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.

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.