Base Metal Bifunctional Catalysis

超过80%的商业化学过程涉及减少能源使用，增加反应选择性和有助于过程强化的催化剂，例如，通过将多个步骤合并为一个。虽然大宗化学品生产通常采用非均相固体催化剂，但高价值化学品的生产通常涉及分子催化剂，可以合理调整以提供所需产品的高产量。虽然贵金属（Ru, Rh, Ir, Pd, Pt）复合催化剂在过去的50年里得到了广泛的开发，但人们一直在大力开发更有效的催化剂，包括毒性更小、土壤储量更丰富的贱金属（Mn, Fe, Co, Ni, Cu）。据报道，在贱金属催化方面取得的一些最伟大的成功，包括在配合物中，金属配位体能够在金属中心提供的机制之外提供额外的机制作用。在几个突出的例子中，伯胺或氨基配体能够作为氢键供体或内部碱，有助于激活E-H键（E = H， B， C， N， O, Si）。在模仿Nature的催化剂中，硫酸盐配体也可以参与双功能E-H键的激活，尽管配位的硫醇S-H伴侣通常比其N-H对应物更酸。最后，氧化还原活性配体可以作为电子源或受体，与贱金属中心协同工作以实现多电子转换。在这个提案中，我们概述了一个计划，将挑战11名研究生和本科生，使用具有五种不同贱金属的简单SNS配体来探索金属-配体在催化反应中的协同性的基本性质。在上一个资助期内，我们开发了易于制备的SNS氨基和硫酸盐配体，并研究了它们的配位化学，以比较硬‘ N ’和软' S内部碱基在许多催化反应中的效率。重点展示了双功能Fe催化剂用于胺-硼烷脱氢，Co催化剂用于醇脱氢，Mn催化剂用于烯烃硅氢化。Fe， Co和Ni SNS硫酸盐配合物的内部氧化还原反应通过亚胺C-C键形成氧化还原非无害N2S2配体。初步研究表明，这一可逆过程可能参与了M（N2S2）的催化循环，多种稳定氧化还原态（Fe为3，Co为4）的存在开启了氧化还原依赖的催化活性和选择性的令人兴奋的可能性。下一个资助期的目标包括通过改变辅助配体的金属和性质来调整供体碱度，以及探测配体供体的协同性和氧化还原活性。通过实验和计算方法的结合，这些双功能催化的基础研究将最终使我们能够开发和优化新的借氢串联催化过程。

More than 80% of commercial chemical processes involve catalysts that decrease energy use, increase reaction selectivity and contribute to process intensification, e.g., by combining multiple steps into one. While commodity chemical manufacturing typically employs heterogeneous solid catalysts, production of higher value chemicals often involves molecular catalysts that can be rationally tuned' to provide high yields of the desired product. Although precious metal (Ru, Rh, Ir, Pd, Pt) complex catalysts have been broadly developed over the last 50 years, there has been an intensive drive to develop more effective catalysts that include base-metals (Mn, Fe, Co, Ni, Cu) that are less toxic and more earth abundant. Some of the greatest reported successes in base metal catalysis include complexes in which the metal-coordinated ligand is able to provide an additional mechanistic role to those offered by the metal center. In several prominent examples a primary amine or amido ligand is able to function as a hydrogen bond donor or internal base that contributes to the activation of E-H bonds (E = H, B, C, N, O, Si). In catalysts modeled after Nature, the thiolate ligand can also participate in bifunctional E-H bond activation although the coordinated thiol S-H partner is typically more acidic than its N-H counterpart. Finally, a redox-active ligand can serve as an electron source or acceptor, working in tandem with the base-metal center to achieve multi-electron transformations. In this proposal we outline a program that will challenge 11 graduate and undergraduate students, using simple SNS ligands with five different base-metals to probe the fundamental properties of metal-ligand cooperativity in catalytic reactions. Over the last funding period we developed easily prepared SNS amido and thiolate ligands and investigated their coordination chemistry to compare the efficiency of hard' N vs. soft' S internal bases for a number of catalyzed reactions. Highlights include demonstration of bifunctional Fe catalysts for amine-borane dehydrogenation, Co catalysts for alcohol dehydrogenation and Mn catalysts for alkene hydrosilylation. An internal redox reaction on Fe, Co, and Ni SNS thiolate complexes afforded a redox non-innocent N2S2 ligand via imine C-C bond formation. Initial studies suggest that this reversible process may be involved in the M(N2S2) catalytic cycles and the presence of multiple stable redox states (3 for Fe, 4 for Co) opens up the exciting possibility of redox-dependent catalytic activity and selectivity. Objectives for the next funding period include tuning donor basicity by changing the metal and nature of the ancillary ligands and probing the cooperativity of ligand donors and redox activity. These fundamental investigations of bifunctional catalysis by a combination of experimental and computational approaches will eventually allow us to develop and optimize new hydrogen-borrowing' tandem catalysis processes.