The University of Southampton
University of Southampton Institutional Repository

A conformational study of phospha(III)- and phospha(V)-guanidine compounds

A conformational study of phospha(III)- and phospha(V)-guanidine compounds
A conformational study of phospha(III)- and phospha(V)-guanidine compounds

Spectroscopic, crystallographic, and computational studies of the substituent distribution about the "NCN" unit in a series of phospha(III)- and phospha(V)-guanidines, R2PC{NR′}{NHR′} and R2P(E)C-{NR′}{NHR′} (R = Ph, Cy; R′ = iPr, Cy; E = S, Se), are reported. In the phosphorus(III) systems, the P-diphenyl substituted compounds are observed as only one isomer, shown by NMR spectroscopy to be the Esyn-(α) configuration. In contrast, the corresponding P-dicyclohexyl derivatives exist as a mixture of E syn-(α) and Zanti in solution. Spectroscopic techniques are unable to determine whether the latter isomer exists as the α- or β-conformer relative to rotation about the P-C amidine bond; however, DFT calculations indicate a low-energy structure for the N,N′-dimethyl model complex in the β-conformation. In their oxidized sulfo and seleno forms, the P-diphenyl compounds are present as an interconverting equilibrium mixture of the Esyn-(β) and Zsyn-(β) isomers in solution (∼3:2 ratio), whereas for the P-dicyclohexyl analogues, the latter configuration (in which the nitrogen substituents are in a more sterically unfavorably cisoid arrangement about the imine double bond) is the dominant form. Intramolecular E⋯HN (E = S, Se) interactions are observed in solution for the Zsyn-(β) configuration of both P-substituted species, characterized by JseH coupling in the NMR spectrum for the P(V)-seleno compounds and a bathochromic shift of the NH absorption in the infrared spectrum. An X-ray crystallographic analysis of representative Ph2P(E)- and Cy2P(E)- substituted species shows exclusively the Esyn-(β) configuration for the P-diphenyl substituted compounds and the ZSyn-(β) form for the P-dicyclohexyl derivatives, independent of the chalcogen and the nitrogen substituents. Results from a DFT analysis of model compounds fail to identify a compelling electronic argument for the observed preferences in substituent orientation, suggesting that steric factors play an important role in determining the subtle energetic differences at work in these systems.

0002-7863
13879-13893
Mansfield, Natalie E.
4d6b9a06-2b2e-4ba9-916e-8f8ff27c2ac5
Grundy, Joanna
0bc72187-8dce-41fc-b809-93a6adbe0980
Coles, Martyn P.
4cb5ee08-daf9-4b58-9627-61732e0a818b
Avent, Anthony G.
6fe5d51d-5f31-454f-938a-ec91c840f2ce
Hitchcock, Peter B.
4c0fe381-c3e8-452c-a284-fe14acd3b748
Mansfield, Natalie E.
4d6b9a06-2b2e-4ba9-916e-8f8ff27c2ac5
Grundy, Joanna
0bc72187-8dce-41fc-b809-93a6adbe0980
Coles, Martyn P.
4cb5ee08-daf9-4b58-9627-61732e0a818b
Avent, Anthony G.
6fe5d51d-5f31-454f-938a-ec91c840f2ce
Hitchcock, Peter B.
4c0fe381-c3e8-452c-a284-fe14acd3b748

Mansfield, Natalie E., Grundy, Joanna, Coles, Martyn P., Avent, Anthony G. and Hitchcock, Peter B. (2006) A conformational study of phospha(III)- and phospha(V)-guanidine compounds. Journal of the American Chemical Society, 128 (42), 13879-13893. (doi:10.1021/ja064212t).

Record type: Article

Abstract

Spectroscopic, crystallographic, and computational studies of the substituent distribution about the "NCN" unit in a series of phospha(III)- and phospha(V)-guanidines, R2PC{NR′}{NHR′} and R2P(E)C-{NR′}{NHR′} (R = Ph, Cy; R′ = iPr, Cy; E = S, Se), are reported. In the phosphorus(III) systems, the P-diphenyl substituted compounds are observed as only one isomer, shown by NMR spectroscopy to be the Esyn-(α) configuration. In contrast, the corresponding P-dicyclohexyl derivatives exist as a mixture of E syn-(α) and Zanti in solution. Spectroscopic techniques are unable to determine whether the latter isomer exists as the α- or β-conformer relative to rotation about the P-C amidine bond; however, DFT calculations indicate a low-energy structure for the N,N′-dimethyl model complex in the β-conformation. In their oxidized sulfo and seleno forms, the P-diphenyl compounds are present as an interconverting equilibrium mixture of the Esyn-(β) and Zsyn-(β) isomers in solution (∼3:2 ratio), whereas for the P-dicyclohexyl analogues, the latter configuration (in which the nitrogen substituents are in a more sterically unfavorably cisoid arrangement about the imine double bond) is the dominant form. Intramolecular E⋯HN (E = S, Se) interactions are observed in solution for the Zsyn-(β) configuration of both P-substituted species, characterized by JseH coupling in the NMR spectrum for the P(V)-seleno compounds and a bathochromic shift of the NH absorption in the infrared spectrum. An X-ray crystallographic analysis of representative Ph2P(E)- and Cy2P(E)- substituted species shows exclusively the Esyn-(β) configuration for the P-diphenyl substituted compounds and the ZSyn-(β) form for the P-dicyclohexyl derivatives, independent of the chalcogen and the nitrogen substituents. Results from a DFT analysis of model compounds fail to identify a compelling electronic argument for the observed preferences in substituent orientation, suggesting that steric factors play an important role in determining the subtle energetic differences at work in these systems.

This record has no associated files available for download.

More information

e-pub ahead of print date: 3 October 2006
Published date: 25 October 2006

Identifiers

Local EPrints ID: 426201
URI: http://eprints.soton.ac.uk/id/eprint/426201
ISSN: 0002-7863
PURE UUID: 0f17a87c-0691-491b-8a4c-d968d126b0cc
ORCID for Joanna Grundy: ORCID iD orcid.org/0000-0003-2583-5680

Catalogue record

Date deposited: 16 Nov 2018 17:30
Last modified: 06 Jun 2024 02:05

Export record

Altmetrics

Contributors

Author: Natalie E. Mansfield
Author: Joanna Grundy ORCID iD
Author: Martyn P. Coles
Author: Anthony G. Avent
Author: Peter B. Hitchcock

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×