Modulation of electronic couplings within Ru2-polyyne frameworks.

Dimers of [Ru2(Xap)4] bridged by 1,3,5-hexatriyn-diyl (Xap are 2-anilinopyridinate and its aniline substituted derivatives), [Ru2(Xap)4]2(μ-C6) (1), were prepared. Compounds 1 reacted with 1 equiv of tetracyanoethene (TCNE) to yield the cyclo-addition/insertion products [Ru2(Xap)4]2{μ-C≡CC(C(CN)2)–C(C(CN)2)C≡C} (2) and 1 equiv of Co2(dppm)(CO)6 to yield the η2-Co2 adducts to the middle C≡C bond, [Ru2(Xap)4]2(μ-C6)(Co2(dppm)(CO)4) (3). Voltammetric and spectroelectrochemical studies revealed that (i) two Ru2 termini in 1 are sufficiently coupled with the monoanion (1–) as a Robin–Day class II/III mixed valence species; (ii) the coupling between two Ru2 is still significant but somewhat weakened in 3; and (iii) the coupling between two Ru2 is completely removed by the insertion of TCNE in 2. The attenuation of electronic couplings in 2 and 3 was further explored with both the X-ray diffraction study of representative compounds and spin-unrestricted DFT calculations.