Short-Lived Orthobenzyne Complexes with Early Transition Metals of Group IV. First Direct Characterization and Electronic Cartography by Coupling FVT/UV-PES with Calculations

Short-lived (2)-benzyne metallocene complexes [Cp2M((2)-c-C6H4)] with group IV metals are important intermediates in organic chemistry, their olefin insertion products being building blocks for aromatic and heterocyclic compounds. For the first time, an electronic cartography of these short-lived species has been obtained through the determination of their ionization potentials. They have been directly characterized in the gas phase by UV photoelectron spectroscopy, by monitoring, in situ, the thermal -H abstraction of benzene from Cp2MPh2. The metal impacts the energetic position of the sigma(MC) orbitals more strongly than the (benzyne)(CC) orbital (HOMO). This study has been supported by DFT calculations and by NBO, AIM, ELF, CDA, and EDA analyses. The electronic structure of the transient Cp2Ti((2)-c-C6H4) complex is peculiar and slightly differs from that of the analogous zirconium and hafnium complexes. The electronic structure is a combination of a metallacyclic and a complex, whereas with Hf and Zr, the metallacyclic structure appears to be more representative.