Conversion of an electron-rich triple bond to a double bond by oxidative addition of diphenyl diselenide to Re2Cl4(.mu.-dppm)2. Preparation and characterization of Re2Cl4(.mu.-SePh)2(.mu.-dppm)2 (dppm = bis(diphenylphosphino)methane)
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The dirhenium(II) complex Cl2Re(μ-dppm)2ReCl2with a σ2π4δ2δ*2triple bond undergoes a clean, facile reaction with PhSeSePh to produce Cl2Re(μ-SePh)2(μ-dppm)2ReCl2in high yield. In this reaction, oxidative addition of the Se-Se single bond to the Re=Re triple bond results in a conversion of the d5-d5M2L8parent compound to a d4-d4M2L10species which possesses a formal double bond (σ2π2δ*2δ2). The identity of the product has been confirmed by a single-crystal X-ray study, and the structural results are compared with the data previously reported for the analogous doubly bonded Re2Cl6(dppm)2. Re2Cl4(SePh)2(dppm)2crystallizes in the monoclinic space group P21/n with a = 13.115 (2) Å, b = 15.463 (5) Å, c = 14.309 (2) Å, β = 102.00 (1)°,V = 2838 (2) Å3, and Z =2. The crystallographic symmetry of the molecule is Ī while the effective molecular symmetry is 2/m (C2h). Important bond distances and angles are Re-Se(av) = 2.462  A, Re-Cl(av) = 2.45  A, Re-P(av) = 2.474  A, zRe-Re-Se = 57.33 (4)°, and zRe-Re-Cl(av) == 140.4 °. The Re-Re distance in Re2Cl4(SePh)2(dppm)2is 2.656 (1) Å, which is 0.04 Å longer than the M-M distance in Re2Cl6(dppm)2. The lengthening of the Re-Re bond is attributed to the difference in size of the bridging groups (SePh vs. Cl). The properties of the title compound were investigated by several other methods, including infrared and UV-visible spectroscopy and electrochemistry. The near-infrared spectrum of Re2Cl4(SePh)2(dppm)2exhibits a broad band at 1480 nm (ϵ ≃ 200), a feature that is also found in the electronic spectrum of Re2Cl6(dppm)2. A cyclic voltammetric study revealed the presence of four reversible one-electron redox couples; two couples located at E1/2= +0.95 and +1.65 V vs. Ag/AgCl correspond to oxidation processes, and two couples at E1/2= -0.46 and -1.30 V represent reductions. These metal-based redox properties are very similar to those observed for Re2Cl6(dppm)2, Re2Cl4(CO)2(dppm)2, and other related dirhenium complexes with an edge-sharing bioctahedral geometry. © 1987, American Chemical Society. All rights reserved.
author list (cited authors)
Cotton, F. A., & Dunbar, K. R.