Facile synthesis of achiral and chiral PCN pincer palladium(II) complexes and their application in the Suzuki and copper-free Sonogashira cross-coupling reactions

Unsymmetrical, oxazolinyl-containing achiral and chiral NCN pincer ligand precursors and their complexes with palladium(II)

“…The Pd-C bond distance is 1.915(7) Å (or 1.910(8) Å) and the bond distances between Pd(II) and the two nitrogen atoms are 2.058(7) (or 2.072(7) Å) and 2.119(6) Å (or 2.126(6) Å) for N(1) and N(2), respectively. The angle of C-Pd-Cl (179.0°or 177.6°) is almost linear, while the N-Pd-N angle (around 161°) is small, which are in accordance with a pincer consisting two five-membered-ring palladacycles [8,19,20,24,26] and reflect a relative steric strain of the almost planar tetracyclic system. All the bond distances and angles around Pd(II) centre are similar to those observed in the related bis(oxazoline) pincer Pd(II) complexes [20,29].…”

“…And the chiral complexes proved to be effective in asymmetric Michael reaction between a-cyanocarboxylates and methyl vinyl ketone (up to 83% ee) [8,17]. Following our interest in the metal pincer complexes and their applications, we recently reported the symmetrical chiral NCN pincer Pt(II) and Pd(II) complexes with 1,3-bis(2 0 -imidazolinyl)benzenes [23,24] and particularly unsymmetrical PCN pincer Pd(II) complexes containing phosphinito group by one-pot phosphorylation/palladation reaction [25,26]. We reasoned that different donors such as ''hard" N and ''soft" P in PCN pincers might provide a better tuning of the catalytic properties or give unique reactivity of the corresponding metal pincer complexes.…”

“…We reasoned that different donors such as ''hard" N and ''soft" P in PCN pincers might provide a better tuning of the catalytic properties or give unique reactivity of the corresponding metal pincer complexes. In fact, some unsymmetrical pincer Pd complexes have been found to be much more active than the related symmetrical ones under certain circumstances [26,27]. Herein, we would like to report a simple protocol for the synthesis of the unsymmetrical, oxazolinyl-containing achiral and chiral NCN pincer ligand precursors (3a-3e) and their corresponding Pd (II) derivatives (4a-4e) (Scheme 2).…”

Synthesis and Characterization of Triphenylphosphine Adducts of Ferrocene-Based Palladacycles and Their Performance in the Suzuki and Sonogashira Reactions with Bromo- and Chloroarenes

“…Thus a lot of efforts are underway toward developing new palladium catalysts and copper-and amine-free conditions for the Sonogashira reaction [23][24][25][26]. Among them, a wide variety of palladacycles have been reported and successfully used in the Sonogashira reaction [5,[27][28][29][30]. To the best of our knowledge, there was no report concerning the effect of halogen anions on the catalytic activity of palladacycle for the Sonogashira reaction.…”

Cyclopalladated complexes of 2-(m-nitrophenyl)imidazolines: synthesis, characterization and catalytic activity in the Suzuki reaction under mild conditions

“…These properties allowed for catalytic experiments to be done in the presence of air and water [16][17][18][19][20]. Connecting with our interest in the palladacycles and their applications [13][14][15][21][22][23][24][25], herein, we would like to report the synthesis and characterization of three cyclopalladated complexes with 2-(m-nitrophenyl) imidazolines (2a-2c) (Schemes 1, 2). It should be pointed out that the imidazoline-NH group in ligand (1a) was acetylated during the palladation reaction, giving the N-acetylated cyclopalladated complex (2a) (Scheme 2).…”