Isolation and Structural Characterization of 1-Zirconacyclopent-3-yne, Five-Membered Cyclic Alkynes

Abstract
Stable five-membered cyclic alkynes were synthesized, isolated, and fully characterized. Divalent zirconium species, bis(cyclopentadienyl)zirconium(II) equivalent, reacted with ( Z )-1,4-disubstituted 1,2,3-butatrienes [( Z )-R-CH=C=C=CH-R, 1a : R = (CH 3 ) 3 Si-, 1b : R = tert -C 4 H 9 -] to give 1-zirconacyclopent-3-yne compounds ( 2a-b ) in good yields. X-ray diffraction analysis revealed their five-membered cyclic structure with a sufficiently short triple bond to regard this compound as a metallacyclopentyne.