Dithiolene metal complexes ligands

Potentially coordinatively unsaturated dithiolene-metal complexes are rare,298-306 and 1 1 dithiolene-transition-metal complexes with no other ligands are, to our knowledge, unprecedented.307 The neutral complex [PdS2C2(COOMe)2]6,308 is homoleptic containing one dithiolene unit for each palladium atom and no other ligands. Electrochemical reduction of the compound depicted in Figue 21 proceeds in four reversible steps. 

Therefore the most common homoleptic bis-dithiolene metal complexes [Mn(S2C2R2)2]n" (M = Ni, Pd, Pt) can potentially take part in the redox sequence illustrated in Scheme 7. Once again, this has to be considered a simplified sequence in that the occurrence of internal metal-to-ligand electron transfer cannot be ruled out. 

Vibrational spectroscopy has not been extensively used in the characterization of tris(dithiolene) metal complexes. Moreover, complete assignments based on both IR and Raman spectra, isotope shifts, and normal mode calculations are not available for any individual complex. However, the available data suggest that the trends in M S and dithiolene ligand vibrational modes as a function of the metal, the charge on the complex, and dithiolene substituents, closely parallel those discussed above for square-plane bis(dithiolene) metal complexes. Accordingly, the vibrational data are consistent with highly delocalized complexes with predominantly ligand-based redox chemistry. 

The case for highly delocalized frontier orbitals and predominantly ligand-based redox chemistry in tris(dithiolene) metal complexes has been most convincingly made by the recent structural, vibrational, and DFT results for members of the related [M(CO)2(S2C2Me2)2]0,1 2 and [M(S2C2Me2)3]0 1 2 (M = Mo, W) series of complexes (39). The latter is the only set of tris(dithio-lene) complexes that has been isolated and structurally characterized in three oxidation states. While the vibrational studies focused on IR spectra of the [M(CO)2(S2C2Me2)2]° 1 2 series of complexes, the close parallel in... 

Another very important group of organic acceptors employed as components for organic metals during the last decade is presented by dithiolene metal complexes [e.g., l,3-dithiole-2-thione-4,5-dithiolate (dmit) ligand and... 

The expansion of the ir-conjugating system with outer heterorings, the idea presented by the ET molecule, can be applied to 1,2-dithiolene metal complexes with the donor character. For example, the M(dddt)2 (dddt=5,6-dihydro-l,4-dithiin-2,3-dithiol M = Ni, Pd, Pt, Au) molecule, where the central C = C double bond in ET is replaced by the transition metal, exhibits various molecular arrangements, some of which are similar to those found in the ET salts [29]. In the frontier molecular orbital of the 1,2-dithiolene complexes, the 3p orbitals of S atoms in the ligand show a significant contribution. In this sense, the molecular design for the 1,2-dithiolene complexes can be discussed in common with that for the organic ir molecules. 

One of the earliest series of metal complexes which showed strong, redox-dependent near-IR absorptions is the well-known set of square-planar bis-dithiolene complexes of Ni, Pd, and Pt (Scheme 4). Extensive delocalization between metal and ligand orbitals in these non-innocent systems means that assignment of oxidation states is problematic, but does result in intense electronic transitions. These complexes have two reversible redox processes connecting the neutral, monoanionic, and dianionic species. 

Figure 6 Metal complexes based on 1,2-dithiolene ligands...

Abstract Metal complexes including the dmit2- (1,3-dithio-2-thione-4,5-dithiolato) ligand are the only class of metal bis-dithiolenes to give rise to superconductive molecular materials. This chapter first focuses on the description of these superconductive phases. Further sections describe the association of M(dmit)2 moieties with three types of magnetic molecules, i.e., metalloceniums, radical cations, and spin crossover complexes. 

As mentioned above for the [Cp2Mo(dithiolene)]+, the [Cp Mo(dithiolene)2] and the [CpNi(dithiolene)] radical complexes, the spin density is not only partially delocalized on the dithiolene ligand but also on the metal and even the Cp rings. This peculiar feature opens new paths for intermolecular interactions in the solid state besides the direct dithiolene/dithiolene overlaps, since Cp/dithiolene and Cp/Cp contacts are also to be considered. 

Square planar 1,3-dithioketonato complexes Ni(R2C3S2)2 are reminiscent of the 1,2-dithiolene complexes and their electrochemical behaviour is comparable. The neutral complexes have been found to undergo a one-electron reduction to the unstable monoanions [NifRjQS J- (89) in the range —0.9 to —1.1 V vs. SCE in MeCN or DMF at a Pt electrode.349 There is also some controversy as to whether the reduction of these complexes is metal- or ligand-based.349,350... 

In the transition metal complexes of ligands like o-phenylenediamine, we find a distinct analogy to the chemistry of dithiolenes. The full equivalence of their redox chemistry with that of dithiolenes suggests a comparably delocalized structure. The outward structural similarity between this ligand and the benzenedithiols is not reflected in the redox properties of their transition metal complexes... 

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