Five-membered metallacyclic alkynes that have no substituents adjacent to the triple bond have been synthesized, isolated, and structurally characterized. Zirconocene dichlorides, Cp'2ZrCl2 (Cp' = C5H5, C5H4-t-Bu), reacted with 1,4-dichlorobut-2-yne in the presence of magnesium to give 1-zirconacyclopent-3-yne compounds (5 (a) Cp' = C5H5, (b) Cp' = C5H4-t-Bu) that have a -CH2CCCH2- moiety in good yields. They are stable enough to be isolated in a pure form, despite the absence of substituents. 5a reacted with an equimolar amount of Cp2Zr(but-1-ene)(PMe3) to produce a bimetallic complex in which the zirconacyclopentyne coordinates to the other zirconocene moiety as an alkyne.

Organo-silicon compoundsOrgano-silicon compounds S 0060 Rhodium Complexes of 1,4-Disubstituted-1,2,3-butatrienes: Their Preparation and Reactivity. -The intermediately formed Rh-complexes with (I) could be isolated. In one case the structure of such a complex is determined by X-ray analysis. -(SUZUKI*, N.; FUKUDA, Y.; KIM, C. E.; TAKAHARA, H.; IWASAKI, M.; SABURI, M.; NISHIURA, M.; WAKATSUKI, Y.; Chem. Lett. 32 (2003) 1, 16-17; RIKEN Inst.,

The 1,4-disubstituted butatrienes, (Z)-R-CH=C=C=CH-R (1, R = SiMe3, t-Bu), reacted with RhCl(PAr3)3 (Ar = Ph, p-tolyl) to give rhodium-(Z)-butatriene complexes 3. The butatrienes coordinated to Rh with the central double bond in an η2-fashion. (Z)-Butatrienes on 3 isomerized to (E)-form at 70 °C to afford (E)-butatriene complexes 4 with excellent E/Z ratios (E/Z = 97/3–99/1). The molecular structure of 4b (R = SiMe3, Ar = p-tolyl) was determined by X-ray diffraction analysis. Hydrosilation of 1 was catalyzed by rhodium complexes to give allenes as major products accompanied by 1,3-dienes as minor ones, which are results of 2,1-addition and 2,3-anti-addition of the silane.