Palladium N(CH<sub>2</sub>CH<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>2</sub>-Dialkylamides: Synthesis, Structural Characterization, and Reactivity
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Palladium(II) aminodiphosphine PNP pincer complexes [PdR(PNPH)]PF6 (1R; R = Cl Me, Ph; PNPH = HN(CH2CH2PiPr2)2) were prepared. Deprotonation with KOtBu affords dialkylamides [PdR(PNP)] (2R; R = Cl Me, Ph; PNP = (NCH2CH2PiPr2)2) in high yield which are stable toward β-H elimination. While AgPF6 oxidizes the amides, cationic amido complexes [PdL(PNP)]PF6 (3L; L = CNtBu, PMe3) were obtained upon chloride abstraction from 1Cl with TlPF6. The reaction of amide 2Cl with MeOTf results in N-methylation yielding [PdCl(PNPMe)]OTf (5) quantitatively. N−H acidities of the amino complexes 1Me (pKa = 24.2(1)) and 1Ph (pKa = 23.2(1)) were determined in dmso. Complexes 1Cl, 1Me, 2Cl 2Me, 3CNtBu, 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 N-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.
