Palladium N(CH2CH2PiPr2) 2-Dialkylamides: Synthesis, structural characterization, and reactivity

Abstract

Palladium(II) aminodiphosphine PNP pincer complexes [PdR(PNPH )]PF6 (1R; R ) Cl Me, Ph; PNPH ) HN(CH2CH 2P'Pr2)2) were prepared. Deprotonation with KO'Bu affords dialkylamides [PdR(PNP)] (2R; R ) Cl Me, Ph; PNP = (NCH2CH2P'Pr2)2) in high yield which are stable toward ß-H elimination. While AgPF6 oxidizes the amides, cationic amido complexes [PdL(PNP)]PF6 (3L; L = CN'Bu, PMe3) were obtained upon chloride abstraction from 1 Cl with TlPF6. The reaction of amide 2Cl with MeOTf results in A/-methylation yielding [PdCl(PNPMe)]OTf (5) quantitatively. N-H acidities of the amino complexes 1Me (pk = 24.2(1)) and 1Ph (pk = 23.2(1)) were determined in dmso. Complexes 1Cl, 1Me, 2Cl 2Me, 3 CNIBu, and 5 were structurally characterized by single crystal X-ray diffraction. The amido complexes feature pyramidal nitrogen atoms in the solid state. The molecular structures, high A/-basicity, and reactivity of the amido complexes can be explained with Pd-Namido bonding that is characterized by strong N→Pd σ-donation and repulsive dπ-pπ π-interactions. This interpretation was confirmed by density functional theory (DFT) calculations of 2Cl. © 2009 American Chemical Society.