Computational Study of Intramolecular Coordination Enhanced Oxidative Addition to form PdIV-Pincer Complexes, and Selectivity in Aryloxide Attack at PdIVCH2CRR′ Motifs in Palladium-Mediated Organic Synthesis

Abstract

Computational studies support the key role of intramolecular coordination by a carboxylate group in the facile oxidative addition of the iodoarene 2,6-(HO2C)2C6H3I to a PdII center to form the pincer-PdIV motif Pd{2,6(O2C)C6H3-O,C,O}, Pd(OCO). Mechanisms of attack by an aryloxide nucleophile at the methylene group in a palladacycle PdIV(OCO)(CH2CRR′–E) to form ArOCH2CMe2–E (E = oxime) are examined; for RR′ = HEt and E = amine, it is mainly the formation of analogous ArOCH2CHEt–E together with CH2═CEt–E arising from β-hydrogen elimination. Computational results are in agreement with recent experimental results by Whitehurst, Gaunt. [ J. Am. Chem. Soc. 2020, 142, 14169]. For β-hydrogen elimination, computation demonstrates that the conformational flexibility in the chelate ring is required to allow the hydrogen atom to be in an axial orientation relative to Pd–C, thus maximizing the dihedral angle Pd···C–C···H in the transition-state fragment Pd···CH2C(R)···H···OAr. Bulky substituents R′ at the β-position, CHR′, favor nucleophilic attack at the methylene carbon.