Steric effects in organometallic compounds. A Rh-103 NMR study of alkylrhodoximes

Three series of alkylrhodoximes [Rh(Hdmg)(2)RL] (Hdmg = monoanion of dimethlyglyoxime) (L = H2O, R = Me, Et, Pr-n, Pr-i, (n)Bu, (i)Bu, (neo)Pent; L = py, R = Me, Et, Pr-n, Pr-i, (n)Bu, (i)Bu, (s)Bu, (t)Bu, (neo)Pent, adam, CH2Cl, CH2CF3; L = PPh(3), R = Me, Et, Pr-n, Pr-i, (n)Bu, (i)Bu, (t)Bu, (neo)Pent, adam) were prepared and characterized by H-1, C-13 acid P-31 NMR spectra; several of the reported compounds are new. The rhodium-103 chemical shifts were measured by (H-1, Rh-103)-2D inverse correlation for the complexes with L = H2O and py and by (P-31, Rh-103)-{H-1}-2D inverse correlation for those with L = PPh(3). Rh shielding decreases in the order Et > Me > (n)Bu > Pr-i > (s)Bu > (neo)Pent > (t)Bu. Discussion of the shift dependence on the various alkyl parameters allows us to conclude that, in these compounds the R ligand affects rhodium shielding mainly through distortions of the coordination site due to its bulk, The (1)J[Rh,P] values reflect the rhodium-phosphine binding interaction.