1,2-Dithiolene Complexes of Transition

Dithiolene Complexes of Transition Metals 1660 Organometallic Intramolecular-Coordination Compounds. Recent Aspects in the 1661... 

RJ. Bums and CA Me Auliffe, 1,2-Dithiolene Complexes of Transition Metals Adv.Inor g.Chem.Radiochem. 22, 303 (1979). 

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). 

CTTS transitions in coordination compounds result in a radial movement of electron density from the metal to the surrounding solution medium. The energies of these transitions generally are very sensitive to environmental parameters such as solvent polarity, temperature and the presence of salts.104 This sensitivity has been used in a diagnostic sense to identify CTTS bands in the spectra of anionic cyanide complexes105 and 1,2-dithiolene complexes of Ni, Pd and Pt.106 Hydrated cations such as Cr2+(aq) and Fe2+ (aqj exhibit absorption bands that are sometimes referred to as CTTS in character. Since the solvent occupies the first coordination sphere of the metal, however, the distinction between CTTS and CTTL transitions in these systems becomes obscured. 

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... 

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]. ... 

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