Tingbin Wen

Stabilization of anti-aromatic and strained five-membered rings with a transition metal

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.

Electrophilic substitution reactions of metallabenzynes.

The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)═C(CH(3))C(R)═CH)Cl(2)(PPh(3))(2) (R = SiMe(3), H) were studied. These metallabenzynes react with electrophilic reagents, including Br(2), NO(2)BF(4), NOBF(4), HCl/H(2)O(2), and AlCl(3)/H(2)O(2) to afford the corresponding bromination, nitration, nitrosation, and chlorination products. The reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes exhibit aromatic properties.

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

Antiaromatic species are substantially less thermodynamically stable than aromatic moieties. Herein, we report the stabilization of two classical antiaromatic frameworks, cyclobutadiene and pentalene, by introducing one metal fragment through the first [2+2] cycloaddition reaction of a late-transition-metal carbyne with alkynes. Experimental observations and theoretical calculations reveal that the metal fragment decreases the antiaromaticity in cyclobutadiene and pentalene simultaneously, leading to air- and moisture-stable products. These molecules show broad absorption from the UV to the near-IR region, resulting in photoacoustic and photothermal effects for metalla-aromatic compounds for the first time. These results will encourage further efforts into the exploration of organometallic compounds for photoacoustic-imaging-guided photothermal therapy.

Reactions of hydrogen with ruthenium and osmium complexes containing tridentate ligands Cy2PCH2CH(CH2)2PCy2 and 2,6-(Ph2PCH2)2C6H3

Abstract Reaction of cis -1,4-dichlorobut-2-ene with dicyclohexylphosphine in the presence of KI in acetone produces [ cis -Cy 2 PHCH 2 CHCHCH 2 PHCy 2 ]I 2 , which is converted to cis -Cy 2 PCH 2 CHCHCH 2 PCy 2 on treatment with NaOH. Reactions of cis -Cy 2 PCH 2 CHCHCH 2 PCy 2 with MHCl(CO)(PPh 3 ) 3 (M=Ru, Os) yield MHCl(CO)(PPh 3 )(Cy 2 PCH 2 CHCHCH 2 PCy 2 ). The ruthenium complex RuCl(CO)(PPh 3 )(Cy 2 PCH 2 CH(CH 2 ) 2 PCy 2 ) is obtained by refluxing RuHCl(CO)(PPh 3 )(Cy 2 PCH 2 CHCHCH 2 PCy 2 ) in methanol–CH 2 Cl 2 . Reaction of RuCl(CO)(PPh 3 )(Cy 2 PCH 2 CH(CH 2 ) 2 PCy 2 ) with H 2 in the presence of NaBPh 4 produces RuHCl(CO)(PPh 3 )(Cy 2 P(CH 2 ) 4 PCy 2 ). Reaction of OsCl(PPh 3 )(2,6-(Ph 2 PCH 2 ) 2 C 6 H 3 ) with H 2 produces OsCl(H⋯H)(PPh 3 )(2,6-(Ph 2 PCH 2 ) 2 C 6 H 3 ) which contains an elongated dihydrogen ligand.