Computational Discovery of Stable Transition-Metal Vinylidene Complexes

Experimental results have long suggested that catalyst optimization is an inherently multivariate process, requiring the screening of reaction conditions (temperature, pressure, solvents, precursors, etc.), catalyst structure (metal and ligands), and substrate scope. With a view to demonstrating the feasibility and utility of multivariate computational screening of organometallic catalysts, we have investigated the structural and electronic properties of a library of transition-metal-coordinated alkyne and vinylidene tautomers in different coordination environments. By varying the substituents on the organic moiety of 60 alkyne/vinylidene pairs we were able to capture and quantify the key structural and electronic effects on tautomer preference. For a carefully selected subset of substituents, the effects of metal and ancillary ligands were then explored. We have been able to formulate a protocol for assessing the stabilization of vinylidenes in transition-metal complexes, suggesting that the d<sup>6</sup> square-based-pyramidal metal fragment [RuCl<sub>2</sub>(PR<sup>2</sup><sub>3</sub>)­(CCHR<sup>1</sup>)], combined with electron-withdrawing substituents R<sup>1</sup> and electron-rich groups R<sup>2</sup>, would provide the ideal conditions favoring the vinylidene form thermodynamically.