Photolytic homolysis of the metal–carbon (sp3 or sp2) bond of alkyl or acyl transition-metal complexes: an electron spin resonance study using spin trapping; and a note on aminyl oxides [MLn{N(Ȯ)R}][MLn= Ru(CO)4(SiMe3), Os(CO)4(SiMe3), or Fe(η-C3H5)(CO)3; R = aryl]

Abstract

Irradiation of the following metal alkyls has been carried out in CH₂Cl₂(or PhMe) in the presence of nitrosodurene, RNO (R = C₆HMe₄-2,3,5,6), in the cavity of an e.s.r. spectrometer: [Mn(CO)₅R′](R′= CH₂Ph or CH₂SiMe₃), [Fe(η-C₅H₅)(CO)₂R′], [Mo(η-C₅H₅)(CO)₃R′](R′= Me, Et, or CH₂Ph), cis-[PtR′₂(PMe₂Ph)₂](R′= CH₂SiMe₃ or CH₂CMe₃), [AuR′(PPh₃)](R′= Me or CH₂SiMe₃), and [CoR′L(oep)](H₂oep = 2,3,7,8,12,13,17,18-octaethylporphyrin and R′= Me, L = NC₅H₅; or R′= Et, L = OH₂). Similar experiments have been performed on (i) the acylmetal complexes [Mn(Co)₅{C(O)R″}](R″= CH₂Cl, Me, Et, CH₂Ph, or CHPh₂) or [Fe(η-C₅H₅)(CO)₂{C(O)R″}](R″= Me or CH₂Ph), and (ii) the metal–metal bonded [M₂(CO)₈(SiMe₃)₂](M = Ru or Os). Finally, the dark reaction between the stable iron(I) complex [Fe(η-C₃H₅)(CO)₃] and RNO in CH₂Cl₂ has been investigated. As a consequence, from the alkyls, metallo-aminyl oxides [ML_n{N(Ȯ)R}] were observed, except for ML_n= a platinum(I), gold(0), or cobalt(II) moiety, but the alkylaminyl oxides RN(Ȯ)R′ were found in every case [although with the molybdenum(II) alkyls as substrates these were not detected at –30 °C but only at 20 °C]; two of these (R′= CH₂SiMe₃ or CH₂CMe₃) are new and show remarkably different β-proton hyperfine couplings, attributed in part to a conformational difference allowing for close Si ⋯ O proximity for R′= CH₂SiMe₃, and also to the greater steric requirements of the neopentyl group. From the acyls, the corresponding metallo-aminyl oxide was invariably detected, but never the spin-trapped acyl radical RN(Ȯ)COR″; however, the corresponding spin-trapped alkyl radical RN(Ȯ)R″ was observed but only for the case of R″= CH₂Ph or CHPh₂. The remaining experiments led to the e.s.r. characterisation of [ML_n{N(Ȯ)R}], ML_n= Ru(CO)₄(SiMe₃), Os(CO)₄(SiMe₃), or Fe(η-C₃H₅)(CO)₃.