Diverse reactivities of aromaticity-unsaturation coexisted metalladithiolene rings

This review paper summarizes the reactivities of metal dithiolene complexes based on the 'coexistence of aromaticity and unsaturation' in the five-membered metallacycle, the so-called metalladithiolene ring (MS2C2). The 16-electron [LM(dithiolene)] (LM = CpMIII, Cp*M-III, (C6R6)M-II) complexes are coordinatively unsaturated and usually show M-S centered cycloaddition reactions with nucleophiles (e.g. diazo-alkanes, organic azides, quadricyclane) and electrophiles (e.g. tetracyanoethylene oxide, activated acetylene). The resulting metalladithiolene cycloadducts, which have three-membered M-S-C or M-S-N rings, further react with protic acids or PR3 to undergo the ring-opening reactions involving the M-C bond, M-S bond or M-N bond cleavages. Furthermore, diverse adduct dissociations are observed by thermal, photochemical or electrochemical redox reactions. Such reactions normally produce the original [LM(dithiolene)] complexes (non-adduct) and the eliminated fragments. Among them, the Co-S centered imido adduct [CpCo(dithiolene)(NR)] (R = Ts, Ms) reacted under thermal conditions in the presence of PR3 to undergo the intramolecular imido migration reaction to the Cp ligand, giving [(C5H4 -NHR) Co(dithiolene)] complexes. The M-S centered multinuclear cluster complexes are obtained by the reaction of [LM(dithiolene)] with low valent M(CO)n complexes. The square-planar bis(dithiolene) complexes [M(dithiolene)(2)](0) (M = Ni, Pd, Pt) or tris(dithiolene) complexes [M(dithiolene)(3)](0) yield cycloaddition products with olefins. These reactions are due to ligand centered reactions made possible by a molecular orbital overlap between dithiolene LUMO and olefin HOMO. Similar ligand centered adducts are obtained by the reaction of dianionic [M(dithiolene)(2)](2) with haloalkanes or dihaloalkanes. Also these adducts of bis(dithiolene) complex are dissociated photochemically and electrochemically. This paper also describes the reactivities of organometallic o-carborane dithiolate complexes, which are generally formulated as [LM(S2C2B10H10)] (LM CpCo, Cp*Rh, Cp*Ir, (p-cymene)Ru and (p-cymene)Os). Diverse addition reactions are reported; in particular, the reaction with acetylene involves B-H bond activation in the carborane moiety. (C) 2011 Elsevier B.V. All rights reserved.