Iodomethane oxidative addition to β-diketonatobis(triphenylphosphite)rhodium(I) complexes: A synthetic, kinetic and computational study

New rhodium(I)- and rhodium(III)-beta-diketonato complexes of the type [Rh(FcCOCHCOR)(P(OPh)(3))(2)] and [Rh(FcCOCHCOR)(P(OPN3)(2)(CH3)(I)], with Fc = ferrocenyl and R = Fc, CH3 and CF3, have been synthesized. The reactivity of complexes of the type [Rh(beta-diketonato)(P(OPh)(3))(2)] increase in the order: beta-diketonato = (CF3COCHCOCF3)(-) < (CF3COCHCOPh)(-) < (CF3COCHCOCH3)(-) < (PhCOCHCOPh)(-) < (CF(3)COCHCOFc)(-) < (CH3COCHCOPh)(-) < (CH3COCHCOCH3)(-) < (CH(3)COCHCOFc)(-) < (FcCOCHCOFc)(-), giving linear relationships between the kinetic parameter In k(2) and the parameters that are related to the electron density on the rhodium centre; the sum of the group electronegativities of the beta-diketonato side groups (chi(R) + chi(R')) and the pK(a) of the uncoordinated beta-diketone RCOCH2COR'. The large negative values of the volume and entropy of activation indicated a mechanism which occurs via a polar transition state. A density functional theory study, at the PW91/TZP level of theory, indicates that oxidative addition of iodo methane to [Rh(FcCOCHCOCF(3))(P(OCH3)(3))(2)] occurs via a two-step mechanism. This mechanism involves a nucleophilic attack by the metal on the methyl carbon to displace iodide to form a metal-carbon bond and the coordination of iodide to the five-coordinated intermediate to give a six-coordinated trans alkyl product. (C) 2011 Elsevier Ltd. All rights reserved.