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

Article abstract of DOI:10.1021/acs.organomet.7b00631

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.