Stereoselective addition reactions of diphenylphosphine: meso- and rac-1,2-diphenyl-1,2-bis(diphenylphosphino)ethane and their Group 6 metal tetracarbonyl complexes. Crystal structures of the molybdenum derivatives

Abstract

The addition of diphenylphosphine, PPh2H, to diphenylethyne in the presence of KOBut has been followed by 31P n.m.r. spectroscopy, and according to the reaction conditions can yield cis, (2) or trans, (3), 1,2-diphenyl(diphenylphosphino)ethene and then meso. (4), or rac, (5), 1,2-diphenyl-1,2-bis(diphenylphosphino)ethane, all of which have been isolated and characterised by elemental analysis and 1H, 13C, and 31P n.m.r. spectroscopy. The M(CO)4(M = Cr, Mo, or W) complexes of (4) and (5) have been prepared, and the structures of the molybdenum derivatives determined by single-crystal X-ray diffraction. In the solid state the chelate rings are puckered with one axial and one equatorial CPh group for the meso diastereomer, and two equatorial for the rac. Carbon-13 n.m.r. data suggest that the latter conformation is not fully maintained in solution.