1 : 1 vs. 2 : 1 coordination of pentadentate hydrazone-type ligands to lanthanide(iii) ions. Formation of cationic as well as dicationic complexes

Abstract

Bis-acylhydrazones of 2,6-pyridinedicarbaldehyde are introduced as planar pentadentate ligands for the coordination of lanthanide(III) ions. With large cations (e.g. lanthanum(III)) 1 : 1 as well as 2 : 1 ligand-to-metal complexes are formed depending on the stoichiometry of the reaction. The different complexes are distinguished by NMR spectroscopy and ESI MS in solution and they can be characterized by X-ray diffraction. With the small lutetium(III) ion only the 1 : 1 complex is formed. In the 1 : 1 compounds, anions such as nitrate fill up the coordination site at the metal ion. However, in some cases anion substitution by solvent molecules is observed in the solid state leading to cationic and even dicationic coordination compounds.

Metal induced folding: synthesis and conformational analysis of the lanthanide complexes of two 44-membered hydrazone macrocycles

“…The two N 3 O 2 binding motifs are arranged at ∼62°with respect to each other, deviating from the orthogonality observed in nonmacrocyclic 2 : 1 complexes. 12 This difference is probably due to the steric constraints imposed by the macrocyclic backbone.…”

“…The Eu 3+ guest is found slightly above (0.59 Å) the plane of the 'lower' N 3 O 2 motif, similar to the other crystal structure of Eu 3+ -N 3 O 2 -acyl hydrazone complexes. 11,12 The remaining coordination sites are occupied by a carbonyl oxygen from the same molecule and three solvent molecules (H 2 O). In the 10-coordinate Eu 3+ complexes, the macrocycle twists around the metal to form a decadentate, helical binding pocket using both N 3 O 2 binding motifs in the molecule (Fig.…”

“…[3][4][5] We have recently demonstrated that a series of large and flexible [1 + 1] and [2 + 2] macrocycles containing acylhydrazone moieties can be efficiently synthesised using a dynamic combinatorial chemistry 6 approach. 7,8 As pentadentate N 3 O 2 acylhydrazone ligands 9 have been shown to be good ligands for lanthanide ions, [10][11][12] we investigated the complexation of lanthanide ions with two 44-membered [2 + 2] acylhydrazone containing macrocycles, the N 10 O 8 1 and the N 8 O 10 2. Here we report solution studies of the interaction of 1 and 2 with lanthanum(III), europium(III) and dysprosium(III) along with the X-ray structures of 1·2MeOH, [Eu (1) …”

Use of Acylhydrazine‐ and Acylhydrazone‐Type Ligands to Promote CuI‐Catalyzed C–N Cross‐Coupling Reactions of Aryl Bromides with N‐Heterocycles

“…The transformation between hindered and functionalized azoles and aryl halides was achieved in good to excellent yields. It is known that acylhydrazine and acylhydrazone derivatives possess high affinity and selectivity to metal ions, [21][22][23] and some insight into their binding and chelating ability to copper has also been explored. [22,23] A broad variety of substituents could also be introduced to the backbone units, which gives an opportunity to flexibly adjust their properties and coordinating ability to metal ions by varying the substituents.…”

“…[22,23] A broad variety of substituents could also be introduced to the backbone units, which gives an opportunity to flexibly adjust their properties and coordinating ability to metal ions by varying the substituents. Although acylhydrazine-and acylhydrazonetype ligands have been extensively used in coordination chemistry, [21][22][23] they are seldom chosen as ligands in catalysis. The success of N,O-ligands in Cu-catalyzed C-N formation reactions prompted us to examine whether these types of ligands could be useful for the N-arylation of azoles with aryl halides, especially with inexpensive aryl and heteroaryl bromides.…”