SYNTHESIS, REACTIONS AND X-RAY CRYSTAL-STRUCTURE OF MO(CO)(5)(PH(2)PCH(2)C=CHC(O)OC(CH3)(2)O), A COMPLEX PREPARED VIA THE UNUSUAL REACTION OF A COORDINATED CHLOROPHOSPHINE LIGAND WITH A CARBANION

The reaction of Mo(CO)(5)(Ph(2)PCl) with the anion of 2,2,5-trimethyl-4H-1,3-dioxin-4-one gives [Mo(CO)(5)(Ph(2)PCH(2)C=CHC(O)OC(CH3)(2)O)] (1), in 73% yield. This is only the second report of a reaction of a coordinated chlorophosphine with a carbanion that gives a good yield of the corresponding phosphine. An X-ray crystal structure of 1 shows that the coordination environment of the molybdenum is an octahedron with the Mo-C distance to the carbonyl trans to the phosphine shorter than those to the carbonyls trans to carbonyls. The conformation of the 1,3-diox-4-enyl group in 1 is a half chair with the isopropylidene C(CH3)(2) group above the plane of the other atoms. Complex 1 reacts with alcohols and mercaptans to yield the expected [Mo(Co)(5)(Ph(2)PCH(2)C(O)CH2C(O)ER)] (2:ER = OCy;3:ER = OMe;4:ER = SPrn) complexes. These complexes have significant amounts of the enol tautomers present in chloroform-d(1), at 23 degrees C with 4 having the highest enol content. Complex 1 reacts with piperidine to,give the unexpected product, [Mo(CO)(5)(Ph(2)PCH(2)C(O)CH3)], (5).