A Metal‐Bridged Tricyclic Aromatic System: Synthesis of Osmium Polycyclic Aromatic Complexes

Abstract

Aromaticity is one of the most important concepts in organic chemistry. A variety of metalla-aromatic compounds have been recently prepared and in most of those examples, the metal participates only in a monocyclic ring. In contrast, metal-bridged bicyclic aromatic molecules, in which a metal is shared between two aromatic rings, have been less developed. Herein, we report the first metal-bridged tricyclic aromatic system, in which the metal center is shared by three aromatic five-membered rings. These metalla-aromatics are formed by reaction between osmapentalyne and arene nucleophiles. Experimental results and theoretical calculations reveal that the three five-membered rings around the osmium center are aromatic. In addition, the broad absorption bands in the UV/Vis absorption spectra of these novel aromatic systems cover almost the entire visible region. This straightforward synthetic strategy may be extended to the synthesis of other metal-bridged polycyclic aromatics.

Stabilizing Two Classical Antiaromatic Frameworks: Demonstration of Photoacoustic Imaging and the Photothermal Effect in Metalla‐aromatics

“…[5] Pentalene, the archetypal antiaromatic compound with eight p electrons, is highly unstable and was first observed in 1997 in argon matrices. [7][8][9][10] As eries of metallapentalenes [8,9] and metallacyclobutadienes [10] have been realized through this strategy.H owever,t he simultaneous stabilization of two antiaromatic systems by one metal fragment has not been reported to date.H erein, we report the stabilization of two typically antiaromatic frameworks,C BD and pentalene,b y introducing am etal fragment (III in Scheme 1) through unprecedented [2+ +2] cycloaddition reactions of alkynes with alate-transition-metal carbyne complex. [7][8][9][10] As eries of metallapentalenes [8,9] and metallacyclobutadienes [10] have been realized through this strategy.H owever,t he simultaneous stabilization of two antiaromatic systems by one metal fragment has not been reported to date.H erein, we report the stabilization of two typically antiaromatic frameworks,C BD and pentalene,b y introducing am etal fragment (III in Scheme 1) through unprecedented [2+ +2] cycloaddition reactions of alkynes with alate-transition-metal carbyne complex.…”

“…[14] Indeed, the Wiberg bond index of Os1 À C8 is calculated to be 0.03, indicating an egligible interaction. [7,8] Theo ther three proton signals on the metallacycle are detected in the aromatic regions (H3:8 .54, H5:8.78, and H8:8.20 ppm). Therefore,w eh ave successfully stabilized two classical antiaromatic systems by using one metal fragment at ambient temperature.T his result demonstrates the ability of ametal fragment to stabilize antiaromatic and/or strained systems.…”

“…[12] Them ost interesting structural feature is that the metal was shared by the CBD and pentalene rings simultaneously.N ote that the geometry can be viewed as ap entagonal bipyramid in which the seven coordination sites are occupied by four carbon atoms (C1, C4, C7, and C9), one chlorine atom, and two phosphorus atoms, leading to ac oordinatively saturated metal center with 18 electrons.M ore interestingly,t he nine conjugated carbon atoms in the equatorial plane constitute ac hain of carbon atoms (C1-C9) as at etradentate ligand coordinating to transition-metal center.T he X-ray structure indicates that complex 2 has an essentially planar metallatricyclicm oiety. [8] TheC À Cb ond lengths in these two five-membered rings (1.376-1.410 ) were between those of single and double CÀCb onds and comparable to those of benzene (1.396 ). [8] TheC À Cb ond lengths in these two five-membered rings (1.376-1.410 ) were between those of single and double CÀCb onds and comparable to those of benzene (1.396 ).…”

Metallapentalenofurans and Lactone‐Fused Metallapentalynes

“…DFT calculations show that the metallapentalenofurans possess planar Craig‐type Möbius aromaticity derived from the 11‐center‐12‐electron d π –p π π‐conjugation. In addition, the examples of metal shared by three aromatic rings are rare ,…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…1548) [1320]. A mechanism that involves nucleophilic addition to the carbyne ligand followed by C-H oxidative addition was proposed.…”