Monoelectronic Processes in Iron Complexes and Controlled Reactions by Ancillary PR3 Ligands

Abstract

Carbon disulfide is markedly activated, by coordination to a metal center, towards alkylhalides and electrophilic alkynes. The resulting metalladithioester or metal-carbene complexes are activated by monoelectronic processes, but the orientation of the reaction is strongly controlled by the nature of ancillary PR3 ligands. Fe(η2CS2R)(CO)2(PR3)2+ cations are reduced by borohydride either by hydride transfer with electron donating PR3 groups or by electron transfer with electron poor PR3 ligands. Their reduction with sodium-amalgam or activated magnesium gives either C-C bond coupling with weak basic and labile phosphine ligands (PPh3) or desulfurization when basic phosphines (PMe3, PMe2Ph, PBu3) are used. These reactions show that the nature of the PR3 ancillary ligand and that of the reducing reagent can be chosen to produce selectively new dithioformate, tetrathiooxalate or thiocarbonyl iron derivatives. Electron-transfer-induced ligand substitution has been used for the selective substitution of phosphines by more electron donating phosphines even in the presence of carbonyl ligands. Electrochemical or chemical oxidation of iron(o)-carbene Fe(=CY2)(CO)2(PR3)2 complexes is a one-electron oxidation and is markedly dependent on the nature of PR3 groups. PR3 ligands can be selected either for the reversibility of the oxidation process, the dimerization of the 17 electron intermediate or the dimerization of the carbene ligand, with carbon-carbon bond coupling and formation of tetrathiafulvalene derivatives.KeywordsMetal CenterCarbon DisulfideLigand SubstitutionCarbene LigandLigand Substitution ReactionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.