Dicarbon(0) C2, the smallest diatomic molecule with a carbon–carbon bond. In contrast to the natural occurrence of F2, O2 and N2 as diatomic species, C2 is too reactive for experimental studies in the condensed phase, which has been only detected at extremely high temperature (> 3500 °C) in the blue flame and in interstellar atmosphere. There have been numerous synthetic attempts to stabilize C2 experimentally with many kinds of chemical ligand strategy. So far, efforts meet deadlock, as bonding situation of the central C2 differ significantly from those of free C2. Thus, the nature of the bond and electronic states in C2 has limited to only theoretical simulations with controversial outcomes and disagreements within the Chemical Science community.

Our recent scientific breakthrough led by Prof. Dr. Tiow-Gan Ong (Research Fellow), Dr. Tsz-Fai Leung (Postdoctoral Research Fellow) and Mr. Ming-Chun Wu (Ph.D. graduate student) at Institute of Chemistry, Academia Sinica successfully presents the first straightforward way to isolated stable C2 molecule at ambient temperature as a R3P→C2 using our special custom-made bulky phosphine ligand bearing super electron-rich imidazolidin-2-iminato groups. This work is manifestation of the most state-of-the-art chemical synthesis ingenuity approach to stabilize C2. This important scientific discovery also provides chemical and electronic insights into long-standing difference of scientific interpretations over nature of C2.

A detail experimental study of R3P→C2 using on single crystal X-ray diffraction analysis has indicated Cα-Cβ bond distance with 1.237(4) Å, which is only marginally shorter than in free C2 (1.2425 Å) and intermediate between typical Csp1-Csp1 triple bonds and unconjugated Csp2-Csp2 double bonds. Through the international collaborative research with outstanding theoretical chemists Prof. Gernot Frenking at Marburg University-Germany and Prof. Lili Zhao at Nanjing Tech University, we deployed the most advanced computational techniques called Energy Decomposition Analysis (EDA) to analyze the electronic states of this unique C2 molecule, which contains P–Cα bond with fragments of C2- and the phosphine+. In addition, our lab also unfolded unprecedented chemical reactivity that the R3P→C2 has two reactive carbene character for intermolecular C–H bond activation. This finding would generate a new paradigm of chemical reactivity in carbon and silicon group.

We anticipate that this isolation of the stable complex of C2 will offer possibilities for further applications in main-group and transition-metal in catalysis as well as new bottom-up synthesis technology and mechanism process for preparing new carbon-type super hybrid materials.

The full article entitled “Isolable dicarbon stabilized by a single phosphine ligand” can be now found at the Nature Chemistry website at https://www.nature.com/articles/s41557-020-00579-w

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