Density functional study of catalytic silane alcoholysis at a [Fe(Cp)(CO)(PR3)]+ center

Catalytic conversion of MeOH and SiH 4 to MeOSiH 3 and H 2 at a [Fe(Cp)(CO)(PR 3 )] + center was studied computationally at a gradient-corrected level of density functional theory (BP86). Intermediates and transition states for R' = H and Ph were characterized along the catalytic cycle, the rate-determining step of which is indicated to be H 2 dissociation from [Fe(Cp)-(CO)(PR 3 )(H 2 )] + , in accord with a mechanistic study for higher substituted substrates (Brookhart, et al. J. Mol. Catal. A 1998, 130, 107). For the model catalyst (R = H), introduction of SiMe 3 , NMe 2 , COMe, NO 2 , CN, or Cl substituents at the Cp ring decreases the rate-determining barrier (up to 6 kcal/mol for NMe 2 ). A loose correlation is found between these barriers and δ( 5 7 Fe) values computed for the correspondingly derivatized precursor models Fe(C 5 H 4 X)(CO)(PH 3 )Me. In the transient, free [Fe(C 5 H 4 X)(CO)(PPh 3 )] + complex, there can be competition between the substituent X and a phenyl group of the PPh 3 ligand for a hemilabile intramolecular coordination to iron. Modification of the phosphine is thus expected to open further possibilities for tuning the catalyst properties and activities.