Dddt ligand

Recently, Kato and coworkers have prepared and fully characterized novel trinu-clear Ni(II) complexes by reacting the corresponding mononuclear Ni-dithiolene complex [Ni(S S)2] (z = 0 or 1—, S S = dddt, edo) (edo = 5,6-dihydro-l,4-dioxine-2,3-dithiolate) with the tetrathiooxalato (60, tto) ligand and a Ni(II) cation, as shown in equation 12 for the dddt ligand. 

In contrast to anionic [M(dmit)2] acceptor molecules, the metal complexes with dddt ligands, [M(dddt)2] (dddt = 5,6-dihydro-l,4-dithiin-... 

The singular electrochemical behaviour of bis-dithiolenes complexes bearing the (dddt) ligand should be mentioned. These complexes may appear as anionic, neutral and cationic species. ° ° Therefore, they may act both as donor or acceptor systems. To our knowledge, they are the only 1,2-bis-dithiolenes complexes to undergo oxidation towards stable cationic species. One-electron oxidation of neutral M(S2C2Ph2)2 (M = Ni, Pd, Pt) complexes was reported,but shown to be irreversible due to ligand de-coordination. 

Some other ligands of the dddt family which are less recognized in research are depicted below. Examples in the literature have often been prepared for other applications such as optical materials. Especially on electrochemical and structural details much work has been done.1074-1080... 

Homoleptic gold(III) complexes with other related dithiolate ligands, as dmit (317),1855-1864 dddt,1865,1866 l,3,5-trithiepin-6,7-dithiolate,1867 dithiosquarate (318),1868,1869 6,7-dihydro-6-methy-lene-5H-l,4-dithiepine-2,3-dithiolate,1870 3,4-thiophenedithiolate (319),1637 quinoxaline-3,3-dithiolate (320),1871 2,2-diacetylethylene-1,1-dithiolate,1872 or o-carborane-1,2-dithiolate have been... 

Uranium complexes analogous to these compounds were also described, but with the cot (cyclooctatetraene dianion) ligand rather than the Cp or Cp ones. Both the dianionic U(IV) [(cot)U(dddt)2]2 [47] and monoanionic U(V) [(cot)U(dddt)2] [48] complexes were isolated and structurally characterized (Fig. 5). Spectacular distortions of the US2C2 metallacycles were rationalized on the basis of DFT calculations, which reproduced the spectacular folding of the endo US2C2 metalla-cycle when the dianionic species undergoes an oxidation. 

We have already mentioned a very strong dyadic association in the formally d5 cobalt complexes such as [Cp Co(dddt)]+ which dimerizes in the solid state to a fully diamagnetic dicationic dyad (Fig. 6a). It represents the extreme situation where the two radicals form a true 2e bond, with the sulfur atom of one dithiolene ligand entering the coordination sphere of the other metal. It should be considered as the consequence of the electron deficiency of these cationic [CpCo(dt)]+ 15-electron complexes. 

We have seen above several examples where [Cp2M(dt)]+ (M = Mo, W) complexes organize in the solid state into low dimensional structures, leading to characteristic magnetic behaviors such as spin chains (eventually alternated) or spin ladders. The extensive use in later years of dithiolene ligands such as dmit or dddt was aimed at... 

Recently, the first U(V) heteroleptic cyclo-octatetraene-dithiolene complex 992 was synthesized by AgBPh4 oxidation in THF of the [(COT)UIV(dddt)2][Na(18-crown-6)]2 precursor, which was synthesized by reacting [(COT)UX2(THF)J (X = BH4, n = 0 X = I, n = 2) with Na2dddt [490]. In general, despite the relatively small number of reported actinide S-containing complexes, they have a potentially rich coordination chemistry of such compounds of hard /-elements with soft S-ligands [489] and possible applications [491]. 

A close structural relationship with I IF derivatives, especially BEDT-TTF, is exhibited by dddt metal complexes [dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate (63)]. The most interesting feature of this dithiolene ligand is the ability of its metal complexes to form not only anionic salts like dmit, but also cationic salts like TTF derivatives [89], to afford non-stoichiometric IR salts of type [M(dddt)2]mX . Thus the cyclic voltam-mogram of [Bu4N][Ni(dddt)2], after its initial oxidation, exhibits the reduction of neutral [Ni(ddt)2]° to anion [Ni(ddt)2]" at 0 V, and its further reduction to the dianion [Ni(dddt)2]2 , as well as the oxidation of [Ni(dddt)2]° to the cation [Ni(dddt)2] + at 0.8 V (MeCN versus Ag/Ag/Cl). The feasible synthesis of conducting donor-acceptor complexes involving dddt metal derivatives as donors and dmit metal derivatives as acceptors has also been demonstrated [90]. 

Dimercapto-l,3-dithiole-2-thione (dmit, 46) and 4,5-dihydro-l,4-dithiin-2,3-dithiolate (dddt, 47) ligands can be reacted with transition metal ions to give M(dmit)2 and M(dddt)2 complexes (M = Pt, Pd, Ni, and Au) [91]. The M(dmit)2 and M(dddt)2 anions, like BEDT-TTF, have numerous peripheral sulfur atoms and are planar. Additionally, they have variable redox potentials that can be adjusted through the metal that is selected. 

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. 

In a related study, reaction of (COT)U(BH4)2(THF) with the dithiocarbonates dddtCO and dmioCO (dmio = l,3-dithiole-2-one-4,5-dithiolate) gave the neutral dithiolene compounds [(COT)U(dithiolene)]2 in good yields (dithiolene = dddt, dmio, or l,3-dithiole-4,5-dithiolate (mdt)). The reactions are accompanied by elimination of formaldehyde and borane. The X-ray crystal structures of [(COT)U(mdt)]2 and monomeric (COT)U(mdt)(pyridine)2 showed an interaction between the C=C double bond of the mdt ligand and the uranium atom, and the H NMR spectra revealed a facile dithiolene ring inversion process in solution.155... 

It should be noted that the synthetic pathway (ii) has been extended to cyclic 1,2-dithiolene and 1,2-diselenolene ligands, such as dddt , ddds , ddt , phdt, medt, and so on. ... 

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