flexibility of the ligand and potential cooperative effect of boron, the complexes were tested for their activity in the transfer hydrogenation of ketones. © 2008 The Royal Society of Chemistry.

Square planar neutral dimethyl and cationic allyl complexes of palladium with the electronically nonsymmetric diphenylphosphinomethyl- and pyridyl-N-heterocyclic carbene ligands have been synthesized and characterized. The products from the protonation of the dimethyl complexes with 1 equiv of acid at low temperatures are monomethyl cations, the exact nature of which is dependent on the type of ligand; in pyridine-carbene complexes the Pd-Me bond cleaved is trans to the carbene, while for the phosphino-carbene complexes it is trans to the phosphine. Density functional calculations suggest that protonation in these complexes occurs directly at the methyl ligands and that the site of protonation determines the selectivity of Pd-Me cleavage. For the pyridine-carbene complexes there is a clear preference for protonation trans to the carbene. For phosphino-carbene complexes, however, the site of protonation depends on the steric bulk of the N-heterocyclic carbene ligand. Protonation trans to carbene is favored with small substituents (H, Me), but the bulky 2,6-Pri2C6H3 susbstituent induces protonation trans to the phosphine, as is seen experimentally. © 2007 American Chemical Society.

Rare examples of (high spin) Co(ii) complexes with geometrically constrained tetrathioether ligands exhibit a very unusual structural isomerism, switching reversibly between tetrahedral monomers in solution and octahedral chain polymers in the solid; the crystal structures of one polymeric species and a tetrahedral monomer model compound are described. © The Royal Society of Chemistry.

A study on the Mizoroki-Heck coupling of selected aryl bromides with acrylates catalysed by a series of Pd complexes of bidentate pyridyl-, picolyl-, diphenylphosphinoethyl- and diphenylphosphinomethyl-functionalised N-heterocyclic carbene (NHC) is reported. The observed activity is dependent on the type of solvent and base used and the nature of the "classical" donors of the mixed-donor bidentate ligand and its bite angle. A mechanistic model is presented for the pyridine-functionalised NHC complexes based on an in situ EXAFS study under dilute catalyst conditions (2 mM Pd). The model involves pre-dissociation of the pyridine functionality and oxidative addition of ArBr in the early stages of the reaction, as well as formation of monomeric and dimeric Pd species at the time of substrate conversion. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

The ligands o-C6H4(CH2EMe)2(E = S or Se) have been prepared and characterised spectroscopically. A systematic study of the coordination chemistry of these, together with the telluroether analogue, o-C6H4(CH2TeMe)2, with late transition metal centers has been undertaken. The planar complexes [MCl2(o-C6H4(CH2SMe)2)] and [M(o-C6H4(CH2EMe)2)2](PF6)2(M = Pd or Pt; E = S or Se), the distorted octahedral [RhCl2(o-C6H4(CH2EMe)2)2]Y (E = S or Se: Y = PF6; E = Te: Y = Cl) and [RuCl2(o-C6H4(CH2EMe)2)2] (E = S, Se or Te), the dithioether-bridged binuclear [(RuCl2(p-cymene))2(μ-o-C6H4(CH2SMe)2)] and the tetrahedral [M′(o-C6H4(CH2EMe)2)2]BF4(M′ = Cu or Ag; E = S, Se or Te) have been obtained and characterised by IR and multinuclear NMR spectroscopy (1H,63Cu,77Se(1H),125Te(1H) and195Pt), electrospray MS and microanalyses. Crystal structures of the parent o-C6H4(CH2SMe)2and seven complexes are described, which show three different stereoisomeric forms for the chelated ligands, as well as the first example of a bridging coordination mode in [(RuCl2(p-cymene))2(μ-o-C6H4(CH2SMe)2)]. These studies reveal the consequences of the sterically demanding o-xylyl backbone, which typically leads to unusually obtuse E–M–E chelate angles of ∼100°. © 2006 The Royal Society of Chemistry.

The pyridine functionalised N-heterocyclic carbene complexes [M(κ2-NCDIPP)(COD)]+A-, NCDIPP=3-(2,6-Pr2iC6H3)-1-[2-(3-picolyl)]-imidazol-2-ylidene, A-=[Ar4FB]-, [{3,5-(CF3)2C6H2}4B] -, M = Rh, 1b, Ir, 4, have been prepared in two steps by reaction of the [M(COD)Cl]2 with the isolated NCDIPP to [Rh(κ1-NCDIPP)(COD)Cl], 2, and [Ir(κ 2-NCDIPP)(COD)Cl], 3, followed by anion exchange with Na+A-. The phosphine functionalised N-heterocyclic carbene complex [Rh(PCH2Cmes)2]Br, 6, PCH 2Cmes = 1-(diphenylphosphino-methyl)-3-(2,4,6-Me 3C6H2)-imidazol-2-ylidene, was prepared by the reaction of the [Rh(COD)Cl]2 with the corresponding N-heterocyclic carbene generated in situ. Monomeric [Rh(PCH2CH2C DIPP)(acac)], 7 was prepared by an analogous reactions from [Rh(COE)2(acac)]. In contrast, phosphine functionalised N-heterocyclic carbene complexes of iridium (I) were not easily accessible. However, the reaction of [Ir(COD)(μ-Cl)2(μ-H)]2 with PCH 2CH2Cmes gave complex [Ir(COD)(PCH 2CH2Cmes)Br], 8, in which the carbene is coordinated to the metal in an 'abnormal' mode. © 2005 Elsevier B.V. All rights reserved.

Six- and five-coordinate Fe(II) complexes with the pincer Iigand 2,6-bis(imidazolylidene)pyridine (C-N-C), [(C-N-C)Fe(MeCN)3][BPh 4]2 and [(C-N-C)FeBr2], respectively, were synthesized. Substitution of tmeda in [FeCl2(tmeda)]2 by C-N-C gave the sixcoordinate {[Fe(C-N-C)(C-N-C*)][FeCl4]}, in which one of the pincer ligands is bound to the metal via the 2- and 5-imidazole carbons.

The (diphenylphosphino)alkyl-functionalized nucleophilic heterocyclic carbene (NHC) complexes of palladium LPdX2 (L = (3-R1)[1-Ph2P(CH2)2]-imidazol-2-ylid ene; R1 = 2,6-Pr2iC6H3, 2,4,6-Me3C6H2; X = CH3 (3a,b), X = Br (4a,b)) have been synthesized by the reaction of the in situ generated functionalized NHC ligand La or Lb with Pd(tmed)(CH3)2 and Pd(COD)Br2, respectively, and structurally characterized. Interaction of 3a with H(Et2O)- {B[3,5-(CF3)2C6H2]4} and pyridine or with (CF3)2CHOH and pyridine in CH2Cl2 gave the monocationic complexes [(La)Pd(CH3)(pyridine)]+(A)- (A- = {B[(3,5-CF3)2C6H2]4}-, (CF3)2CHO-); acetonitrile and benzonitrile analogues can be prepared in an analogous way. Reaction of 4a with AgBF4 in MeCN gave the dicationic complexes [(La)Pd(MeCN)2](BF4)2. Complexes 3 show moderate catalytic activity for the coupling of acrylates with aryl bromides but not chlorides. The cationic species generated in situ from 3a and H(Et2O){B[(3,5-CF3) 2C6H2]4} in CH2Cl2 under CO/ethylene acts as a copolymerization catalyst under mild conditions.

The first authenticated example of migration of a methyl group from palladium(ii) to a coordinated N-heterocyclic carbene is described. © 2003 The Royal Society of Chemistry.