Electrophilic Additions to η2-Thiophene Complexes:  Synthesis of Novel Thiophenium and Thiafulvenium Species

A series of complexes of the form [Os(NH 3 ) 5 (η 2 -L)](OTf) 2 (where L = thiophene and OTf = trifluoromethanesulfonate, i.e., triflate) are synthesized and characterized and their reactivities with electrophilic reagents are examined. Depending on the electrophile and the substitution pattern of the coordinated thiophene, direct electrophilic addition occurs at either the sulfur, C2, or C3, affording thiophenium complexes. Some elementary transformations of selected thiophene complexes are exploited to prepare novel 1- and 2-thiafulvenium salts.