Formation of six-membered palladacycles from phenanthroline Pd(II) bisacetate precursors and phenylisocyanate

Abstract

Synthesis and characterization of 5a-d. CCDC-221834 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via: www.ccdc.cam.ac.uk/data_request.cif.International audiencePhenylisocyanate reacts with palladium(II) bis-acetate phenanthroline complexes to give six-membered palladacycles in nearly quantitative yields. In this new reaction, the acetate ligands act as decarbonylating agents toward the isocyanate functionality by possibly forming the isolated palladacycles via an intramolecular rearrangement

Can Donor Ligands Make Pd(OAc)2a Stronger Oxidant? Access to Elusive Palladium(II) Reduction Potentials and Effects of Ancillary Ligands via Palladium(II)/Hydroquinone Redox Equilibria

“…72−74 The higher energy of the dmbpy-and dmphen-ligated Pd(OAc) 2 , relative to the bpy-and phen-ligand complexes, arises from destabilizing steric interactions between the ligand methyl groups and the acetate groups, which distort the coordination geometry of the planar ligand, forcing it out of the Pd II square plane (Scheme 3). This geometrical distortion has been noted in previously reported crystal structures of these complexes; 23,75,76 however, the work here provides the first insight into the impact of this effect on the Pd II reduction potential.…”

Diazafluorenone-Promoted Oxidation Catalysis: Insights into the Role of Bidentate Ligands in Pd-Catalyzed Aerobic Aza-Wacker Reactions

“…The plane of the 6,6′-Me 2 bpy ligand lies at a 33° angle with respect to the Pd II square plane, which reduces the steric interaction between the two ligand methyl groups and the acetate ligands. Similar structural behavior has been reported previously for Pd­(2,9-Me 2 phen)­(OAc) 2 , in which the phen ligand bends out of the square plane by 34° . One difference is evident between the 6,6′-Me 2 bpy and 2,9-Me 2 phen ligands: the 6,6′-Me 2 bpy ligand exhibits an unfavorable steric interaction between the hydrogen atoms in the 3- and 3′-positions (Figure B), whereas the phenanthroline ligand has a covalent CC bond in this position.…”

“…Similar structural behavior has been reported previously for Pd(2,9-Me 2 phen)(OAc) 2 , in which the phen ligand bends out of the square plane by 34°. 30 One difference is evident between the 6,6'-Me 2 bpy and 2,9-Me 2 phen ligands: the 6,6'-Me 2 bpy ligand exhibits an unfavorable steric interaction between the hydrogen atoms in the 3 and 3' positions (Figure 4B), whereas the phenanthroline ligand has a covalent C=C bond in this position. This feature is believed to destabilize the binding of 6,6'-Me 2 bpy relative to 2,9-Me 2 phen, as elaborated below.…”

Palladium-Mediated CO2 Extrusion Followed by Insertion of Isocyanates for the Synthesis of Benzamides: Translating Fundamental Mechanistic Studies To Develop a Catalytic Protocol

“…Subsequent addition of excess phenyl isocyanate at room temperature and protodemetalation with formic acid afforded N -phenyl-2,6-dimethoxybenzamide ( 5-Ph ), as identified by HRMS of the crude reaction mixture. This compound was separated from the side products, 1,3-diphenylurea and 1,3-dimethoxybenzene, by column chromatography and isolated in good yield (Scheme ). With the optimized reaction conditions in hand, we explored the scope of possible substrates with an electron-withdrawing aryl isocyanate, 4-(trifluoromethyl)­phenyl isocyanate.…”