Reaction of (μ-S)₂Fe₂(CO)₆ dianion with 1,2-vinyl and aryl diiodides

The inorganic dithiolate, (μ-S)₂Fe₂(CO) ₆ ^2-, reductively deiodinates trans-1,2-diiodo-1,2- diphenylethene to afford diphenylacetylene in 79% yield. Reaction of (μ-S)₂Fe₂(CO)₆ ^2- with 1,2-diiodobenzene and 2,3-diiodotoluene results in the formation of the benzenedithiolate complex (μ-S)₂Fe₂(CO)₆ and toluenedithiolate complex (μ-S₂C₆H₄Me) Fe₂(CO)₆ in 42% and 48% isolated yields, respectively. These reactions appear to involve reductive deiodination of 1,2-diiodobenzene and 2,3-diiodotoluene with (μ-S)₂Fe₂(CO)₆ ^2- to the corresponding benzynes followed by trapping with the concomitantly formed disulfide (μ-S₂)Fe₂(CO) ₆, to give the observed complexes. As such, these reactions involve the first examples of thermal [2+2] cycloaddition of benzyne to the S-S bond of an inorganic disulfide. Although the reaction was not observed on treatment of other substituted 1,2-diiodobenzenes, 1,2,4,5-tetraiodobenzene was monodeiodinated to 1,2,4-triiodobenzene in 62% isolated yield.