Espinosa Matthew R, Doppiu Angelino, Hazari Nilay
Department of Chemistry, Yale University, P. O. Box 208107, New Haven, Connecticut, 06520, USA.
Precious Metals Chemistry, Umicore AG & Co. KG, Rodenbacher Chaussee 4, Hanau-Wolfgang, Germany.
Adv Synth Catal. 2020 Nov 18;362(22):5062-5078. doi: 10.1002/adsc.202000987. Epub 2020 Aug 27.
Palladium(II) precatalysts are used extensively to facilitate cross-coupling reactions because they are bench stable and give high activity. As a result, precatalysts such as Buchwald's palladacycles, Organ's PEPPSI species, Nolan's allyl-based complexes, and Yale's 1--butylindenyl containing complexes, are all commercially available. Comparing the performance of the different classes of precatalysts is challenging because they are typically used under different conditions, in part because they are reduced to the active species via different pathways. However, within a particular class of precatalyst, it is easier to compare performance because they activate via similar pathways and are used under the same conditions. Here, we evaluate the activity of different allyl-based precatalysts, such as (η-allyl)PdCl(L), (η-crotyl)PdCl(L), (η-cinnamyl)PdCl(L), and (η-1--butylindenyl)PdCl(L) in Suzuki-Miyaura reactions. Specifically, we evaluate precatalyst performance as the ancillary ligand (NHC or phosphine), reaction conditions, and substrates are varied. In some cases, we connect relative activity to both the mechanism of activation and the prevalence of the formation of inactive palladium(I) dimers. Additionally, we compare the performance of generated precatalysts with commonly used palladium sources such as tris(dibenzylideneacetone)dipalladium(0) (Pddba), bis(acetonitrile)dichloropalladium(II) (Pd(CHCN)Cl), and palladium acetate. Our results provide information about which precatalyst to use under different conditions.
钯（II）预催化剂被广泛用于促进交叉偶联反应，因为它们在实验室条件下稳定且活性高。因此，诸如布赫瓦尔德的钯环配合物、奥根的PEPPSI类配合物、诺兰的烯丙基基配合物以及耶鲁大学含1-丁基茚基的配合物等预催化剂都有商业供应。比较不同类别的预催化剂的性能具有挑战性，因为它们通常在不同条件下使用，部分原因是它们通过不同途径还原为活性物种。然而，在特定类别的预催化剂中，比较性能更容易，因为它们通过相似途径活化且在相同条件下使用。在此，我们评估不同烯丙基基预催化剂，如（η-烯丙基）PdCl（L）、（η-巴豆基）PdCl（L）、（η-肉桂基）PdCl（L）和（η-1-丁基茚基）PdCl（L）在铃木-宫浦反应中的活性。具体而言，我们在辅助配体（NHC或膦）、反应条件和底物变化时评估预催化剂性能。在某些情况下，我们将相对活性与活化机制以及无活性钯（I）二聚体形成的普遍性联系起来。此外，我们将生成的预催化剂的性能与常用的钯源，如三（二亚苄基丙酮）二钯（0）（Pddba）、双（乙腈）二氯钯（II）（Pd（CHCN）Cl）和醋酸钯进行比较。我们的结果提供了在不同条件下使用哪种预催化剂的信息。
