Redox-induced conversion pathways in rhodium and iridium complexes containing C-S bond cleaved benzo[b]thiophene

Article abstract of DOI:10.1021/om00009a049

The thermally generated 16-electron fragments [(triphos)MH] (M = Rh, Ir) react with benzo[b]thiophene by C-S bond scission to yield the 2-vinylthiophenolate derivatives (triphos)M[η³-S(C₆H₄)CH=CH₂] (M = Rh, 1; Ir, 2) which display a rich redox-induced reactivity [triphos = MeC(CH₂PPh₂)₃]. Removal of one electron from 1 or 2 leads to the corresponding paramagnetic cations I⁺ and 2⁺, respectively; these compounds undergo a radical reaction with H^? in solution to form the diamagnetic 2-ethylidenecyclohexadienethione complexes anti-[(triphos)M{η⁴-S(C₆H₄)CH(CH ₃)}]⁺ (M = Rh, anti-3⁺; Ir, anti-6⁺) which isomerize to syn-3⁺ and syn-6⁺, respectively. Addition of one electron to syn-3⁺ and syn-6⁺ gives the neutral paramagnetic derivatives syn-[(triphos)M{η⁴-S(C₆H₄)CH(CH ₃)}] (M = Rh, syn-3; Ir, syn-6) which convert back to the starting complexes 1 and 2 by homolytic C-H bond cleavage liberating H^?, and thus completing a full electrochemical cycle by addition/ elimination of one electron and one H atom. The related 2-(3,3,3-triphenylpropylidene)-cyclohexadienethione complex [(triphos)Rh{η⁴-S(C₆H₄)CH(CH ₂CPh₃)}]PF₆ (4PF₆) undergoes similar reactions including loss of a trityl radical by a C-C bond cleavage reaction in the neutral derivative (triphos)Rh{η⁴-S(C₆H₄)CH(CH ₂CPh₃)} (4). Removal of a second electron from I⁺ or 2⁺ leads to the dicationic species I²⁺ and 2²⁺, which spontaneously lose a proton and produce the cationic metallabenzothiabenzene complexes [(triphos)M(η²-C,S-C₈H₆S)]⁺ (M = Rh, 5⁺; Ir, 7⁺). Finally, addition of one elecytron to 5⁺ or 7⁺ produces the corresponding neutral paramagnetic metallabenzothiabenzene complexes [(triphos)M(η²-C,S-C₈H₆S)] (M = Rh, 5, Ir, 7). All the long-lived paramagnetic compounds have been characterized by X-band ESR spectroscopy.