Five‐Membered Cyclic Metal Carbyne: Synthesis of Osmapentalynes by the Reactions of Osmapentalene with Allene, Alkyne, and Alkene

Abstract

The synthesis of small cyclic metal carbynes is challenging due to the large angle strain associated with the highly distorted nonlinear triple bonds. Herein, we report a general route for the synthesis of five‐membered cyclic metal carbyne complexes, osmapentalynes, by the reactions of an osmapentalene derivative with allene, alkyne, and alkene. Experimental observations and theoretical calculations document the aromaticity in the fused five‐membered rings of osmapentalynes. The realization of transforming osmapentalene to osmapentalyne through this general route would not only allow further exploration of metallapentalyne chemistry but also show promising applications of this novel aromatic system with broad absorption band and high molar absorption coefficient.

Synthesis and Characterization of a Metallacyclic Framework with Three Fused Five‐membered Rings

“…Thenon-aromatic character of complex 3 is probably due to the weak d p -p p p-conjugation between the osmium center and the coordinated carbon chain, as reflected by the single-bond character of all the OsÀCb onds in the three fused 5MRs.Therefore,complex 3 is an interesting nonaromatic species that is different from the aromatic character observed in the other metallapentalene derivatives with at least one Os À Cm ultiple bond (I, II, III,and V). [7][8][9][10] Foro rganic compounds,r ed-shifted absorption is observed for larger conjugation. With these novel metalcontaining polycyclic complexes in hand, the UV/Vis absorption spectra of complexes 2 and 3 were also examined.…”

“…[5] However,the metallapentalenes,by replacing one of the carbons in pentalene framework with at ransition metal, are much more stable and are characterized by X-ray diffraction. [7][8][9][10][11] Specifically,t he first fused 5MRs with am etalcarbon triple bond (I in Scheme 1), namely metallapentalyne, was reported in 2013. [7][8][9][10][11] Specifically,t he first fused 5MRs with am etalcarbon triple bond (I in Scheme 1), namely metallapentalyne, was reported in 2013.…”

“…[6] Recently,wereported the formation of anovel polycyclic system that is comprised of fused metallacyclic rings and stabilized by at ransition metal positioned at ab ridgehead position. [7][8][9][10][11] Specifically,t he first fused 5MRs with am etalcarbon triple bond (I in Scheme 1), namely metallapentalyne, was reported in 2013. [7] Thereafter,aseries of metallapentalene fused with 3MR (II), [8] 4MR (III), [9] and 6MR (V) [10] have been synthesized.…”

“…[7][8][9][10][11] Specifically,t he first fused 5MRs with am etalcarbon triple bond (I in Scheme 1), namely metallapentalyne, was reported in 2013. [7] Thereafter,aseries of metallapentalene fused with 3MR (II), [8] 4MR (III), [9] and 6MR (V) [10] have been synthesized. All of these species show excellent stability and interesting properties.T hus,the isolation of species with three fused 5MRs (IV)s eems to be the next logical step.…”