Reactivity of a Palladacyclic Complex: A Monodentate Carbonate Complex and the Remarkable Selectivity and Mechanism of a Neophyl Rearrangement

The
ligand N­(CH2-2-C5H4N)2(CH2CH2CH2OH), L1,
reacted with [Pd­(CH2CMe2C6H4)­(COD)] to give a new fluxional “cycloneophyl”
organopalladium complex [Pd­(CH2CMe2C6H4)­(κ2-L1)], 1, which on attempted recrystallization from THF gave the monodentate
carbonate complex [Pd­(CO3)­(κ3-L1)], 2. Complex 2 was prepared in designed
syntheses by reaction of [PdCl­(κ3-L1)]+ with silver carbonate or by reaction of [Pd­(OH)­(κ3-L1)]+ with CO2. Complex 1 reacted with aqueous CO2 to give the cationic
neophylpalladium complex [Pd­(CH2CMe2C6H5)­(κ3-L1)]+(HCO3)−, 6. Complex 6 reacts with hydrogen peroxide to give complex 2 with
release of a mixture of organic products, the major one being 2-phenyl-2-butanol, PB. The formation of PB involves a neophyl rearrangement
with the unprecedented preference for methyl over phenyl migration.
A mechanistic basis for this unexpected reaction is proposed, involving
β-carbon elimination at a palladium­(IV) center.