Cu-I click catalysis with cooperative noninnocent pyridylphosphine ligands

We describe the synthesis and characterization of compound L1H, 2-di(tert-butyl)phosphinomethyl-6-methylpyridine, and the first dimeric CuI complex 3 with this novel bidentate NPtBu ligand. We also demonstrate for the first time that this ligand scaffold exhibits noninnocent reactivity through dearomatization behavior, similar to its well-studied tridentate analog L2H, 2,6-bis((di-tert-butylphosphino)methyl)pyridine PNPtBu. The molecular structure of [Cu(CCPh)(L2H)]2 is reported, which is a rare case of a crystallographically characterized copper-acetylide dimer. We also demonstrate that copper(I) complexes with either ligand L1H or L2H or their dearomatized counterparts may act as active, cooperative catalysts for the [2+3] polar cycloaddition of azides and acetylenes. These results represent the first indications of selective Cu-based cooperative catalysis, using non-innocent lutidine-based PNP backbone and catalysts 2 and 5 could thus be termed all-inclusive systems for this reaction.