The formation of metal-carbon bonds is a fundamental principle in organometallic chemistry. Construction of organometallics with more than two metal-carbon σ bonds remains a great challege. Recently, we reported a novel organometallic complex, metallapentalyne, containing three metal-carbon σ bonds in the equatorial plane. X-ray study reveals that the carbyne angle is only 129.5°, which is the smallest carbyne angles observed thus far. Theoretical study shows that it is the first example of planar Möbius aromatic species. Metallapentalyne formally consists of a seven-atoms carbon chain and a transition metal (M+7C). Thereafter, with the extension of this carbon chain (ranging from seven atoms to twelve atoms), a series carbon-based polydentate organometallics (M+8C to M+12C) chelates containing four or five metal-carbon σ bonds were synthesized. For all of these complexes, the binding atoms, even the backbones, are carbon atoms. These carbon-based polydentate chelates are named as “carbolong complexes”. A number of exceptional organometallic complexes delineated in this work. For example, M+8C represents the first example of σ-aromaticity in an unsaturated three-membered ring; M+10C is the first metal-bridged tricyclic aromatic system, in which the metal center is shared by three aromatic five-membered rings; M+12C represents the upper limit of coordination number of a metal atom bonding with carbon ligands in a planar geometry. In general, organometallic complexes are highly sensitive towards air, water, and heat. However, these new metallacycles exhibit remarkable stability, which can even be stable at 100 °C in air. Unique properties, such as aggregation induced emission enhancement, large Stokes shifts and long lifetime (Nat. Chem. 2013, 5, 698), broad absorption from the ultraviolet-visible to the near-infrared region (Angew. Chem. Int. Ed. 2015, 54, 6181), and excellent photoacoustic and photothermal properties (Sci. Adv. 2016, 2, e1601031) have been demonstrated. Application of these carbonloong complexes on biomedicine and solar energy utilization is in progress in our laboratory.

Carbolong complexes: Novel organometallic species with three to five metal-carbon bonds

254th National Meeting (2017)

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