ИСТИНА

Free radicals, both organic and metal-centered ones, are much more reactive than closed-shell molecules, but can be generated from the latter by single electron transfer process (SET). Generation of radicals may in turn trigger new reaction pathways and significantly change reactivity and selectivity of reaction. First realized in SRN1 nucleophilic aromatic substitution [1] this kind of activation is now attracting increasing interest in the form of redox-catalysis [2]. Metal carbonyl anions are good one-electron donors, and in this communication we show that SET-mediated reactions of carbonylate anions, especially [Re(CO)5]-, with alkenyl and aryl halides can lead to unexpected and otherwise inaccessible products. Binuclear [R-Re2(CO)9]- complexes are the first and most frequent type of such products. Radical-chain reactions of [Re(CO)5]- with bromostilbene and 3-bromocyclohexen-2-one furnish another type of products, [R-Re(CO)4Br]- which can subsequently convert to binuclear complexes. Binuclear acyl complexes [R(CO)Re2(CO)9]- are formed in slow halogenophilic (SN2Hal) reactions of RX (X=Cl,Br) with [Re(CO)5]- by CO-ligand substitution in initially generated halo(acyl)rhenates (Scheme ). In all these cases, mechanistic tests (light-stimulation, effect of radical-traps and initiators) suggest the involvement of odd-electron species in CO substitution step and possibly in the main nucleophilic substitution/oxidative addition reaction of RX with [Re(CO)5]-.