Unexpected Reactions of 2,5-Dimethylthiophene (2,5-Me2T) in Cp*Ir(η5-2,5-Me2T)2+, Cp*Ir(η4-2,5-Me2T), and Cp*Ir(C,S-2,5-Me2T) with Cobaltocene

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