Reversible haptotropic shift in zirconocene-hexapentaene complexes.

Low-valent zirconocene species reacted with 1,1,6,6-tetraalkyl-1,2,3,4,5-hexapentaenes to form both 1-zirconacyclopent-3-ynes and eta2-pi-coordinated complexes according to the alkyl groups (R) and the existence of the neutral ligand (L). Haptotropic interconvertion between these two complexes was observed. It was proposed that double insertion of isocyanide into the Zr-C bond of 1-zirconacyclopent-3-ynes takes place via the isocyanide adduct of the eta2-pi-complex as an intermediate.

An experimental electron density study on "1-zirconacyclopent-3-yne".

An electron density analysis of the 1-zirconacyclopent-3-yne complex has been carried out based on X-ray diffraction data, showing that the coordination mode of the but-2-yne-1,4-diyl ligand to the metal is a resonance hybrid between eta2-sigma, sigma-coordination, as the major contributor, and eta4-pi, pi-coordination.

Synthesis and structure of 1-zirconacyclopent-3-yne complexes without substituents adjacent to the triple bond.

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.

Syntheses, Structures, FAB Mass Spectra, and Magnetic Properties of Chromium Chalcogenide Cluster Complexes [Cr(6)Se(8)(PEt(3))(6)], [Cr(6)Se(8)(H)(PEt(3))(6)], and [Cr(6)S(8)(H)(PEt(3))(6)].

Chromium selenide cluster complexes [Cr(6)Se(8)(PEt(3))(6)] (1) and [Cr(6)Se(8)(H)(PEt(3))(6)] (2) were prepared by the reaction of anhydrous chromium dichloride, Na(2)Se(x)(), and triethylphosphine in methanol. A similar procedure except for the use of NaS(x)()H in place of Na(2)Se(x)() gave a sulfide cluster complex [Cr(6)S(8)(H)(PEt(3))(6)] (3). The partly deuterated derivative [Cr(6)S(8)(D)(0.