Aromatic PCN pincer palladium complexes: forming and breaking C C bonds

Carboxylation of the Ni–Me Bond in an Electron-Rich Unsymmetrical PCN Pincer Nickel Complex

“…hydride, hydroxide, and alkyl ligands, which play a crucial role in the activation of small molecules, has been greatly enhanced in comparison to those based on other labile ligands. − In addition, the fourth ligand is influenced by a strong trans donor, giving it an increased reactivity. Indeed, a number of hydride, hydroxide, and hydrocarbyl complexes with pincer ligand scaffolds have been successfully isolated and structurally characterized. − ,− These complexes have been useful in the study of insertion reactions of small molecules, particularly CO 2 . ,,− ,− ,,− Thus, a (PCP)­Pd-Me complex was shown to have a reactive Pd–Me bond and was the first example of an insertion of CO 2 into a Pd–C bond . A great deal of work has been devoted to using nickel as a nonprecious alternative to palladium.…”

“…Similarly, the nickel methyl complex based on an aliphatic phosphinite pincer ligand displayed a low reactivity and required harsh reaction conditions . We and others have found that complexes based on unsymmetrical pincer ligand scaffolds display unique chemical reactivities in comparison to the symmetrical scaffolds. ,,,− We recently reported the first example of an unsymmetric aromatic PCN pincer nickel methyl complex and inter alia studied its reactivity toward CO 2 . However, this complex also showed low reactivity toward CO 2 and only 75% conversion was achieved at 150 °C and decomposition was observed during the carboxylation reaction.…”

Enhancing the Stability of Aromatic PCN Pincer Nickel Complexes by Incorporation of Pyridine as the Nitrogen Side Arm

“…Despite the fast expansion of the field of pincer complexes, [1][2][3][4][5][6][7][8][9] those with unsymmetric pincer ligands have received limited attention compared to the symmetric ones in part as a result of the long synthetic routes used to prepare the unsymmetric ligand scaffolds. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] However, unique reactivity has sometimes been documented for these ligands, and for PCN ligands such reactivity includes selective C-C vs. C-H bond activation and hemilability through de-coordination of the weak side arm of the unsymmetric pincer ligand. [10][11][12]18] Also increased reactivity in CO 2 insertion has been reported.…”

Reactivity of a Palladacyclic Complex: A Monodentate Carbonate Complex and the Remarkable Selectivity and Mechanism of a Neophyl Rearrangement

“…One approach is to trap CO 2 by complexes of catalytically active metals, often to give carbonate or carboxylate derivatives, followed by conversion to organic derivatives. In this context, several carbonate and bicarbonate complexes of palladium­(II) are known, and they can often be prepared by reactions involving CO 2 /H 2 O or carbonic acid. − For example, J (Scheme ) can be prepared from corresponding dimethylpalladium­(II) complex, I , by protonolysis with CO 2 /H 2 O and can then undergo further loss of methane to give bidentate carbonate complex K . Hydroxopalladium­(II) complex L reacts with CO 2 to give monodentate bicarbonate complex M , which can eliminate water to give binuclear bridging carbonate complex N .…”

“…In this context, several carbonate and bicarbonate complexes of palladium­(II) are known, and they can often be prepared by reactions involving CO 2 /H 2 O or carbonic acid. − For example, J (Scheme ) can be prepared from corresponding dimethylpalladium­(II) complex, I , by protonolysis with CO 2 /H 2 O and can then undergo further loss of methane to give bidentate carbonate complex K . Hydroxopalladium­(II) complex L reacts with CO 2 to give monodentate bicarbonate complex M , which can eliminate water to give binuclear bridging carbonate complex N . However, to the best of our knowledge, no monodentate carbonate complexes of palladium have been reported.…”