Zhixin Chen

Metallapentalenofurans and Lactone-Fused Metallapentalynes

Metalla-aromatics are attractive species because they exhibit the properties of both organometallics and aromatics. Reported metal-bridged polycyclic aromatic complexes, as well as Möbius aromatic species, are still rare. Herein, we present the construction of two new metal-bridged polycyclic aromatic frameworks, α-metallapentalenofurans and lactone-fused metallapentalynes, by the reactions of osmapentalyne with terminal aryl alkynes in the presence of H2 O or HBF4 /H2 O, respectively. DFT calculations show that the α-metallapentalenofurans possess rare planar Craig-type Möbius aromaticity derived from the 11-center-12-electron dπ -pπ π-conjugation. This study offers a new route for the construction of polycyclic metalla-aromatics as well as planar Möbius aromatic species.

Reactions of osmapyridinium with terminal alkynes

We have synthesized a new type of ten-membered osmacycles by reaction of osmapyridinium with HCCCH(OH)R (R = Ph, Et). We propose that these reactions take place initially by coordination of the alkynes, [2 + 2] cycloaddition, subsequent 1,2-hydrogen migration and a final reductive elimination. The reactions with phenylacetylenes do not afford the corresponding derivatives but rather give η4-coordinated cyclopentadiene complexes, which are proposed to derive from a [4 + 2] cycloaddition process. Related reactions of the η4-coordinated cyclopentadiene complexes are also discussed.

A highly sensitive and selective antioxidant probe based on a bi-modally functionalized conjugated polyelectrolyte

A new water-soluble anionic conjugated polyelectrolyte with a nitroxide radical covalently linked to the sulfonated poly(phenylene ethynylene) backbone (PPE-SO(3)) is reported. This radical-functionalized PPE-SO(3) (RF-PPE-SO(3)) demonstrates fluorescence and electron spin resonance (ESR) bimodal signaling function and shows sensitive and selective response to antioxidants.

Multiyne chains chelating osmium via three metal-carbon σ bonds

Although the formation of metal–carbon σ bonds is a fundamental principle in organometallic chemistry, the direct bonding of one organic molecule with one metal center to generate more than two metal–carbon σ bonds remains a challenge. Herein, we report an aromaticity-driven method whereby multiyne chains are used to construct three metal–carbon σ bonds in a one-pot reaction under mild conditions. In this method, multiyne chains act as ligand precursors capable of chelating an osmium center to yield planar metallapolycycles, which exhibit aromaticity and good stability. The direct assembly of various multiyne chains with commercially available metal complexes or even simple metal salts provides a convenient and efficient strategy for constructing all carbon-ligated chelates on the gram scale.Metal-carbon σ bonds mark the basis of organometallic chemistry, but the formation of multiple such bonds between single organic and metal entities remains a challenge. Here, the authors report a one-pot aromaticity-driven method to construct osmium-based multidentate complexes containing three metal-carbon σ bonds from multiyn chains.

Switching of Charge Transport Pathways via Delocalization Changes in Single-Molecule Metallacycles Junctions

To explore the charge transport through metalla-aromatics building blocks, three metallacycles complexes were synthesized, and their single-molecule conductances were characterized by using mechanically controllable break junction technique. It is found that the conductance of the metallacycles junction with phosphonium group is more than 1 order of magnitude higher than that without phosphonium group. X-ray diffraction and UV-vis absorption spectroscopy suggested that the attached phosphonium group makes metallacycles more delocalized, which shortened the preferred charge transport pathway and significantly enhanced the single-molecule conductance. This work revealed that the delocalization of metalla-aromatics could be used to switch the charge transport pathway of single-molecule junctions and thus tune the charge transport abilities significantly.

Constraint of a ruthenium-carbon triple bond to a five-membered ring

The first incorporation of a second-row transition metal carbyne unit into a ring is realized by virtue of aromaticity. The incorporation of a metal-carbon triple bond into a ring system is challenging because of the linear nature of triple bonds. To date, the synthesis of these complexes has been limited to those containing third-row transition metal centers, namely, osmium and rhenium. We report the synthesis and full characterization of the first cyclic metal carbyne complex with a second-row transition metal center, ruthenapentalyne. It shows a bond angle of 130.2(3)° around the sp-hybridized carbyne carbon, which represents the recorded smallest angle of second-row transition metal carbyne complexes, as it deviates nearly 50° from the original angle (180°). Density functional theory calculations suggest that the inherent aromatic nature of these metallacycles with bent Ru≡C–C moieties enhances their stability. Reactivity studies showed striking observations, such as ambiphilic reactivity, a metal-carbon triple bond shift, and a [2 + 2] cycloaddition reaction with alkyne and cascade cyclization reactions with ambident nucleophiles.

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.

Constructing canopy-shaped molecular architectures to create local Pt surface sites with high tolerance to H2S and CO for hydrogen electrooxidation

Rational design and construction of the local environment of active sites on noble metal surfaces is a promising, but challenging, approach for developing high-selectivity catalysts. This study presents an effective approach, via engineering local active sites, aiming to solve the critical problem of H2S and CO poisoning of Pt catalysts for H2 electrooxidation, the anode reaction of polymer electrolyte membrane fuel cells. A canopy-shaped molecular architecture was constructed by immobilizing an organic molecule, 2,6-diacetylpyridine (DAcPy), on Pt surface, which exhibits high H2S (1 ppm) and CO (100 ppm) tolerance. Through electrochemical, spectroscopic, and DFT studies, as well as comparative investigation of analogous structure molecules, it was revealed that DAcPy can be strongly adsorbed on Pt surface through tridentate coordination (two Pt–C and one Pt–N bonds), allowing it to compete with CO and H2S adsorption. The pyridine ring of DAcPy is in a tilted orientation, providing some protection underneath the ring for Pt atoms. Such a height-limited space is just accessible for small-sized H2, but not for relatively large H2S and CO. This study demonstrates that regulating steric hindrance to protect active sites is a promising approach for designing highly selective electrocatalysts.