Soluble monometallic salen complexes derived from O-functionalised diamines as metalloligands for the synthesis of heterobimetallic complexes

Abstract

O-Functionalised salen ligands were employed as bridging ligands in the synthesis of homo- and heterometallic salen complexes with early and late transition metals (H(2)salen: N,N'-bis(salicylidene)ethylenediamine, systematic name: 2,2'-{ethane-1,2-diylbis(nitrilomethylidine)}diphenol). A new type of O-functionalised salen ligand was synthesised, which contains alkyl groups to enhance the solubility in organic solvents as well as carboxyl groups to allow introduction of an early transition metal. Two new salen ligands derived from O-functionalised diamines were synthesised from 3,5-di-tert-butylsalicylaldehyde (bsal) and 3,4-diaminobenzoic acid (4cpn) or (R)-2,3-diaminopropionic acid (cen). By using the aryl diamines, a conjugated backbone is obtained, and the alkyl diamines can be used to introduce a chiral centre. The salen ligand derived from 3,4-diaminobenzoic acid was accessible only via a zinc(II)-mediated template reaction. Monometallic salen complexes could be obtained by template synthesis with nickel(II) and copper(II). The analogous chromium(III), manganese(III) and molybdenum(IV) salen complexes were synthesised directly from the salen ligands. The crystal structures of the molybdenum(IV) salen complex and a decomposition product thereof gave insight into the stability of this compound. Starting from (R)-2,3-diaminopropionic acid the corresponding nickel(II), chromium(III), manganese(III) and molybdenum(IV) salen complexes were obtained. Reactions of the conjugated nickel(II) salen complex with metallocene derivatives resulted in the formation of soluble di- and trinuclear heterobimetallic complexes, depending on the stoichiometry used. The compounds were characterised by NMR, IR and EPR spectroscopy, mass spectrometry and, for selected complexes, by X-ray crystallography. For selected mono- and bimetallic salen complexes the catalytic activity in the epoxidation of styrene was tested under different reaction conditions and with different oxidising agents. The highest values (up to 24%) for the conversion of styrene to styrene oxide were obtained with manganese(III) salen complexes.

Advantages of Covalent Immobilization of Metal‐Salophen on Amino‐Functionalized Mesoporous Silica in Terms of Recycling and Catalytic Activity for CO2 Cycloaddition onto Epoxides

“…A convenient salophen ligand that meets all the criteria is N,N'-bis(3,5-di-tert-butylsalicylidene)-1-carboxy-3,4phenylene-diamine, denoted H 2 Salophen (1, Figure 2) whose synthesis, in the present study, was adapted from the literature. [42] Hence, the Schiff-base ligand 1 was synthesized with 95 % yield (see SI for the details of the preparation) using a classical condensation reaction of 1,2-diamino-4-carboxybenzene with 2 equivalents of 3,5-di-tert-butyl-2-hydroxybenzaldehyde (3,5-di-tert-butylsalicylaldehyde). It is noteworthy that this reaction required the presence of Zn 2 + that played the dual role of a templating agent and a Lewis acid that was not recovered in the final product.…”

Facile preparation of a novel nickel-containing metallopolymer via RAFT polymerization

“…Particularly, in order to avoid the formation of benzimidazole derivatives (Figure S3),[ 37 ] HSNi was obtained in a template synthesis using the Ni(CH 3 COO) 2 ·4H 2 O, which prefers tetrahedral coordination with salicylaldehyde derivatives. [ 38 ] Monomers and polymers containing copper and zinc were accordingly systhesized in supporting information.…”

“…As shown in Figure 4 , monomer HSNi and polymer PHSNi displayed an reversible reduction peak at −1.2 and −1.0 V respectively vs. the saturated calomel electrode (SCE), due to the reduction of salphen-Ni to [salphen-Ni] − . [ 38 ] HSNi showed a reversible oxidation peak at 1.25 V vs. the SCE, which can be attributed to the oxidation of salphen-Ni to [salphen-Ni] + , an nickel–radical species. [ 41 ] Compared with HSNi, the curve PHSNi was irreversible in oxidation, The irreversibility might because of the solubility change of HSNi under redox process.…”

Oxovanadium(IV) Schiff Base Complex Derived From Phenylalanine Analogue Containing 2,3-Diaminopropionic Acid (DAP): Synthesis, Computational Study, and Biological Evaluation

“…[15][16][17] Nevertheless, very limited researches on metal Schiff base complexes derived from DAP or its derivatives are carried out. [18][19][20] Costa Pessoa et al [21] explored the chemical properties of vanadyl Schiff base complexes by condensation of DAP with salicylaldehyde using potentiometric and spectroscopic techniques; however, so far theoretical computations have not yet been reported. As is known to all, density functional theory (DFT) computations are quite successful in the description and explanation of transition-metal complexes for their formation, structures, energies, and barriers.…”