Stiel Jonah P, Henke Wade C, Moore William N G, Barker Nathaniel M, Oliver Allen G, Day Victor W, Blakemore James D
Department of Chemistry, University of Kansas, 1567 Irving Hill Road, Lawrence, Kansas 66045, USA.
Department of Chemistry & Biochemistry, University of Notre Dame, 149 Stepan Chemistry Hall, Notre Dame, Indiana 46545, USA.
Dalton Trans. 2024 Oct 22;53(41):16956-16965. doi: 10.1039/d4dt01766h.
The redox properties of half-sandwich rhodium complexes supported by 2,2'-bipyridyl (bpy) ligands can be readily tuned by selection of an appropriately substituted derivative of bpy, but the influences of single substituents on the properties of such complexes are not well documented, as disubstituted bpy variants are much more common. Here, the synthesis, characterization, and redox properties of two new [CpRh] complexes (where Cp is η-1,2,3,4,5-pentamethylcyclopentadienyl) supported by the uncommon mono-substituted ligands 4-chloro-2,2'-bipyridyl (mcbpy) and 4-nitro-2,2'-bipyridyl (mnbpy) are reported. Single-crystal X-ray diffraction studies and related spectroscopic experiments confirm installation of the single substituents (-Cl and -NO, respectively) on the bipyridyl ligands; the precursor monosubstituted ligands were prepared a divergent route from unsubstituted bpy. Electrochemical studies reveal that each of the complexes undergoes an initial net two-electron reduction at potentials more positive than that associated with the parent unsubstituted complex of bpy, and that the complex supported by mnbpy can undergo a third, chemically reversible reduction at -1.62 V ferrocenium/ferrocene. This redox behavior is consistent with inductive influences from the substituent groups on the supporting ligands, although the nitro group uniquely enables addition of a third electron. Spectrochemical studies carried out with UV-visible detection confirm the redox stoichiometry accessible to these platforms, highlighting the rich redox chemistry and tunable behavior of [Cp*Rh] complexes supported by bpy-type ligands.
由2,2'-联吡啶（bpy）配体支撑的半夹心铑配合物的氧化还原性质可通过选择适当取代的bpy衍生物轻松调节，但单个取代基对这类配合物性质的影响尚未得到充分记录，因为二取代的bpy变体更为常见。本文报道了由不常见的单取代配体4-氯-2,2'-联吡啶（mcbpy）和4-硝基-2,2'-联吡啶（mnbpy）支撑的两种新型[CpRh]配合物（其中Cp为η-1,2,3,4,5-五甲基环戊二烯基）的合成、表征及氧化还原性质。单晶X射线衍射研究和相关光谱实验证实了在联吡啶配体上分别安装了单个取代基（-Cl和-NO₂）；前体单取代配体是通过与未取代的bpy不同的路线制备的。电化学研究表明，每种配合物在比与母体未取代的bpy配合物相关的电位更正的电位下经历初始净双电子还原，并且由mnbpy支撑的配合物在-1.62 V（相对于二茂铁鎓/二茂铁）下可进行第三次化学可逆还原。这种氧化还原行为与支撑配体上取代基的诱导影响一致，尽管硝基独特地能够添加第三个电子。用紫外-可见检测进行的光谱化学研究证实了这些平台可达到的氧化还原化学计量，突出了由bpy型配体支撑的[Cp*Rh]配合物丰富的氧化还原化学和可调行为。
