This study is led by Dr. Haiping Xia (Southern University of Science and Technology). The team described the synthesis and characterization of two kinds of complexes with five coplanar M–C σ bonds, whose nature was supported by both experimental and computational data. The successful construction of those structures is attributed to the use of a carbon chain as a rigid and polydentate ligand (see right image below) and the conjugation effect between sp 2 carbons and the metal center, which maintains the M–C σ bonds in a single plane and prevents elimination of the two neighboring carbons that bind to the metal. Those complexes were found to be exceptionally stable at temperatures even up to 100 ℃ in moisture or air. Those novel structures expanded the coplanar M–C σ bonds to five.
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See the article:
Experimental and theoretical evidences for the formation of transition metal complexes with five coplanar metal-carbon σ bonds
https://doi.org/10.1093/nsr/nwad325
National Science Review