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Arnold PL, Kerr RWF, Weetman C, Docherty SR, Rieb J, Cruickshank FL, Wang K, Jandl C, McMullon MW, Pöthig A, Kühn FE, Smith AD. Selective and catalytic carbon dioxide and heteroallene activation mediated by cerium N-heterocyclic carbene complexes. Chem Sci 2018; 9:8035-8045. [PMID: 30568765 PMCID: PMC6262539 DOI: 10.1039/c8sc03312a] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 09/05/2018] [Indexed: 11/21/2022] Open
Abstract
A series of rare earth complexes of the form Ln(LR)3 supported by bidentate ortho-aryloxide-NHC ligands are reported (LR = 2-O-3,5-tBu2-C6H2(1-C{N(CH)2N(R)})); R = iPr, tBu, Mes; Ln = Ce, Sm, Eu). The cerium complexes cleanly and quantitatively insert carbon dioxide exclusively into all three cerium carbene bonds, forming Ce(LR·CO2)3. The insertion is reversible only for the mesityl-substituted complex Ce(LMes)3. Analysis of the capacity of Ce(LR)3 to insert a range of heteroallenes that are isoelectronic with CO2 reveals the solvent and ligand size dependence of the selectivity. This is important because only the complexes capable of reversible CO2-insertion are competent catalysts for catalytic conversions of CO2. Preliminary studies show that only Ce(LMes·CO2)3 catalyses the formation of propylene carbonate from propylene oxide under 1 atm of CO2 pressure. The mono-ligand complexes can be isolated from reactions using LiCe(NiPr2)4 as a starting material; LiBr adducts [Ce(LR)(NiPr2)Br·LiBr(THF)]2 (R = Me, iPr) are reported, along with a hexanuclear N-heterocyclic dicarbene [Li2Ce3(OArCMe-H)3(NiPr2)5(THF)2]2 by-product. The analogous para-aryloxide-NHC proligand (p-LMes = 4-O-2,6-tBu2-C6H2(1-C{N(CH)2NMes}))) has been made for comparison, but the rare earth tris-ligand complexes Ln(p-LMes)3(THF)2 (Ln = Y, Ce) are too reactive for straightforward Lewis pair separated chemistry to be usefully carried out.
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Affiliation(s)
- Polly L Arnold
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK .
| | - Ryan W F Kerr
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK . .,EaStCHEM School of Chemistry , University of St. Andrews , North Haugh, St. Andrews , KY16 9ST , UK, E-mail:
| | - Catherine Weetman
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK .
| | - Scott R Docherty
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK .
| | - Julia Rieb
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK . .,Molecular Catalysis, Faculty of Chemistry and Catalysis Research Center , Technical University Munich , Lichtenbergstr. 4 , 85748 Garching bei München , Germany
| | - Faye L Cruickshank
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK .
| | - Kai Wang
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK .
| | - Christian Jandl
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK . .,Molecular Catalysis, Faculty of Chemistry and Catalysis Research Center , Technical University Munich , Lichtenbergstr. 4 , 85748 Garching bei München , Germany
| | - Max W McMullon
- EaStCHEM School of Chemistry , University of Edinburgh , The King's Buildings , Edinburgh , EH9 3FJ , UK . .,Molecular Catalysis, Faculty of Chemistry and Catalysis Research Center , Technical University Munich , Lichtenbergstr. 4 , 85748 Garching bei München , Germany
| | - Alexander Pöthig
- Molecular Catalysis, Faculty of Chemistry and Catalysis Research Center , Technical University Munich , Lichtenbergstr. 4 , 85748 Garching bei München , Germany
| | - Fritz E Kühn
- Molecular Catalysis, Faculty of Chemistry and Catalysis Research Center , Technical University Munich , Lichtenbergstr. 4 , 85748 Garching bei München , Germany
| | - Andrew D Smith
- EaStCHEM School of Chemistry , University of St. Andrews , North Haugh, St. Andrews , KY16 9ST , UK, E-mail:
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