“COVALENT SELF-ASSEMBLY” OF ACYCLIC DIAMINOCARBENE LIGANDS AT METAL CENTERS

Abstract

Chelating bis(acyclic diaminocarbene) ligands can be prepared by addition of diamines or hydrazines to coordinated isocyanide ligands in a process that resembles self-assembly. This procedure is potentially generalizable to a range of structurally and electronically diverse bis(carbene) ligands with catalytic utility. A series of 12 palladium complexes of 5-membered chelate bis(carbene) ligands have been prepared by a simple aqueous protocol and screened to identify moderately active, air tolerant Suzuki-Miyaura cross-coupling catalysts. Aryl isocyanide synthons provided more structurally elaborate acyclic diaminocarbenes, including chiral examples that supported enantioselective electrophilic catalysis at palladium. These carbene ligands have distinct stereoelectronic properties that complement those of the widely used N-heterocyclic carbenes.