Bonding and Substituent Effects in Electron-Rich Mononuclear Ruthenium σ-Arylacetylides of the Formula [(η2-dppe)(η5-C5Me5)Ru(C⋮C)-1,4-(C6H4)X][PF6]n(n= 0, 1; X = NO2, CN, F, H, OMe, NH2)

This study reports the isolation and the structural (X-ray), UV−vis, and NMR characterization of a series of electron-rich Ru(II) acetylide complexes of the formula (η 2 -dppe)(η 5 -C 5 Me 5 )Ru(C⋮C)-1,4-(C 6 H 4 )X ( 1a − f; X = NO 2, CN, F, H, OMe, NH 2 ) and (η 2 -dppe)(η 5 -C 5 Me 5 )Ru(C⋮C)-1,3-(C 6 H 4 )F ( 1c- m ), as well as the spectroscopic (near-IR and ESR) in situ characterization of the corresponding elusive Ru(III) radical cations. The spectroscopic data are discussed in connection with DFT computations, and a consistent picture of the electronic structure of these Ru(II) and Ru(III) acetylide complexes is proposed. Notably, the strong reactivity of the Ru(III) radicals evidenced in this contribution constitutes a major difference with the relative stability of the known iron analogues.