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Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl substituents at phosphorus on intramolecular nitrogen to phosphorus hypervalent coordinative interactions

Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl substituents at phosphorus on intramolecular nitrogen to phosphorus hypervalent coordinative interactions
Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl substituents at phosphorus on intramolecular nitrogen to phosphorus hypervalent coordinative interactions
The synthesis of tri(2-fur)(8-quinolylmethyl)phosphonium bromide and 2-[2-tri(2-furyl)phosphoniophenyl]benzimidazole perchlorate is described, the latter involving a nickel(II)-catalysed displacement of bromine from 2-(2-bromophenyl)benzimidazole by tri(2-furyl)phosphine. X-ray structural Studies of the phosphoniobenzimidazole salt reveals the existence of a significant hypervalent coordinative interaction between heterocyclic nitrogen and the phosphonium centre, which also appears to be retained in solution, the P-31 NMR spectrum showing a significantly shielded phosphorus atom, delta(31)P = ca. -40 ppm in CDCl3. The structure of the phosphoniophenylbenzimidazole cation reveals major distortion of bond angles about phosphorus away from the idealised tetrahedral angles expected for a tetraarylphosphonium salt, in the range 102-116degrees. Three of the angles are reduced below the tetrahedral angle and three are increased, the structure about phosphorus approaching that of a trigonal bipyramid, in which the heterocyclic imino nitrogen forms part of a five-membered ring spanning apical-equatorial positions. The apical axis of the trigonal bipyramid is formed by this nitrogen atom and one of the 2-furyl groups, the apical axial bond angle (N2-P-Cl4) being an average of 178degrees. The remaining 2-furyl groups occupy equatorial positions, along with the phenyl ring. Significantly, the nitrogen-phosphorus distance is an average of 2.67 Angstrom (for two independent molecules in the unit cell), being the shortest observed in structures of this type, a consequence of the electron-withdrawing properties of the 2-furyl substituents at phosphorus. The structure also shows edge to face associations of 2-furyl substituents of one cation with the phenyl ring of the benzimidazole unit of another cation. The perchlorate anion is hydrogen-bonded to the nitrogen bearing the hydrogen atom in the benzimidazole ring system. In contrast, the N-P interaction in the quinolylmethylphosphonium salt is much less developed. with an N-P distance of 3.511 Angstrom, although there is considerable deformation of bond angles at phosphorus. The crystal structure is dominated by the existence of hydrogen-bonded interactions between the cation, anion and a molecule of water, and by face to face interactions between cations. Both salts undergo loss of a 2-furyl group on treatment with hydroxide ion.
crystal structures, heteroaryl substituents, hypercoordination, hypervalency, p-31 nmro donor action, alkaline-hydrolysis, heteroarylphosphorus compounds, arylphosphonium salts, catalyzed formation, chemistry, silicon, phosphines, betaines, cations
0020-1693
1558-1564
Allen, David W.
4cbcd21b-4bb9-40e8-baa9-27b1b3e5a7b2
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Light, Mark E.
cf57314e-6856-491b-a8d2-2dffc452e161
Hursthouse, Michael B.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da
Allen, David W.
4cbcd21b-4bb9-40e8-baa9-27b1b3e5a7b2
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Light, Mark E.
cf57314e-6856-491b-a8d2-2dffc452e161
Hursthouse, Michael B.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da

Allen, David W., Coles, Simon J., Light, Mark E. and Hursthouse, Michael B. (2004) Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl substituents at phosphorus on intramolecular nitrogen to phosphorus hypervalent coordinative interactions. Inorganica Chimica Acta, 357 (5), 1558-1564. (doi:10.1016/j.ica.2003.12.001).

Record type: Article

Abstract

The synthesis of tri(2-fur)(8-quinolylmethyl)phosphonium bromide and 2-[2-tri(2-furyl)phosphoniophenyl]benzimidazole perchlorate is described, the latter involving a nickel(II)-catalysed displacement of bromine from 2-(2-bromophenyl)benzimidazole by tri(2-furyl)phosphine. X-ray structural Studies of the phosphoniobenzimidazole salt reveals the existence of a significant hypervalent coordinative interaction between heterocyclic nitrogen and the phosphonium centre, which also appears to be retained in solution, the P-31 NMR spectrum showing a significantly shielded phosphorus atom, delta(31)P = ca. -40 ppm in CDCl3. The structure of the phosphoniophenylbenzimidazole cation reveals major distortion of bond angles about phosphorus away from the idealised tetrahedral angles expected for a tetraarylphosphonium salt, in the range 102-116degrees. Three of the angles are reduced below the tetrahedral angle and three are increased, the structure about phosphorus approaching that of a trigonal bipyramid, in which the heterocyclic imino nitrogen forms part of a five-membered ring spanning apical-equatorial positions. The apical axis of the trigonal bipyramid is formed by this nitrogen atom and one of the 2-furyl groups, the apical axial bond angle (N2-P-Cl4) being an average of 178degrees. The remaining 2-furyl groups occupy equatorial positions, along with the phenyl ring. Significantly, the nitrogen-phosphorus distance is an average of 2.67 Angstrom (for two independent molecules in the unit cell), being the shortest observed in structures of this type, a consequence of the electron-withdrawing properties of the 2-furyl substituents at phosphorus. The structure also shows edge to face associations of 2-furyl substituents of one cation with the phenyl ring of the benzimidazole unit of another cation. The perchlorate anion is hydrogen-bonded to the nitrogen bearing the hydrogen atom in the benzimidazole ring system. In contrast, the N-P interaction in the quinolylmethylphosphonium salt is much less developed. with an N-P distance of 3.511 Angstrom, although there is considerable deformation of bond angles at phosphorus. The crystal structure is dominated by the existence of hydrogen-bonded interactions between the cation, anion and a molecule of water, and by face to face interactions between cations. Both salts undergo loss of a 2-furyl group on treatment with hydroxide ion.

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More information

Published date: 25 March 2004
Keywords: crystal structures, heteroaryl substituents, hypercoordination, hypervalency, p-31 nmro donor action, alkaline-hydrolysis, heteroarylphosphorus compounds, arylphosphonium salts, catalyzed formation, chemistry, silicon, phosphines, betaines, cations

Identifiers

Local EPrints ID: 20116
URI: https://eprints.soton.ac.uk/id/eprint/20116
ISSN: 0020-1693
PURE UUID: b3783b44-3841-45e6-b517-64005256ec68
ORCID for Simon J. Coles: ORCID iD orcid.org/0000-0001-8414-9272
ORCID for Mark E. Light: ORCID iD orcid.org/0000-0002-0585-0843

Catalogue record

Date deposited: 23 Feb 2006
Last modified: 20 Jul 2019 01:10

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