Nickel(II) complexes bearing N,O-chelate ligands: Synthesis, solid-structure characterization, and reactivity toward the polymerization of polar monomer

Two new moisture- and air-stable bis(beta-ketoamino)nickel(II) complexes Ni[R1C(O)CHC-(NAr)R2](2) (Ar = 2,6-(Pr2C6H3)-Pr-i; R1 = R2 = CH3, 1; R1 = C6H5, R2 = CH3, 2), together with the moderately stable complex Ni-2[CH3C(O)CHC(O)CH3](4)[(H2NBu)-Bu-t](2) (3), which bears a monoanionic 0,O-chelate bidentate beta-diketone and an sp(3)-N atom of (BuNH2)-Bu-t mixed ligands, were synthesized and characterized. The solid-state structures of the complexes have been determined by single-crystal X-ray diffractions. Additionally, these new complexes act as catalyst precursors for methyl methacrylate polymerization after activation with methylaluminoxane (MAO). The polymers obtained by 1 and 2 show broader polydispersity than that obtained by 3. C-13 NMR analyses indicate that these catalytic systems initiate MMA polymerization to yield PMMA with rich syndiotacticity microstructure.