Olefin Complexes of Low‐Valent Rhenium

Abstract

AbstractReplacement of the MeCN group in the acetonitrile‐cis‐dibromo(nitrosyl)‐trans‐bis(phosphane)rhenium compounds 1a,b (R = iPr a, R = Cy b) with ethylene afforded the olefin derivatives [Re(η2‐H2C=CH2)(NO)(PR3)2Br2] (2a,b) (R = iPr a, R = Cy b). Compound 1a could be converted into the dimethyl species [Re(MeCN)(NO)(PiPr3)2Me2] (3a) applying MeLi in toluene; the related methylation of 1b, however, failed. Abstraction of a Br– ion from 1a,b with [Na][BAr′4] in acetontrile yields the air‐stable salts [Re(MeCN)2(NO)(PR3)2Br]+[BAr′4]– (4a,b) (R = iPr a, R = Cy b) and under 1 bar of H2 complexes 1a,b were converted into the known dihydrogen species [Re(η2‐H2)(NO)(PR3)2(Br)2] (5a,b) (R = iPr a, R = Cy b). Reduction of [Re(MeCN)(NO)(PR3)2Br2] (1a,b) with Na/Hg under 1 bar of C2H4 afforded the butadiene complex [Re(η4‐C4H6)(η2‐H2C=CH2)(NO)(PR3)2] (6a,b) (R = iPr a, R = Cy b) via oxidative coupling of two coordinated ethylene groups followed by double β‐H shift and subsequent reductive H2 elimination from the formed dihydride complex. Reduction of the complexes [Re(CO)(NO)(PR3)2Cl2] (7a,b) (R = iPr a, R = Cy b) with Na/Hg yields the pentacoordinate species [Re(CO)(NO)(PR3)2(η2‐H2C=CH2)] (8a,b) (R = iPr a, R = Cy b) under the same conditions as for 6a,b. Reaction of 8a with 1 equiv. of B(C6F5)3 leads to the [Re(CO)2{NOB(C6F5)3}(PiPr3)2] compound (9a) and to the carbonyl nitrosyl complexes [Re(CO)2(NO)(PiPr3)2] (10a) with evolution of ethylene. The same reaction of 8a and 8b, but applying 1 bar of CO, leads to exclusive formation of 9a,b. Complexes 4a, 4b, 6b, 8a, 9a, and 9b were characterized by X‐ray diffraction studies.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)