Adducts of trimethylaluminium with phosphine ligands; electronic and steric effects
Complexes of the type Me3AlPR2R′ have been synthesised and studied by 1H, 13C, and 31P n.m.r. spectroscopy. The change in 31P chemical shift on co-ordination, Δ(31P), decreases, becoming more negative, with sterically bulkier phosphines and with increasing donor ability. The aluminiummethyl 13C resonance shifts downfield with increasing phosphine steric bulk, and with increased donor ability. Steric effects, however, are found to be the major factor contributing to the changes in both Δ(31P) and methyl 13C chemical shifts.