Oxidative dimerization of aryldiynyl-ruthenium complexes

Abstract

Chemical oxidation of Ru(C≡CC≡CR)(dppe)Cp with [FeCp 2]PF 6 affords the binuclear cations [{Ru(dppe)Cp} 2C 8R 2] 2+(PF 6-) 2 (R = Ph, 7 2+(PF 6-) 2; R = Fc, 8 2+(PF 6-) 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 7 2+(PF 6-) 2, 1:1 for 8 2+(PF 6-) 2), shown by single-crystal X-ray diffraction structure determinations of 7 2+-asym(PF 6-) 2 and 8 2+-sym(AsF 6-) 2. 8 2+-sym consists of a central C 4 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 7 2+-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 C β and C δ, suggesting that radical coupling (C δ + C δ) or (C β + C δ) affords the sym and asym isomers, respectively. © 2012 American Chemical Society.