Mechanistic insights into the rhodium catalysed dehydrogenative cycloaddition of cyano-yne-allene substrates

Abstract

The continued progress in creating novel acceptorless dehydrogenations for environmentally friendly and efficient chemical synthesis is anticipated to be significantly shaped by the design of efficient catalysts that can do the job. In this study, we present a comprehensive mechanistic investigation utilizing DFT calculations to elucidate the mechanism of the [RhCl(PPh3)3]-catalysed dehydrogenative cycloaddition of cyano-yne-allene substrates. Overall, the reaction can be described as a cycloaddition involving the three unsaturations, followed by a hydrogen shift, 6π electrocyclization and acceptorless H2 elimination. The crucial factors contributing to the observed reactivity are as follows: (i) the favoured cycloaddition pathway involves the external double bond of the allene in the formation of the initial metallacycle; (ii) the stabilization of the alkyne insertion intermediate that occurs through η3-coordination to the rhodium; and (iii) the presence of a weak base that assists in deprotonation

We are grateful for the financial support from the Ministerio de Ciencia, Innovación y Universidades (Projects PID2020-113711GB-I00 MCIN/AEI/10.13039/50110001103, RED2022-134074-T, RED2022-134331-T, and predoctoral fellowship FPU18/02912 to A. D.-J.) and the Generalitat de Catalunya (Project 2021-SGR-623)

Open Access funding provided thanks to the CSUC agreement with Royal Society of Chemistry (RSC)