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 (η 3 -1- t Bu-indenyl) 2 (μ-Cl) 2 Pd 2, a versatile precatalyst scaffold for Pd-catalyzed cross-coupling. Our new system is more active than commercially available (η 3 -cinnamyl) 2 (μ-Cl) 2 Pd 2 and is compatible with a range of NHC and phosphine ligands. Precatalysts of the type (η 3 -1- t Bu-indenyl)Pd(Cl)(L) can either be isolated through the reaction of (η 3 -1- t Bu-indenyl) 2 (μ-Cl) 2 Pd 2 with the appropriate ligand or generated in situ, which offers advantages for ligand screening. We show that the (η 3 -1- t Bu-indenyl) 2 (μ-Cl) 2 Pd 2 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 (η 3 -1- t Bu-indenyl) 2 (μ-Cl) 2 Pd 2 scaffold compared to (η 3 -cinnamyl) 2 (μ-Cl) 2 Pd 2 is that inactive Pd I dimers are not formed during catalysis.