Oxidative Dimerisation of Aryldiynyl-ruthenium Complexes
Résumé
Chemical oxidation of Ru(C≡CC≡CR)(dppe)Cp with [FeCp2]PF6 affords the binuclear cations [{Ru(dppe)Cp}2C8R2]2+(PF6-)2 (R = Ph, 72+(PF6-)2; R = Fc, 82+(PF6-)2) by radical coupling at electron-rich sites involving the inner and outer C≡C triple bonds, to give cyclobutenediylidene derivatives. In each case, mixtures of symmetrical and asymmetrical isomers were obtained (2:1 for 72+(PF6-)2, 1:1 for 82+(PF6-)2), shown by single-crystal X-ray diffraction structure determinations of 72+-asym(PF6-)2 and 82+-sym(AsF6-)2. 82+-sym consists of a central C4 ring with two ═C═C═Ru(dppe)Cp groups in the 1,2-positions and two Fc substituents in the 3,4-positions, whereas for 72+-asym the substituent ═Ru(dppe)Cp is in the 1-position, ═C═C═Ru(dppe)Cp is in the 2-position, Ph is in the 3-position, and −C≡CPh is in the 4-position. DFT calculations reveal that the precursor cationic diynyl complexes show important electron density on Cβ and Cδ, suggesting that radical coupling (Cδ + Cδ) or (Cβ + Cδ) affords the sym and asym isomers, respectively.