Reduction of [ML(alkyne)(2)(eta-C5R '(5))](+) (M = Mo or W, L = MeCN or CO, R ' = H or Me, C5R '(5) = C5HPh4): Characterization of radical intermediates in the reductive coupling of coordinated alkynes
Ng. Connelly et al., Reduction of [ML(alkyne)(2)(eta-C5R '(5))](+) (M = Mo or W, L = MeCN or CO, R ' = H or Me, C5R '(5) = C5HPh4): Characterization of radical intermediates in the reductive coupling of coordinated alkynes, ORGANOMETAL, 18(16), 1999, pp. 3201-3207
The complexes [M(NCMe)(RC2R)(2)(eta-C5R5')](+) (M = Mo or W, R = Me or Ph;
R' = H or Me, C5R5' = C5HPh4) undergo one-electron reduction to [M(NCMe)(RC
2R)(2)(eta-C5R5')], which rapidly lose acetonitrile to give the 17-electron
complexes [M(RC2R)(2)(eta-C5R5')]. The stability of [M(RC2R)(2)(eta-C5R5')
] depends on R and R'; for R = Ph, the radical is sufficiently stable so th
at its reduction to the 18-electron anion [M(RC2R)(2)(eta-C5R5')](-) is det
ected in the cyclic voltammogram. Chemical reduction of [Mo(NCMe)(PhC2Ph)(2
)(eta-C5HPh4)](+) with [Co(eta-C5H5)(2)] gives the air-sensitive solid [Mo(
PhC2Ph)(2)(eta-C5HPh4)], characterized as an alkyne-based radical by ESR sp
ectroscopy, which gives [Mo(NCMe)(PhC2Ph)(2)(eta-C5HPh4)](+) when treated w
ith [Fe(eta-C5H5)(2)](+) in acetonitrile. The carbonyl cations [M(CO)(RC2R)
(2)(eta-C5R5')](+) (M = Mo, Tm) undergo two sequential one-electron reducti
ons, the first of which is reversible and gives the 19-electron species [M(
CO)(RC2R)(2)(eta-C5R5')]. The 19-electron radical [Mo(CO)(PhC2Ph)(2)(eta-C5
Me5)] has been characterized in solution by IR and ESR spectroscopy.