Abnormal N‑Heterocyclic Carbene-Phosphine Ruthenium(II)
Complexes as Active Catalysts
for Transfer Hydrogenation
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Abstract
The
bifunctional phosphine–abnormal N-heterocyclic carbene
ruthenium(II) complex RuBr(OAc)(PPh<sub>3</sub>)(P–aNHC) (<b>1</b>) has been synthesized in high yield by reaction of Ru(OAc)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub> with a phosphine imidazolium
bromide (P–NHC × HBr) and characterized by X-ray diffraction.
This compound shows high catalytic activity for the transfer hydrogenation
of ketones to alcohols in 2-propanol. Rate and efficiency of <b>1</b> can be enhanced by the addition of ethylenediamine or benzylamine,
affording TOFs up to 140 000 h<sup>–1</sup>. Reaction
of <b>1</b> with ethylenediamine leads to the Ru carbene/amine
complex [Ru(OAc)(PPh<sub>3</sub>)(P–aNHC)(H<sub>2</sub>NCH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>)]Br (<b>2</b>), which displays
the same activity of the <i>in situ</i> generated species
