Enabling and Accelerating Metallocatalysis with Hydrogen Bonding

有许多重要的催化反应需要从催化中心解离/置换氢键阴离子，如卤化物和醋酸盐阴离子，或官能团，如胺或羰基。在许多这样的反应中，解离/位移过程影响反应速率和选择性。事实上，这种与催化剂配位的功能的存在可以完全抑制催化作用。我们最近发现，添加简单、容易获得的氢键供体（HBD）可以显著加速钯催化的反应，如芳基溴对烯烃的内部芳基化反应。我们观察到这些反应的反应速率等于或超过所有以前的催化体系。我们认为，HBD的功能是通过络合卤化物阴离子，帮助其从金属配位球中去除，而不需要，例如，化学计量，有毒的铊盐作为添加剂。最近有人指出，控制阴离子-阳离子相互作用的能力是优化收率、化学选择性、区域选择性和化学过程立体选择性....的关键(化学。Rev. 2005, 105, 2039)。在这个项目中，我们希望证明我们可以用氢键来做到这一点。特别是，我们将证明我们可以应用HBDs来：(i)加速和指导金属定位催化；（ii）实现级联金属-有机催化反应；因此（iii）表明HBDs提供了一种控制催化活性和选择性的新手段，并且应该始终考虑涉及氢键阴离子/官能团的反应。将均相催化与有机催化相结合，实现级联金属-有机催化的能力，将开辟一个令人兴奋的催化新领域——金属-有机催化，因为新兴的有机催化正在展现出前景。

There are numerous important catalytic reactions that require the dissociation/displacement of a hydrogen bonding anion, e.g. halide and acetate anions, or a functional group, such as amines or carbonyls, from the catalytic centre. In many such reactions, the dissociation/displacement process impacts on the reaction rates and selectivities. Indeed, the presence of such a functionality coordinated to the catalyst can inhibit the catalysis entirely. We have recently discovered that the addition of simple, readily accessible hydrogen bond donors (HBD) can dramatically accelerate palladium-catalysed reactions such as the internal arylation of olefins by aryl bromides. The reaction rates we observed equal or exceed all previous catalytic systems for these reactions. We believe that the HBD functions by complexing the halide anion, aiding its removal from the metal coordination sphere without the need for, e.g., stoichiometric, toxic thallium salts as additives. It has recently been stated that The capacity to control anion-cation interactions is key to optimizing yield, chemoselectivity, regioselectivity, and stereoselectivity of chemical processes .... (Chem. Rev. 2005, 105, 2039). In this project, we wish to demonstrate that we can use hydrogen bonding to do this. In particular we will show that we can apply HBDs in order to: (i) accelerate, and direct, metallocatalysis; (ii) enable cascade metallo-organo catalytic reactions; and thus (iii) show that HBDs afford a new means of controlling catalytic activity and selectivity, and should always be considered for reactions in which hydrogen bonding anions/functionalities are involved. The capability to integrate homogeneous catalysis with organocatalysis to enable cascade metallo-organo catalysis would open up an exciting new area of catalysis, metallo-organo catalysis, given the promise being demonstrated by the emerging organocatalysis.