Dehydrogenative route to metallo dithiolenes: The reaction of zinc polysulfides and alkenes

Complexes of the type ZnS6(TMEDA), ZnS4(PMDETA), and ZnS4(Me(3)TACN) react with electrophilic alkenes to give dithiolene complexes ZnS2C2R2(amine)(n). The Me(3)TACN complex is the most reactive, while the more conveniently pr epared PMDETA complex also undergoes this reaction at useful rates. The fol lowing alkenes were successfully tested: C2H2(CO2Me)(2) (cis and trans isom ers), C2H3(CO2Me), C2H3(CN), 1,2-C2H2Me(CN), C2H3(CHO), and 1,2-C2H2(CN)(Ph ). Crystallographic analysis shows that the highly reactive complex ZnS4(Me (3)TACN) is structurally similar to ZnS4(PMDETA), including the presence of an elongated Zn-N-ax bond. Model studies indicate that the reaction of alk enes with LnZnSx proceeds via the reversible formation of a dipolar interme diate, as indicated by the ability of the polysulfido complexes to catalyze the isomerization of cis-C2H2(CO2Me)(2). It is proposed that such dipolar species undergoes ring closure to give alkanedithiolato intermediates, e.g. , Zn[S2C2H2(CO2Me)(2)](PMDETA). The dithiolato complexes Zn[S2C2H2(CO2Me)(2 )](PMDETA) and Zn[S2C2H2(CO2Me)(2)](TMEDA) were prepared from ZnMe2, the di - and triamines, and the dithiol meso-(HS)(2)C2H2(CO2Me)(2). These dithiola tes undergoes dehydrogenation upon treatment with S-8 to give the dithiolen e Zn[S2C2(CO2Me)(2)]L-n at a rate that is independent of the ancillary liga nd L. The dithiolene ligands can be removed from the Zn center by treatment with [COCl2](3) and Cp2TiCl2; in this way Zn[S2C2H(CN)](PMDETA) was conver ted to OCS2C2H(CN) and Cp2TiS2C2H(CN).