Electrophiles dithiolene complexes

Even an olefin may be sufficiently electrophilic to react with co-ordinated thiolate, and some nickel dithiolene complexes have been shown to react smoothly with norbornadiene (Fig. 5-84). Naturally, the dithiolene complexes also react with more conventional electrophiles, such as methyl iodide (Fig. 5-85). 

This chapter is divided into two main parts. The first part focuses on reactions where the dithiolene ligand is generated independently of the metal center. For the most part, these preparations give alkenedithiolate dianions, which ordinarily are treated with metal electrophiles to form dithiolene complexes. In the second part, transition metals actively participate in the assembly of the dithiolenes, usually via the reaction of a metal sulfido species with an alkyne or hydrocarbon in an equivalent oxidation state. 

DMAD is a highly reactive electrophile, so caution should be exercised in using this reagent. Illustrative of the complications that one can encounter, the reaction of Mo(S2)(S2CNEt2)3 with DMAD gives melded dithiolene complexes wherein the Et2NC fragment has inserted into the dithiolene M—S bond (230). 

The electron-rich complex Fe(CO)2[(P(OMe)3]2(r 2-CS2) adds electrophilic alkynes via an apparent 1,3-dipolar addition process to give carbene derivatives that in turn undergo efficient air oxidation to afford the 16 e dithiolene complexes Fe(CO)[(P(OMe)3]2(S2C2RR ) (R, R = C02Me, Ph, CHO, etc.) (298). 

The reactions of electrophilic alkynes, such as DMAD (dimethyl acetylene-dicarboxylate), with metal per- and poly-chalcogenido complexes have been exploited for the synthesis of homoleptic and heteroleptic 1,2-dithiolene,... 

Vlcek and Vlcek149 have summarized the reactivity of dithiolenes in a general way. The n-delo-calization in the dithiolenes favors an extensive redox series but restricts axial interactions. Reaction in this position can only occur if the incoming ligand can incorporate its own 7t-orbitals into that of the planar complex. The dianions are nucleophilic at sulfur oxidation to the anion or neutral species lets them become electrophilic and Diels-Alder-type additions may occur. 

The mildly electrophilic complex MeRe03 condenses with 2 equiv of benzenedithiol to give MeRe(0)(S2C6H4)2 (28), a rare alkyl metal dithiolene. 

Metal per- and polysulfido complexes react with electrophilic alkynes to give dithiolenes. The readily available diester DM AD is most commonly employed... 

The complex Fe2(S2)(CO)6 reacts with alkynyllithium reagents to give dithiolenes after treatment with electrophiles (303). The synthesis proceeds... 

Metal-nitrido complexes containing dithiolene ligands have been reported recently. Reaction of electrophiles such as R3OBF4 (R = Me, Et) and Ph3CPF6 with [M(N)(bdt)2] (M = Ru, Os) has been studied by Sellmann et al. (123) While the Ru-nitrido complex gives an intractable mixture of products, the Os-nitrido complex yields clean products (Eqs. 20-21). Alkylation at sulfur is... 

The pentasulfido complex reacts with tertiary phosphines to give dimers [Ti(MeCp)2]2Sj, (x = 4 and 6). The pentasulfido complex also gives heterocycles of the type Ti(MeCp)2S4CR2 when treated with ammonium sulfide in the presence of certain alkylating agents. In fact, the Me2CS4 chelate is a minor side product in the synthesis of Ti(MeCp)2Sj. The compound Ti(MeCp)2S5 reacts with electrophilic acetylenes to give dithiolenes... 

The polysulfide species [Mo=S(S4)2] (20 in Scheme 2.19) was reported to react with an alkyne producing a metal dithiolene unit in situ. The metal insertion reaction proceeds via electrophilic attack by dimethylacetylene-carboxylate (DMAC). It was observed that replacing the sulfido ligand with an 0X0 makes the tetrasulfide ligand less reactive towards the electrophilic attack by DMAC and changes the product of the reaction of DMAC and complexes possessing a Mo(S4) as shown in Scheme 2.19. 

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