Electronic structure of 7-membered zirconacyclocumulenes by Vibrational spectra and QTAIM

The vibrational spectra (IR and Raman) for seven-membered zirconacyclocumulenes of the type Cp2Zr[eta(3)-(RC)-C-1=C=C=C(R-1)-C(R-3)=CR2], R-1 = SiMe3, Bu-t, R-2 ,R-3 =Ph, SiMe3, Bu-t, -C C-SiMe3 -C C-Bu-t] were ob tained and studied using normal coordinate analysis. For metallacycles of this type, three lines are pronounced: 1870 and 1650 cm(-1) bands corresponding to symmetric (nu(1)) and antisymmetric (nu(2)) vibrations of cumulene fragment, as well as at similar to 1400 cm(-1) the nu C=C vibration, respectively. These data are consistent with the geometric parameters of the cycles and the results of QTAIM analysis, within which the molecular graph demonstrated three Zr-C bond paths. For a crystalline sample of the Cp2Zr[eta(3)-Me3SiC4(SiMe3)-C(Ph)=CPh] complex (2Zr(e)), irreversible isomerization under the action of a He-Ne laser into the cyclopentadiene structure Cp2Zr[eta(2)-(Me3SiC C)C=C(SiMe3)-C(Ph)=CPh] with a pendant alkyne substituent. Based on the IR spectra data for the Cp2Zr[eta(3)-Me3SiC4(SiMe3)-C(SiMe3)=C--C C-SiMe3] (2Zr(d)) complex, the preservation of the cyclocumulene structure in the dynamic process of its isomerization was proved. (C) 2021 Elsevier B.V. All rights reserved.