Structural Analysis of Chiral Complexes of Palladium(0) with 15‐Membered Triolefinic Macrocyclic Ligands

Abstract

The complete structural analysis of the palladium complexes of the triolefinic macrocycles (E,E,E)-1,6,11-tris(arylsulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-trienes, which featured from three identical to three different aryl groups, was achieved by performing X-ray diffraction studies, NMR spectroscopy, and other calculations. The stereochemical complexity is determined by the different isomers formed through complexation of the metal to one or other face of each of the three olefins involved. The palladacyclopropane formulation of the palladium-olefin interaction offers a clear picture of the stereogenicity of the olefin carbon atoms that are complexed to the metal. The energetically favorable isomers were identified in the solid-state and in solution by performing X-ray diffraction and NMR spectroscopic analysis, respectively.

Synthesis and structure of a chiral dinuclear palladium(0) complex with a 30-membered hexaolefinic macrocyclic ligand

“…The simple 1 H and 13 C NMR spectra of complex 5 confirm the presence of a high symmetry in the molecule. The general conclusions regarding the structure of 5 in solution are in line with those reached after performing detailed NMR studies into similar 15-, 20-and 25-membered azamacrocylic complexes [8]. Each palladium atom coordinates independently with three olefin systems to form a highly rigid five-ring system consisting of consecutively fused three and six-membered rings, as shown in Fig.…”

“…Mononuclear palladium(0) complexes of types 1-4 ( Fig. 1) have been prepared and fully characterized by means of NMR spectroscopy and X-ray diffraction [8]. These studies have demonstrated that the incorporation of a palladium atom into the cavity of a variety of sizeable polyunsaturated azamacrocyclic ligands forms stable tricoordinate complexes.…”

Structural Differences between Open-Chain and Macrocyclic Triene Ligands for Palladium(0): Influence on the Stability and Catalytical Properties

“…These distorsions are observed to a greater extent for the open-chain complex than for the macrocyclic one. For example, the olefinic CC bond distances in 3 (1.376(4) and 1.394(6) Å) are longer than distances in 1 , containing three ferrocenyl units (1.320(3), 1.326(3), and 1.325(3) Å). On the other hand, the loss of planarity, observed by the extent to which the olefinic substituents are bent away from the palladium, is also slightly greater for palladium(0) complex 3 (on average for the three double bonds approximately 19°) than for the macrocyclic complexes 1 (17°) .…”

“…One aspect that has attracted our attention throughout the study is the characteristic structural features of complexes 1 , which confer an intrinsic chirality and high stability. The complexation of the metal on one of the two stereotopic faces of each of the olefins present in the structure may form various isomers, of which only the energetically favorable ones are experimentally observed by means of both NMR and X-ray techniques . The conformation of the six-membered chelate rings determines the stability of the compound and, hence, its formation.…”

An efficient synthesis combining phosphorus dendrimers and 15-membered triolefinic azamacrocycles: towards the stabilization of platinum nanoparticles

“…A splitting of the signals of the three CH 2 -CHQCH-CH 2 linkages of the macrocycle was observed, both by 1 H and 13 C NMR, as previously described. 29 This is due to the fact that the 3 olefins are not involved in the same manner in the complexation with Pt, and this is complicated by the presence of two different aryl substituents on the macrocycle.…”