Well-Defined BisMETAMORPhos PdI–PdI Complex: Synthesis, Structural Characterization, and Reactivity

The formation of a bisMETAMORPhos PN-bridged dimeric Pd I complex ( 3 ) from ligand 1 and Pd(dba) 2 is described. The addition of 1 to Pd(dba) 2 initially leads to the formation of Pd 0 complex 2, which has a highly distorted tetrahedral environment and binds two neutral ligands 1 . Complex 2 converts to {Pd I } 2 complex 3 upon heating. Complex 3 consists of a completely flat Pd–Pd core, with a Pd–Pd bond length of 2.6199(4) Å, and the Pd centers display a highly distorted square planar coordination environment. The formation of complex 3 from 2 is suggested to proceed via an in situ comproportionation pathway. Initial decoordination of one ligand from 2 followed by oxidative addition of one neutral coordinated ligand arm leads to a 1- Pd II H complex. Insertion of free dba into the Pd–H bond generates a 1 -Pd II dba complex that releases 1,5-diphenylpent-1-en-3-one via intra- or intermolecular protonolysis. Concomitantly, comproportionation with 1 -Pd 0 yields 3 . Complex 3 was found to function as a precatalyst in the Suzuki–Miyaura cross-coupling of p -chloroacetophenone with good conversions.