Computational study of selectivity in the [PtIICl4]2−-catalysed arylation of arenes by diaryliodonium reagents: arene activation at PtIV centres

Abstract

The mechanism for the [Pt^IICl₄]²⁻-catalysed reaction of Ph₂I^III(TFA) (TFA = trifluoroacetate) with naphthalene (NapH) to give β-phenylation over α-phenylation of naphthalene has been examined by computational methods. In support of the mechanism proposed by Sanford based on experimental evidence, reaction commences by oxidative phenyl transfer from [Ph₂I]⁺ to [Pt^IICl₄]²⁻, giving trans-[PhPt^IVCl₄(TFA)]²⁻. Transformation to cis-[PhPt^IVCl₃(TFA)]⁻ leads to reaction with NapH at the β-position in an inner-sphere Concerted Metalation Deprotonation (CMD) manner to give cis-[Ph(Nap)Pt^IVCl₃]⁻ and trifluoroacetic acid. Reductive elimination yields β-PhNap, and coordination of chloride regenerates [Pt^IICl₄]²⁻ for subsequent catalytic cycles. The selectivity for β-phenylation over α-phenylation is attributable to steric factors in the CMD Pt^IV transition state containing a higher coordination number than that occurring for related reactions in Pd^II catalysis that gives α-phenylation.