Reaction of “Non-Symmetrical” 1,2,4-Trithiolanes with [(phosphane)Pt0(η2-nbe)] Complexes†

Two unsymmetrical 1,2,4-trithiolanes (1d and 1e) were reacted with [Pt0(PPh3)2(η2-nbe)] (6; nbe=norborn-2-ene) and [Pt0(dppn)(η2-nbe)] (11; dppn=1,8-bis(diphenylphosphanyl)naphthalene)), respectively. Their treatment with compound 6 resulted in the formation of six-membered platinacycles of type 7, which selectively underwent fragmentation into dithiolato complexes and thiobenzophenone (4b). The isolation of the first stable C-substituted member of this class of compounds (i.e., compound 7e) permitted kinetic studies of this process by using UV/Vis spectroscopy. These results, together with DFT calculations, allowed us to propose a mechanism for the reactions of compound 6 with 1,2,4-trithiolanes. In contrast, similar treatment of compound 11 with compounds 1d and 1e at room temperature did not result in any reaction. Heating the appropriate samples to 110 °C led to the formation of dithiolato complexes and η2-thioketone compounds, thus pointing to a thermally induced [3+2]-cycloreversion of the heterocycles as an initial step of the reaction.