Xumin He

Stable Iso‐osmabenzenes from a Formal [3+3] Cycloaddition Reaction of Metal Vinylidene with Alkynols

The investigation on the synthesis and reactivity of metal vinylidene complexes has always been an active area, especially given their applications as well-known catalysts for metathesis and carbon–carbon and carbon–heteroatom coupling reactions. 2] Compared with other reactions of metal vinylidenes, the cyclization reactions are underdeveloped. Previous studies showed that the vinylidene M=Ca bond participated in cycloadditions (see a) as key steps in carbon– carbon coupling reactions, and some cycloaddition products have also been isolated. Interestingly, similar reactions of the metal vinylidene Ca=Cb bond (see b) have been realized as well. [5] However, cyclizations of the skeleton of metal vinylidene (M=Ca=Cb) as a unit (see c) remain scarce. In fact, the reported cyclization is a formal [3+2] cycloaddition reaction. To the best of our knowledge, the [3+3] cyclization reactions of metal vinylidene to construct six-membered rings have not been reported. Moreover, since the first isolation of metallabenzene was achieved by Roper and co-workers, considerable research interest has been attracted in this field. Nevertheless, the metallabenzene analogue isometallabenzene, which can be seen as a metal-containing 1,2,4-cyclohexatriene, has not been thoroughly explored. Until now, only the 16e isometallabenzene [Os{=C=C(Ph) CH(Ph) CH=C(CH2Ph)}Cl(PiPr3)2], prepared by double coupling reactions, was reported by Esteruelas and co-workers in 2004. Herein, we report an unprecedented formal [3+3] cycloaddition reaction between the hydride vinylidene complex [OsHCl2{=C=CH(PPh3)}(PPh3)2] (2) and alkynols under mild conditions to give stable 18e iso-osmabenzenes. The origin of the unexpected stability of these iso-osmabenzene complexes and their isomerization into h-cyclopentadienyl complexes through metalated cyclopentadiene intermediates is also described. Stirring of the osmium hydride alkenylcarbyne complex [OsHCl2( C C(PPh3)=CHPh)(PPh3)2]BF4 (1) in a mixture of H2O/CH3OH (3:2 v/v) at reflux produced the osmium hydride vinylidene complex 2, which was isolated as a lightyellow solid in 60% yield (Scheme 1). The other product, PhCHO, was detected by H NMR (d= 9.3 ppm; PhCHO) and GC analysis of the reaction mixture (see Figure S1 in the Supporting Information). Complex 2 was characterized by NMR spectroscopy and elemental analysis, and the structure was additionally confirmed by single-crystal X-ray diffraction (Figure S2).

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

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.

Osmabenzenes from Osmacycles Containing an η2‐Coordinated Olefin

Treatment of HC[triple bond]CC(CH3)(OH)CH=CH2 with [OsCl2(PPh3)3] in dichloromethane yielded the eta2-olefin-coordinated osmacycle [Os{CH=C(PPh3)C(=CH2)-eta2-CH=CH2}Cl2(PPh3)2] (9). Transformations of osmacycle 9 by treatment with benzonitrile under various conditions have been investigated. Reaction of 9 with excess benzonitrile at room temperature afforded the dicationic osmacycle [Os{CH=C(PPh3)C(=CH2)-eta2-CH=CH2}(PhCN)2(PPh3)2]Cl2 (11) by ligand substitution, which reacted further to the intramolecularly coordinated eta2-allene complex [Os{CH=C(PPh3)C(CH3)=(eta2-C=CH2)}(PhCN)2(PPh3)2]Cl2 (12). In contrast, heating a chloroform solution of 9 to the reflux temperature in the presence of excess benzonitrile generated osmabenzene [Os{CHC(PPh3)C(CH3)CHCH}(PhCN)2(PPh3)2]Cl2 (14). Complexes 11, 12 and 14 are in fact isomers. In the absence of excess benzonitrile, the isolated dicationic 12 and 14 readily dissociate the benzonitrile ligands in solution to produce the neutral complex [Os{CH=C(PPh3)C(CH3)=(eta2-C=CH2)}Cl2(PPh3)2] (13) and the monocationic osmabenzene [Os{CHC(PPh3)C(CH3)CHCH}Cl(PhCN)(PPh3)2]BPh4 (15), respectively. Mechanisms for the formation of osmabenzene 14 from 11 and 12 are proposed based on DFT calculations.

Synthesis and characterization of a novel dialdehyde and cyclic anhydride

The acid treatment of a ruthenabenzene yielded an unusual dialdehyde. Interestingly, this dialdehyde has notable anti-oxidative properties and resists even nitric acid. This stability is confirmed by chemical and electrochemical experiments. In addition, a stable cyclic anhydride is synthesized from the dialdehyde via an environmentally friendly electrochemical method.

1,2-Migration in the reactions of ruthenium vinyl carbene with propargyl alcohols

Reactions of the ruthenium vinyl carbene complex [Ru{CHC(PPh3)CH(2-Py)}Cl2PPh3]BF4 (1) with five propargyl alcohols HCCC(OH)R1R2, (R1 = R2 = Ph; R1 = Ph, R2 = CH3; R1 = H, R2 = Ph; R1 = H, R2 = CH3; R1 = CHCH2, R2 = CH3) have been investigated, which led to the formation of several ten-membered η2-olefin coordinated ruthenacycles [Ru{OCR2CHR1-η2-CHCHC(PPh3)CH(2-Py)}Cl2PPh3]BF4 (R1 = R2 = Ph, 2; R1 = Ph, R2 = CH3, 3; R1 = H, R2 = Ph, 4; R1 = H, R2 = CH3, 5; R1 = CHCH2, R2 = CH3, 6), respectively. In these reactions, insertion of alkynes and intramolecular 1,2-migration of propargyl alcohols were performed in tandem. The results show that the 1,2-migratory preference of the groups is in the order of H > Ph > CH3. Complexes 2, 3, 5, and 6 were characterized by X-ray diffraction analysis and NMR spectra.

Unusual η2-Allene Osmacycle with Apoptotic Properties

Screening of a library of structurally unusual osmacyclic complexes for their antiproliferate properties in HeLa cells led to the discovery of a highly cytotoxic η2‐allene osmacycle. In this remarkably stable complex, osmium constitutes part of a metallacycle through the formation of a σ‐bond to a carbon in combination with coordination to an allene moiety. The osmacycle strongly induces apoptosis in Burkitt‐like lymphoma cells at submicromolar concentrations. The reduction of the mitochondrial membrane potential, the induction of DNA fragmentation, and the activation of caspases‐9 and ‐3 reveal that programmed cell death occurs through the intrinsic mitochondrial pathway. From the lipophilic and cationic nature of the osmacycle, in addition to a low oxidation potential (E1/2=+0.27 V vs. Fc/Fc+, Fc=ferrocene) it is proposed that mitochondria are the cellular target where oxidative decomposition initiates apoptosis.

Amphipathic metal-containing macromolecules with photothermal properties

Metal-containing macromolecules with extraordinary properties have attracted a great deal of interest owing to their potential application in the development of functional materials. Here, we report the synthesis of novel amphipathic metal-containing macromolecules by the click reaction of methoxypolyethylene glycol azides with a unique metalla-aromatic complex containing a terminal alkynyl group. The resultant amphipathic macromolecules self-assembled into micellar nanoparticles with diameters of ca. 145 nm in water, which exhibited high stability, water-dispersibility, biocompatibility, and excellent photothermal behavior under 808 nm laser irradiation. Our study opens promising avenues for providing metal-containing macromolecules as photothermal materials.

Photothermal Möbius aromatic metallapentalenofuran and its NIR-responsive copolymer

Mobius aromatics are very interesting and rare complexes owing to their brand-new chemistry and interesting properties. In this work, metallapentalenofurans with thiophene groups were easily prepared from the reaction of metallapentalyne, terminal arylalkynes, and water in air. The metallapentalenofuran containing a terthiophene moiety showed a good photothermal effect and was the first photothermal Mobius aromatic complex induced by J-aggregates. This photothermal metallapentalenofuran was chemically modified to carry an olefinic group and then was co-polymerized with oligo-(ethylene glycol)methacrylate to afford a thermoresponsive copolymer, whose phase transition behavior can be triggered by near-infrared radiation at 808 nm. This near-infrared-responsive metal-containing copolymer represents a new stimuli-responsive macromolecule.

Synthesis and Characterization of Photothermal Osmium Carbolong Complexes

Metallacycles with chelating polydentate conjugated-carbon chain ligands are called carbolong complexes, which are expected to have interesting properties. In this work, the preparation of 12-carbon carbolong complexes in which all of the coordinated atoms in the equatorial plane are carbon atoms was studied. With the help of the well-established mechanism, a new approach to prepare coplanar carbolong complexes bearing different organic functional groups was developed by adding different terminal alkynes in sequence. In the presence of HBF4 , these coplanar carbolong complexes were converted to η3 -allyl osmapentalene derivatives, which can be produced directly from the reaction of cyclopropaosmapentalene 1 with terminal alkynes in the presence of AgBF4 under anhydrous conditions. This study offers a new route for the preparation of functional osmium carbolong complexes with excellent photothermal properties, which can be used to prepare photothermal materials.

Correction: Photothermal Möbius aromatic metallapentalenofuran and its NIR-responsive copolymer

Correction for ‘Photothermal Mobius aromatic metallapentalenofuran and its NIR-responsive copolymer’ by Zhengyu Lu et al., Polym. Chem., 2018, 9, 2092–2100.