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
Media Contact:
Dr. Tiow-Gan Ong, Research Fellow/Professor, Institute of Chemistry, Academia Sinica
Email: tgong@gate.sinica.edu.tw
(Tel) +886-2-5572-8648