The metal-carbon stretching frequencies in methyl complexes of Rh, Ir, Ga and In with porphyrins and a tetradentate pyridine-amide ligand

Interactions of trans -[Rh(bpb)(CH3)(H2O)] (1) [bpb = 1,2-bis(2-pyridinecar boxamido)benzene] with Lewis bases L afford the respective adducts trans-[R h(bpb)(CH3)(L)], where L = 4-substituted pyridine 4-Xpy (X = H (2), 'Bu (3) , NMe2 (4) CN (5)), PMe2Ph (6) or benzimidazole (7), The structures of comp lexes 3 and 6 have been established by X-ray crystallography. The Rh-C dist ance in complex 6 (2.095(6) Angstrom) is longer than that in complex 3 (2.0 2(1) Angstrom), indicating that PMe2Ph has a stronger trans influence than 4-'Bupy. The metal-carbon stretching frequencies for trans -[Rh(bpb)(CH3)(L )] and [M(TTP)(CH3)] [TTP = 5,10,15,20-tetrakis(4-methylphenyl)porphyrin di anion; M = Rh, Ir, Ga, In] have been determined by near IR FT-Roman spectro scopy. Complex 1 exhibits v(Rh-C) at 562 cm(-1), which downshifts to 532 cm (-1) upon deuteriation of the axial methyl group. Replacement of the aquo l igand in complex 1 with nitrogen ligands or phosphine resulted in downshift in v(Rh-C). The v(Rh-C) for trans-[Rh(bpb)(CH3)(L)] was found to decrease in the order L: PMe2Ph much greater than 4-Xpy similar to BzIm > H2O, consi stent the order of trans influence of L. For [M(TTP)(CH3)] (M = Co, Rh, Ir, Ga, or In) the M-C force constant was found to decrease in the orders Ir > Rh > Co and Ga > In, consistent with the trends of metal-carbon bond stren gth for these metals. For trans[Rh(bpb)(CH3)(4-Xpy)] and trans-[Rh(TTP)(CH3 )(4-Xpy)], the v(Rh-C) were found to be not very sensitive to the nature of X, suggesting that the electronic factors of the axial pyridine ligand do not have a significant effect on the Rh-C bonds for these rhodium alkyl com plexes. (C) 2001 Published by Elsevier Science B.V.