Photolytic homolysis of the metal–carbon (sp³or sp²) bond of alkyl or acyl transition-metal complexes: an electron spin resonance study using spin trapping; and a note on aminyl oxides [ML_n{N(Ȯ)R}][ML_n= 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 [MLn{N(Ȯ)R}] were observed, except for MLn= 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 [MLn{N(Ȯ)R}], MLn= Ru(CO)4(SiMe3), Os(CO)4(SiMe3), or Fe(η-C3H5)(CO)3.