The reactivity of a range of pyridone and pyrazinone derivatives towards alkynes in the presence of cyclopentadienylcobaltbis(ethene) has been investigated. Depending on the nature of the substrates,[2+2+2]- or [2+2] cycloaddition, C--H, or N--H activation may occur. In the case of pyridones, the first three predominated with N-protected derivatives, whereas substrates containing N--H bonds followed an N--H activation pathway. The [2+2+2] cycloaddition of an N-butynylisoquinolone was applied successfully to the total synthesis of anhydrolycorinone. Pyrazinone substrates showed similar patterns of reactivity.

Hexaferrocenylbenzene has been synthesized by six-fold Negishi type ferrocenylation of hexabromo- or hexaiodobenzene.

Reaction of FvW(2)(H)(2)(CO)(6) with 2/8S(8) in THF results in rapid and quantitative formation of FvW(2)(SH)(2)(CO)(6). The crystal structure of this complex is reported and shows that the two tungsten-hydrosulfide groups are on opposite faces of the fulvalene ligand in an anti configuration. Nevertheless, treatment of FvW(2)(SH)(2)(CO)(6)(1) with PhN[double bond]NPh produces FvW(2)(mu-S(2))(CO)(6)(2) and Ph(H)NN(H)Ph. The crystal structure of the bridging disulfide, which cocrystallizes with 1 in a 2:1 ratio, is also described. Exposure of 2 equiv of *CrCp*(CO)(3) to 1 effects similar H atom transfers yielding 2 HCrCp*(CO)(3) and 2. Attempts to obtain crystals of the latter from solutions derived from this reaction mixture furnished a third product, FvW(2)(mu-S)(CO)(6)(3), which was analyzed crystallographically. The enthalpy of sulfur atom insertion into FvW(2)(H)(2)(CO)(6), yielding 1, has been measured by solution calorimetry.

[reaction: see text] The first X-ray crystal structure of a mononuclear metallacyclopentadiene(alkyne) complex has been obtained. This type of metallacycle is believed to be the key intermediate in the cobalt-mediated [2 + 2 + 2]cycloaddition of alkynes. Thermal treatment leads to the generation of angular [4]phenylene, the X-ray structural details of which are described. Under photochemical conditions, the cobaltacycle isomerizes to a highly strained (cyclobutadieno)dibenzocyclooctatrienyne complex.