Iridium(III) Complexes Bearing Chelating Bis‐NHC Ligands and Their Application in the Catalytic Reduction of Imines
2016; Wiley; Volume: 2016; Issue: 28 Linguagem: Inglês
10.1002/ejic.201600922
ISSN1099-0682
AutoresFrancisco Aznárez, Manuel Iglesias, Alexander Hepp, Benjamin Veit, Pablo J. Sanz Miguel, Luis A. Oro, Guo‐Xin Jin, F. Ekkehardt Hahn,
Tópico(s)Catalytic Cross-Coupling Reactions
ResumoThe Ir III complexes 4 and 5 bearing bis‐NHC ligands (NHC = N‐heterocyclic carbene) composed of one classical NR,NR NHC and one N,NR NHC donor were prepared by the reaction of the azolium/azole compounds 2 I and 3 Br, respectively, with [{Cp*IrCl(µ‐Cl)} 2 ] (Cp*=η 5 ‐C 5 Me 5 ) in the presence of NaOAc as base. Most likely, the salts 2 I and 3 Br were first selectively deprotonated at the C2 position of the disubstituted (NR,NR) diazaheterocycle to generate an NHC donor, which then coordinated to the Ir III center. Subsequently, NaOAc promoted C–H bond activation at the pendant imidazole moiety of the intermediate Ir III mono‐NHC complexes led to the formation of the six‐membered iridacycles 4 and 5 , which bear a chelating, doubly C ‐metalated C(NHC) ^ C(NHC′) bis‐NHC ligand. The Ir III complexes 4 and 5 were tested as precatalysts for the reduction of imines with molecular hydrogen. Moderate to good activity was observed at a catalyst loading of 5 mol‐% and an H 2 pressure of 3 bar in MeOH.
Referência(s)