PC(sp3)P pincer carbonyl complexes of iridium(i), and iridium(iii)

Abstract

The previously reported complex trans-[IrHCl{cis-1,3-bis-(di-tert-butylphosphino)methyl}cyclohexane] (2) forms the 18-electron carbonyl compound anti-[Ir(CO)HCl{cis-1,3-bis-((di-tert-butylphosphino)methyl)}cyclohexane] (5a) upon reaction with 1 atm CO. The structural isomer syn-[IrH(CO)Cl{cis-1,3-bis-((di-tert-butylphosphino)methyl)}cyclohexane] (5b) is obtained directly upon complexation of the ligand (1) with IrCl₃·H₂O in refluxing DMF. syn-5b is the first iridium aliphatic pincer complex with this orientation of the hydrogens and is the thermodynamically more stable isomer. Both compounds 5a and 5b afford the Ir(I) complex trans-[Ir(CO){cis-1,3-bis-((di-tert-butylphosphino)methyl)}cyclohexane] (4) upon treatment with KO^tBu. Complex 4 was also synthesised in a more straightforward fashion from the previously known terminal nitrogen complex trans-[Ir(N₂){cis-1,3-bis-((di-tert-butylphosphino)-methyl)}cyclohexane] (3) under atmospheric CO. The complexes 4, 5a and 5b were characterised spectroscopically and in the solid state. IR data point to a more electron rich metal centre as compared to the corresponding aromatic complexes.