Hydride Abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz = C5(CH2Ph)5): New Cationic Complexes Stabilized by η5:η2-C5H4:C6H5 Bonding of the Pentabenzylcyclopentadienyl Ligand

Hydride abstraction from [MCpBz(CO)(3)H] (M = Mo, W; Cp8z = C-5(CH2Ph)(5)) using trityl cations led to [M{eta(5):eta(2)-C(5)Bz(4)CH(2)Ph}(CO)(3)]BArF (BArF = B(3,5-C6H3(CF3)(2))(4); M = Mo (3), W (4)) or [MCpBz(CO)(3)(FBF3)] (M = Mo (5), W (6)) depending on the trityl counterions. The stabilization of the acidic metal centers in 3 and 4 is made through the coordination of a C=C bond of one phenyl ring, generating ansa-bridged cyclopentadienyl phenyl carbonyl complexes. 5 and 6 are zwitterionic compounds stabilized by the coordination of the BF4 anion. An exchange process between coordinated and noncoordinated phenyl rings occurs in dichloromethane solutions of 3. VT NMR experiments gave the exchange rate at various temperatures and Delta G double dagger(298) = 10.1 +/- 0.2 kcal mol(-1). In 4 the phenyl bonding is static at room temperature, on the NMR time scale. Reactions of 3 and 4 with CO and H2O led to [MCpBz(CO)(4)]BArF (M = Mo (7), W (8)) and [MCpBz(CO)(3)(OH2)]BArF (M = Mo (11), W (12)). In CH2Cl2 solutions 3 and 4 convert slowly to 7 and 8, respectively. DFT calculations attest to the stability of 3 to H2O bonding and also show that the replacement of phenyl coordination by CO is a favorable process (Delta H = -13.8 kcal mol(-1)).