Elaborate Network of Hydrolysis and Methanolysis Reactions Involving the 2,5-Dimethylthiophene Ligand in Cp*Ir(η5-2,5-Me2T)2+

Abstract

Reactions of aqueous base with the dicationic iridium and rhodium thiophene complexes [Cp*Ir(η5-2,5-Me2T)](X)2 (X = BF4, 1(BF4); X = OSO2CF3, 1(OTf)) and [Cp*Rh(η5-2,5-Me2T)](BF4)2 (8(BF4)) and the acid/base reactivity of these products are discussed. The reaction of 1(BF4) with 1 equiv of aqueous KOH (0.01 M) affords the following mixture of mono-, di-, and tetranuclear compounds: [Cp*Ir(η4-SC(Me)CHCHC(O)Me)] (3), (Cp*Ir)[Cp*Ir(η4-SC(Me)CHCHC(O)Me)]3(BF4)2 (4(BF4)), [(Cp*Ir)2(μ2,η4-SC(Me)CHCC(O)Me)](BF4) (5(BF4)), and [Cp*Ir(μ2,η3-SC(Me)CHCH2C(O)Me)]2(BF4)2 (6(BF4)). The 1H and 13C NMR data are consistent with the single-crystal X-ray diffraction structures of the cationic complexes 4(BF4), 5(OTf), and 6(BF4). These products are formed by a complex series of reactions that begin with the displacement of the 2,5-dimethylthiophene (2,5-Me2T) ligand from 1 and reaction of the resulting “[Cp*Ir]2+” fragment with 3. In the synthesis of 8(BF4), the new complex [(Cp*Rh)2(μ2,η4-SC(Me)CHCC(O)Me)](BF4) (9(BF4)), analogous to 5(BF4), is produced. Studies of the reactions of [Cp*Rh(η5-2,5-Me2T)](BF4)2 (8(BF4)) with OH- and MeO- show a type of reactivity quite different from that observed for 1(BF4) and 1(OTf). The solvolysis of 8(BF4) in acetone affords the mononuclear complex [Cp*Rh(OCMe2)2(OH)](BF4) (10(BF4)), whose crystal structure is described. Detailed NMR studies establish the pathways by which [Cp*Ir(η5-2,5-Me2T)]2+ (1) and [Cp*Rh(η5-2,5-Me2T)]2+ (8) react with H2O/OH- and MeOH/MeO- to give the variety of observed products.