Catalytic heteroarylation as synthetic approach towards polydentate ligands

Drev, Miha (author), Požgan, Franc (mentor), Perdih, Franc (co-mentor)

In the first part, an efficient (hetero)arylation of ortho-C–H bonds of the benzene ring of 2-arylpyrimidines is achieved by Ru(II)–carboxylate-catalyzed reaction with (hetero)aryl bromides in water under microwave irradiation. This ''green'' methodology provides a series of polyconjugated pyrimidines with high site-selectivity. As established from Hammett plots, electron-withdrawing groups on phenyl ring of the pyrimidine substrates facilitate the arylation, while both electron-withdrawing and electron-donating groups on the aryl bromides assure a faster reaction. Applicability of heteroaryl-pyrimidines was demonstrated by their ligation to ruthenium or palladium center. In the second part, a series of hexa(heteroaryl)benzenes were synthesized by the Ru(II)–carboxylate-catalyzed multiple C–H activation of benzenes carrying pyridyl, pyrimidyl, or pyrazolyl directing groups using N-heteroaryl bromides as coupling partners. The reactions proceeded with high selectivity under microwave irradiation in water. Iterative penta-arylation could be implemented via sequential activation of C–H bonds of generated intermediates by cascade chelation assistance of in situ installed pyridyl groups. In the third part, the preliminary study on N-pyridylpyridin-2-one formation from substituted 2-bromopyridines was obtained. The pyridones were formed in the presence of Ru(II)-pivalate-Na2CO3 catalytic system. The study suggested that oxygen for 2-pyridone formation comes from pivalate which is regenerated with carbonate during the catalytic cycle. In the fourth part, the synthesized multiheteroaryl-substituted benzenes were used as ligands in coordination to selected transition metals (Ru, Pd and Ag) to obtain multinuclear complexes. Novel seven-membered bidentate Ru(II) complexes with one or two metal centres were prepared. The strategy was also employed in coordination of two Pd(II) and two Pt(II) cations as well as mixed Ru(II)-Pd(II) and Ru(II)-Pt(II) complexes. The poly(hetero)arylated benzenes were further used as ligands in coordination with Ag(I) ions, to obtain tetra- and pentanuclear complexes. The Ag(I) ions are in square or pentagon orientation, with F- ion in the centre of complex, between two hexa-coordinating ligands.

• Language: English
• Keywords: ruthenium, water, hexaheteroarylbenzene, pyridones, microwaves, complexes
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2020
• PID: 20.500.12556/RUL-113758
• COBISS.SI-ID: 1538527939
• Publication date in RUL: 31.01.2020

Secondary language

• Language: Slovenian
• Title: Katalitsko heteroariliranje kot sintezni pristop v pripravi polidentatnih ligandov

Abstract

V prvem delu smo razvili učinkovito metodo (hetero)ariliranja orto-C–H vezi na benzenovem obroču 2-arilpirimidina. Z Ru(II)–karboksilatom katalizirane reakcije s (hetero)aril bromidi smo izvajali v vodi pod pogoji mikrovalovnega segrevanja. Na ta način smo po načelih zelene kemije in z visoko regioselektivnostjo pripravili serijo polikonjugiranih pirimidinov. Mehanistične študije na podlagi Hammettove korelacije nakazujejo, da elektronprivlačne skupine na pirimidinskem substratu pospešujejo ariliranje, medtem ko skupine na aril bromidih, tako elektronprivlačne kakor tudi elektrondonorske, zagotavljajo hitrejše reakcije. Prikazali smo tudi koordinacijske lastnosti heteroaril-pirimidinov pri koordinaciji rutenija(II). V drugem delu smo pripravili serijo heksa(heteroaril)benzenov z uporabo Ru(II)-karboksilatnega katalitskega sistema. Reakcije večkratne C–H aktivacije z N-heteroaril bromidi so potekale regioselektivno na benzenovih obročih, ki so vsebovali piridilnske, pirimidilnske ali pirazolnske usmerjajoče skupine. Reakcije smo izvajali v vodi pod pogoji mikrovalovnega segrevanja. Zaporedno penta-ariliranje poteka preko sekvenčne aktivacije C–H vezi, kjer vsaka nova uvedena skupina usmerja nadaljnjo C–H aktivacijo. V tretjem delu smo raziskovali nastanek N-piridilpiridin-2-onov iz različno substituiranih 2-bromopiridinov. Preliminarne študije potrjujejo, da je za nastanek piridona ključna sinergija Ru(II) katalizatorja, kalijevega pivalata in Na2CO3. Rezultati eksperimentov z izotopsko označenim kisikom nakazujejo, da kisik pri tvorbi piridona najverjetneje pride iz pivalata, ki se tekom katalitskega cikla regenerira s karbonatom. V četrtem delu smo pripravljene polidentatne ligande uporabili v koordinaciji izbranih kovin prehoda (Ru, Pd, Pt and Ag). Na ta način smo pripravili nove bidentatne Ru(II) komplekse s sedemčlenskim kelatnim obročem z eno ali dvema koordiniranima kovinama. Metodo koordinacije dveh kovin smo nato aplicirali še na Pd(II) in Pt(II), kakor tudi za pripravo mešanih Ru(II)-Pd(II) in Ru(II)-Pt(II) kompleksov. S koordinacijo Ag(I) ionov na polidentate smo pripravili štiri- in petjederne komplekse, kjer so Ag(I) ioni med dvema ligandoma. Na sredini kompleksa je F- ion, ki je koordiniran na štiri Ag(I) ione.

• Keywords: rutenij, voda, heksa(hetero)arilbenzeni, piridoni, mikrovalovi, kompleksi