Dithiolate complexes reactions

The reaction of toluene-3,4-dithiol(3,4-dimercaptotoluene) and antimony trichloride ia acetone yields a yeUow soHd Sb2(tdt)2, where tdt is the toluene-3,4-dithiolate anionic ligand (51). With the disodium salt of maleonitnledithiol ((Z)-dimercapto-2-butenedinitrile), antimony trichloride gives the complex ion [Sb(mnt)2] , where mat is the maleonitnledithiolate anionic ligand. This complex has been isolated as a yeUow, crystalline, tetraethyl ammonium salt. The stmctures of these antimony dithiolate complexes have apparendy not been unambiguously determiaed. 

A nice example of a degenerate rearrangement has been reported for the complex pentacarbonyltungsten(0)-thioaldehyde-l,2-dithiol 177 (R = H) or the thioketone-1,2-dithiol complex 177 (R = CH3). These compounds (obtained by the reaction of silver nitrate with tetraethylammonium pentacar-bonyliodotungstate(O) in the presence of l,6,6 z -trithiapentalenes) appeared to exist as an equilibrium mixture of the two isomers 177/178 (Scheme IV.70) [83JCS(CC)289]. The symmetrically substituted 1,2-dithiol (R = CH3, R = H) displays fluxional behavior as appears by NMR spectroscopy... 

The significant changes imposed on the dithioaromatic ligands and complexes upon sulfur addition are illustrated in the structure of the Ni(p-/-PrPhDtaXp-(-PrPhDtaS) complex (Fig. 48) (Table XXII), determined by Fackler et al. (233, 257). The same workers explored the sulfur addition and abstraction reaction in depth (232) (see also Section IV). The rates and mechanisms of substitution reactions of square planar nickel(II) 1,1 -dithiolate complexes (502) is discussed in Section IV. 

A similar study of the rates and mechanisms of substitution reactions of the Pt(II) 1,1-dithiolate complexes, Pt(L)2 (L = /-MNT2, NED2, CDC2 and CPD2-), also has been reported (352). The mechanism proposed for the substitution reactions of the Pt(L)2- complexes with bidentate 1,1-dithio chelates is the same as that shown in Fig. 60. 

Proposed mechanism for substitution reactions in the 1,1-dithiolate complexes... 

The question of whether sulfur insertion occurs at the C-S or the M- S bond was raised following the first isolation of the perthio-l,l-dithiolate complexes (156). Early studies of the sulfur-addition and sulfur-abstraction reactions using 33S were reported for Ni(CS3)2" (Eq. 54). It was concluded that the added sulfur was inserted into the C -S bond (156). 

In [Fe(NO)(S2CNR2)2] the iron is ligated by four sulfur atoms as well as by the nitrosyl ligand similar Fe(NO)S4 chromophores are found (49) in complexes of dithiolenes (7) and dithiols (8). For both dithiolene and dithiol derivatives, reaction of [FeL2]2 (L = 7 or 8) with NO gas yields the nitrosyl derivatives [Fe(NO)L2] (50), in which the nitrosyl ligand has effected a net oxidation. Certain of the mononegative complexes can be oxidized by iodine to neutral Fe(NO)L2 or reduced with borohydride to dinegative [Fe(NO)L2]2 (50). 

The long lifetimes of CT excited states of the Pt(diimine)(dithiolate) complexes allow for bimolecular photochemistry, often involving oxidation of the complex. The earliest report of photoreactivity of these complexes dealt with the photooxidation of Pt(bpy)(tdt) (20) following excitation at 577 nm in chloroform (118). The reaction proceeds with a quantum yield of < ) = 0.03 and was attributed to ET to the halocarbon solvent (Eq. 8) similar to the CTTS photooxidation chemistry of the platinum bis(dithiolate) dianions described above. 

With respect to reactivity and synthetic aspects, various specific transition metal-mediated syntheses of new 1,2-dithioles and reactions, thereof, have been reported. Novel metal complexes have been isolated in a number of cases and they provide insight into new chemistry of 1,2-dithioles. 

Fig. 2.47. The reaction between [Re(0)3(Tp )], PPI13, and ethylene sulfide yields a dithiolate complex.

Another celebrated example of the template effect is the synthesis of crown ethers by Pedersen [11], but it was Busch who first intentionally used templates in synthesis and who first articulated the concept of the template effect in the 1960s [12]. Busch used the reaction of a nickel(Il) dithiolate complex 7 with l,2-bis(bromomethyl)benzene 8 to illustrate his ideas (Scheme 1-3) [13]. Once one end of the l,2-bis(bromomethyl)ben-zene has reacted with the nickel complex, the nickel template induces the reactive ends of the intermediate 9 to come into close proximity and favors cyclization. The metal template allows the synthesis of a metallated macrocycle 10 the free ligand cannot be prepared by the reaction of l,2-bis(bromomethyl)benzene with the unbound thiol (in the absence of a template other cyclic and acyclic products are formed). 

Garner and Joule next adapted the protected dithiolene strategy to target heterocyclic dithiolene complexes. This approach, first reported in 1988 by Larsen et al is illustrated in Scheme 2.25 with the formation of a cobalt quinoxalyldithiolene complex. Reaction of [CoCp(COD)] (COD = 1,5-cyclooc-tadiene) with 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione (26) affords a quinox-aline dithiolene complex (27) that has been structurally characterized. This cobalt complex undergoes extensive proton-coupled electron transfer process (see Section 2.3.4). This system was further elaborated when the pyrazine ring in 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione 26 was selectively... 

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