New polydentate ligands based on sterically hindered o-benzoquinones (pyrocatechols) containing the 1,4-diazadiene group

Abstract

New bifunctional ligands containing the 1,4 diazadiene and 1,2 benzoquinone groups were synthesized by the reactions of 4 amino 3,6 di tert butylpyrocatechol with glyoxal and its derivatives. Their o semiquinone complexes with transition and nontransition metals were studied in solution by the ESR method.Key words: 1,4 diaza 1,3 diene, sterically hindered quinones and pyrocatechols, NMR spectroscopy, ESR spectroscopy. 1,4 Diazadienes form a large class of organic com pounds used in coordination and organometallic chemis try as neutral ligands. 1-4 In recent three decades, sterical ly hindered o quinones and pyrocatechols found wide use in the chemistry of o semiquinone and catecholate metal complexes. 5-7 The o quinone ligand in the o semiquino ne or catecholate form is valence bonded in mixed ligand metal complexes due to high differences in the values of reduction potentials of diazadienes and o quinones. 8,9 To date there are no published data on bifunctional ligands containing simultaneously the diazadiene and o quinone groups. In our opinion, these ligands are of doubtless in terest for the chemistry of organometallic and coordina tion compounds, such as bridging ligands for the synthesis of bi and polynuclear coordination compounds contain ing radical ligands along with magnetic metallocenters. In addition, they possess at least two electron withdrawing groups and, hence, can act as "electron reservoirs."The purpose of the present work is the synthesis of new bifunctional sterically hindered pyrocatechols and o qui nones with the 1,4 diazadiene group.

Ethylene Polymerization by Xanthene‐Bridged Dinuclear α‐Diimine NiII Complexes

“…Dichloromethane, toluene, THF, and hexanes were purified by solvent purification systems. 6‐Bromo‐3,5‐diisopropylaniline, 6‐bromo‐3,5‐dimethylaniline, 9,9‐dimethylxanthene‐4,5‐diboronic acid, 3‐(2,6‐diisopropylphenylimino)‐butan‐2‐one, 3‐(2,6‐dimethylphenylimino)‐butan‐2‐one, 1‐(2,6‐diisopropylphenylimino) acenaphthylen‐2‐one, Ni‐ i Pr, Ni‐Me, and Ni‐Nap were prepared according to reported procedures. All other reagents were purchased from commercial sources and used without purification.…”

PdII(P‐P) Derivatives of o‐Quinone Annulated with Dithiete Cycle: Electrochemical Properties and Coordination Regioisomerism

“…There are several examples of o‐quinones possessing additional coordination sites (Scheme 1). [ 6 ] Recently synthesized 4‐ImPy‐3,6‐DBQ [ 7 ] DAD‐3,6‐DBQ [ 8 ] and 4,5‐bis‐guanidino‐o‐quinone [ 9 ] demonstrate a coordination flexibility: they can form mononuclear complexes either on dioxolene or diimine site, or even display bridging behavior giving binuclear species. Coordination properties of 1,10‐phenanthroline‐5,6‐dione (pdon) have been studied for several decades, and this ligand has already been used for design of photosensitive materials, [ 10 ] thin film electrodes [ 11 ] and coordination polymers.…”

Hydrogen Bonding Behavior of Amide-Functionalized α-Diimine Palladium Complexes

“…The reaction of 1 with thionyl chloride to generate the corresponding acyl chloride in situ, followed by reaction with aqueous dimethylamine, afforded o -aminobenzamide 2a . Acid-catalyzed condensation of 2a and α-ketaimine 3 yielded 4a . The 1 H NMR spectrum of 4a at room temperature contains three sets of isopropyl resonances, which implies that rotation around the C aryl –N bonds is slow on the NMR time scale.…”

“…Toluene- d 8 was purchased from Cambridge Isotope Laboratories and used as received. 3-Isopropylanthranilic acid ( 1 ), N,N,N ′ ,N ′-tetramethyl-2-nitroisophthalamide, α-ketaimine 3 , (cod)PdMeCl (cod = 1,5-cyclooctadiene), and complex 5e were synthesized by literature procedures or modifications thereof.…”