Synthesis and Characterization of PBP Pincer Iridium Complexes and Their Application in Alkane Transfer Dehydrogenation.

This work reports on the synthesis of several new complexes of Ir supported by a diarylboryl/bis(phosphine) PBP pincer ligand. The previously reported complexes (PBP)Ir(Ph)(Cl) (<bold>1</bold>) and (PBP)Ir(H)(Cl) (<bold>2</bold>) were converted to the new complexes (PBP)IrH4 (<bold>3</bold>) and (PBP)Ir(Ph)(H) (<bold>4</bold>). Complexes <bold>3</bold> and <bold>4</bold> serve similarly as precatalysts for transfer dehydrogenation of cyclooctane. The turnover numbers achieved were relatively modest but were increased (to 220 at 200 °C) when 1-hexene was used as a sacrificial hydrogen acceptor vs tert-butylethylene. The dicarbonyl complex (PBP)Ir(CO)2 (<bold>6</bold>) was also synthesized, by the reaction of CO with either <bold>3</bold> or <bold>4</bold>. Intermediates (PBPhP)Ir(H)(CO)2 (<bold>5</bold>) and (PBP)IrH2(CO) (<bold>7</bold>) were observed in these reactions. Complex 7 could be obtained in pure form by comproportionation of <bold>3</bold> and <bold>6</bold>. Solid-state structures of <bold>3</bold> and <bold>6</bold> were determined by X-ray crystallography. [ABSTRACT FROM AUTHOR]