Electrophilic additions to eta(2)-thiophene complexes: Synthesis of novel thiophenium and thiafulvenium species

A series of complexes of the form [Os(NH3)(5)(eta(2)-L)](OTf)(2) (where L = thiophene and OTf = trifluoromethanesulfonate, i.e., triflate) are synthes ized and characterized and their reactivities with electrophilic reagents a re examined. Depending on the electrophile and the substitution pattern of the coordinated thiophene, direct electrophilic addition occurs at either t he sulfur, C2, or C3, affording thiophenium complexes. Some elementary tran sformations of selected thiophene complexes are exploited to prepare novel 1- and 2-thiafulvenium salts.