title: Mechanistic information on the reductive elimination from cationic trimethylplatinum(IV) complexes to form carbon-carbon bonds.
abstract: Cationic complexes of the type fac-[(L(2))Pt(IV)Me(3)(pyr-X)][OTf] (pyr-X = 4-substituted pyridines; L(2) = diphosphine, viz., dppe = bis(diphenylphosphino)ethane and dppbz = o-bis(diphenylphosphino)benzene; OTf = trifluoromethanesulfonate) undergo C-C reductive elimination reactions to form [L(2)Pt(II)Me(pyr-X)][OTf] and ethane. Detailed studies indicate that these reactions proceed by a two-step pathway, viz., initial reversible dissociation of the pyridine ligand from the cationic complex to generate a five-coordinate Pt(IV) intermediate, followed by irreversible concerted C-C bond formation. The reaction is inhibited by pyridine. The highly positive values for DeltaS()(obs) = +180 +/- 30 J K(-1) mol(-1), DeltaH(obs) = 160 +/- 10 kJ mol(-1), and DeltaV()(obs) = +16 +/- 1 cm(3) mol(-1) can be accounted for in terms of significant bond cleavage and/or partial reduction from Pt(IV) to Pt(II) in going from the ground to the transition state. These cationic complexes have provided the first opportunity to carry out detailed studies of C-C reductive elimination from cationic Pt(IV) complexes in a variety of solvents. The absence of a significant solvent effect for this reaction provides strong evidence that the C-C reductive coupling occurs from an unsaturated five-coordinate Pt(IV) intermediate rather than from a six-coordinate Pt(IV) solvento species.
authors.affiliation: Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Germany.
authors.forename: Joanna
authors.initials: J
authors.lastname: Procelewska
authors.forename: Achim
authors.initials: A
authors.lastname: Zahl
authors.forename: Günter
authors.initials: G
authors.lastname: Liehr
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Smythe
authors.forename: B Scott
authors.initials: BS
authors.lastname: Williams
authors.forename: Karen I
authors.initials: KI
authors.lastname: Goldberg