Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X = Cl or Br; dppm = Ph2PCH2PPh2) with isocyanides. 4. Dinuclear species containing two or three isocyanide ligands
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The triply bonded dirhenium(II) compound Re2Cl4(dppm)2(dppm = Ph2PCH2PPh2) reacts with 2 equiv of t-BuNC to yield the bis(isocyanide) species [Re2Cl3(dppm)2(CN-t-Bu)2]+(isolated as its PF6- salt) in two isomeric forms (green and yellow). The reaction between the monoisocyanide complexes Re2Cl4(dppm)2(CNR) (R = t-Bu or xylyl) and an excess of a nitrile R'CN (R' = Me, Et, or Ph) in the presence of KPF6 produces the mixed isocyanide-nitrile complexes [Re2Cl3(dppm)2(CNR)(NCR')]PF6. The probable structures of these new products are discussed in light of structural data for the previously characterized bis(nitrile) derivatives. Complexes containing three RNC ligands [Re2Cl3(dppm)2(CNR)3]+(R =t-Bu or xylyl) have been isolated by the reaction of [Re2Cl3(dppm)2(CN-t-Bu)(NCEt)]PF6 or Re2Cl4(dppm)2 with ca. 4 equiv of t-BuNC and of [Re2Cl3(dppm)2-(CNxyl)(NCPh)]PF6 with 2.5-equiv of xylNC. These products provide further examples of structural isomerism in compounds with edge-shared bioctahedral geometries. A novel complex that contains a μ-iminyl ligand, [Re2(μ-Cl)(μ-C=NH-t-Bu)(μ-dppm)2Cl2(CN-t-Bu)2]PF6, has been isolated as a byproduct in the synthesis of the green isomer of stoichiometry [Re2Cl3-(dppm)2(CN-t-Bu)2]PF6. This complex, which has been characterized by X-ray crystallography, forms monoclinic crystals in space group P21/a, with the following unit cell dimensions: a = 22.841 (4) Å, b = 25.949 (5) Å, c = 24.076 (4) Å; β = 93.34 (1)°. With Z = 8, the asymmetric unit is defined by two independent molecules of the complex cation 5 and two hexafluorophosphate anions, all of which reside on general positions. The dirhenium molecules 5a and 5b are structurally identical, and their corresponding bond distances and angles are very similar. Some average values: Re-Re = 2.704  A, Re-Cl(terminal) = 2.437  Å, Re-Cl(bridge) = 2.434  Å, Re-C(terminal) = 1.98  Å, Re-C(bridge) = 1.98  Å, Re-P = 2.455  Å; Re-Cl-Re = 67.45 °, Re-C-Re = 85.9 °, C(bridge)-N-CMe3= 131 °. All new products have been fully characterized by electrochemical and spectroscopic measurements. In addition, the redox chemistry of some of the complexes has been explored. Of special note is the chemical oxidation and reduction of [Re2Cl3(dppm)2(CNxyl)3]PF6 to give paramagnetic [Re2Cl3-(dppm)2(CNxyl)3](PF6)2 and Re2Cl3(dppm)2(CNxyl)3, respectively. © 1986, American Chemical Society. All rights reserved.
author list (cited authors)
Anderson, L. B., Barder, T. J., Cotton, F. A., Dunbar, K. R., Falvello, L. R., & Walton, R. A.