OXIDATIVE TRANSFORMATION OF [R(CP)(CO)2MNSR]. RADICALS INTO INIDENE COMPOUNDS [R(CP)(CO)2MN]2SR+

Stable radical compounds [(R)Cp(CO)2MnSR]. ((R)Cp = Cp, Cp', Cp*; 1.) have been obtained by air oxidation of the primary products formed from RSH and (R)Cp(CO)2Mn(THF) for a wide variety of alkyl and aryl substituents R. EPR spectra and bulk susceptibility measurements together with solution and solid-state UV/vis spectra show that compounds 1. are stable monomeric radicals. Preparative oxidation of 1. by AgPF6 yields the binuclear species [(R)Cp(CO)2Mn]2SR+PF6- ([2+][PF6-]). The cations 2+ exist either as "inidene"-type compounds L(n)M..S(R)..ML(n) (L(n)M = (R)Cp(CO)2Mn) with a trigonal-planar coordination at the bridging sulfur or in the ring-closed isomeric form [L(n) activated M-S(R)-ML(n)]+ with a metal-metal bond and a pyramidal sulfur. The two isomeric forms of 2+ are easily distinguished by their UV/vis spectra. Intense long-wavelength pi-pi* absorptions are characteristic of the inidene-type isomers. Cyclic voltammetry reveals reversible one-electron redox reactions for 1. as well as for 2. corresponding to 1- half-arrow-right-over-half-arrow-left 1. half-arrow-right-over-half-arrow-left 1+ and 2- half-arrow-right-over-half-arrow-left 2. half-arrow-right-over-half-arrow-left 2+, respectively. It is observed that the reduction of 1+ is about 500 mV less negative as compared to the reduction of 2+ throughout. This finding corresponds to the relative stability of the LUMO's of 1+ (olefinic type pi-system) versus those of 2+ (allylic type pi-system) as visualized by qualitative MO reasoning. X-ray structural data are presented for [(R)Cp(CO)2MnSR]. ((R)Cp = Cp, R = Ph, 1a.; (R)Cp = Cp', R = C6F5, 1f.) and [(R)Cp(CO)2Mn]2SR+PF6- ((R)Cp = Cp, R = (p)NO2-C6H4, [2b+][PF6-]; (R)Cp = Cp', R = (i)Pr, [2h+][PF6-]; (R)Cp = Cp', R = (t)Bu, [2i+][PF6-]).