Evidence of an unexpectedly long C-C bond (>2.7 A) in 1,3-metalladiyne complexes [Cp2MCCR]2 (M = Ti, Zr): QTAIM and ELF analyses.

Topological analyses of the electron density using the quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF) have been carried out, at the B3LYP/DGVZVP and MP2/DGVZVP theoretical levels, on different 1,3-metalladiyne cyclic compounds [Cp2M(CCR)]2, (M = Ti, Zr; R = F, CH3, H, SiH3). The QTAIM results indicate the presence of an extraordinarily long C-C bond (in a 2.7-3.0 A range) connecting the CCR moieties, contrary to the common geometrical assumption of a M-M bond in similar metallacycles. The existence of this C-C bond is also supported by the distinct consequences on the reaction profiles for the Ti and Zr complexes, the CC oxidative coupling reactions being favored only for the Ti complexes. Moreover, the consequences of this bonding in the coupling/cleavage reactions of these metallacyclic complexes are reported and analyzed, revealing the transcendence of these long-range bonds in the overall behavior of these compounds.