Environmental Control of Triplet Emission in Donor–Bridge–Acceptor Organometallics

Carbene‐metal‐amides (CMAs) are a promising family of donor–bridge–acceptor molecular charge‐transfer (CT) emitters for organic light‐emitting diodes. A universal approach is demonstrated to tune the energy of their CT emission. A blueshift of up to 210 meV is achievable in solid state via dilution in a polar host matrix. The origin of this shift has two components: constraint of thermally‐activated triplet diffusion, and electrostatic interactions between guest and polar host. This allows the emission of mid‐green CMA archetypes to be tuned to sky blue without chemical modifications. Monte‐Carlo simulations based on a Marcus‐type transfer integral successfully reproduce the concentration‐ and temperature‐dependent triplet diffusion process, revealing a substantial shift in the ensemble density of states in polar hosts. In gold‐bridged CMAs, this shift does not lead to a significant change in luminescence lifetime, thermal activation energy, reorganization energy, or intersystem crossing rate. These discoveries offer new insight into coupling between the singlet and triplet manifolds in CMA materials, revealing a dominant interaction between states of CT character. The same approach is employed using materials which have been chemically modified to alter the energy of their CT state directly, shifting the emission of sky‐blue chromophores into the practical blue range.     

Reactions of cellulose and wood superficial hydroxy groups with organometallic compounds

Various lignocellulosic substrates, including microcrystalline cellulose, pinewood and hemp fibres, were treated with triethylaluminium and triethylboron in suspensions, in non‐swelling media. Chemical and spectroscopic analyses show that coupling surface reactions took place between one or two metal‐to‐carbon (Mt–C) bonds and the OH groups of the natural polymers. The remaining unreacted Mt–C bonds were exploited to graft numerous molecular structures derived from alcohols and amines. The occurrence of the second reaction was proved by Fourier‐transform infrared spectroscopy, elemental analyses, X‐ray photoelectron spectroscopy and contact angle measurements. Copyright © 2004 Society of Chemical Industry     

Increasing the Reactivity of Amides towards Organometallic Reagents: An Overview

The nucleophilic addition of carbon nucleophiles to amides has traditionally been a difficult task, both due to reactivity and selectivity problems. When successful, these processes would represent straightforward routes towards carbonyl‐type or amine compounds, depending on the fate of the generated tetrahedral intermediate. The direct addition of nucleophiles to amides for the preparation of ketones has been studied and applied to the syntheses of several natural products. On the other hand, the addition of nucleophiles to amides to obtain substituted amines represented a major challenge, and only scattered applications on particular substrates have appeared. Initial improvements were based on the activation of amides by introduction of particular substituents, such as in N‐methoxy amides (Weinreb amides) or electron‐withdrawing groups able to increase the carbon nucleophilicity. Although these strategies facilitate the introduction of nucleophiles, chemoselectivity issues arise when additional electrophilic moieties (i.e., carbonyls) are present, thus decreasing the versatility of the methods. In recent years, important advancements towards fully chemoselective methods have been realized. The capture of tetrahedral intermediates with acids generates highly electrophilic iminium species able to undergo chemoselective additions of various nucleophiles, thus accessing substituted amines. Alternatively, the in situ generation of an iminium triflate ion allows highly chemoselective additions of nucleophiles, yielding amines, ketones or ketimines. Also thioamides can be used as precursors of ketones or α‐substituted amines. The success of the above methodologies is further showcased by the application in various syntheses of natural products or biologically active molecules.

     

Polystannanes: Polymers of a Molecular,Jacketed Metal–Wire Structure

Organometallic polymers comprising a backbone of covalently connected metal atoms can be regarded as molecular metal wires surrounded by a jacket of organic matter. Such polymers are rare and their materials properties are largely unexplored. Here, we report on polystannanes, (SnR₂)_n, that is, polymers with a backbone of tin atoms, which are synthesized by dehydropolymerization of dialkylstannanes (H₂SnR₂) with the catalyst [RhCl(PPh₃)₃]. The polystannanes feature reversible phase transitions into liquid‐crystalline states, remarkably, even below room temperature, and, interestingly, oriented either parallel or perpendicular to external driving forces, depending on the length of the alkyl substituents.     

Evaluation of the Toxicity of Two Electron-Deficient Half-Sandwich Complexes against Human Lymphocytes from Healthy Individuals

Electron-deficient half-sandwich complexes are a class of under-studied organometallics with demonstrated potential as metallodrug candidates. This study investigates the effect of two 16-electron organoruthenium complexes ([(p-cym)Ru(benzene-1,2-dithiolato)] ( 1 ) and [(p-cym)Ru(maleonitriledithiolate)] ( 2 )) on the cell viability of non-immortalised human lymphocytes from healthy individuals. The genotoxic effects of 1 and 2 in lymphocytes are also investigated by using the Comet and cytokinesis-block micronucleus assays. Gene expression studies were carried out on a panel of genes involved in apoptosis and the DNA damage-repair response. Results show that the two 16-electron complexes do not have significant effect on the cell viability of human lymphocytes from healthy individuals. However, an increase in DNA damage is induced by both compounds, presumably through oxidative stress production.     

金属有机RReO3化合物研究进展

RReO₃是一种过渡金属有机化合物，其中，甲基三氧化铼是最早被发现的一种稳定的RReO₃型化合物，然而由于当时未能得到一种有效的合成路线，所以对甲基三氧化铼的研究没有引起重视。直到1988年德国Herrmann W A等发明了一种简便有效的合成方法，并且发现这类化合物可以高效催化烯烃环氧化反应后，RReO₃型化合物才引起重视。综述了迄今为止报道的含有不同R基团的RReO₃类化合物的合成方法，主要包括锌路线和锡路线两种合成方法，系统阐述了不同类型R基取代基对化合物稳定性的影响，同时总结了不同类型RReO₃型化合物催化性能的研究进展。然而，除甲基三氧化铼外，目前发现的大多数RReO₃型化合物在空气及潮湿环境下稳定性较差，限制了其催化应用。分析了影响催化剂稳定性的因素，并建议通过深入研究分子构效关系，探讨稳定性与催化性能的作用规律，从而指导催化剂的设计与合成，并对未来的发展方向进行展望。     

Effect of stannous octoate on the thermal decomposition of 2,2′‐azobis(isobutyronitrile)

The thermal decomposition rate constant k_d of 2,2′‐azobis(isobutyronitrile) (AIBN) in ethyl acetate was determined at 60 °C in the presence of various amounts of stannous octoate (SnOc₂). The k_d values were found to be dependent on the concentration of SnOc₂ in the solution. This dependence is not a linear function of the concentration because k_d goes through a maximum when [SnOc₂]/[AIBN] = 1. These features were explained by assuming the formation of a 1:1 cyclic complex between the nitrile groups of AIBN and the tin atom of SnOc₂. This complex induces steric constraints in the azo bond of AIBN, thus increasing its rate of decomposition. © 2000 Society of Chemical Industry     

金属有机物电合成研究的进展

综述了近年来金属有机物电合成的研究情况。内容包括 :“牺牲”电极法合成金属有机物 ,常规电极法合成金属有机物以及电合成中使用的金属有机物催化剂。