Phosphorus-31 NMR spectra of cobaloximes: Influence of electronic and steric effects of axial ligands

Abstract The 31 P NMR spectra of a large number of cobaloxime compounds having the general formula trans -Co(DH) 2 (L)X (where DH = the monoanion of dimethylglyoxime) have been measured. Series examined include those where L = tri- n -butylphosphine or trimethylphosphite, X = various ligands and L = various phosphorus donors, X = Cl − or CH − 3 . Several factors were found to influence the 31 P coordination chemical shifts (Δ's) such as ligand cone angle, hybridization of the phosphorus donor orbital, substituent groups on the phosphorus, and the trans -influence (or -effect) of the X groups. The data are discussed in the context of other NMR and structural studies of cobaloximes. The results lend support to a common trans -effect/influence series for octahedral complexes [1, 2].