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)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 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.