REDOX-INDUCED CONVERSION PATHWAYS IN RHODIUM AND IRIDIUM COMPLEXES CONTAINING C-S BOND CLEAVED BENZO[B]THIOPHENE

The thermally generated 16-electron fragments [(triphos)MH] (M = Rh, I r) react with benzo[b]thiophene by C-S bond scission to yield the 2-vi nylthiophenolate derivatives (triphos)M[eta(3)-S(C6H4)CH=CH2] (M = Rh, 1; Ir, 2) which display a rich redox-induced reactivity [triphos = Me C(CH(2)PPh(2))(3)]. Removal of one electron from 1 or 2 leads to the c orresponding paramagnetic cations 1(+) and 2(+), respectively; these c ompounds undergo a radical reaction with H in solution to form the dia magnetic 2-ethylidenecyclohexadienethione complexes anti-[(triphos)M{e ta(4)-S(C6H4)CH(CH3)}](+) (M = Rh, anti-3(+); Ir, anti-6(+)) which iso merize to syn-3(+) and syn-6(+), respectively. Addition of one electro n to syn-3(+) and syn-6(+) gives the neutral paramagnetic derivatives syn-[(triphos)M{eta(4)-S(C6H4)CH(CH3)}] (M = Rh, syn-3; Ir, syn-6) whi ch convert back to the starting complexes 1 and 2 by homolytic C-H bon d cleavage liberating H., and thus completing a full electrochemical c ycle by addition elimination of one electron and one H atom. The relat ed 2-(3,3,3-triphenylpropylidene)cyclohexadienethione complex [(tripho s)Rh{eta(4)-S(C6H4)CH(CH(2)CPh(3))}]PF6 (4PF(6)) undergoes similar rea ctions including loss of a trityl radical by a C-C bond cleavage react ion in the neutral derivative (triphos)Rh{eta(4)-S(C6H4)CH(CH(2)CPh(3) )} (4). Removal of a second electron from 1(+) or 2(+) leads to the di cationic species 1(2+) and 2(2+), which spontaneously lose a proton an d produce the cationic metallabenzothiabenzene complexes [(triphos)M(e ta(2)-C,S-C8H6S)](+) (M = Rh, 5(+); Ir, 7(+)). Finally, addition of on e elecytron to 5(+) or 7(+) produces the corresponding neutral paramag netic metallabenzothiabenzene complexes [(triphos)M(eta(2)-C,S-C8H6S)] (M = Rh, 5; Ir, 7). All the long-lived paramagnetic compounds have be en characterized by X-band ESR spectroscopy.