UNEXPECTED REACTIONS OF 2,5-DIMETHYLTHIOPHENE (2,5-ME(2)T) IN A(5)-2,5-ME(2)T)(2-ASTERISK-IR(ETA(4)-2,5-ME(2)T), AND CP-ASTERISK-IR(C,S-2,5-ME(2)T) WITH COBALTOCENE(), CP)

The reaction of CpIr(eta(5)-2,5-Me(2)T)(2+) (1) (Cp* = eta(5)-C(5)Me( 5)) with the reducing agent Cp(2)Co yields CpIr(eta(4)-2,5-Me(2)T) (2 ) and CpIr(C,S-2,5Me(2)T) (3), as well as the unexpected Cp*Ir-(eta(4 )-2,5-Me(2)T . C5H4) (4), which can also be prepared by reacting 1 wit h Cp(-). An X-ray diffraction study of 4 shows the eta(4)-2,5Me(2)T . C5H4 ligand to be a ring-opened 2,5-Me(2)T allyl thiolate conjugated t o a cyclopentadienylidene unit. The reduced products 2 and 3 react wit h Cp(2)Co to give a ferrole-type product Cp[IrC(Me)=CHCH=C(Me)]CoCp i n which the planar iridacyclopentadiene ring is pi-bonded to the cobal t, as established by a structural investigation. The CpCo analog of 5 is prepared by the reaction of 2 or 3 with CpCo-(CH2=CH2)(2). These studies demonstrate that cobaltocene and CpCo(CH2=CH2)(2) readily des ulfurize the 2,5-dimethylthiophene ligand in 2 and 3, which supports a previously proposed mechanism for thiophene hydrodesulfurization.