The Reduction of Sterically Hindered o‐Quinone and o‐Iminoquinone with Gallium and “GaI”

Abstract

Keywords: Gallium / Quinones / Reduction / EPR spectroscopyMetallic gallium reacts with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in THF to produce a gallium tris-o-semiquinolate complex, whereas the same interaction with 4,6di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone (imQ) does not proceed. The reduction of imQ is possible with amalgamed gallium in THF and produces a gallium complex that contains two o-iminobenzoquinone ligands in different redox states. In the case of 3,6-Q, the analogous reaction leads to dimeric derivative [Cat 2 Ga(Et 2 O) 2 ]-[a] G.A. Razuvaev 4318[CatGa] (in which Cat is the dianion of 3,6-Q). The structure of this compound was determined by X-ray diffraction analysis. The gallium(III) amidophenolate derivative can only be obtained by exchange reaction of APNa 2 with GaI 3 (in which AP is the dianion of imQ). The reduction of 3,6-Q and imQ with "GaI" results in the formation of corresponding compounds that contain redox-active ligands in the dianionic state. The structure of [AP 2 Ga][GaI 2 ] was determined by Xray diffraction analysis. Scheme 1. The reaction of digallane with alkynes.o-Quinone and o-Iminoquinone with Gallium and "GaI" One of the most convenient methods of synthesis of metal complexes with redox-active ligands is the direct reduction of o-quinones and their hetero-analogues by metals or metal amalgams. [8] (BIAN)Ga-Ga(BIAN) [9a] and the tris-o-semiquinolate gallium(III) derivatives that contain different o-quinones were synthesized by this method. [6,9b-9d] In some cases, the direct interaction of quinones with gallium leads to the formation of the respective dianionic catecholate derivatives. As reported in the literature, [6] heating of the gallium metal with 1,2-naphthoquinone (NQ) in refluxing toluene results in a deeper reduction of NQ and gives the dimeric catecholate complex [Ga II -(NCat)] 2 (NCat is the dianion of NQ). Catecholate gallium derivatives [(Hal 4 Cat)Ga II ·(phen)] 2 (Hal 4 Cat are dianions of tetrahalo-substituted o-quinones Hal 4 Q; phen = 1,10phenanthroline) form as the result of the reaction of metal with quinones in the presence of phen. [10a] Unfortunately, the authors [6,10a] did not produce sufficient evidence of such structures, and the last ones are questionable. Moreover, the minor product obtained in the reaction of Cl 4 Q with Ga in the presence of phen is the structurally characterized monomeric complex (Cl 4 Cat)GaCl·py·phen (py = pyridine). [10b] It indicates the more complicated nature of the interaction of metallic gallium with Hal 4 Q, which includes elimination of halides from the initial o-quinone.Low-oxidation-state metal derivatives are widely known to reduce 1,2-diketones and related ligands to give chelated compounds with reduced forms of the redox-active ligands. Thus the interaction of benzil with "GaI" results in the formation of a novel trimetallic bis(enediolato) complex. [11a] "GaI" was shown to be a convenient initial reagent for the synthesis of α-diimine gallium derivatives. [11b-11e] The reducti...

Structures and Magnetic Properties of Group 13 Metal Tris‐O‐benzosemiquinonato Complexes

“…Complexes 1 and 3 were obtained by the exchange reaction between the sodium salt of NN‐3,6‐Q with metal iodides, whereas 2 was synthesized by the direct interaction of gallium amalgam with NN‐3,6‐Q, similarly to the published procedure (Scheme ) 8. All of the complexes were isolated as finely crystalline powders and characterized by IR and EPR spectroscopy, magnetic measurements, and X‐ray diffraction.…”

Reprogramming Human Siderocalin To Neutralize Petrobactin, the Essential Iron Scavenger of Anthrax Bacillus

“…Another interesting feature that distinguishes the crystal form of petrocalin with bound PB⋅Ga III (accommodating three polypeptides in the asymmetric unit) relates to additional Ga III binding sites at residue Glu143 of each chain B and C. There, a dimer of Ga III ions is coordinated by the side chain carboxylate together with the catechol moiety of one PB molecule (in an open conformation), the citryl group of another PB as well as a second catechol group of a symmetry‐related PB (Figure S10). This ancillary complexation of the surrogate metal ion Ga III , which resembles its complexes with anguibactin and synthetic catechol derivatives, results in a network of PB/Ga III /protein interactions that appears to stabilize the protein packing in this crystal form.…”

“…Interestingly, three of the residues that contact PB show achanged side or main chain conformation:P he36 is rotated outwards (by 4.5 for the Cz atom) in the complex to accommodate the inner wing of PB,and loop #3 moves toward the ligand, thus influencing the side chain conformations of Arg100 as well as Ser99, which shifts closer to the ligand by 2.0 (at its Ca atom). This ancillary complexation of the surrogate metal ion Ga III ,which resembles its complexes with anguibactin [20] and synthetic catechol derivatives, [21] results in an etwork of PB/Ga III /protein interactions that appears to stabilize the protein packing in this crystal form. This ancillary complexation of the surrogate metal ion Ga III ,which resembles its complexes with anguibactin [20] and synthetic catechol derivatives, [21] results in an etwork of PB/Ga III /protein interactions that appears to stabilize the protein packing in this crystal form.…”

Neuprogrammierung von humanem Siderocalin zur Neutralisierung von Petrobactin, dem essenziellen Eisenfänger des Milzbrand‐Bazillus

“…Diese zusätzliche Komplexierung des Stellvertreter-Metallions Ga III ,d ie dessen Komplexen mit Anguibactin [20] sowie mit synthetischen Catecholderivaten [21] ähnelt, resultiert in einem Netzwerk aus PB/Ga III /Protein-Wechselwirkungen, was die Proteinpackung in dieser Kristallform zu stabilisieren scheint. Interessanterweise zeigen drei der Reste,d ie in Kontakt mit PB stehen, eine geänderte Seiten-oder Hauptkettenkonformation:Phe36 ist in dem Komplex nach außen rotiert (um 4.5 fürd as Cz-Atom), um den inneren Flügel von PB zu beherbergen, und Schleife #3 bewegt sich auf den Liganden zu, sodass die Seitenkettenkonformationenvon Arg100 wie auch von Ser99 beeinflusst werden, wobei sich Letzteres um 2.0 (an seinem Ca-Atom) dem Liganden nähert.…”

“…Ein weiteres interessantes Merkmal, das die Kristallform von Petrocalin mit gebundenem PB·Ga III (mit drei Polypeptiden in der asymmetrischen Einheit) unterscheidet, betrifft zusätzliche Ga III -Bindungsstellen an Rest Glu143 in den Ketten Bund C. Dort ist jeweils ein Dimer von Ga III -Ionen durch das Seitenkettencarboxylat zusammen mit der Catecholgruppe eines PB-Moleküls (in offener Konformation), der Citrylgruppe eines weiteren PB sowie der zweiten Catecholgruppe eines symmetrieverwandten PB koordiniert (Abbildung S10). Diese zusätzliche Komplexierung des Stellvertreter-Metallions Ga III ,d ie dessen Komplexen mit Anguibactin [20] sowie mit synthetischen Catecholderivaten [21] ähnelt, resultiert in einem Netzwerk aus PB/Ga III /Protein-Wechselwirkungen, was die Proteinpackung in dieser Kristallform zu stabilisieren scheint.…”