| 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 studiesindicate that these reactions proceed by a two-step pathway, viz., initial reversible dissociation of the pyridineligand from the cationic complex to generate a five-coordinate PtIV intermediate, followed by irreversible concertedC−C bond formation. The reaction is inhibited by pyridine. The highly positive values for ΔS⧧obs = +180 ± 30 JK-1 mol-1, ΔH⧧obs = 160 ± 10 kJ mol-1, and ΔV⧧obs = +16 ± 1 cm3 mol-1 can be accounted for in terms ofsignificant 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 eliminationfrom cationic PtIV complexes in a variety of solvents. The absence of a significant solvent effect for this reactionprovides strong evidence that the C−C reductive coupling occurs from an unsaturated five-coordinate PtIV intermediaterather than from a six-coordinate PtIV solvento species.
- Cationic complexes of the type fac-[(L2)PtIVMe3(pyr-X)]+ (L2 = diphosphine) undergo C−C reductive elimination reactions to form [L2PtIIMe(pyr-X)][OTf] and ethane. Detailed mechanistic studies indicate that these reactions proceed by initial reversible dissociation of the pyridine ligand to generate a five-coordinate PtIV intermediate, followed by irreversible concerted C−C bond formation.
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