Novel enantiopure non-C2-symmetric NCN-pincer palladium complexes with l-proline chiral auxiliaries: mer η3-N,C,N versus square planar η4-N,C,N,O coordination

Diastereopure Cationic NCN‐Pincer Palladium Complexes with Square Planar η4‐N,C,N,O Coordination

“…The Pd-coordination environment in these complexes, including bond lengths and angles, is very similar to that observed for structurally related cationic NCNpincer palladium complexes containing methyl or benzyl prolinate substituents, where one carbonyl group of the ester moieties is coordinated to palladium ( Figure 1). [9] In cationic NCN-pincer complexes which do not contain additional donor atoms in the ligand, the mer-η 3 -N,C,N coordination of the pincer ligand is complemented by an η 1 -O water molecule. [11,12] Apparently, the intramolecular 4 , both coordinated and noncoordinated hydroxy groups donate hydrogen bonds, and thus, this results in four independent donor groups.…”

“…This observation is in line with those for neutral Pd-halide complexes derived from prolinate ester NCN-pincers. [9] In that case, a mixture of three diastereoisomers [(S N ,S N ,S C ,S C ), (R N ,S N ,S C ,S C ), and (R N ,R N ,S C ,S C )] is present in the temperature range of -80°C to +95°C. The 1 H and 13 C{ 1 H} NMR spectra were analyzed for these ester derivatives by applying a number of different one-and two-dimensional NMR techniques [ 1 H-1 H COSY, 1 H- 13 C HETCOR, 1 H NOESY, EXSY, and DEPT (angle) experiments].…”

“…Previously, we reported the synthesis and structural analysis of neutral and cationic palladium(II) complexes of monoanionic NCN-pincer ligands in which ester prolinate auxiliaries were used as the N-donor (Figure 1). [9] Depending on both the bulkiness of the prolinate ester substituents and the actual η 3 -N,C,N or η 4 -N,C,N,O coordination mode of the ligand, the palladium complexes were formed either as mixtures of three diastereoisomers or as single diastereoisomers both in the solid state and solution. These studies led us to develop a new class of enantiopure NCNpyrrolidine ligands where the ester groupings were replaced by CR 2 OH groups (R = H, Ph; Figure 1).…”

Synthesis and structural characterization of enantiopure exo and endo six-membered oxazoline-derived palladacycles

“…Metal complexes of unsymmetrically substituted 2-oxazolines obtained from chiral amino acids and their derivatives have found a variety of applications, particularly in asymmetric synthesis [47]. Recently, a number of C * -chiral enantiopure exo [48][49][50], endo [48,[50][51][52][53][54][55][56][57][58][59][60][61][62] and pincer-type [58,[63][64][65][66][67][68][69][70] cyclopalladated oxazolines with a five-membered metalacycle have been reported (Chart 2). Other cyclopalladated oxazolines with planar and central chirality have also been studied [38,[71][72][73][74][75][76][77][78][79][80].…”

Catalytic Isonitrile Insertions and Condensations Initiated by RNC–X Complexation

“…(14)]. [34] No enantioselectivity was reported, which is typical for this type of pincer-catalyzed condensation. The iminocyclohexane pincer complex 64b exhibits a very similar profile affording 13a with a dr of 4:1.…”