Oxidation of Organometallic Platinum and Palladium Complexes Obtained from C−H Activation

η^3-Cyclohexenyl and -indenyl Pt(II) and Pd(II) diimine complexes, which are generated via C−H activation of cyclohexene and indene by Pt and Pd hydroxy dimers, are selectively oxidized by Br_2, Na_2PtCl_6, and CuCl_2 to give halogenated organic products along with well-defined Pd(II) and Pt(II) species

C-H Bond Activation by [{(Diimine)Pd(μ-OH)}2]2+ Dimers: Mechanism-Guided Catalytic Improvement

These conclusions—that the hydroxy-bridged dimer 1b is the most reactive species in the Pd system, considerably more reactive than either 2a or 2b towards C-H bond activation, and that there is an important solvent-assisted component in the rate law—suggest a way to substantially improve the catalytic conversion of cyclohexene into benzene [Eq. (3)]. Our previous studies involved 2b (or mixtures of 1b and 2b) in the noncoordinating solvent dichloroethane. In a typical experiment, after 24 h under 1 atm of O2 with 5 mol% of 2b as the catalyst, 8% of the cyclohexene had been converted into benzene; furthermore, there was an initiation period before any reaction occurred, and competing disproportionation of cyclohexene to benzene and cyclohexane was a major side reaction.[3] In contrast, under the same conditions but using only 1 mol% of pure 1b as the catalyst and TFE as solvent, conversion was 25% after 24 h, with no induction period or competing isomerization.[7

C−H Bond Activation by Air-Stable [(Diimine)M^(II)(μ_2-OH)]_2^(2+)Dimers (M = Pd, Pt)

Air- and water-tolerant C−H activation is observed in reactions of [(diimine)Pt(μ_2-OH)]_2^(2+) dimers with allylic and benzylic C−H groups. The reactions proceed in good yields under mild conditions. Mechanistic studies indicate that the active species is the monomeric [(diimine)Pt(OH_2)]^(2+) dication. The related palladium species, [(diimine)Pd(μ_2-OH)_2]^(2+), exhibit similar stoichiometric activations and also effect catalytic oxidation of cyclohexene to benzene with molecular oxygen as the terminal oxidant