Syntheses of Sterically Bulky Schiff-Base Magnesium Complexes and Their Application in the Hydrosilylation of Ketones

The sterically bulky Schiff-base ligand 1 ((LH)-H-1) was treated with CH3MgI in toluene to give the unexpected homoleptic magnesium complex 2 ((LMgL1)-Mg-1) in good yield. However, the reaction of sterically more bulky ligand 3 ((LH)-H-2) with CH3MgI in diethyl ether yielded the desired heteroleptic magnesium iodide 4 [(LMgI)-Mg-2(OEt2)], which was further reduced with sodium to produce the Mg-Na heterodimetallic complex 5. The crystal structures of all new magnesium complexes were determined by single-crystal X-ray diffraction. All new magnesium complexes have been investigated as catalysts for the hydrosilylation of ketones with (EtO)(3)SiH. The study showed that catalytic activity of the Mg-Na dimetallic complex 5 is superior to those of monometallic magnesium complexes 2 and 4 and is applicable to a series of subatrates.