title: Stabilization of anti-aromatic and strained five-membered rings with a transition metal.
abstract: Anti-aromatic compounds, as well as small cyclic alkynes or carbynes, are particularly challenging synthetic goals. The combination of their destabilizing features hinders attempts to prepare molecules such as pentalyne, an 8π-electron anti-aromatic bicycle with extremely high ring strain. Here we describe the facile synthesis of osmapentalyne derivatives that are thermally viable, despite containing the smallest angles observed so far at a carbyne carbon. The compounds are characterized using X-ray crystallography, and their computed energies and magnetic properties reveal aromatic character. Hence, the incorporation of the osmium centre not only reduces the ring strain of the parent pentalyne, but also converts its Hückel anti-aromaticity into Craig-type Möbius aromaticity in the metallapentalynes. The concept of aromaticity is thus extended to five-membered rings containing a metal-carbon triple bond. Moreover, these metal-aromatic compounds exhibit unusual optical effects such as near-infrared photoluminescence with particularly large Stokes shifts, long lifetimes and aggregation enhancement.
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Congqing
authors.initials: C
authors.lastname: Zhu
authors.forename: Shunhua
authors.initials: S
authors.lastname: Li
authors.forename: Ming
authors.initials: M
authors.lastname: Luo
authors.forename: Xiaoxi
authors.initials: X
authors.lastname: Zhou
authors.forename: Yufen
authors.initials: Y
authors.lastname: Niu
authors.forename: Minglian
authors.initials: M
authors.lastname: Lin
authors.forename: Jun
authors.initials: J
authors.lastname: Zhu
authors.forename: Zexing
authors.initials: Z
authors.lastname: Cao
authors.forename: Xin
authors.initials: X
authors.lastname: Lu
authors.forename: Tingbin
authors.initials: T
authors.lastname: Wen
authors.forename: Zhaoxiong
authors.initials: Z
authors.lastname: Xie
authors.forename: Paul V R
authors.initials: PV
authors.lastname: Schleyer
authors.forename: Haiping
authors.initials: H
authors.lastname: Xia
mesh_terms: D018360:Crystallography, X-Ray; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D008670:Metals; D028561:Transition Elements