Transition metal complexes of bis(carbene)pyridine 'pincer' ligands : synthesis and reactivity
Transition metal complexes of bis(carbene)pyridine 'pincer' ligands : synthesis and reactivity
A new (CNC) pincer ligand, (2,6-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)-3,5- dimethylpyridine, has been synthesised. Along with the previously reported ligand (2,6- bis(2,6-diisopropylphenyl)imidazol-2-ylidene)pyridine, (CNC) pincer complexes of transition metals across the periodic table, from titanium to iridium, have been synthesised, fully characterised and their reactivity investigated. A comparison of the a-donating properties of NHCs, trialkylphosphines and imines as part of pincer ligands has been carried out. Ti(lV) complexes of (CNC) and (PNP) ligands revealed that (CNC) ligands were better a-donors than (PNP) ligands, in keeping with literature reports. However, Fe(0) complexes of (CNC), (PNP) and (NNN) ligands revealed that (PNP) ligands were better a-donors, contrary to literature reports. Novel ring opening reactions of NHCs to coordinated vinyl groups have been observed with nickel and iridium complexes of (CNC) ligands. Proposed mechanisms indicate the former is caused by methyl migration to the CNHC followed by base-catalysed deprotonation whereas it is thought the latter occurs via a 4-membered nitrogen- containing heterocycle. An unprecedented binding mode for NHCs has also been observed where the unsaturated backbone of an imidazol-2-ylidene ring bonds in an rj1 fashion to another metal centre.
University of Southampton
Pugh, David Charles
9f16a243-26a6-4600-8e82-fee2a2f59425
2008
Pugh, David Charles
9f16a243-26a6-4600-8e82-fee2a2f59425
Pugh, David Charles
(2008)
Transition metal complexes of bis(carbene)pyridine 'pincer' ligands : synthesis and reactivity.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
A new (CNC) pincer ligand, (2,6-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)-3,5- dimethylpyridine, has been synthesised. Along with the previously reported ligand (2,6- bis(2,6-diisopropylphenyl)imidazol-2-ylidene)pyridine, (CNC) pincer complexes of transition metals across the periodic table, from titanium to iridium, have been synthesised, fully characterised and their reactivity investigated. A comparison of the a-donating properties of NHCs, trialkylphosphines and imines as part of pincer ligands has been carried out. Ti(lV) complexes of (CNC) and (PNP) ligands revealed that (CNC) ligands were better a-donors than (PNP) ligands, in keeping with literature reports. However, Fe(0) complexes of (CNC), (PNP) and (NNN) ligands revealed that (PNP) ligands were better a-donors, contrary to literature reports. Novel ring opening reactions of NHCs to coordinated vinyl groups have been observed with nickel and iridium complexes of (CNC) ligands. Proposed mechanisms indicate the former is caused by methyl migration to the CNHC followed by base-catalysed deprotonation whereas it is thought the latter occurs via a 4-membered nitrogen- containing heterocycle. An unprecedented binding mode for NHCs has also been observed where the unsaturated backbone of an imidazol-2-ylidene ring bonds in an rj1 fashion to another metal centre.
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Published date: 2008
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Local EPrints ID: 466457
URI: http://eprints.soton.ac.uk/id/eprint/466457
PURE UUID: ace4a5d1-8aad-4278-94c7-c3200bd3f208
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Date deposited: 05 Jul 2022 05:17
Last modified: 16 Mar 2024 20:42
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Author:
David Charles Pugh
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