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 d6 square-based-pyramidal metal fragment
[RuCl2(PR23)­(CCHR1)], combined with electron-withdrawing substituents R1 and electron-rich groups R2, would provide the
ideal conditions favoring the vinylidene form thermodynamically.