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[η3-R1C=C=C=C(R1)–C(R3)=CR2], R1= SiMe3, tBu, R2,R3=Ph, SiMe3, tBu, -C C-SiMe3, -C C-tBu] were obtained and studied using normal coordinate analysis. For metallacycles of this type, three lines are pronounced: ~1870 and ~1650 cm–1 bands corresponding to symmetric (ν1) and antisymmetric (ν2) vibrations of cumulene fragment, as well as at ~1400 cm–1 the νС=С 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[η3-Me3SiC4(SiMe3)–C(Ph)=CPh] complex (2Zr(e)), irreversible isomerization under the action of a He-Ne laser into the cyclopentadiene structure Cp2Zr[η2-(Me3SiC C)C=C(SiMe3)–C(Ph)=CPh] with a pendant alkyne substituent. Based on the IR spectra data for the Cp2Zr[η3-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.