Well-​defined BisMETAMORPhos PdI-​PdI complex: synthesis, structural characterization, and reactivity

The formation of a bisMETAMORPhos PN-​bridged dimeric PdI complex (3) from ligand 1 and Pd(dba)​2 is described. The addn. of 1 to Pd(dba)​2 initially leads to the formation of Pd0 complex 2, which has a highly distorted tetrahedral environment and binds two neutral ligands 1. Complex 2 converts to {PdI}​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 addn. of one neutral coordinated ligand arm leads to a 1-​PdIIH complex. Insertion of free dba into the Pd-​H bond generates a 1-​PdIIdba complex that releases 1,​5-​diphenylpent-​1-​en-​3-​one via intra- or intermol. protonolysis. Concomitantly, comproportionation with 1-​Pd0 yields 3. Complex 3 was found to function as a precatalyst in the Suzuki-​Miyaura cross-​coupling of p-​chloroacetophenone with good conversions.