title: Experimental observation of spin delocalisation onto the aryl-alkynyl ligand in the complexes [Mo(C≡CAr)(Ph2PCH2CH2PPh2)(η-C7H7)]+ (Ar = C6H5, C6H4-4-F; C7H7 = cycloheptatrienyl): an EPR and ENDOR investigation.
abstract: The paramagnetic aryl-alkynyl complexes [Mo(C≡CAr)(dppe)(η-C(7)H(7))](+) (dppe = Ph(2)PCH(2)CH(2)PPh(2); Ar = C(6)H(5), [1](+); C(6)D(5), [2](+); C(6)H(4)-4-F, [3](+); C(6)H(4)-4-Me, [5](+)) and [Mo(C≡CBu(t))(dppe)(η-C(7)H(7))](+) [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)((19)F) = 4.5 MHz, (1.6 G)] in addition to couplings attributable to (95/97)Mo, (31)P and (1)H of the C(7)H(7) ring. A full analysis of the (1)H ENDOR spectra is restricted by the low g anisotropy of the system which prevents the use of orientation selection. However, inter-comparison of the (1)H 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)((1)H) hyperfine couplings of [1](+) including the ortho, ±3.7 MHz (±1.3 G) and para, ±3.9 MHz (±1.4 G) positions of the C(6)H(5) substituent of the aryl-alkynyl ligand.
authors.affiliation: School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, UK CF10 3AT.
authors.forename: Emma
authors.initials: E
authors.lastname: Carter
authors.forename: David
authors.initials: D
authors.lastname: Collison
authors.forename: Ruth
authors.initials: R
authors.lastname: Edge
authors.forename: Emma C
authors.initials: EC
authors.lastname: Fitzgerald
authors.forename: Hannah N
authors.initials: HN
authors.lastname: Lancashire
authors.forename: Damien M
authors.initials: DM
authors.lastname: Murphy
authors.forename: Joseph J W
authors.initials: JJ
authors.lastname: McDouall
authors.forename: Joseph
authors.initials: J
authors.lastname: Sharples
authors.forename: Mark W
authors.initials: MW
authors.lastname: Whiteley