STEREOSELECTIVE ADDITION-REACTIONS OF DIPHENYLPHOSPHINE - MESO-1,2-DIPHENYL-1,2-BIS(DIPHENYLPHOSPHINO)ETHANE AND RAC-1,2-DIPHENYL-1,2-BIS(DIPHENYLPHOSPHINO)ETHANE AND THEIR GROUP-6 METAL TETRACARBONYL COMPLEXES - CRYSTAL-STRUCTURES OF THE MOLYBDENUM DERIVATIVES

The addition of diphenylphosphine, PPh2H, to diphenylethyne in the presence of KOBu(t) has been followed by P-31 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 H-1, C-13, and P-31 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.