80006-29-7Relevant academic research and scientific papers
Dinuclear Polyhydrides of Rhenium: Isolation and Characterization of Diamagnetic and Paramagnetic Complexes Containing the n+, (n+1)+, and (n+1)+ Cores (n = 0 or 1) Stabilized by Phosphine, Nitrile, and Isocyanide Ligands
Allison, Joe D.,Walton, Richard A.
, p. 163 - 168 (2007/10/02)
The electrochemical oxidation of the dirhenium octahydrides Re2(μ-H)4H4(PR3)4 (PR3 - PPh3, PEtPh2, or PEt2Ph) and Re2(μ-H)4H4(AsPh3)4 occurs at potentials between -0.15 and -0.40V vs.SCE, to produce the corresponding paramagnetic, ESR-active monocations.This oxidation has been accomplished chemically in the case of the PPh3 derivative using Ph3C+PF6- and C7H7+PF6- as oxidants, dichlormethane as solvent, and a reaction temperature of 0 deg C; the resulting product is PF6.However, when the reaction with Ph3C+PF6- is carried out in nitrile solvents, RCN (R = Me, Et, or Ph), then hydride abstraction occurs in preference to oxidation and the diamagnetic complexes PF6 are formed.The reaction of PF6 with t-BuNC affords the substitution product PF6.The complexes containing the + moiety have been shown by cyclic voltammetric measurements (on 0.2M Bu4NPF6-CH2Cl2 solutions) to exhibit two quasi-reversible one-electron oxidations (at ca. 0.0 and +0.70 V for the RCN derivatives and +0.19 and +0.94 V vs.SCE for the t-BuCN derivative).Oxidation to paramagnetic (PF6)2 (for L = RCN or t-BuNC) has been achieved by using NO+PF6-.In contrast to the sluggish reaction of Re2(μ-H)4H4(PPh3) with t-BuNC, the oxidized monocation reacts extremely rapidly (in CH2Cl2 at 0 deg C) to give PF6.Like the other polyhydrides this complex possesses two accessible one-electron oxidations, and it may be oxidized chemically to (PF6)2 very easily by using NO+PF6-.While the diamagnetic complexes PF6 and PF6 do not react significantly with excess t-BuNC within reasonable periods of time, their paramagnetic oxidized congeners do so extremely rapidly, the rhenium(I) complex PF6 and gaseous H2 being the final products of these reactions.The complexes desriebed in this report that contain the +, 2+, and 2+ cores constitute very rare examples of isolable radical cations of transition-metal hydrides, the first to be prepared for dimetal polyhydrides.The highly reactive nature of these species, compared to their far less reactive diamagnetic precursors, provides an important extension of the notion that paramagnetic electron-deficient organometallic species exhibit enhanced substitution lability relative to their 18-electron analogues.
Activation of Mono- and Di-nuclear Polyhydrides of Rhenium: Protonation, Solvation, and Oxidation
Allison, Joe D.,Walton, Richard A.
, p. 401 - 403 (2007/10/02)
Activation of the rhenium polyhydrides ReH5(PPh3)2L (L=monodentate ligand) and Re2H8(PPh3)4 has been achieved through their protonation (using HBF4), the formation of solvento-complexes, and their oxidation to reactive paramagnetic cations, strategies which have led to a range of novel species, including 2+, +, and t)2>+ together with their '17-electron' paramagnetic congeners.
Reactions of alkyl isocyanides with polyhydride complexes of rhenium and with binuclear dirhenium complexes containing quadruple or triple bonds: Nonreductive and reductive cleavage of Re-Re multiple bonds to afford mononuclear isocyanide complexes of rhenium(I) and rhenium(III)
Allison, Joe D.,Wood, Thomas E.,Wild, Robert E.,Walton, Richard A.
, p. 3540 - 3546 (2008/10/08)
Treatment of the dinuclear quadruply bonded complexes Re2(O2CR)4Cl2 (R = CH3 or C6H5) with alkyl isocyanides (RNC; R = CMe3 or C6H11) affords solutions from which salts of the [Re(CNR)6]+ cations can be isolated in good yield. While [Re(CNR)6]+ is inert to substitution by monodentate tertiary phosphines, routes to species of the type [Re(CNR)4(PR3)2]+ are afforded by (a) the reductive cleavage of the triply bonded complexes Re2Cl4(PR3)4 by RNC ligands or (b) the reductive elimination of H2 from the polyhydride complexes ReH7(PR3)2 and ReH5(PR3)2L in the presence of an excess of RNC. In contrast to the preceding reductive-cleavage reductions, the halide-rich salts (n-Bu4N)2Re2X8 (X = Cl or Br) react with tert-butyl isocyanide to give mononuclear seven-coordinate rhenium(III) species [Re(CNCMe3)5X2]+, which have been isolated as their PF6- salts. The mixed isocyanide-halide-phosphine complexes of rhenium(III) [Re(CNCMe3)4(PEtPh2)Cl2]PF 6 and [Re(CNCMe3)3(dppe)Cl2]PF6 (dppe = Ph2PCH2CH2PPh2) are likewise prepared by isocyanide cleavage of quadruply bonded Re2Cl6(PEtPh2)2 and dimeric Re2Cl6(dppe)2 (the latter containing Re(μ-Cl)2Re bridges but no Re-Re bond). The spectroscopic and electrochemical properties of these complexes are reported, and the significance of the cleavage reactions by π-acceptor ligands (such as RNC) is discussed in the context of their constituting an important synthetic route to mononuclear transition-metal complexes.
REDOX REACTIONS OF POLYHYDRIDE COMPLEXES OF RHENIUM: ELECTROCHEMISTRY AND REACTIONS WITH ALKYL ISOCYANIDES
Allison, J. D.,Cameron, C.J.,Wild, R.E.,Walton, R.A.
, p. C62 - C66 (2007/10/02)
The dark red octahydride complex of dirhenium, Re2H8(PPh3)4, undergoes a reversible one-electron oxidation to the blue mono-cation + (E1/2 -0.24 V vs.SCE by cyclic voltammetry).The X-band ESR spectrum of a dichloromethane glass (-160 deg C) containing the monocation is in accord with the HOMO being a delocalized metal-based orbital.Treatmentof the heptahydrides ReH7(PR3)2 (PR3 = PPh3 or PEtPh2) with C6H11NC or Me3CNC in the presence of KPF6 leads to the elimination of hydrogen and the formation of PF6.Electrochemical oxidation of ReH5(PPh3)2L (L = PPh3, PEtPh2, pyridine, piperidine or cyclohexylamine) activates these molecules to attack by RNC to afford rhenium(I) species.
