A combined QM/MM study of ligand substitution enthalpies in the L2Fe(CO)(3), RuCpL2Cl, and RuCp*L2Cl systems

A combined density functional and molecular mechanics approach (QM/MM) has been validated in a study of the substitution reactions: (i) (PH3)(2)Fe(CO) (3) + 2ER(3) <-> (ER3)(2)Fe(CO)(3) + 2PH(3) (ER3 = PMe3, PEt3, PMePh2, PPh3 , PCyPh2, (PPr3)-Pr-i, PBz(3), PCy3, AsEt3, AsPh3); and (ii) Cp'Ru(PH3)(2)C l + 2ER(3) <-> Cp'Ru(ER3)(2)Cl + 2PH(3) (Cp' = C5H5, C-5(CH3)(5); ER3 = PMe 3, PEt3, (PBu3)-Bu-n, PMe2Ph, PMePh2, PPh3, AsEt3, P(OMe)(3), P(OPh)(3), P( OCH2)(3)CEt). The steric influence of the R substituents on the substitutio n enthalpies correlates well with experimental data. The combined QM/MM app roach is also able to afford molecular structures in good accord with exper imental estimates.