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*(PMe 3 )IrCl 2 ( 1 ) catalyzes H/D exchange between D 2 O and water-soluble organic and organometallic molecules in aqueous solution. This complex undergoes a ligand redistribution reaction to produce [Cp*(PMe 3 ) 2 IrCl](Cl) and (Cp*IrCl 2 ) 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 (η 5:η 1 -Me 2 PCH 2 CMe 2 C 5 H 4 )IrX 2 (X = I ( 3 ), OTf ( 4 )) are reported, as are one-pot procedures for the synthesis of (η 5:η 1 -Me 2 PCH 2 SiMe 2 C 5 Me 4 )IrX 2 (X = I ( 7 ), Br ( 8 )) and (η 5:η 1 -Me 2 PCH 2 SiMe 2 C 5 Me 4 )RhX 2 (X = I ( 11 ), Br ( 12 )). We further report the preparation of (η 5:η 1 -Me 2 PCH 2 SiMe 2 C 5 Me 4 )Ir(OSO 2 CF 3 ) 2 ( 9 ) and [(η 5:η 1 -Me 2 PCH 2 SiMe 2 C 5 Me 4 )Ir(OH 2 ) 2 ](SO 4 ) ( 10 ). Complexes 3 and 4 are not catalysts for the exchange of deuterium between D 2 O and organic substrates. Although the water-insoluble complexes 7, 8, 11, and 12 are also not active catalysts, the water-soluble complexes bearing the η 5:η 1 -Me 2 PCH 2 SiMe 2 C 5 Me 4 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.