Iridium(III) and rhodium(III) complexes bearing chelating cyclopentadienyl-phosphine ligands as C-H activation catalysts for the deuteration of hydrocarbons in D2O

The complex Cp*(PMe3)IrCl2 (1) catalyzes H/D exchange between D2O and water-soluble organic and organometallic molecules in aqueous solution. This complex undergoes a ligand redistribution reaction to produce [Cp*(PMe3)(2)IrCl](CI) and (Cp*IrCl2)(2), which is believed to be responsible for an erosion of exchange activity at long reaction times. We therefore have devised strategies for synthesizing metal complexes which feature chelating cyclopentadienyl-phosphine ligands to inhibit the redistribution reaction. Multistep syntheses of the chelating cyclopentadienyl-phosphine complexes (eta(5):eta(1)-Me2PCH2CMe2C5H4)IrX2 (X = I (3), OTf (4)) are reported, as are one-pot procedures for the synthesis of (eta(5):eta(1)-Me2PCH2-SiMe2C5Me4)IrX2 (X = I (7), Br (8)) and (eta(5):eta(1)-Me2PCH2SiMe2C5Me4)RhX2 (X = I (11), Br (12)). We further report the preparation of (eta(5):eta(1)-Me2PCH2SiMe2C5Me4)Ir(OSO2CF3)(2) (9) and [eta(5):eta(1)-Me2PCH2SiMe2C5Me4)Ir(OH2)(2)](SO4) (10). Complexes 3 and 4 are not catalysts for the exchange of deuterium between D2O and organic substrates. Although the water-insoluble complexes 7, 8, 11, and 12 are also not active catalysts, the water-soluble complexes bearing the eta(5):eta(1)-Me2PCH2SiMe2C5Me4 ligand (9 and 10) are. These results imply that an electron-rich iridium center promotes catalytic C-H activation. The activities and lifetimes of these complexes in aqueous H/D exchange reactions with unactivated C-H bonds are similar to those of catalysts which do not contain chelating ligands. This suggests that catalyst deactivation occurs even when a chelating ligand is used. The relevance of these results to ligand redistribution reactions of Ir(III) is discussed.