http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Chemical and physical studies of paramagnetic transition metal carbonyls
xiii, 166 leaves : illustrations ; 29 cm
The group 6 anionic transition metal alkyls, CH₃W(CO) ₅- (M = Cr, W) were found to react with organic substrates via radical pathways. No reactivity involving CH₃ - group transfer was observed. With organometallic substrates, the group 6 anionic alkyls reacted to give products indicative of radical intermediates. For example, the neutral metal alkyl CH₃Mn(C0)₅ reacted with anionic alkyls to give the heterobimetallic species MnM(CO)₁₀- and acetone as major products. Electron transfer from CH₃W(CO)₅- to C0₂(CO)₈ resulted in dimer reduction and disruption yielding CoW(CO)₉- and acetone. The production of acetone is proposed to occur via an oxidatively promoted migratory insertion pathway involving 17-electron intermediates. The anionic group 6 acyl [Li] [CH₃ C(0)W(CO)₅] underwent a photo-induced electron transfer to give a neutral acyl radical characterized by ESR spectroscopy. The ESR spectrum of a solution of [Li] [CH₃C(0)W(CO)₅] flowed together with [Fc] [BF₄] indicated a septet with ¹⁸³W coupling. The thermally unstable radical was tentatively assigned to the diacyl (OC)₄ W(C(0)CH₃)₂ the dimeric diacetyl bridged (OC)₅W(0)C(CH₃ )-C(CH)₃(0)W(CO)₅, or the oxygen-bound chelate (OC)₄W(OC(CH₃)C(CH₃)0⁻) . The radical species was transient and only observed under flow conditions. The oxidation of the chromium thiolate complexes, RSCr(CO)₅- (R = Et, t-Bu) resulted in the sulfur-coupled dimers (μ-RSSR)Cr₂(CO)₁₀ via dimerization of the 17-electron species [RSCr(CO)₅]. Attempts to characterize the short-lived monomer radicals using ESR were unsuccessful. A series of bridging chromium thiolates, μ-RSCr₂ (CO)₁₀- (R = H, Me, Et, i-Pr, t-Bu, Ph) were oxidized and the resulting radicals were characterized by ESR and IR v(C0) at low temperatures. The radicals were assigned to the neutral species [μ-RSCr₂(CO)₁₀]. Protonation at the sulfur site in RSCr(CO)₅- leads to a new series of thiol chromium complexes, (RSH)Cr(CO)₅ (R = Et, i-Pr, t-Bu). Alternatively, reaction of Cr(C0)₅. THF with thiols (RSH) can be used as preparative method. The effect of chromium complexation to the thiol ligand results in an increased acidity as compared to free RSH.