Abstract
Herein we report the synthesis and characterization of new heterobimetallic Zr/Co complexes incorporating chiral phosphinoamide ligands. The chiral phosphinoamine ligand (R-PhCH3CH)NHPiPr2 (1) is used to synthesize a tris(phosphinoamide) Zr metalloligand ClZr((R-PhCH3CH)NPiPr2)3 (2), which can be further treated with CoI2 to afford the chiral Zr/Co heterobimetallic complex ClZr((R-PhCH3CH)NPiPr2)3CoI (3). Complex 3 can be reduced by two electrons to produce Zr((R-PhCH3CH)NPiPr2)3CoN2 (4). In an alternative strategy, a mixed-ligand derivative featuring two achiral phosphinoamide ligands and one chiral ligand was targeted. Thermolysis of Zr(NMe2)4 with iPr2PNHXyl in toluene produces (Me2N)2Zr(iPr2PNXyl)2 (5, Xyl=3,5-dimethylphenyl), which can be transformed into I2Zr(iPr2PNXyl)2 (6) via in situ treatment with Me3SiI. A third chiral phosphinoamide ligand can then be installed to generate IZr((R-PhCH3CH)NPiPr2)(XylNPiPr2)2 (7). Treatment of complex 7 with CoI2 affords IZr((R-PhCH3CH)NPiPr2)(XylNPiPr2)2CoI (8). Complexes 3, 7, and 8 were structurally characterized and a preliminary screening of the catalytic hydrosilylation of acetophenone with reduced complex 4 revealed a very poor yield and essentially no enantioselectivity.