Bonding and Electron Delocalization in Ruthenium(III) σ-Arylacetylide Radicals [trans-Cl(η2-dppe)2RuCC(4-C6H4X)]+ (X = NO2, C(O)H, C(O)Me, F, H, OMe, NMe2): Misleading Aspects of the ESR Anisotropy

The bonding within the series of [trans-Cl(eta(2)-dppe)(2)RuC C(4-C6H4X)](n+) complexes (1-Xn+; n = 1, 0 and X = NO2, C(O)H, C(O)Me, F, H, OMe, NMe2) has been examined by IR, ESR, and UV-vis-near-IR spectroscopy together with computational modelin. A strong substituent effect is evidenced for radical delocalization from the metal to the functional arylacetylide fragment. This effect is also apparent in the large anisotropy change of their ESR signatures. DFT calculations substantiate these experimental observations and permit discussion of the influence of the X substituent on spin delocalization in compounds containing. isolobal metal fragments. Evidence is given that the ESR anisotropy alone cannot reliably be used to compare the metallic character of the unpaired electrons in closely related families of pseudooctahedral cationic Ru(III) functional arylacetylides with rhombic symmetry when the complexes possess different coordination spheres. ESR anisotropy constitutes nevertheless a useful benchmark for this purpose within the presently investigated 1-X+ family.