Henke Wade C, Stiel Jonah P, Day Victor W, Blakemore James D
Department of Chemistry, University of Kansas, 1567 Irving Hill Road, Lawrence, KS 66045, USA.
Chemistry. 2022 Feb 16;28(9):e202103970. doi: 10.1002/chem.202103970. Epub 2022 Jan 27.
Ligands based upon the 4,5-diazafluorene core are an important class of emerging ligands in organometallic chemistry, but the structure and electronic properties of these ligands have received less attention than they deserve. Here, we show that 9,9'-dimethyl-4,5-diazafluorene (Me daf) can stabilize low-valent complexes through charge delocalization into its conjugated π-system. Using a new platform of [CpRh] complexes with three accessible formal oxidation states (+III, +II, and +I), we show that the methylation in Me daf is protective, blocking Brønsted acid-base chemistry commonly encountered with other daf-based ligands. Electronic absorption spectroscopy and single-crystal X-ray diffraction analysis of a family of eleven new compounds, including the unusual CpRh(Me daf), reveal features consistent with charge delocalization driven by π-backbonding into the LUMO of Me daf, reminiscent of behavior displayed by the workhorse 2,2'-bipyridyl ligand. Taken together with spectrochemical data demonstrating clean conversion between oxidation states, our findings show that 9,9'-dialkylated daf-type ligands are promising building blocks for applications in reductive chemistry and catalysis.
基于4,5-二氮芴核心的配体是有机金属化学中一类重要的新兴配体，但这些配体的结构和电子性质并未得到应有的关注。在此，我们表明9,9'-二甲基-4,5-二氮芴（Me daf）可通过电荷离域到其共轭π体系中来稳定低价配合物。利用具有三种可及形式氧化态（+III、+II和+I）的[CpRh]配合物新平台，我们表明Me daf中的甲基化具有保护作用，可阻止其他基于daf的配体常见的布朗斯特酸碱化学。对包括不寻常的CpRh(Me daf)在内的11种新化合物家族进行电子吸收光谱和单晶X射线衍射分析，揭示了与通过π反馈键合到Me daf的LUMO中驱动的电荷离域一致的特征，这让人联想到常用的2,2'-联吡啶配体所表现出的行为。结合表明氧化态之间能实现完全转化的光谱化学数据，我们的研究结果表明9,9'-二烷基化daf型配体是还原化学和催化应用中很有前景的构建单元。
