Donor-Functionalised Expanded Ring N-Heterocyclic Carbenes: Highly Effective Ligands in Ir-Catalysed Transfer Hydrogenation
✍ Scribed by Abeer Binobaid; Manuel Iglesias; Dirk Beetstra; Athanasia Dervisi; Ian Fallis; Kingsley J. Cavell
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 243 KB
- Volume
- 2010
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
The performances of a number of Rh^I^ and Ir^I^ complexes of type [M(NHC)(COD)Cl] in the transfer hydrogenation of ketones were tested under a variety of reaction conditions, and with a variety of substrates, allowing comparison of Rh‐ and Ir‐NHC complexes, and also comparison of the influence of the NHC ligand on catalytic performance. Notably, of the Rh^I^ and Ir^I^ complexes with symmetrically substituted NHCs only those bearing cyclohexyl substituents were active, with Rh^I^ complexes of saturated 5‐, 6‐ and 7‐NHCs with N‐Mes substituents, [Rh(5,6,7‐Mes)(COD)Cl], showing no activity in transfer hydrogenation under the test conditions. Rh^I^ and Ir^I^ complexes of unsymmetrical o‐methoxyphenyl donor‐functionalised NHCs (df‐NHC) with differing carbene ring sizes were also tested in transfer hydrogenations, with the Rh^I^ complexes displaying no catalytic activity. However, the corresponding df‐NHC Ir^I^ complexes were found to be extremely effective catalysts. Catalyst tests also demonstrated the excellent stability of these complexes.