NMR studies of phosphorus ligand complexes of silver and cobalt

Investigations of the coordination of phosphorus ligands to silver(I) show that both steric and electronic effects are of importance in the determination of ligand binding ability. A crystal structure of a non-linear two-coordinate molecule, Ag(P(NMe(,2))(,3))(,2)BPh(,4), shows that both ligands are in an approximate C(,s) configuration with one nitrogen on each ligand assuming significant pyramidal character;The scope of the Co(II) disproportionation reaction below was found to be a function of the steric size and the electronic properties of the phosphite ligand L. 2 Co(II) + 11 L (---\u3e) CoL(,5)(\u27+) + CoL(,6)(\u273+). Phosphorus ligands must be below a certain steric limit and must possess minimums of both sigma basicity and pi acceptor ability to disproportionate Co(II). (\u2759)Co NMR studies show that the ligand field in Co(P)(,6)(\u273+) complexes is a function of both the steric and electronic properties of the ligands, with ligands which are small and better (pi) acceptors inducing higher ligand fields. In two CoL(,6)(\u273+) complexes, two temperature-dependent resonances separated by ca. 150 ppm were seen in the (\u2759)Co NMR spectrum corresponding to two isomeric complexes in which only the spatial arrangement of three of the ligands appear to be different. When monocyclic phosphite ligands react with Co(II) in the presence of methanol, catalytic transesterification of the exocyclic group can occur giving mixed-ligand complexes. Reducing the symmetry of the ligands in CoP(,6)(\u273+) complexes gives rise to higher electric field gradients of Co and hence shorter relaxation times of (\u2759)Co