Synthesis and some properties of binuclear ruthenocenes bridged by oligoynes: Formation of bis(cyclopentadienylidene)cumulene diruthenium complexes in the two-electron oxidation

摘要

The monoynes [Rc*C CRc*] and [Rc'C CRc'] were obtained in improved yields using [MO(CO)(6)]/2FC(6)H(5)OH as a catalyst in the alkyne metathesis of [Rc*C CMe] and [Rc'C CMe], respectively (Rc=ruthenocenyl, Rc* = 1 '',2 '',3 '',4 '',5 ''-pentamethylruthenocenyl, and Rc'=2',3',4',5'-tetramethylruthenocenyl groups). The diynes [Rc*(C C)(2)Rc*] and [Rc'(C C)(2)Rc'] were synthesized by the oxidative coupling of the corresponding terminal ethynes in good yields. The triyne [Rc*(C C)(3)Rc*] and the tetrayne [Rc*(C C)(4)Rc*] were prepared by the hetero- and homocoupling of [Rc*C CC=CH], which was obtained from the reaction of [Rc*C CCHO] with Li-[N2CSiMe3], respectively. Although the oxidation waves did not always exhibit a clear two-electron oxidation process, the oxidation potentials shifted to a lower potential with an increase in the number of methyl substituents on the ruthenocenyl ring, and shifted to a higher potential with the increase in the number of (C C units; this result is in contrast to that found in the [Rc-(CH--CH)(n)Rc] series. The chemical oxidation of [Rc'C CRc'] yielded a stable two-electron-oxidized species, the structure of which was confirmed by Xray crystallography to be [Ru-2( mu(2)-eta(6):eta(6)-C5Me4C=CC5Me4)(eta-C5H5)(2)](BF4)(2.) Changing the substituents (Rc, Rc*, and Rc') had no effect on the chemical oxidation, but in the case of the Rc' series the Me substituent increased the stability of the two-electron-oxidized species in solution. The diyne [Rc*(C C)2Rc*] and the triyne [Rc*(C-L C),Rc*] also gave a similar but unstable two-electron-oxidized species. In acetone or acetonitrile, the two-electron-oxidized species of [Rc*C CRc*] and [Rc*(C C)(2)Rc*] gradually formed the corresponding bis(fulvene)-type complexes. This implies that the two-electron-oxidized species of [Rc*(C C)(n)Rc*] are destabilized with the increasing n.