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Water-Promoted Generation of a Diazairida Homobarrelene by C—C Coupling Between an Iridacyclic Alkylidene and Acetonitrile

IIQ

M. F. Espada, J. López-Serrano, M. L. Poveda, E Carmona Angewandte Chemie International Edition 2015, Vol. 54, 8751–8755

The stable cationic iridacyclopentenylidene [TpMe2Ir(=CHC(Me)=C(Me)CH2(NCMe)]PF6(A;TpMe2=hydrotris (3,5dimethylpyrazolyl)borate) has been obtained by α-hydride abstraction from the iridacyclopent-2-ene [TpMe2Ir(CH2C(Me)=C(Me)CH2)(NCMe)]. Complex A exhibits Brønsted–Lowry acidity at the Ir-CH2 and proximal (relative to Ir-CH2) methyl sites. The coordination of an extra molecule of acetonitrile to the iridium center initiates the reversible isomerization of the chelating carbon chain of A to the monodentate butadienyl ligand of complex [TpMe2Ir(CH=C(Me)C(Me)=CH2)(NCMe)2]PF6, which is capable to engage in a water-promoted C-C coupling with the MeCN co-ligands. The product is an aesthetically appealing bicyclic structure that resembles the hydrocarbon barrelene.