CAS: Can 1st Row Transition Metals Express the Covalency Typifying 2nd and 3rd Row Transition Metals: Comparative Studies

在化学部化学合成计划的支持下，康奈尔大学的Peter T. Wolczanski教授和他的研究小组将研究是否可以诱导第一行过渡金属表达第二行和第三行金属的典型共价。大多数商品和精细化学品都是利用催化化学合成的，第二排过渡金属最常用来催化碳的键形成。这些金属中有许多丰度低且价格昂贵；所谓的贵金属。这项研究旨在开发更可持续的替代化学品；也就是说，通过建立利用更丰富的金属的方法，这些金属被配体修饰，以提供取代现有催化剂所需的化学反应性。变革性配体通过独特的反应性扩大了应用范围，是该计划的基石。许多涉及不同金属配体结合模式和不同电子能力的方法有望有效地调节催化剂的反应性。一个具体的应用是合成简单的配位复合物，使光引发的过程更可持续，更容易地发生。将建立一个互联网节目/网站，为社区提供一个问答论坛，并作为与公众的新闻界面。该项目将对无机和有机金属化学领域的研究生和本科生进行过渡金属化合物合成和反应性方面的培训。作为一项辅助工作，有机金属化学的口述历史将被汇编并通过互联网提供。利用强场和非氧化还原（RNI）配体的协同作用来扩大目标第一过渡系金属的氧化还原能力。目标是开发这些金属的催化性能，这些金属是典型的第二和第三行金属。由于强电场赋予共价，具有阴离子或中性M-C键的双齿嘧啶基螯合物将被用作感应撤回配体。由于预测这些配合物具有低洼的pi-反键轨道和相应的低洼电荷转移（CT）激发态，因此它们作为光活性材料在光催化中具有潜在的应用前景。可逆C-C键断裂将在低配位配合物中应用，以限制RNI的2e-变化。四齿铬螯合物的化学特性证明了这一概念。具有空间/电子保护成分的新型螯合物将阻碍降解并稳定配体平台，从而通过瞬时亚胺/亚硝基络合激活CH。以苯并咪唑二胺为基础的非辅助配体可用于可逆掩膜开环复分解聚合和烯烃复分解的烷基烯。利用该配体体系，实现了一个可逆的亚甲基/二氢复分解循环。从比较Cr与Mo或W、Ti与Zr或V与Nb中收集额外的基本信息，其中比较化学（元化学与协同化学）将得出基于共价的解释。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemical Synthesis Program of the Chemistry Division, Professor Peter T. Wolczanski and his research team at Cornell University will investigate whether 1st row transition metals can be induced to express covalency typical of 2nd and 3rd row metals. Most commodity and fine chemicals are synthesized utilizing catalytic chemistry, with 2nd row transition metals being used to catalyze bond formations to carbon most commonly. Many of these metals are in low abundance and expensive; so-called precious metals. This research is directed at developing more sustainable alternative chemistries; namely by establishing ways of utilizing more abundant metals that are modified by ligands to provide the chemical reactivity necessary to supplant the current catalysts. Transformative ligands that expand the scope of applications via unique reactivity are a cornerstone of the program. A number of approaches involving different metal-ligand binding modes, and different electronic capabilities are expected to allow for the effective modulation of catalyst reactivity. One specific application is the synthesis of simple coordination complexes to enable light-initiated processes to occur more sustainably and with greater facility. An internet program/website will be established to provide a forum for Q&A for the community, and to serve as a news interface with the general public. The project will train graduate and undergraduate students in the fields of inorganic and organometallic chemistry in the synthesis and reactivity of transition metal compounds. As an ancillary effort an oral history organometallic chemistry will be assembled and made accessible through the internet.The coordination of strong field and redox non-innocent (RNI) ligands will be utilized with the goal of expanding the redox capability of targeted 1st transition series metals. The goal is the development of catalytic properties of these metals that are typical of 2nd and 3rd row metals. As strong fields impart covalency, bidentate pyrimidine-based chelates featuring anionic or neutral M-C bonds will be employed as inductively withdrawing ligands. As these complexes are predicted to have low-lying pi-antibonding orbitals and corresponding low-lying charge-transfer (CT) excited states, the complexes have potential applications as photoactive materials in photocatalysis. Reversible C-C bond breaking will be employed in low coordinate complexes to restrict RNI to 2e- changes. Chromium tetradentate chelates manifest chemistry that provides proof of this concept. New chelates with sterically/electronically protected components will hamper degradation and stabilize ligand platforms that will enable CH activation through transient imide/nitrene complexation. Non-ancillary ligands based on benzimidazole diamides will be used to reversibly mask alkylidenes that are capable of ring-opening metathesis polymerization and olefin metathesis. Using this ligand system, a reversible cycle involving a net methylene/dihydrogen metathesis will be realized. Additional fundamental information will be gleaned from comparisons of Cr vs Mo or W, Ti vs Zr, or V vs Nb, where comparative chemistry (metalaradical vs concerted) will elicit interpretations based on covalency.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.