Tuneable Phosphaamidinate Ligands: Alkyl-Magnesium Complexes Responsive to Increased Ligand Bulk

The syntheses of five new phosphaamidines RNC(tBu)P(H)(R’’) of readily variable steric bulk are described. Crystallographic and multinuclear NMR studies indicate the geometry of the phosphaamidine is dependent on the steric bulk of the peripheral substituents. In one case, multiple isomers were observed in solution. Complexation of the phosphaamidines to magnesium by reaction of either 0.5 or 1 equivalents of nBu2Mg forms either hetero- (LMgnBu) or homoleptic (L2Mg) species respectively, culminating in the isolation of a monomeric, unsolvated three-coordinate magnesium phosphaamidinate.