An Unexpectedly Stable Chiral Hydrido‐Solvent Complex of RuII: A mechanistic link in the enantioselective hydrogenation of pyrones. Preliminary communication

Abstract
The ligand (6,6′‐dimethoxybiphenyl‐2,2′‐diyl)bis[3,5‐di(tert‐butyl)phenylphosphine] (1) forms an unexpectedly stable hydrido‐bis‐solvento complex of composition [RuH(isopropanol)2(1)]BF4, (2) under the conditions used in the enantioselective hydrogenation of pyrones. The structure of 2, determined by X‐ray diffraction, represents the first well‐characterized chiral five‐coordinate bis‐phosphine ruthenium‐hydride complex stable as a solvento complex, and provides a structural link in the enantioselective pyrone hydrogenation cycle catalyzed by [Ru(OAc)2(1)]. Using the arene complex [RuH(p‐cymene)(1)]BF4 (3), the chiral pocket of coordinated 1 is shown to be relatively rigid, via NMR spectroscopy. This is reflected in restricted rotation about one of the four P–[3,5‐di(tert‐butyl)phenyl] PCipso bonds at room temperature.

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