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The compounds [Cp2M(S2C2(H)R)] (M = Mo or W; R = phenyl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl or quinoxalin-2-yl) and [Cp2Mo(S2C2(Me)(pyridin-2-yl)] have been prepared by a facile and general route for the synthesis of dithiolene complexes, viz.the reaction of [Cp2MCl2] (M = Mo or W) with the dithiolene pro-ligand generated by reacting the corresponding 4-(R)-1,3-dithiol-2-one with CsOH. These Mo compounds were reported previously (Hsu et al., Inorg. Chem.1996, 35, 4743); however, the preparative method employed herein is more versatile and generates the compounds in good yield andall of the W compounds are new. Electrochemical investigations have shown that each compound undergoes a diffusion controlled one-electron oxidation (OXI) and a one-electron reduction (REDI) process; each redox change occurs at a more positive potential for a Mo compound than for its W counterpart. The mono-cations generated by chemical or electrochemical oxidation are stable and the structures of both components of the [Cp2Mo(S2C2(H)R)]+/[Cp2Mo(S2C2(H)R)] (R = Ph or pyridin-3-yl) redox couples have been determined by X-ray crystallography. For each redox related pair, the changes in the Mo–S, S–C and C–C bond lengths of the {MoSCCS} moiety are generally consistent with OXIinvolving the loss of an electron from a π-orbital that is Mo–S and C–S antibonding and C–C bonding in character. These results have been interpreted successfully within the framework provided by DFT calculations accomplished for [Cp2M(S2C2(H)Ph)]n(M = Mo or W; n = +1, 0 or −1). The HOMO of the neutral compounds is derived mainly from the dithiolene π3orbital (65%); therefore, OXIis essentially a dithiolene-based process. The similarity of the potentials for OXI(ca. 30 mV) for analogous Mo and W compounds is consistent with this interpretation and the EPR spectra of each of the Mo cations show that the unpaired electron is coupled to the dithiolene proton but relatively weakly to 95,97Mo. The DFT calculations indicate that the unpaired electron is more localised on the metal in the mono-anions than in the mono-cations. In agreement with this, the EPR spectrum of each of the Mo-containing mono-anions manifests a larger 95,97Mo coupling (Aiso) than observed for the corresponding mono-cation and REDIfor a W compound is significantly (ca.300 mV) more negative than that of its Mo counterpart. [Cp2W(S2C2(H)(quinoxalin-2-yl))] is anomalous; REDIoccurs at a potential ca.230 mV more positive than expected from that of its Mo counterpart and the EPR spectrum of the mono-anion is typical of an organic radical. DFT calculations indicate that these properties arise because the electron is added to a quinoxalin-2-yl π-orbital. [ABSTRACT FROM AUTHOR]

As Jørgensen pointed out in 1966 (Coord. Chem. Rev., 1966, 1, 164), a ligand is to be regarded as ‘innocent’ if it allows the oxidation state of a metal in a complex to be defined. In this respect, the vast majority of ligands are ‘innocent’ and, therefore, ligands that are ‘non-innocent’ have received special attention. Dithiolenes have been regarded as ‘non-innocent’ ligands since it is possible to consider a ligand of this type to be present in a complex as either: (i) an ene-1,2-dithiolate dianion or (ii) a neutral dithioketone. On this basis, the electronic structure of a dithiolene complex can be described by a set of resonance structures, each of which involves the dithiolene in one of the two forms with the oxidation state of the metal centre being adjusted accordingly. The relative importance of these structures is expected to be reflected in the corresponding molecular structure and spectroscopic properties. In this paper we present a theoretical study of the pair of related ?5-cyclopentadienyl cobalt dithiolene complexes, [CpCo(S2C2(H)Ph)] and [CpCo(S2C2(H)Ph)(PMe3)]. Density functional theory calculations successfully predict their different structures and NMR chemical shifts, which we have measured. These wavefunctions have been analysed, particularly in terms of Natural Bond Orbitals and Nucleus Independent Chemical Shifts in an attempt to understand how “innocence” or otherwise is reflected in the experimental data. To this end, a similar analysis is applied to the gold complexes [Au(S2C2(H)Ph)2]? and [Au(S2C2(H)Ph)2]. [ABSTRACT FROM AUTHOR]

A new method has been developed to synthesise bis η5-cyclopentadienyl dithiolene complexes of molybdenum and tungsten. This procedure involves the in situthermolysis of the azo compounds, 2,2′-azobisisobutyronitrile (AIBN) or 1,1′-azobiscyclohexanecarbonitrile (ACCN) (R′2N2, R′ = CMe2CN or C6H10CN, respectively), which initiates a reaction between [Cp2M(S4)] (M = Mo or W) and an alkyne (HC2R, R = Ph, 2-pyridyl or 2-quinoxalinyl) and produce the corresponding [Cp2M(S2C2RR′)] compound. [ABSTRACT FROM AUTHOR]