Ground- and Excited-State Oxidation-Reduction Chemistry of (Triphenyltin)- and (Triphenylgermanium)tricarbonyl(1,10-phenanthroline)rhenium and Related Compounds

Article abstract of DOI:10.1021/ja00547a012

Optical absorptions and emission spectroscopy and the photochemistry and electrochemistry are reported for complexes of the general formula R3EM(CO)3L (R = Ph or Me; E = Ge or Sn; M = Mn or Re; L = 1,10-phenanthroline, 2,2'-bipyridine, or 2,2'-biquinoline).The lowest excited state in each system results from charge-transfer, (E-M)?_b -> ?^*L, absorption.Several of the Re complexes (R = Ph; E = Ge or Sn; L = 2,2'-bipyridine or 1,10-phenanthroline) exhibit optical emission from the lowest excited state at 298 K in fluid solution; emission lifetimes under such conditions for these complexes are ca. 10^-6 s.These excited complexes can be quenched by both electron-donor quenchers and by electron-acceptor quenchers.Detailed quenching studies of Ph3SnRe(CO)3(phen) (phen = 1,10-phenanthroline) have been carried out, and quenching obeys Stern-Volmer kinetics.Electron donors, Q, for which E<*>(Q⁺/Q) is more negative than ca.+0.2 V vs.SCE quench at an essentially diffusion-controlled rate.Electron acceptors, P⁺, for which E<*>(P⁺/P) is more positive than ca.-0.1 V vs.SCE also quench at nearly a diffusion-controlled rate.Cyclic voltammetry of the complexes in CH3CN/0.1 M ClO4 typically shows a one-electron, reversible reduction in the -1.1 to -1.7 V vs.SCE range associated with the population of the lowest available ?^* orbital principally localized on L.An irreversible oxidation current peak is observed in the range +0.5 to +0.8 V vs.SCE.The M-containing oxidation product is fac-<(CH3CN)M(CO)3L>⁺.Consistent with the groung state electrochemistry, quenching by reversibly electron-donor quenchers (e.g., N,N,N',N'-tetramethyl-p-phenylenediamine) results in no net photoredox reaction (Φ < 10^-3) whereas quenching by reversible electron-acceptor quenchers (e.g., N,N'-dimethyl-4,4'-bipyridinium) results in net redox chemistry to reduce the quencher and to form fac-<(CH3CN)M(CO)3L>⁺ from the complex.The data are consistent with primary formation of R3E^. and the 16-valence electron ⁺ from cleavage of the ^+. formed by excited-state electron transfer.Rate of ^+. cleavage is similar to the dissociative E-M bond cleavage induced by the (E-M)?_b -> ?^*L optical excitation.