Platinum-Catalysed Hydrofluorination of Alkynes at Room Temperature Promoted by a Fluoride Shuttle.

Abstract

Hydrofluorination of alkynes provides a synthetic route to access fluoroalkenes, a class of compounds with wide applications in chemical research. Herewith, we describe an exceptional hydrofluorination process of alkynes catalysed by Pt(II) complexes at room temperature. Various Pt(II) dichloride complexes bearing chelating phosphines were synthesised and studied towards their catalytic behaviour. Mechanistic investigations suggest the involvement of a dicationic Pt(II) bis(alkyne) species as well as a cationic ß-fluorovinyl Pt(II) complex in the catalytic cycle. Remarkably, the hydrofluorination is enabled by fluorinated anions. The corresponding acids BF3, HF as well as PF5 act as fluoride shuttles to allow for an outer-sphere fluorination of the metal-bound substrate. Detailed DFT analyses for BF3 show that the hydrofluorination is mediated by complexes between the fluorinated anion and HF. This lowers the hydrofluorination barriers sufficiently to outcompete the simultaneously occurring, more exergonic cyclisation of two coordinated alkynes to a structurally characterised cycloallyl complex. The catalytic system can be applied to a wide substrate scope to generate fluoroalkenes bearing bulky alkyl, aryl and electron withdrawing groups, such as ester and carbonyl substituents.