Rhenium Nitrosyl Complexes for Hydrogenations and Hydrosilylations

Abstract

The tris(acetonitrile)dibromonitrosylrhenium(I) compound (1a) was obtained by reduction of the paramagnetic [NMe4]2[Re(NO)Br5] salt with Zn in MeCN. Subsequent reaction of 1a with THF produced the THF derivative [Re(NO)(THF)(MeCN)2Br2] (1b). Reaction of 1b with PiPr3, Pcy3, or P(p-tolyl)3 yielded bis(acetonitrile)-cis-dibromo(nitrosyl)-trans-bis(phosphine)rhenium complexes (R = iPr 2a, cy 2b, p-tolyl 2c). Treatment of 2a,b with excess NaBH4 produced the known borohydride complexes [Re(H)(η2-BH4)(NO)(PR3)2] (R = iPr 3a, cy 3b). Replacement of the BH3 moiety of 3a,b in THF by ethylene (1 bar) produced the dihydride complexes [Re(H)2(η2-C2H4)(NO)(PR3)2] (4) (R = iPr a, cy b). Protonation of 4a,b with HBF4·OEt2 afforded H2 and the monohydrido tetrafluoroborato species [Re(H)(NO)(PR3)2(η2-C2H4)(BF4)] (R = iPr 5a, cy 5b). X-ray diffraction studies were carried out on 1a, 2b,c, and 5b. Complexes 4a,b are catalytically active in olefin, imine, and ketone hydrogenations and in olefin and ketone hydrosilylations, as well as in the scrambling of H2/D2 to give HD under mild conditions.