Mechanism of palladium-catalyzed diene cyclization/hydrosilylation: direct observation of intramolecular carbometalation

The results of kinetic, deuterium-labeling, and low-temperature NMR studies have established a mechanism for the palladium-catalyzed cyclization/hydrosilylation of dimethyl diallylmalonate (1) with triethylsilane involving rapid, irreversible conversion of the palladium silyl complex (phen)Pd(SiEt(3))(NCAr)](+) BAr(4)](-) Ar = 3,5-C(6)H(3)(CF(3))(2)] (4b) and 1 to the palladium 5-hexenyl chelate complex (phen)Pdeta(1),eta(2)-CH(CH(2)SiEt(3))CH(2)C(CO(2)Me)(2)CH(2)CH=CH(2)]](+) BAr(4)](-) (5), followed by intramolecular carbometalation of 5 to form the palladium cyclopentylmethyl complex trans-(phen)PdCH2CHCH2C(CO2Me)2CH2CHCH2SiEt3](NCAr)]+ BAr4]- (6), and associative silylation of 6 to release 3 and regenerate 4b.