Transition metal complexes with 1,2-dithiolene

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. 

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... 

The four systems listed in Table 6 consist of stacks of planar organic molecules surrounded by transition-metal complexes that are not closely associated with each other. All but the [Pt(bipy)2][TCNQ]3 system contain planar organic cations and metal dithiolene anions. The properties of these compounds vary considerably, so each system will be described briefly. 

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. 

The 0/1 couple in Au(tfd)21 (tfd = bis(trifluoromethyl)ethylenedithiolate, lb) occurs at a slightly lower potential (+1.32 V vs SCE in CH2CI2) than the mnt counterpart911. This is in accord with observations that in other transition metal 1,2-dithiolene complexes the ease of oxidation is dependent on X with X = Ph > CF3 > CN9. Replacing sulfur with the less electronegative atom, selenium, results in a lower oxidation potential for Aul lds)2 (tds = bis(trifluoromethyl)ethylenediselenolate, lc) relative to [Au( ltd) 12. More electronegative substituents make a complex easier to reduce, as expected. Thus, the 1/2 couple for Au(mnt)2 occurs approximately 500 mV more positive than the same couple for [Au(tds)2]. ... 

A recent review on transition metal complexes of 1,2-dithiolenes summarizes the virtually non-existent literature dealing with silver complexes. Only one general report exists for then-production, which gave complexes of the type [AgL (CI04)] [where n = 1, 2 and L = various thioethers, C2H2(SH)2, C6H4(SH)2, o-MeC6H3(SH)2, maleonitriledithiolate (mnt ) and toluene 3,4-dithiolate (tdt )]. An early report claimed the existence of an ESR-detectable Ag(mnt)2 species however, this could not be obtained free from impurities °... 

Dichalcogenolene ligands form complexes with main group and d transition metal ions.103 Bis( 1,2-dithiolene) complexes have been obtained for metals, such as Cr, Mn, Ni, Cu, Zn, for the first row, Pd, Ag, and Cd for the second row, and Pt, Au, and Hg for the third row. Homoleptic /ra(l,2-dithiolcnc) complexes have been obtained for Ti, V, Cr, Zr, Nb, Mo, Tc, Ru, Ta, W, Re, and Os. Fe and Co have been found both in bis and /ra(l,2-dithiolene) complexes, although /ra(l,2-dithiolene) complexes containing these metal ions... 

The first metal bis-dithiolene complex with an SCO moiety as counter-ion was reported in 2005 [99], namely [Fe(sal2-trien)][Ni(dmit)2] (Fig. 8). Usually, [Fe(sal2-trien)]+ is a Fera complex which exhibits very modest magnetic properties a gradual and incomplete spin transition is observed when it is combined with (PF6) and (BPI14), and the complex remains in the LS state with Cl-, I-and (NO3)-. 

Lowe and Garner (1993a,b) have synthesized three new dithiolene ligands and formed complexes with a variety of transition metals (Fig. 23) including molybdenum [40]-[42], tungsten [43] and [44] and nickel [45]—[48]. The electrochemical properties of the complexes and free ligands were studied by... 

Mdssbauer spectra of bonding and structure in, 15 184-187 reactions with diborane, 16 213 stabilization of, 5 17, 18-19 cyanates, 17 297, 298 cyanide complexes of, 8 143-144 cyclometallated bipyridine complex, 30 76 diazene complexes, 27 231-232 dinitrogen complexes, 27 215, 217 diphosphine complexes of, 14 208-219 dithiocarbamates, 23 253-254 -1,2-dithiolene complexes, 22 323-327 hydrogen bonding, 22 327 halide complexes with phosphine, etc., 6 25 hexaflouride, structure, 27 104 hydride complexes, 20 235, 248-281, see also Transition metal-hydride complexes... 

Several transition metal ions form stable complexes with aliphatic 1,2-dithiols, which absorb in the near-lR. Known as dithiolenes, their nickel complexes in particular have been found to have valuable properties. The physical properties of dithiolenes can be readily tailored by variations on the substituents attached to the dithiols, see (4.13). Although they have low molar absorption coefQcients, when compared to cyanines etc., they do have one big advantage in that they show very little absorption in the visible region." Stracturally analogous dyes can be made from aromatic dithiols and oxothiols (4.14), and the much more bathochromic naphthalene derivatives (4.15), but they are much weaker absorbers. 

During the period 1965-1975 the chemistry of the 1,2-dithiolene complexes of the transition metals was the subject of considerable study.86,87,91-98 However, during this period of great activity few complexes of the early transition metals were reported aside from those of vanadium. The problem had much to do with synthetic procedures, since reaction of, say, the anhydrous metal chlorides with the dithiolene or its sodium salt did not prove successful. However, the use of metal dialkylamides99 did result in clean reactions (e.g. equation 21). 

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