A Water-Stable Organometallic Rhodium Quinone Catalyst and Its Recyclability

When the insoluble dimers [Rh(COD)X]2 (X = OH−, Cl−) are in contact with a basic aqueous solution of hydroquinone dianion, the precipitate dissolves to afford (benzoquinone)Rh(COD)− (2). Complex 2 is very stable and can be recycled many times as a homogeneous catalyst for the conjugate addition of boronic acids to olefins. NMR spectra suggest that the catalytic species is indeed the quinone complex 2.