Well-Stabilized but Strained Frustrated Lewis Pairs Based on Rh/N and Ir/N Couples

Abstract

The dimers [(Cp*MCl)2(μ-Cl)2] (Cp∗ = η5-C5Me5) react with N-pyridin-2-ylmethyl-N′,N″-bis-(2,6-diisopropylphenyl)guanidine (H2L) in the presence of NaSbF6, giving rise to chlorido compounds of formula [Cp*MCl(κ2N,N′-H2L)][SbF6] (M = Rh, 1; Ir, 2), in which the guanidine ligand adopts a κ2N,N′ chelate coordination mode. Compounds 1 and 2 react with NaOH, rendering the complexes [Cp*M(κ3N,N′,N″-HL)][SbF6] (M = Rh, 3; Ir, 4), in which the HL ligand exhibits a fac κ3N,N′,N″ coordination. Complexes 3 and 4 activate the H-H and O-H bonds of dihydrogen and water. The hydrido complex [Cp*IrH(κ2N,N′-H2L)][SbF6] (6) was isolated from the reaction of the iridium complex 4 with H2. In the reaction of the rhodium complex 3 with D2O, its Cp∗ ligand is gradually and reversibly deuterated. A plausible mechanism for this H/D exchange is proposed. The new complexes have been characterized by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1-4 and 6 by X-ray diffractometric methods.