Alkyne <i>gem</i>‐Hydrogenation: Formation of Pianostool Ruthenium Carbene Complexes and Analysis of Their Chemical Character

Abstract

Parahydrogen (p-H₂ ) induced polarization (PHIP) NMR spectroscopy showed that [Cp^X Ru] complexes with greatly different electronic properties invariably engage propargyl alcohol derivatives into gem-hydrogenation with formation of pianostool ruthenium carbenes; in so doing, less electron rich Cp^X rings lower the barriers, stabilize the resulting complexes and hence provide opportunities for harnessing genuine carbene reactivity. The chemical character of the resulting ruthenium complexes was studied by DFT-assisted analysis of the chemical shift tensors determined by solid-state ¹³ C NMR spectroscopy. The combined experimental and computational data draw the portrait of a family of ruthenium carbenes that amalgamate purely electrophilic behavior with characteristics more befitting metathesis-active Grubbs-type catalysts.