Evidence for a S(N)2-type pathway for phosphine exchange in phosphine-phosphenium cations, [R2P-PR3 '](+)

John M. Slattery; Cheryl Fish; Michael Green; Thomas N. Hooper; John C. Jeffery; Richard J. Kilby; Jason M. Lynam; John E. McGrady; Dimitrios A. Pantazis; Christopher A. Russell; Charlotte E. Willans

doi:10.1002/chem.200601742

Evidence for a S(N)2-type pathway for phosphine exchange in phosphine-phosphenium cations, [R2P-PR3 '](+)

John M. Slattery, Cheryl Fish, Michael Green, Thomas N. Hooper, John C. Jeffery, Richard J. Kilby, Jason M. Lynam, John E. McGrady, Dimitrios A. Pantazis, Christopher A. Russell, Charlotte E. Willans

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

Abstraction of a Cl- ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the PP bonded cations [R4C4PP(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl2) of [Et4C4P(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with S=(-106.3±6.7) J mol-1 K-1, H=(14.9±1.6) kJ mol-1 and G (298.15 K)=(46.6±2.6) kJ mol-1, values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (SN1-type) pathway reported for the analogous exchange reactions of the [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong - interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective -donation from the amide groups reduces the intrinsic electrophilicity of [Ar[bar NCH2CH2N(Ar)P ]]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway.

Original language	English
Pages (from-to)	6967-6974
Number of pages	8
Journal	Chemistry - A European Journal
Volume	13
Issue number	24
DOIs	https://doi.org/10.1002/chem.200601742
Publication status	Published - 31 May 2007

Keywords

carbene homologues
cations
density functional calculations
phosphorus
structure elucidation
LIGAND-EXCHANGE
AB-INITIO
PHOSPHORUS CATIONS
STABLE CARBENES
MAIN-GROUP
CHEMISTRY
COMPLEXES
ION
HETEROCYCLES
ACCEPTOR

Access to Document

10.1002/chem.200601742

http://dx.doi.org/10.1002/chem.200601742

Cite this

@article{b4225a634b0d4770a1267b430f2c411a,

title = "Evidence for a S(N)2-type pathway for phosphine exchange in phosphine-phosphenium cations, [R2P-PR3 '](+)",

abstract = "Abstraction of a Cl- ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the PP bonded cations [R4C4PP(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl2) of [Et4C4P(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with S=(-106.3±6.7) J mol-1 K-1, H=(14.9±1.6) kJ mol-1 and G (298.15 K)=(46.6±2.6) kJ mol-1, values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (SN1-type) pathway reported for the analogous exchange reactions of the [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong - interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective -donation from the amide groups reduces the intrinsic electrophilicity of [Ar[bar NCH2CH2N(Ar)P ]]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway.",

keywords = "carbene homologues, cations, density functional calculations, phosphorus, structure elucidation, LIGAND-EXCHANGE, AB-INITIO, PHOSPHORUS CATIONS, STABLE CARBENES, MAIN-GROUP, CHEMISTRY, COMPLEXES, ION, HETEROCYCLES, ACCEPTOR",

author = "Slattery, {John M.} and Cheryl Fish and Michael Green and Hooper, {Thomas N.} and Jeffery, {John C.} and Kilby, {Richard J.} and Lynam, {Jason M.} and McGrady, {John E.} and Pantazis, {Dimitrios A.} and Russell, {Christopher A.} and Willans, {Charlotte E.}",

year = "2007",

month = may,

day = "31",

doi = "10.1002/chem.200601742",

language = "English",

volume = "13",

pages = "6967--6974",

journal = "Chemistry - A European Journal",

issn = "0947-6539",

publisher = "Wiley-Blackwell",

number = "24",

}

TY - JOUR

T1 - Evidence for a S(N)2-type pathway for phosphine exchange in phosphine-phosphenium cations, [R2P-PR3 '](+)

AU - Slattery, John M.

AU - Fish, Cheryl

AU - Green, Michael

AU - Hooper, Thomas N.

AU - Jeffery, John C.

AU - Kilby, Richard J.

AU - Lynam, Jason M.

AU - McGrady, John E.

AU - Pantazis, Dimitrios A.

AU - Russell, Christopher A.

AU - Willans, Charlotte E.

PY - 2007/5/31

Y1 - 2007/5/31

N2 - Abstraction of a Cl- ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the PP bonded cations [R4C4PP(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl2) of [Et4C4P(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with S=(-106.3±6.7) J mol-1 K-1, H=(14.9±1.6) kJ mol-1 and G (298.15 K)=(46.6±2.6) kJ mol-1, values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (SN1-type) pathway reported for the analogous exchange reactions of the [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong - interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective -donation from the amide groups reduces the intrinsic electrophilicity of [Ar[bar NCH2CH2N(Ar)P ]]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway.

AB - Abstraction of a Cl- ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the PP bonded cations [R4C4PP(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl2) of [Et4C4P(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with S=(-106.3±6.7) J mol-1 K-1, H=(14.9±1.6) kJ mol-1 and G (298.15 K)=(46.6±2.6) kJ mol-1, values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (SN1-type) pathway reported for the analogous exchange reactions of the [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [Ar[bar NCH2CH2N(Ar)P ](PMe3)]+ is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong - interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective -donation from the amide groups reduces the intrinsic electrophilicity of [Ar[bar NCH2CH2N(Ar)P ]]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway.

KW - carbene homologues

KW - cations

KW - density functional calculations

KW - phosphorus

KW - structure elucidation

KW - LIGAND-EXCHANGE

KW - AB-INITIO

KW - PHOSPHORUS CATIONS

KW - STABLE CARBENES

KW - MAIN-GROUP

KW - CHEMISTRY

KW - COMPLEXES

KW - ION

KW - HETEROCYCLES

KW - ACCEPTOR

U2 - 10.1002/chem.200601742

DO - 10.1002/chem.200601742

M3 - Article

SN - 0947-6539

VL - 13

SP - 6967

EP - 6974

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

IS - 24

ER -