REACTIONS OF CPMOCL2L2 (CP = ETA-5-C5H5, L = PME3, PME2PH) WITH METHYLLITHIUM - PREPARATION AND STRUCTURE OF A MOLYBDENUM(II) COMPOUND CONTAINING AN ORTHO-METALATED PME2PH LIGAND - CPMO(O-C6H4PME2)(PME2PH)2

The reaction of CpMoCl2(PMe3)2 with methyllithium in the presence of PMe3 generates CpMoMe(PMe3)3. The intermediate 17-electron dimethyl derivative, CpMoMe2(PMe3)2, can be identified by EPR. The analogous methylation of CpMoCl2(PMe2Ph)2 generates low yields of the ortho-metalated complex, CpMo(o-C6H4PMe2)(PMe2Ph)2, which has been structurally characterized. Crystal data: monoclinic, space group P2(1)/n, a = 14.855 (3) angstrom, b = 13.655 (2) angstrom, c = 15.174 (2) angstrom, beta = 110.887 (13)-degrees, V = 2875.8 (8) angstrom 3, Z = 4, R = 0.0393, R(w) = 0.0437. The four-legged piano stool structure shows variation in bond distances and angles that can be rationalized in terms of Mo-P pi-back-bonding. The instability and susceptibility to reduction of the 17-electron CpMoX2(PMe3)2 (X = alkyl) with respect to the stability and susceptibility to oxidation of the same compounds with X = halogen is rationalized on the basis of the pi-bonding properties of the ligands.