952065-12-2Relevant academic research and scientific papers
Metal-stabilized thiyl radicals as scaffolds for reversible alkene addition via C-S bond formation/cleavage
Ouch, Kagna,Mashuta, Mark S.,Grapperhaus, Craig A.
, p. 9904 - 9914 (2011)
The one-electron oxidation of metal thiolates results in an increased oxidation state of the metal ion or the formation of a sulfur-based, thiyl radical in limiting extremes. For complexes with highly covalent M-S bonds, the unpaired electron may be delocalized over the metal and the sulfur, yielding a metal-stabilized thiyl radical. Oxidation of the metal thiolate precursors [Ru(DPPBT)3]-, [Ru-1]-, and Re(DPPBT) 3, Re-1 (DPPBT = diphenylphosphinobenzenethiolate), generates metal-stabilized thiyl radicals that react with alkenes to yield dithioether-metal products. Alkene addition to [Ru-1]+ and [Re-1]+ is symmetry-allowed due to the meridional arrangement of the DPPBT chelates. Combined bulk electrolysis and cyclic voltammetry experiments reveal the addition of alkenes to [Ru-1]+ as an irreversible process with experimentally determined rate constants ranging from 4.6(5) × 107 M-1 s-1 for electron-rich alkenes to 2.7(2) × 104 M-1 s-1 for electron-poor alkenes. Rate constants for cyclic alkenes range from 4(2) × 107 to 2.9(3) × 103 M-1 s-1. Chemical oxidation of [Ru-1]- by ferrocenium hexafluorophosphate (FcPF6) in the presence of m-methylstyrene or p-methylstyrene yields the dithioether complexes [Ru-1?m-methylstyrene]+ and [Ru-1?p- methylstyrene]+, respectively. Each complex was crystallized and the structure determined by single-crystal X-ray diffraction. 31P NMR of the samples reveals a major and minor product, each displaying a second-order spectrum. The oxidized intermediate [Re-1]+ binds alkenes reversibly with equilibrium binding constants that vary with the complex charge from 1.9 × 10-11 M-1 for n = 0 to 4.0 M-1 for n = +1 to 2.5 × 109 M-1 for n = +2. The three binding regimes are separated by 240 mV. Crystalline samples of [Re-1?C 2H4]2+ are obtained upon chemical oxidation of Re-1 with silver hexafluorophosphate (AgPF6) in the presence of ethylene. Strategies for the addition of alkenes to other metal-stabilized thiyl radicals are suggested.
Carbon-sulfur bond formation via alkene addition to an oxidized ruthenium thiolate
Grapperhaus, Craig A.,Venna, Kiran B.,Mashuta, Mark S.
, p. 8044 - 8050 (2008/10/09)
Bulk oxidation of [Ru(DPPBT)3], 1b, (DPPBT = 2-diphenylphosphinobenzenethiolate) in the presence of ethylene yields [(ethane-1,2-diylbis(thio-2,1-phenylene)diphenylphosphine) ruthenium(II)] hexafluorophosphate, [2a]PF6, from the addition of the alkene across eis sulfur sites. During oxidation, the absorption bands of 1b at 540, 797, and 1041 nm decrease in intensity. The resulting complex [2a]+ displays a single redox couple at +804 mV. The +ESI-MS of [2a]+ shows a parent ion peak at m/z = 1009.1013, and the 31P NMR spectrum displays chemical shift values of δ1 = 61.0, δ2 = 40.3, and δ3 = 37.5 with coupling constants of J12 ≈ J13 ≈ 30 Hz and J23 = 304 Hz. Oxidation of [2a] + by one electron at a holding potential of +1000 mV yields [(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl phosphine)ruthenium(III)] hexafluorophosphate, [2b][PF6]2. The EPR of [2b][PF 6]2 displays a rhombic signal with g1 = 2.09, g2 = 2.04, and g3 = 2.03. Oxidation of 1b in the presence of alkenes including 1-hexene, styrene, cyclohexene, and norbornene yields products similar to [2a]+. Each of these products was further oxidized to an analogue of [2b]2+. Complex [2a]+ was also prepared, as the bromide salt, from [PPN][Ru-(DPPBT)3] (PPN [1a]; PPN = bis(triphenylphosphoranylidene)ammonium) and 1,2-dibromoethane. The complex [2a]Br crystallizes as thin yellow plates in the monoclinic space group P2 1/c with unit cell dimensions of a = 10.2565(9) A, b = 13.2338(12) A, c = 38.325(3) A, and β = 93.3960(10)°.
