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Synthesis of phosphine- and pyridine- functionalised N-heterocyclic carbene complexes of platinum group metals

Synthesis of phosphine- and pyridine- functionalised N-heterocyclic carbene complexes of platinum group metals
Synthesis of phosphine- and pyridine- functionalised N-heterocyclic carbene complexes of platinum group metals

A new and improved method for the preparation of phosphine functionalised imidazolium salt NHC precursors with the systematic name 3-(aryl)-1-(n-diphenylphosphanyl-alkyln)-3H-imidazole-1-ium (n = 1 then alkyl = methyl; aryl = 2,4,6-Me3-C6H2: 2.2b, 2,6-(iPr)2-C6H3: 2.2a/ n = 2, alkyl = ethyl; aryl = 2,4,6-Me3-C6H2: 2.4b, 2,6-(iPr)2-C6H3: 2.4a / n = 3, alkyl = propyl; aryl = 2,4,6-Me3-C6H2: 2.6) has been developed. Pyridine functionalised imidazolium salts of the systematic name 3-(aryl)-1-(3-R-pyridine-2-yl)-3H-imidazol-1-ium (aryl = 2,6-(iPr)2-C6H3, R = H: 2.8c; aryl = 2,6-(iPr)2-C6H3, R = Me: 2.8d/ aryl = 3,5-(CF3, R = H: 2.7) have also been synthesised. Interaction of 2.8c or 2.8d with KN(SiMe3)2 leads to the formation of carbenes 3-(2,6-diisopropyl-phenyl)-1-(pyridine-2-yl)-2,3 dihydro-1H-imidazole-2-ylidene (2.9c = CN(1)) and 3-(2,6-diisopropyl-phenyl)-1-(3-methyl-pyridin-2-yl)-2,3 dihydro-1H-imidazole-2-ylidene (2.9d = CN(2)) respectively.

The phosphine functionalised imidazolium salts 2.2a, 2.4b, 2.4a and 2.6 were used to generate the corresponding ylidines by their reaction with KN(SiMe3)2, that were trapped with an appropriate Pd(II) metal precursor. Metal precursors of the type cis-PdLX2 (L = tmed: X = Me; L = COD:X = Br) led to the isolation of complexes of the type (PC)PdX2 (PC = 3-(aryl)-1-(n-diphenylphosphanyl-alkyln)-2,3 dihydro-1 H-imidazol-2-ylidene (n = 1, 14yl = 2,6-(iPr)2-C6H3 (=PC(1)), X = Me: 3.3; n = 2, aryl = 2,6-(iPr)2-C6H3 ( = (PC(2)) or 2,4,6-Me3-C6H2 (=PC(2)), X = Me: 3.1a and 3.1b respectively; n = 3, aryl = 2,4,6-Me3-C6H2 ( =PC(3)), X = Me: 3.4; n = 2, aryl = 2,6-(iPr)2-C6H3 or 2,4,6-Me3-C6H2, X = Br: 3.2a and 3.2b respectively). Interaction of [Pd(η;3-methallyl)(PC(2))]+C1- (3.8b), which undergoes salt exchange reactions with Na+BAr4- to give compounds [Pd(η;3 – methallyl)(PC(2))]+BAr4- (Ar = 3,5-(CF3)2-C6H3: 3.8a; Ar = Ph: 3.8c). Interaction of ylidenes 2.9c (CN(1)) or 2.9d (CN(2)) with Pd(timd)Me2 in a 1.4:1 and 1:1 stoichiometry respectively leas to the isolation of complexes [(CN(1))PdMe2] (3.5a) and [(CN(2))PdMe2](3.5b) respectively where the pyridine functionalised NHCs act as chelates. When 2.9c is reacted with Pd(tmed)Me2 in a 2:1 stoichiometry the C2 symmetric complex [(CN(1))2PdMe2] (3.6) is formed in which the pyridine functionalities are not participating in the coordination sphere. Finally, [Pd(η;3-methallyl)(CN(1))]+BPh4- (3.7) is formed by interactions of [Pd(η;3-methallyl)C1]2 with 2 equivalents of 2.9c followed by addition of Na+BPh4-.

The thermally stable Pd(II) dimethyl complexes described above (3.1a/b, 3.3, 3.5b and 3.6) show moderate catalytic activity towards Heck coupling, probably due to the reductive elimination of P, N functionalised 2-methyl-imidazolium salts.

Reaction of the in situ generated PC(2), 2.9c or 2.9d with 0.5 equivalents of [Pt(μ;-SMe2)2Me2]2 gives complexes [Pt(PC(2))Me2] (5.6), [Pt(CN(1))Me2] (5.7a) and [Pt(CN(2))Me2] (5.7b) respectively. 5.7b reacts slowly with dichloromethane at room temperature to give complex [Pt(CN(2))MeC1] (5.8).

University of Southampton
Tsoureas, Nikolaos
b40771a1-8870-43bc-8989-3c6eee2f325f
Tsoureas, Nikolaos
b40771a1-8870-43bc-8989-3c6eee2f325f

Tsoureas, Nikolaos (2005) Synthesis of phosphine- and pyridine- functionalised N-heterocyclic carbene complexes of platinum group metals. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A new and improved method for the preparation of phosphine functionalised imidazolium salt NHC precursors with the systematic name 3-(aryl)-1-(n-diphenylphosphanyl-alkyln)-3H-imidazole-1-ium (n = 1 then alkyl = methyl; aryl = 2,4,6-Me3-C6H2: 2.2b, 2,6-(iPr)2-C6H3: 2.2a/ n = 2, alkyl = ethyl; aryl = 2,4,6-Me3-C6H2: 2.4b, 2,6-(iPr)2-C6H3: 2.4a / n = 3, alkyl = propyl; aryl = 2,4,6-Me3-C6H2: 2.6) has been developed. Pyridine functionalised imidazolium salts of the systematic name 3-(aryl)-1-(3-R-pyridine-2-yl)-3H-imidazol-1-ium (aryl = 2,6-(iPr)2-C6H3, R = H: 2.8c; aryl = 2,6-(iPr)2-C6H3, R = Me: 2.8d/ aryl = 3,5-(CF3, R = H: 2.7) have also been synthesised. Interaction of 2.8c or 2.8d with KN(SiMe3)2 leads to the formation of carbenes 3-(2,6-diisopropyl-phenyl)-1-(pyridine-2-yl)-2,3 dihydro-1H-imidazole-2-ylidene (2.9c = CN(1)) and 3-(2,6-diisopropyl-phenyl)-1-(3-methyl-pyridin-2-yl)-2,3 dihydro-1H-imidazole-2-ylidene (2.9d = CN(2)) respectively.

The phosphine functionalised imidazolium salts 2.2a, 2.4b, 2.4a and 2.6 were used to generate the corresponding ylidines by their reaction with KN(SiMe3)2, that were trapped with an appropriate Pd(II) metal precursor. Metal precursors of the type cis-PdLX2 (L = tmed: X = Me; L = COD:X = Br) led to the isolation of complexes of the type (PC)PdX2 (PC = 3-(aryl)-1-(n-diphenylphosphanyl-alkyln)-2,3 dihydro-1 H-imidazol-2-ylidene (n = 1, 14yl = 2,6-(iPr)2-C6H3 (=PC(1)), X = Me: 3.3; n = 2, aryl = 2,6-(iPr)2-C6H3 ( = (PC(2)) or 2,4,6-Me3-C6H2 (=PC(2)), X = Me: 3.1a and 3.1b respectively; n = 3, aryl = 2,4,6-Me3-C6H2 ( =PC(3)), X = Me: 3.4; n = 2, aryl = 2,6-(iPr)2-C6H3 or 2,4,6-Me3-C6H2, X = Br: 3.2a and 3.2b respectively). Interaction of [Pd(η;3-methallyl)(PC(2))]+C1- (3.8b), which undergoes salt exchange reactions with Na+BAr4- to give compounds [Pd(η;3 – methallyl)(PC(2))]+BAr4- (Ar = 3,5-(CF3)2-C6H3: 3.8a; Ar = Ph: 3.8c). Interaction of ylidenes 2.9c (CN(1)) or 2.9d (CN(2)) with Pd(timd)Me2 in a 1.4:1 and 1:1 stoichiometry respectively leas to the isolation of complexes [(CN(1))PdMe2] (3.5a) and [(CN(2))PdMe2](3.5b) respectively where the pyridine functionalised NHCs act as chelates. When 2.9c is reacted with Pd(tmed)Me2 in a 2:1 stoichiometry the C2 symmetric complex [(CN(1))2PdMe2] (3.6) is formed in which the pyridine functionalities are not participating in the coordination sphere. Finally, [Pd(η;3-methallyl)(CN(1))]+BPh4- (3.7) is formed by interactions of [Pd(η;3-methallyl)C1]2 with 2 equivalents of 2.9c followed by addition of Na+BPh4-.

The thermally stable Pd(II) dimethyl complexes described above (3.1a/b, 3.3, 3.5b and 3.6) show moderate catalytic activity towards Heck coupling, probably due to the reductive elimination of P, N functionalised 2-methyl-imidazolium salts.

Reaction of the in situ generated PC(2), 2.9c or 2.9d with 0.5 equivalents of [Pt(μ;-SMe2)2Me2]2 gives complexes [Pt(PC(2))Me2] (5.6), [Pt(CN(1))Me2] (5.7a) and [Pt(CN(2))Me2] (5.7b) respectively. 5.7b reacts slowly with dichloromethane at room temperature to give complex [Pt(CN(2))MeC1] (5.8).

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Published date: 2005
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Local EPrints ID: 466573
URI: http://eprints.soton.ac.uk/id/eprint/466573
PURE UUID: f3a9cd99-b53c-4315-91f5-acb0903cb1fb

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Date deposited: 05 Jul 2022 05:51
Last modified: 16 Mar 2024 20:47

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Author: Nikolaos Tsoureas

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