Reactions of the Dirhenium(II) Complexes Re₂X₄(μ-dppm)₂ (X = Cl, Br; dppm = Ph₂PCH₂PPh₂) with Isocyanides. 21.¹ A Comparison with the Complexes Re₂Cl₄(μ-dppE)₂ and Re₂Cl₄(μ-dcpm)₂ (dppE = Ph₂PC(CH₂)PPh₂; dcpm = Cy₂PCH₂PCy₂) and the Structural Characterization of Complexes of the Types Re₂Cl

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.

Reaction of Re2(μ-O2CCH3)4Cl2 with Bis(dicyclohexylphosphino)methane (dcpm): Isolation of the Mixed-Valent Complex O3ReReCl(η2-dcpm)2 Containing an Unsupported Re−Re Bond

“…This difference in behavior of dmpm, when compared to that of its phenyl analogue Ph 2 PCH 2 PPh 2 (dppm), had been noted previously and is shown most strikingly in the formation of the tris complex Re 2 Cl 4 (μ-dmpm) 3 , , while dppm forms only Re 2 Cl 4 (μ-dppm) 2 . To understand the effects of the smaller size of dmpm and its greater basicity compared to Ph 2 PCH 2 PPh 2 and related aryl phosphines, we have been studying the dirhenium complexes of Cy 2 PCH 2 PCy 2 (dcpm), − a phosphine that has a basicity comparable to that of dmpm but exhibits a size more like that of dppm. In this paper, we describe the reaction of dcpm with Re 2 (μ-O 2 CCH 3 ) 4 Cl 2 that leads to an unusual mixed-valent dirhenium complex O 3 ReReCl(η 2 -dcpm) 2 which contains formally Re(VI) and Re(I) centers and has an unsupported Re−Re bond.…”