Reactions of the dirhenium(II) complexes Re2X4(mu-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides. 21. A comparison with the complexes Re2Cl4(mu-dppE)2 and Re2Cl4(mu-dcpm)2 (dppE = Ph2PC(=CH2)PPh2; dcpm = Cy2PCH2PCy2) and the structural characterization of complexes of the types Re2Cl4(mu-LL)2(CNR), Re2Cl4(mu-LL)2(CNR)2, and [Re2Cl3(mu-LL)2(CNR)3]+ (LL = dppm, dppE, dcpm; R = t-Bu, Xyl).

Abstract

A study of the reactions between the triply bonded dirhenium(II) complexes Re2Cl4(mu-LL)2, where LL = Ph2PCH2PPh2 (dppm), Ph2PC(=CH2)PPh2 (dppE), or Cy2PCH2PCy2 (dcpm), with the isocyanides t-BuNC and XylNC (Xyl = 2,6-dimethylphenyl) show that complexes of the type Re2Cl4(mu-LL)2(CNR), Re2Cl4(mu-LL)2(CNR)2, and [Re2Cl3(mu-LL)2(CNR)3]+ are formed sequentially. Several of these have been structurally characterized by X-ray crystallography: Re2Cl4(mu-dppm)2(CNXyl) (2), Re2Cl4(mu-dcpm)2(CNXyl) (11), Re2Cl4(mu-dppE)2(CN-t-Bu)2 (6), Re2Cl4(mu-dcpm)2(CN-t-Bu)2 (12), and [Re2Cl3(mu-dppE)2(CN-t-Bu)3]Cl (7). Complex 2 has an A-frame-like structure with a single mu-Cl bridging ligand, whereas for 11 the structure is like that of 2 but without this bridge, viz., Cl2Re(mu-dppm)2ReCl2(CNXyl) with a Re-Cl bond approximately collinear with Re identical to Re. The symmetrical complexes 6 and 12 are essentially isostructural and have an anti-arrangement of the two t-BuNC ligands. Complex 7 has the open bioctahedral structure [(t-BuNC)2ClRe(mu-dppE)2ReCl2(CN-t-Bu)]+, which is quite different from that of the edge-sharing bioctahedron found in salts of the [Re2Cl3(mu-dppm)2(CNXyl)3]+ cation and its neutral congener Re2Cl3(mu-dppm)2(CNXyl)3; preliminary crystallographic data for the latter compound show the structure to be (XylNC)ClRe(mu-Cl)(mu-CNXyl)(mu-dppm)2ReCl(CNXyl) with an all-cis arrangement of XylNC ligands. The Re-Re bond distances of 2, 6, 7, 11, and 12 occur in the range 2.289-2.380 A and are consistent in all instances with the retention of a Re identical to Re bond, albeit weakened by some degree of Re-->CNR(pi*) back-bonding.