The novel P-C-P pincer complex, [IrH2{C6H3(CH2PBuf2)2-2,6}] has long-term stability at 200 "C and catalyses the transfer dehydrogenation of cyclooctane to cyclooctene at the rate of 12 turnovers min-'.

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The pincer ligand dihydride complex [IrH 2 {( t Bu 2 )PCH 2 CH 2 CHCH 2 CH 2 P( t Bu 2 )}] interacts with carbon dioxide to give an isolable bicarbonate [IrH(κ 2 -O 2 COH)}{( t Bu 2 )PCH 2 CH 2 CHCH 2 CH 2 P( t Bu 2 )}] derivative and a metal hydride carbonyl compound. An intermediate metallo-formate complex can be detected by NMR spectroscopy. The reaction described is a reverse water gas shift process, CO 2 + H 2 h CO + H 2 O.

The new pincer ligand 1,6-bis((tert-butylphosphino)methyl)-1,3,5-cycloheptatriene is metalated by Ir(CO) x Cl at the 7-position to give a pincer complex. This complex when treated with LiBEt 3 H gives a mixture of products which result from the unusual migration of both an ethyl group and the replacement of the chlorine atom with a hydride. Individual components of the mixture can be prepared separately by treatment of the pincer complex with NaH to give dehydrochlorination followed by a prototopic rearrangement and NaBEt 4 , which generates the corresponding ethyl derivative.