Ene-1,1-dithiols

Enedisulfides Ene-1,1-dithiols Ketene mercaptal monosulfonium salts Ketene mercaptals... 

As happens for dioxolenes, dithiolenes can undergo the reversible sequence 1,2-dithionej 1,2-dithione monoanion/ene-1,2-dithiolate illustrated in Scheme 6. 

The metal is chelated by an ene-1,2-dithiolate (dithiolene) of the dihydropyran ring which is fused to a partially reduced pteridine 178. The syntheses of these molybdopterin-related proligands were described as model compounds for verification of the stability in vitro <2001CC 123>. The proligand 179 is a relatively stable compound however, after several weeks, the pyran ring opened and oxidation to the diol derivatives 180 was observed (Scheme 35). 

The interesting ligand (l)136 has two potential chelating modes upon ionization. Depending on its tautomeric state, either N,S or S,S coordination allows it to act as a bidentate chelating ligand. Apparently, it acts as a 2-aminocyclopent-l-ene-l-carbodithioate, i.e. as a 1,1-dithiolate, to form Mo02L2 complexes.136... 

Figure 1. Valence bond description of the various dithiolene ligand forms. Two-electron oxidation of the dianionic ene-1,2-dithiolate results in the formation of the 1,2-dithione and 1,2-dithiete resonance forms.

Figure 2. Qualitative MO description of the four dithiolene ti valence orbitals. Electron occupancies are given for the l,2-dithione/l,2-dithiete resonance forms (A) and the dianionic ene-1,2-dithiolate (B). [Adapted from (283)].

With respect to the oxo-molybdenum mono(dithiolenes), cpM are the Mo d orbitals (e.g.,

atomic sulfur p orbital functions. Experimental studies have shown that the dominant contributor to the oscillator strengths of all transitions are integrals of the form (xnMXn) (310-312), which, in the limit of no overlap between the two sulfur p orbitals on different atoms reduces to (311). 

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