The search for new hydrogenation catalyst motifs based on N-heterocyclic carbene ligands

Vazquez‐Serrano, Leslie D.; Owens, Bridget; Buriak, Jillian M.

doi:10.1016/j.ica.2005.10.049

Cited by 119 publications

(124 citation statements)

References 63 publications

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“…In particular, we have 22 were synthesised using literature procedures. All other solvents and reagents are commercial products and were used as received.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Reactivity of NHC-Based Rhodium Macrocycles

Andrew

Chaplin

2014

Inorg. Chem.

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Using a general synthetic procedure employing readily accessed terminal alkene functionalised pro-ligands and macrocyclisation by ring-closing olefin metathesis, rhodium carbonyl complexes have been prepared that contain lutidine-(1a; n = 1) and pyridine-(1b; n = 0) derived tridentate CNC macrocycles with dodecamethylene spacers. In solution 1a shows temperature invariant time averaged C 2 symmetry by 1 H NMR spectroscopy (CD 2 Cl 2 , 500 MHz), while in the solid-state two polymorphs can be obtained showing different conformations of the alkyl spacer about the metal-carbonyl bond (asymmetric and symmetric). In contrast, time-averaged motion of alkyl spacer in 1b can be halted by cooling below 225 K (CD 2 Cl 2 , 500 MHz) and the complex crystallises as a dimer with an interesting unsupported Rh···Rh bonding interaction (3.2758(6) Å). Oxidative addition reactions of 1a and 1b, using MeI and PhICl 2 , have been studied in situ by 1 H NMR spectroscopy, although pure Rh(III) adducts can ultimately only be isolated with the pyridine-based macrocyclic ligand. The lutidine backbone of 1a can be deprotonated by addition of K[N(SiMe 3 ) 2 ] and the resulting neutral dearomatised complex (5) has been fully characterised in solution, by variable temperature 1 H NMR spectroscopy, and in the solid-state, by X-ray diffraction.

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“…In particular, we have 22 were synthesised using literature procedures. All other solvents and reagents are commercial products and were used as received.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Reactivity of NHC-Based Rhodium Macrocycles

Andrew

Chaplin

2014

Inorg. Chem.

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“…21 Crabtree and co-workers 34 Parahydrogen induced polarization (PHIP) 1 H NMR experiments indicated that a dihydride mechanism was operating, but other mechanisms could not be ruled out. 35 Roseblade and Pfaltz also considered a related mechanism, 36 to form H which, by coordination of another alkene and a solvent molecule, reforms E (the suggested catalyst resting state).…”

Section: Mechanistic Aspectsmentioning

confidence: 99%

Asymmetric Hydrogenation of Olefins Using Chiral Crabtree-type Catalysts: Scope and Limitations

et al. 2013

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“…[2c,9] In view of the issues associated with Crabtree's catalyst, it is evident that alternative metal-based complexes for use in hydrogen isotope exchange would be beneficial to pharmaceutical partners with, in particular, the desired catalysts being capable of labelling an assortment of substrates to high levels of incorporation under mild reaction conditions and with lowered catalyst loadings. Following the work of Nolan [10] and Buriak [11] in the field of olefin hydrogenation, we felt that in order to enhance catalytic activity in HIE processes, relative to Crabtree's catalyst, greater steric demand around the metal centre, coupled with balanced electronic parameters, was required. [12] In this regard, we have reported on the preparation and application of a series of new iridium complexes bearing a bulky Nheterocyclic carbene (NHC), 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), alongside an appreciably encumbered phosphine, and which have appreciable potential as highly active catalysts for HIE with deuterium.…”

Section: Introductionmentioning

confidence: 99%

The Synthesis of Highly Active Iridium(I) Complexes and their Application in Catalytic Hydrogen Isotope Exchange

et al. 2014

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This version is available at https://strathprints.strath.ac.uk/49161/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Abstract. : A series of robust iridium(I) complexes bearing a sterically encumbered N-heterocyclic carbene ligand, alongside a phosphine ligand, has been synthesised and investigated in hydrogen isotope exchange processes. These complexes have allowed isotope incorporation over a range of substrates with the use of practically convenient deuterium and tritium gas. Moreover, these active catalysts are capable of isotope incorporation to particularly high levels, whilst employing low catalyst loadings and in short reaction times. In addition to this, these new catalyst species have shown flexible levels of chemoselectivity, which can be altered by simple manipulation of preparative approaches.Furthermore, a number of industrially-relevant drug molecules have also been labelled, including the sulfonamide containing drug, Celecoxib. Alongside detailed NMR experiments, initial mechanistic investigations have also been performed, providing insight into both substrate binding energies, and, more importantly, relative energies of key steps in the mechanistic cycle as part of the overall exchange process.

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The search for new hydrogenation catalyst motifs based on N-heterocyclic carbene ligands

Cited by 119 publications

References 63 publications

Synthesis and Reactivity of NHC-Based Rhodium Macrocycles

Synthesis and Reactivity of NHC-Based Rhodium Macrocycles

Asymmetric Hydrogenation of Olefins Using Chiral Crabtree-type Catalysts: Scope and Limitations

The Synthesis of Highly Active Iridium(I) Complexes and their Application in Catalytic Hydrogen Isotope Exchange

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