Substrate‐Mediated Deactivation of a Ru(PtBu2NBn2) Cooperative Complex

Abstract

AbstractLigand design for metal–ligand cooperative (MLC) catalysis is inherently more complex than that for traditional non‐cooperative ligands. The basicity, sterics and structure of the acid/base group in MLC proton‐transfer (PT) complexes, for instance, undoubtedly influence catalyst performance. Herein, we evaluate the highly tunable PR2NR′2 (1,5‐R′‐3,7‐R‐1,5‐diaza‐3,7‐diphosphacyclooctane) ligand family for the first time in an organic transformation. With [Ru(Cp)(PtBu2NBn2)(MeCN)][PF6] as the catalyst, no turnover was observed in the anti‐Markovnikov hydration of alkynes, a known PT MLC reaction. Treatment of the cooperative complex with phenylacetylene affords a vinylammonium product in which the pendant nitrogen atom of the PtBu2NBn2 ligand forms a Lewis acid–base adduct with the alpha‐carbon atom of the vinylidene intermediate. Characterization by X‐ray crystallography and NMR spectroscopy conclusively assign this structure in both the solid and the solution state. The adduct formation is irreversible, and the adduct is characterized as a catalyst deactivation product.