Design of a Versatile and Improved Precatalyst Scaffold for Palladium-Catalyzed Cross-Coupling: (η3‑1‑tBu-indenyl)2(μ-Cl)2Pd2

We describe the development of (η3-1-tBu-indenyl)2(μ-Cl)2Pd2, a versatile precatalyst scaffold for Pd-catalyzed cross-coupling. Our new system is more active than commercially available (η3-cinnamyl)2(μ-Cl)2Pd2 and is compatible with a range of NHC and phosphine ligands. Precatalysts of the type (η3-1-tBu-indenyl)­Pd­(Cl)­(L) can either be isolated through the reaction of (η3-1-tBu-indenyl)2(μ-Cl)2Pd2 with the appropriate ligand or generated in situ, which offers advantages for ligand screening. We show that the (η3-1-tBu-indenyl)2(μ-Cl)2Pd2 scaffold generates highly active systems for a number of challenging cross-coupling reactions. The reason for the improved catalytic activity of systems generated from the (η3-1-tBu-indenyl)2(μ-Cl)2Pd2 scaffold compared to (η3-cinnamyl)2(μ-Cl)2Pd2 is that inactive PdI dimers are not formed during catalysis.

本研究报道了(η³-1-叔丁基茚基)₂(μ-氯)₂二钯（(η³-1-tBu-indenyl)₂(μ-Cl)₂Pd₂）的开发，它是一种可用于钯催化交叉偶联反应的多功能预催化剂骨架。我们开发的新体系活性优于市售的(η³-肉桂基)₂(μ-氯)₂二钯（(η³-cinnamyl)₂(μ-Cl)₂Pd₂），且可兼容多种N-杂环卡宾（NHC）配体与膦配体。(η³-1-叔丁基茚基)钯(氯)(L)型预催化剂既可通过(η³-1-叔丁基茚基)₂(μ-氯)₂二钯与合适配体的反应分离得到，也可原位生成，这为配体筛选带来了便利。本研究证实，(η³-1-叔丁基茚基)₂(μ-氯)₂二钯骨架可构建出对多种挑战性交叉偶联反应具有高催化活性的催化体系。相较于(η³-肉桂基)₂(μ-氯)₂二钯体系，由(η³-1-叔丁基茚基)₂(μ-氯)₂二钯骨架构建的催化体系活性提升的原因在于，催化过程中不会生成失活的一价钯二聚体。