Exploring coordination chemistry and reactivity of formazanate ligands

Een groot aantal industriële chemische processen maakt gebruik van katalysatoren op basis van dure edelmetalen (goud, platina, iridium etc.), die in staat zijn bindingen in moleculen te maken/breken door 2 elektronen op te nemen of af te staan. Tegenwoordig wordt er veel onderzoek gedaan naar zogenaamde ‘redox-actieve’ liganden, simpele organische verbindingen die deze rol kunnen overnemen, waardoor het mogelijk wordt goedkopere, meer duurzame alternatieven te ontwikkelen bijvoorbeeld met metalen zoals magnesium, calcium, zink of ijzer. In dit proefschrift worden de eigenschappen van het redox-actieve ligand ‘formazanaat’ beschreven. We bestuderen de synthese, coördinatiechemie en toepassing van formazanaat liganden in complexen met verschillende goedkope metalen. Formazanaat complexen met magnesium en calcium zijn getest als katalysatoren voor de polymerisatie van lactide naar biologisch afbreekbare plastics. In een andere toepassing laten we zien dat deze formazanaat-moleculen kunnen worden omgezet naar nieuwe, stabiele moleculaire schakelaars. De mogelijkheid om de eigenschappen van een molecuul te schakelen met licht is interessant in verschillende gebieden, zoals biomedische toepassingen en informatieopslag. Daarnaast heeft dit onderzoek een nieuw type formazanaat-ijzer moleculen opgeleverd waarvan de eigenschappen (magnetisme, reactiviteit) gestuurd kunnen worden door verandering in temperatuur. Deze nieuwe toepassingen zijn toe te schrijven aan de ongebruikelijke (elektronische) eigenschappen van het formazanaat ligand. Het onderzoek laat nieuwe manieren zien om de eigenschappen/reactiviteit te controleren van moleculen die gebaseerd zijn op goedkope, duurzame alternatieven voor edelmetalen.Many reactions in industrial processes require expensive metals as catalysts, such as gold, platinum, iridium, etc., which take or give two electrons in order to break/make chemical bonds. However, nowadays there are extensive researches on so-called 'redox-active' ligands because these can store electrons and do the job of these expensive metals, using instead cheap and abundant metals such as magnesium, calcium, zinc or iron.In this thesis we explore the properties of the redox-active ligand 'formazanate'. We study the synthesis, coordination chemistry and application of several formazanate ligands in complexes with different earth-abundant metals. With formazanate complexes of magnesium and calcium, we examined their properties as catalysts for polymerization of lactide to produce biodegradable plastics. In another application, we show how formazanate-containing molecules can be used to synthesize new, stable light-switchable molecules. The ability to change molecular properties with light is interesting in various fields, including biomedical applications and information storage. In addition, in this research we have developed molecules with formazanate ligands bound to an iron center for which the properties (magnetism, reactivity) can be switched by varying temperature. These newly developed applications derive from the unusual (electronic) properties of the formazanate ligand. The research suggests novel ways to control the properties/reactivity of molecules containing cheap, abundant alternatives to the noble metals

Three-Coordinate Zinc Methyl Complexes with Sterically Demanding Formazanate Ligands

A series of heteroleptic three-coordinate mono(formazanate)zinc methyl complexes were synthesized, and the influence of the ligand on the structure as well as redox and optical properties of these complexes was investigated. The heteroleptic mono(formazanate)zinc methyl complexes were found to show ligand redistribution in solution, reminiscent of the Schlenk equilibrium, to generate an equilibrium mixture containing the corresponding homoleptic complexes as well. Monitoring the approach to equilibrium by NMR spectroscopy in benzene-d(6) allowed determination of the forward and backward rate constants. A correlation was found between the steric environment around the zinc center and equilibrium concentration of (formazanate)zinc methyl compounds, whereas the kinetics for approach to equilibrium are also dependent on the electronic properties

Spin-Crossover in a Pseudo-tetrahedral Bis(formazanate) Iron Complex

Spin-crossover in a pseudo-tetrahedral bis(formazanate) iron(II) complex (1) is described. Structural, magnetic, and spectroscopic analyses indicate that this compound undergoes thermal switching between an S=0 and an S=2 state, which is very rare in four-coordinate complexes. The transition to the high-spin state is accompanied by an increase in Fe-N bond lengths and a concomitant contraction of intraligand N-N bonds. The latter suggests that stabilization of the low-spin state is due to the π-acceptor properties of the ligand. One-electron reduction of 1 leads to the formation of the corresponding anion, which contains a low-spin (S=1/2) Fe(I) center. The findings are rationalized by electronic structure calculations using density functional theory

Alkali metal salts of formazanate ligands:diverse coordination modes as a result of the nitrogen-rich [NNCNN] ligand backbone

Alkali metal salts of redox-active formazanate ligands were prepared, and their structures in the solid-state and in solution are determined. The nitrogen-rich [NNCNN] backbone of formazanates results in a varied coordination chemistry, with both the internal and terminal nitrogen atoms available for bonding with the alkali metal. The potassium salt K[PhNNC(p-tol)NNPh]center dot 2THF (1-K) is dimeric in the solid state and even in THF solution, as a result of the K atom bridging via interaction with a terminal N atom and the aromatic ring of a second unit. Conversely, for the compounds Na[MesNNC(CN)NNMes]center dot 2THF (2-Na) and Na[PhNNC(Bu-t)NNPh] (3-Na) polymeric and hexameric structures are found in the solid state respectively. The preference for binding the alkali metal through internal N atoms (1-K and 2-Na) to give a 4-membered chelate, or via internal/external N atoms (5-membered chelate in 3-Na), contrasts with the 6-membered chelate mode observed in our recently reported formazanate zinc complexes

CCDC 1020940: Experimental Crystal Structure Determination

Related Article: Raquel Travieso-Puente, Mu-Chieh Chang, Edwin Otten|2014|Dalton Trans.|43|18035|doi:10.1039/C4DT02578D,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1020939: Experimental Crystal Structure Determination

Related Article: Raquel Travieso-Puente, Mu-Chieh Chang, Edwin Otten|2014|Dalton Trans.|43|18035|doi:10.1039/C4DT02578D,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1020938: Experimental Crystal Structure Determination

Related Article: Raquel Travieso-Puente, Mu-Chieh Chang, Edwin Otten|2014|Dalton Trans.|43|18035|doi:10.1039/C4DT02578D,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1020937: Experimental Crystal Structure Determination

Related Article: Raquel Travieso-Puente, Mu-Chieh Chang, Edwin Otten|2014|Dalton Trans.|43|18035|doi:10.1039/C4DT02578D,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 2033366: Experimental Crystal Structure Determination

Related Article: Folkert de Vries, Raquel Travieso-Puente, Peter Roewen, Edwin Otten|2020|Organometallics|40|63|doi:10.1021/acs.organomet.0c0072

CCDC 2033364: Experimental Crystal Structure Determination

Related Article: Folkert de Vries, Raquel Travieso-Puente, Peter Roewen, Edwin Otten|2020|Organometallics|40|63|doi:10.1021/acs.organomet.0c0072