The paramagnetic aryl-alkynyl complexes [Mo(CCAr)(dppe)(η-C7H7)]+ (dppe = Ph2PCH2CH2PPh2; Ar = C6H5, +; C6D5, +; C6H4-4-F, +; C6H4-4-Me, +) and [Mo(CCBut)(dppe)(η-C7H7)]+ +, 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, +, exhibits resolved hyperfine coupling to the remote para position of the aryl group [aiso(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 +, +, + and +, combined with spectral simulation informed by calculated values derived from DFT investigations, has facilitated estimation of the experimental aiso(1H) hyperfine couplings of + 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.