Dithiolate complexes substitution reactions

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. 

The kinetics of the substitution reactions of the planar Ni(L)2" complexes with 1,1-dithiolate nucleophiles have been studied in aqueous solution at 25°C by a stopped-flow technique (502) (L = CPD2, NED2-, CDC2", and /-MNT). 

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... 

Dithiolane-fused oxadithiepins, widely used in the synthesis of charge-transfer complexes, are available by [3+4] substitution reactions of dithiolane dithiolates with di(chloromethyl) ether (see Section 13.16.9.4.1). 

Pearson and Sweigart have reported one of the first kinetic studies involving substitution at square-planar nickel(n), in Ni"-dithiolate complexes. They discuss nucleophilic reactivity, leaving group, and trans effects, and report that the reactions follow an associative pathway, as expected. The solvent path is not important and, although for Pt" the formation of a five-co-ordinate intermediate may be rate-determining, for Ni" this step is fast compared with subsequent steps. The formation constant of the five-co-ordinate intermediate does, however, markedly affect the overall rates, and it seems that the trans effect for nickel(ii) operates through the stability of this intermediate. 

Miscellaneous. Hynes and Moran have carried out kinetic studies on substitution reactions of Pt dithiolate complexes with CN and with several dithiolate ions. In the reactions with the bidentate ligands the mechanism is similar to that proposed for the corresponding reactions of the nickel and palladium complexes, and the order of reactivities is Ni Pd Pt = 10 10 1. Evidence for an unusual mechanism in some reactions of Pt complexes has been reported in the case of the process... 

A number of processes catalyzed by the dithiolate-bridged species have been mentioned already however, the extensive reactivity of alkynes within these systems has led to a number of more recent reports on their use in catalysis. The allenylidene complex 363 (R = Tol, R = Me 864 salt) has been identified as an intermediate in the catalysis of propargylic alcohol substitution reactions with alcohols in high yields and with complete regioselectivities... 

Substituted thioureas have been extensively studied over the decades. Reaction of CoX2 (X = C1, Br) with substituted phenylthioureas yield a range of complexes involving halide and thiourea as ligands, characterized by spectroscopy and thermogravimetric analysis.503 Both [Co(Rtu)4(OH2)2]2+ (Rtu = thiourea, phenylthiourea, allylthiourea) and [Co(Rtu)2(OH2)4]2+ (Rtu = diphenylthiourea) have been prepared and characterized as low-spin octahedral species.504 The octahedral bis(phenylthiourea)bis(dithiolate)cobalt(II) complex, one of a number of complexes of phenylthiourea, chlorophenylthiourea and bis(diphenylphospinothioyl)methane prepared and characterized,505 proved the most biologically active of those tested. 

In the synthesis of the parent dithiolenes, the reaction of the disodium salt of ethylene-cts-dithiolate with metal salts is the only useful method.15 For the preparation of substituted dithiolenes the use of substituted ethylenedithiolates is the most efficient choice. In the synthesis of 1,2-dicyanoethylene-l,2-dithiolato ( mnt ) complexes, it is the only available method.16... 

Several complexes between tin(rv) centers and the l,3-dithiole-2-thione-4,5-dithiolato or l,3-dithiole-2-one-4,5-dithiolato ligands have been prepared by Wardel s group by methathesis reactions involving addition, elimination, and substitution at the metal atom (Scheme 5) C1998POL4475, 1999JOM140>. 

Nucleophilic aromatic substitution of the fluorine substituents by benzene-dithiolate sulfur atoms (step a), reduction of the nitro compound (step b), diazotization, reaction with KSaCOEt, alkaline hydrolysis, and acidification gave tpS4 H2 (step c). It could be purified via the [Ni(tpS4)]2 complex (Fig. 1), which is readily hydrolyzed with dilute hydrochloric acid to give pure tpS4 H2. 

TTF may be obtained by dethiooxygenation of 2-thioxo-l,3-dithioles by transition metal complexes. Thus, the reaction of 2-thioxo-l,3-dithioles (233), (un)substituted in the 3- and/or... 

---