NEW (ETA-C5ME5)M(PR2)X COMPLEXES (M = TA, MO, AND W) - REVERSIBLE P-H BOND ACTIVATION, SP3 C-H BOND ACTIVATION, AND P-C BOND FORMATION

Reduction of Cp*MC14(PMe3) (CP* = 17-C5Me5, M = Mo, W) with 3 equiv of Na/Hg amalgam in the presence of 1 equiv of PMe3 under nitrogen gives dinitrogen complex Cp*MoCl(N2)(PMe3)2 (1) and metalated-phosphine complex Cp*WHCl(PMe3)(eta2-CH2PMe2) (3) in good yield. The molecular structure of 1, determined by X-ray diffraction, consists of a square-pyramidal geometry about Mo with ''trans'' PMe3 ligands. A similar structure is found for paramagnetic CP*MoCl2(PMe3)2, Which is obtained using 2 equiv of Na/Hg. The molecular structure of 3 is also a''four-legged piano stool'', with H trans to Cl and with the C atom of the (CH2PMe2)- ligand located between the two P atoms in the P-W-P plane. Complexes 1 and 3 are both good preparative sources of 16e- ''[Cp*MCI(PMe3)2]'', as shown by their reaction with P(OMe)3 to give Cp*MCI[P(OMe)3]n(PMe3)3-n (n = 1, 2). While 1 reacts with LiPR2 (R = Ph, cyclohexyl) to form Cp*Mo(PR2)(PMe3)2 (5a,b) with a Mo-P double bond, 3 affords a novel divalent product, (C5Me4CH2PR2)WH(PMe3)2 (6a,b) resulting from sp3 C-H bond activation and subsequent P-C bond formation. The molecular structure of 6b consists of a distorted four-legged piano stool with H trans to the PCy2 arm of the (C5Me4CH2PCY2)- ligand. Oxidative addition of PPh2H to complexes 1 and 3 gives Cp*MHCl(PPh2)(PMe3), which react in turn with LiPPh2 to afford divalent Cp*Mo(PPh2)(PPh2H)(PMe3) (5c) and tetravalent Cp*WH(PPh2)2(PMe3) (8a). Substitution of PMe3 in 8a by PPh2H gives divalent Cp*W(PPh2)(PPh2H)2 (5e). In solution, tetravalent 8a,b are in equilibrium with their divalent tautomers 5d,e as a result of reversible P-H bond activation. The molecular structure of 8a shows that the PCipso2 planes of the terminal (PPh2)- ligands are pseudoparallel to the C5Me5 ring plane and constitute a delocalized P-W-P unit with W-P bond orders of 1.5. Reaction of Cp*TaMe2(eta-C2H4) With PPh2H gives methane and Cp*TaMe(PPh2)(eta-C2H4) (9); barriers to rotation about Ta-P and Ta-olefin bonds were estimated from C-13 DNMR spectra. Hydrogenation of 9 in the presence of PPh2H affords methane, ethane, and fluxional complex Cp*TaH(PPh2)3, which contains two types of Ta-P multiple bonds.