Experimental and Computational Studies on the Reactivity and Binding Mode of Thiophene with N-Heterocyclic Carbene Iridium Complexes
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- 作者：Laura Rubio-Pérez ; E. A. Jaseer ; Nestor García ; Victor Polo ; Manuel Iglesias ; Luis A. Oro
- 刊名：Organometallics
- 出版年：2016
- 出版时间：February 22, 2016
- 年：2016
- 卷：35
- 期：4
- 页码：569-578
- 全文大小：430K
- ISSN：1520-6041
文摘
The reactivity of thiophene (T), 2-methylthiophene (2-MeT), and benzothiophene (BT) with [Ir(cod)(IPr)(L)]BF4 complexes (L = acetone (1), pyridine (2) or dimethylphenylphosphine (3); IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) in the presence of molecular hydrogen has been investigated. Under these conditions the 1,5-cyclooctadiene ligand is hydrogenated to cyclooctane, which renders an unsaturated species (Ir-IPr-L) able to coordinate the thiophene moiety. The coordination mode of T, 2-MeT, and BT depends on the nature of the substrate and the ligand trans to the IPr (L). The reaction of 1 with T and 2-MeT leads to dissociation of the acetone ligand to afford the complexes [Ir(H)2(IPr)(η5-T)]BF4 (4) and [Ir(H)2(IPr)(η2-2-MeT)(κS-2-MeT)]BF4 (5), respectively, but no stable complex is observed on reaction with BT. Analogously to 1, complex 2 does not give a stable complex on reaction with BT, while reaction with 2-MeT yields complex 5 again. Conversely, reaction with T affords a mixture of complexes, [Ir(H)2(IPr)(η2-T)(Py)]BF4 (6) and [Ir(H)2(IPr)(κS-T)2(Py)]BF4 (6′), both featuring a coordinated pyridine ligand. The reaction of 3 with T, 2-MeT, and BT yields in all cases κS complexes, namely [Ir(H)2(IPr)(κS-T)2(PPhMe2)]BF4 (7), [Ir(H)2(IPr)(κS-2-MeT)2(PPhMe2)]BF4 (8) in equilibrium with [Ir(H)2(IPr)(κS-2-MeT)(PPhMe2)]BF4 (8′), and [Ir(H)2(IPr)(κS-BT)2(PPhMe2)]BF4 (9). Finally, DFT calculations were employed to rationalize the coordination modes of T, 2-MeT, and BT, as well as the tendency of these complexes to undergo hydrogenation instead of hydrogenolysis of the thiophene moiety under catalytic conditions.