Computational study of intramolecular coordination enhanced oxidative addition to form Pd^IV-pincer complexes, and selectivity in aryloxide attack at Pd^IVCH₂CRR′ 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. Show more