Important Steric Effects Resulting from the Additional Substituent at Boron within Scorpionate Complexes Containing κ3-NNH Coordination Modes

The complexes [Ru(Tai)H(PPh3)(2)] (4) [Tai = HB(7-azaindolyl)(3)] and [Ru((Ar)Bai)H(PPh3)(2)] [(Ar)Bai = 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 kappa 3-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 center dot center dot center dot 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.