New iridathiaboranes with reversible isonido ↔ nido cluster Flexibility

The reaction between [IrCl(CO)(PMe3)2] and the Cs[arachno-6-SB9H12] salt in CH2Cl2 yields pale-yellow 11-vertex [8,8,8-(CO)(PMe3)2-nido-8,7- IrSB9H10] (4). Reaction of this CO-ligated iridathiaborane with Me3N -O affords pale-yellow 11-vertex [1,1,1-(H)(PMe 3)2-isonido-1,2-IrSB9H9] (6), which is also formed from the thermal decarbonylation of 4. Compound 4 has a conventional cluster structure based on classical 11-vertex nido geometry, with the iridium center and the sulfur atom in the adjacent 8-and 7-positions on the pentagonal open face. Compound 6 exhibits an 11-vertex isonido structure based on an octadodecahedron with the {Ir(H)(PMe3)2} occupying the apical position of connectivity six, but with one long non-bonding Ir-B distance generating the quadrilateral isonido open-face. Compound 6 reverts to 4 upon reaction with CO, and the Lewis acid character of 6 is further demonstrated in the reaction with EtNC to give [8,8,8-(EtNC)(PMe 3)2-nido-8,7-IrSB9H10] (7). The three new compounds 4, 6, and 7 have been characterized by single-crystal X-ray diffraction analyses and by NMR spectroscopy. Each of the nido iridathiaboranes 4 and 7 exhibits two different {Ir(L)(PMe3)2}-to-{SB 9H10} conformers in solution and in the solid state. Density functional theory (DFT) calculations reveal that the iridium atom inverts the nido-isonido-closo energy profile previously found for the rhodathiaborane congener [8,8-(PPh3)2-nido-8,7-RhSB 9H10] (3), demonstrating how the structure of these 11-vertex clusters can be controlled and fine-tuned by the tailoring of the metal center. © 2010 American Chemical Society.We acknowledge the Spanish Ministry of Science and Innovation (CTQ2009-10132, CONSOLIDER INGENIO, CSD2009-00050, MULTICAT and CSD2006-0015, Crystallization Factory) for support of this work. R.M. thanks the MEC-Universidad de Zaragoza and the European Social Fund for his Research Contract in the framework of the “Ramón y Cajal” Program. J.B. was supported by the Diputación General de Zaragoza and Caja Inmaculada (Grant CB5/09); and, in part, by the Grant Agency of the Czech Republic, project no. 203/06/P398 and the Grant Agency of the Academy of Sciences of the Czech Republic, project no. IAA400320601.Peer Reviewe