Four-Electron-Donor Hemilabile η³-PPh₃Ligand that Binds through a CC Bond Rather than an Agostic C−H Interaction, and Displacement of the CC by Methyl Iodide or Water

Hydride transfer from CP(CO)(2)(PPh3)MoH to Ph3C(+)BAr'4(-) [Ar' = 3,5-bis(trifluorometliyl)phenyl] produces [CP(CO)(2)(eta(3)-PPh3)Mo](+)[BAr'4](-), Spectroscopic and crystallographic data indicate that one C = C of a Ph ring is weakly bound to the Mo, so that the PPh3 ligand is a four-electron-donor ligand. Computations (DFT/B3LYP and MP2 on [CP(CO)(2)(eta(3)-PPh3)Mo](+) and [Cp(CO)(2)(eta(3)-PH2Ph)Mo](+), and DFT/B3LYP on [CP(CO)(2)(eta(3)-(PHBuPh)-Bu-t)Mo](+) and [CP(CO)(2)(eta(3)-PH2Ph)Nb]) provide further information on the bonding and on the preference for bonding of the metal to the C = C bond rather than an agostic C-H interaction found in many related complexes. The hemilabile C = C bond is readily displaced by CH3I or H2O, and crystal structures are reported for [CP(CO)(2)(PPh3)Mo(ICH3)](+) and [CP(CO)(2)(PPh3)Mo(OH2)](+). The equilibrium constant for [CP(CO)(2)(eta(3)-PPh3)Mo](+) + ICH3 to give [CP(CO)(2)(PPh3)MO(ICH3)](+) is K-eq = 5.2 x 10(2) m(-1) in CD2Cl2 at 22 degrees C.