Base Metal Bifunctional Catalysis

超过80%的商业化学过程涉及减少能源使用、增加反应选择性并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步骤。 虽然商品化学品制造通常使用非均相固体催化剂，但更高价值的化学品的生产通常涉及可以合理调节以提供所需产物的高产率的分子催化剂。 尽管贵金属（Ru、Rh、Ir、Pd、Pt）络合物催化剂在过去50年中得到了广泛的开发，但是一直强烈地推动开发更有效的催化剂，所述催化剂包括毒性更小且地球更丰富的贱金属（Mn、Fe、Co、Ni、Cu）。 在贱金属催化中，一些最成功的报道包括金属配位配体能够提供金属中心所提供的额外机械作用的络合物。 在几个突出的实例中，伯胺或酰胺基配体能够起到氢键供体或内部碱的作用，其有助于E-H键（E = H、B、C、N、O、Si）的活化。 在模仿自然的催化剂中，硫醇盐配体也可以参与双官能E-H键活化，尽管配位的硫醇S-H配偶体通常比其N-H对应物更酸性。 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。在这个建议中，我们概述了一个程序，将挑战11个研究生和本科生，使用简单的SNS配体与五种不同的贱金属探测催化反应中的金属配体协同性的基本性质。在上一个资助期内，我们开发了易于制备的SNS酰胺基和硫醇基配体，并研究了它们的配位化学，以比较硬N与软S内部碱在许多催化反应中的效率。重点包括用于胺-硼烷脱氢的双功能铁催化剂、用于醇脱氢的钴催化剂和用于烯烃硅氢加成的锰催化剂的演示。Fe、Co和Ni SNS硫醇盐配合物上的内部氧化还原反应通过亚胺C-C键的形成提供氧化还原非无辜的N2 S2配体。初步研究表明，这一可逆过程可能参与了M（N2 S2）催化循环和存在多个稳定的氧化还原态（3为Fe，4为Co）开辟了令人兴奋的氧化还原依赖的催化活性和选择性的可能性。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，并探测配体供体和氧化还原活性的协同性。通过实验和计算方法相结合的双功能催化的这些基础研究将最终使我们能够开发和优化新的氢借用串联催化过程。

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.