Experimental observation of spin delocalisation onto the aryl-alkynyl ligand in the complexes [Mo(CCAr)(Ph2PCH2CH2PPh2)(η-C7H7)]+ (Ar = C6H5, C6H4-4-F; C7H7 = cycloheptatrienyl): an EPR and ENDOR investigation

Emma Carter; David Collison; Ruth Edge; Emma C. Fitzgerald; Hannah N. Lancashire; Damien M. Murphy; Joseph J. W. McDouall; Joseph Sharples; Mark W. Whiteley

doi:10.1039/C0DT00642D

Experimental observation of spin delocalisation onto the aryl-alkynyl ligand in the complexes [Mo(CCAr)(Ph₂PCH₂CH₂PPh₂)(η-C₇H₇)]⁺ (Ar = C₆H₅, C₆H₄-4-F; C₇H₇ = cycloheptatrienyl): an EPR and ENDOR investigation†

Emma Carter,^a David Collison,*^b Ruth Edge,^b Emma C. Fitzgerald,^c Hannah N. Lancashire,^c Damien M. Murphy,*^a Joseph J. W. McDouall,^c Joseph Sharples^c and Mark W. Whiteley*^c

Author affiliations

* Corresponding authors

^a School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, UK
E-mail: MurphyDM@cardiff.ac.uk

^b EPSRC National Service for EPR Spectroscopy, School of Chemistry, University of Manchester, Manchester, UK

^c School of Chemistry, University of Manchester, Manchester, UK
E-mail: Mark.Whiteley@manchester.ac.uk
Tel: 0161 275 4634

Abstract

The paramagnetic aryl-alkynyl complexes [Mo(C [triple bond, length as m-dash] CAr)(dppe)(η-C₇H₇)]⁺ (dppe = Ph₂PCH₂CH₂PPh₂; Ar = C₆H₅, [1]⁺; C₆D₅, [2]⁺; C₆H₄-4-F, [3]⁺; C₆H₄-4-Me, [5]⁺) and [Mo(CCBu^t)(dppe)(η-C₇H₇)]⁺ [4]⁺, have been investigated in a combined EPR and ENDOR study. Direct experimental evidence for the delocalisation of unpaired spin density over the framework of an aryl-alkynyl ligand has been obtained. The X-band solution EPR spectrum of the 4-fluoro derivative, [3]⁺, exhibits resolved hyperfine coupling to the remote para position of the aryl group [a_iso(¹⁹F) = 4.5 MHz, (1.6 G)] in addition to couplings attributable to ^95/⁹⁷Mo, ³¹P and ¹H of the C₇H₇ ring. A full analysis of the ¹H ENDOR spectra is restricted by the low g anisotropy of the system which prevents the use of orientation selection. However, inter-comparison of the ¹H cw-ENDOR frozen solution spectra of [1]⁺, [2]⁺, [4]⁺ and [5]⁺, combined with spectral simulation informed by calculated values derived from DFT investigations, has facilitated estimation of the experimental a_iso(¹H) hyperfine couplings of [1]⁺ including the ortho, ±3.7 MHz (±1.3 G) and para, ±3.9 MHz (±1.4 G) positions of the C₆H₅ substituent of the aryl-alkynyl ligand.

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Article information

DOI: https://doi.org/10.1039/C0DT00642D
Article type: Paper
Submitted: 11 Jun 2010
Accepted: 23 Sep 2010
First published: 27 Oct 2010

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Dalton Trans., 2010,39, 11424-11431

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Experimental observation of spin delocalisation onto the aryl-alkynyl ligand in the complexes [Mo(CCAr)(Ph₂PCH₂CH₂PPh₂)(η-C₇H₇)]⁺ (Ar = C₆H₅, C₆H₄-4-F; C₇H₇ = cycloheptatrienyl): an EPR and ENDOR investigation

E. Carter, D. Collison, R. Edge, E. C. Fitzgerald, H. N. Lancashire, D. M. Murphy, J. J. W. McDouall, J. Sharples and M. W. Whiteley, Dalton Trans., 2010, 39, 11424 DOI: 10.1039/C0DT00642D

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