Web Release Date: October 4,
Mechanistic Information on the Reductive Elimination from Cationic Trimethylplatinum(IV) Complexes to Form Carbon-Carbon Bonds
and
Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany, and Department of Chemistry, University of Washington, Seattle, Washington 98195-1700
Received April 1, 2005
Abstract:
Cationic complexes of the type fac-[(L2)PtIVMe3(pyr-X)][OTf] (pyr-X = 4-substituted pyridines; L2 = diphosphine,
viz., dppe = bis(diphenylphosphino)ethane and dppbz = o-bis(diphenylphosphino)benzene; OTf = trifluoromethanesulfonate) undergo C-C reductive elimination reactions to form [L2PtIIMe(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 PtIV intermediate, followed by irreversible concerted
C-C bond formation. The reaction is inhibited by pyridine. The highly positive values for 
S
obs = +180 ± 30 J
K-1 mol-1, Hobs = 160 ± 10 kJ mol-1, and Vobs = +16 ± 1 cm3 mol-1 can be accounted for in terms of
significant bond cleavage and/or partial reduction from PtIV to PtII 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 PtIV 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 PtIV intermediate
rather than from a six-coordinate PtIV solvento species.
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