A coordination strategy to realize a sextuply-bonded complex†
The synthesis of higher-order multiple bonds is a great challenge in chemistry. However, no stable compound with a sextuple bond has been reported, except for Mo2 in an inert matrix at low temperatures. Herein, we propose a strategy to construct a sextuple bond in a dinuclear transition metal complex based on complete active space second-order perturbation theory (CASPT2) and density functional theory calculations. When the dinuclear core M2 (M = W, Mo, and Re+) is capped by two neutral electron-donating ligands at both M–M ends, a sextuple bond can be realized. The proposed ligands stabilize the M2 core by the coordination, conserve the six bonding orbitals in the occupied space, and suppress the weight of the δ–δ* excited electronic configuration. Calculated large formation energies of these complexes indicate the large possibility of the synthesis. Electronic structures and sextuply bonding interactions were analyzed in detail.