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 KOBu^t 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.