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

Article abstract of DOI:10.1016/0022-328X(95)06052-X

Three series of alkylrhodoximes [Rh(Hdmg)₂RL] (Hdmg = monoanion of dimethlyglyoxime) (L = H₂O, R = Me, Et, ⁿPr, ⁱPr, ⁿBu, ⁱBu, ^neoPent; L = py, R = Me, Et, ⁿPr, ⁱPr, ⁿBu, ⁱBu, ^sBu, ^tBu, ^neoPent, adam, CH₂Cl, CH₂CF₃; L = PPh₃, R = Me, Et, ⁿPr, ⁱPr, ⁿBu, ⁱBu, ^tBu, ^neoPent, adam) were prepared and characterized by ¹H, ¹³C and ³¹P NMR spectra; several of the reported compounds are new. The rhodium-103 chemical shifts were measured by (¹H, ¹⁰³Rh)-2D inverse correlation for the complexes with L = H₂O and py and by (³¹P, ¹⁰³Rh)-{¹H}-2D inverse correlation for those with L = PPh₃. Rh shielding decreases in the order Et > Me > ⁿBu > ⁱPr > ^sBu > ^neoPent > ^tBu. 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 ¹J[Rh,P] values reflect the rhodium-phosphine binding interaction.