scholarly journals Facile N9-Alkylation of Xanthine Derivatives and Their Use as Precursors for N-Heterocyclic Carbene Complexes

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3705
Author(s):  
Moloud Mokfi ◽  
Jörg Rust ◽  
Christian W. Lehmann ◽  
Fabian Mohr
Keyword(s):  
Alkylating Agents ◽  
Silver Complexes ◽  
X Ray Diffraction ◽  
Ammine Complexes ◽  
Carbene Complexes ◽  
Ethyl Sulfate ◽  
X Ray ◽  
Xanthine Derivatives ◽  
Sulfate Salts ◽  
Chloride Salts

The xanthine-derivatives 1,3,7-trimethylxanthine, 1,3-dimethyl-7-benzylxanthine and 1,3-dimethyl-7-(4-chlorobenzyl)xanthine are readily ethylated at N9 using the cheap alkylating agents ethyl tosylate or diethyl sulfate. The resulting xanthinium tosylate or ethyl sulfate salts can be converted into the corresponding PF6- and chloride salts. The reaction of these xanthinium salts with silver(I) oxide results in the formation of different silver(I) carbene-complexes. In the presence of ammonia, ammine complexes [Ag(NHC)(NH3)]PF6 are formed, whilst with Et2NH, the bis(carbene) salts [Ag(NHC)2]PF6 were isolated. Using the xanthinium chloride salts neutral silver(I) carbenes [Ag(NHC)Cl] were prepared. These silver complexes were used in a variety of transmetallation reactions to give the corresponding gold(I), ruthenium(II) as well as rhodium(I) and rhodium(III) complexes. The compounds were characterized by various spectroscopic methods as well as X-ray diffraction.

scholarly journals Metal(II) Coordination Polymers from Tetracarboxylate Linkers: Synthesis, Structures, and Catalytic Cyanosilylation of Benzaldehydes

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 204
Author(s):  
Yu Li ◽  
Chumin Liang ◽  
Xunzhong Zou ◽  
Jinzhong Gu ◽  
Marina V. Kirillova ◽  
...  
Keyword(s):  
Coordination Polymers ◽  
Polycarboxylic Acid ◽  
X Ray Diffraction ◽  
X Ray ◽  
Trimethylsilyl Cyanide ◽  
Effect Of Solvent ◽  
Highly Active ◽  
Solvent Type ◽  
Metal Organic ◽  
Chloride Salts

Three 2D coordination polymers, [Cu2(µ4-dpa)(bipy)2(H2O)]n∙6nH2O (1), [Mn2(µ6-dpa)(bipy)2]n (2), and [Zn2(µ4-dpa)(bipy)2(H2O)2]n·2nH2O (3), were prepared by a hydrothermal method using metal(II) chloride salts, 3-(2′,4′-dicarboxylphenoxy)phthalic acid (H4dpa) as a linker, as well as 2,2′-bipyridine (bipy) as a crystallization mediator. Compounds 1–3 were obtained as crystalline solids and fully characterized. The structures of 1–3 were established by single-crystal X-ray diffraction, revealing 2D metal-organic networks of sql, 3,6L66, and hcb topological types. Thermal stability and catalytic behavior of 1–3 were also studied. In particular, zinc(II) coordination polymer 3 functions as a highly active and recoverable heterogeneous catalyst in the mild cyanosilylation of benzaldehydes with trimethylsilyl cyanide to give cyanohydrin derivatives. The influence of various parameters was investigated, including a time of reaction, a loading of catalyst and its recycling, an effect of solvent type, and a substrate scope. As a result, up to 93% product yields were attained in a catalyst recoverable and reusable system when exploring 4-nitrobenzaldehyde as a model substrate. This study contributes to widening the types of multifunctional polycarboxylic acid linkers for the design of novel coordination polymers with notable applications in heterogeneous catalysis.

Synthesis and coordination chemistry of silver(I), gold(I) and gold(III) complexes with picoline-functionalized benzimidazolin-2-ylidene ligands

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Mareike C. Jahnke ◽  
F. Ekkehardt Hahn
Keyword(s):  
Coordination Chemistry ◽  
Silver Oxide ◽  
Lithium Bromide ◽  
Metal Center ◽  
Molecular Structures ◽  
Transfer Reactions ◽  
Silver Complexes ◽  
X Ray Diffraction ◽  
X Ray ◽  
Halide Exchange

Abstract The reactions of N-alkyl-N′-picolyl-benzimidazolium bromides or N,N′-dipicolyl-benzimidazolium bromide with silver oxide yielded the silver dicarbene complexes of the type [Ag(NHC)2][AgBr2] 1–4 (NHC = picoline-functionalized benzimidazolin-2-ylidene). The silver complexes 1–4 have been used in carbene transfer reactions to yield the gold(I) complexes of the type [AuCl(NHC)] 5–8 in good yields. A halide exchange at the metal center of complexes 5–8 with lithium bromide yielded the gold bromide complexes 9–12. Finally, the oxidation of the gold(I) centers in complexes 9–12 with elemental bromine gave the gold(III) complexes of the type [AuBr3(NHC)] 13–16. Molecular structures of selected Au(I) and Au(III) complexes have been determined by X-ray diffraction studies.

Silver and Gold Complexes with Benzimidazolin-2-ylidene Ligands

2009 ◽  
Vol 64 (11-12) ◽  
pp. 1458-1462 ◽  
Author(s):  
Mareike C. Jahnke ◽  
Jennifer Paley ◽  
Florian Hupka ◽  
Jan J. Weigand ◽  
F. Ekkehardt Hahn
Keyword(s):  
Carbon Atom ◽  
Silver Oxide ◽  
Silver Complexes ◽  
X Ray Diffraction ◽  
Gold Complexes ◽  
X Ray ◽  
Linear Fashion ◽  
Diffraction Structure ◽  
Benzimidazolium Salts

The dicarbene silver complexes 1a, b of the type [Ag(NHC)2][AgBr2] (NHC = N,N'-dialkylbenzimidazolin- 2-ylidene) have been prepared from the parent benzimidazolium salts by reaction with silver oxide. The silver complexes have been used for the transfer of the carbene ligand to gold(I) giving the gold complexes [AuCl(NHC)] 2a, b in good yields. Crystals of 2a, b have been obtained from chloroform/pentane solutions, and X-ray diffraction structure analyses revealed gold(I) atoms coordinated in a linear fashion by an NHC carbon atom and a chloro ligand

Digold(I) Complexes Derived from 5,5′-Bibenzimidazolin-2-ylidene Ligands

2014 ◽  
Vol 69 (11-12) ◽  
pp. 1248-1252 ◽  
Author(s):  
Mareike C. Jahnke ◽  
Christian Schulte to Brinke ◽  
F. Ekkehardt Hahn
Keyword(s):  
Molecular Structure ◽  
Silver Oxide ◽  
Silver Complexes ◽  
X Ray Diffraction ◽  
Gold Complexes ◽  
Metal Centers ◽  
X Ray ◽  
Steric Crowding ◽  
Aurophilic Interactions

Abstract The 5,5′-bibenzimidazolium dibromide salts 2 and 3 have been prepared by fourfold N-alkylation of 5,5′-bibenzimidazole (2: R=Pr; 3: R=Bu). The diazolium salts were treated with silver oxide, and the in situ-formed silver complexes were subsequently reacted with [AuCl(SMe2)] to give the dinuclear gold complexes 4 and 5. The molecular structure of complex 5 has been determined by X-ray diffraction showing linearly coordinated gold(I) centers and, most likely due to steric crowding around the metal centers, no aurophilic interactions.

Polynuclear silver complexes of 2,5-dimethyl-2,5-diisocyanohexane (TMB). Influence of the anions

1988 ◽  
Vol 66 (9) ◽  
pp. 2386-2394 ◽  
Author(s):  
Michèle Dartiguenave ◽  
Yves Dartiguenave ◽  
Alain Mari ◽  
André Guitard ◽  
Marc J. Olivier ◽  
...  
Keyword(s):  
Bidentate Ligand ◽  
Methyl Groups ◽  
Silver Complexes ◽  
X Ray Diffraction ◽  
X Ray ◽  
N Value ◽  
Coordination Sites ◽  
Weakly Interacting ◽  
Silver Atoms ◽  
Infrared Data

Two series of complexes have been prepared by reaction of 2,5-dimethyl-2,5-diisocyanohexane (TMB) with AgX [Formula: see text]. Complexes of the first series, Ag(TMB)X, have been obtained with [Formula: see text]. The structures have been determined by X-ray diffraction for [Formula: see text] and [Formula: see text]. The crystals contain infinite chains of silver atoms alternating with bridging TMB ligands. When [Formula: see text], the Ag atom is best described as (2 + 2)-coordinated, with two of the coordination sites filled by [Formula: see text] acting as a bidentate ligand. When [Formula: see text], the Ag—TMB chain is of a different type and Ag can be considered two-coordinated and weakly interacting with a monodentate [Formula: see text] ion. The second series includes Ag2(TMB)3X2 complexes whose structure consists of pairs of chains cross-linked by extra TMB ligands leading to a ladder-like pattern. A weak unidentate interaction involving [Formula: see text] or [Formula: see text] is also apparent. The infrared data are in agreement with the X-ray results, since the highest v(C≡N) value is obtained for Ag(TMB)BF4, where Ag—CN distance is the shortest. The conformation of TMB is always trans about the central CH2—CH2 bond. The methyl groups render one of the staggered orientations of the —C(CH3)2(NC) groups unfavorable, leaving two conformations for coordinated TMB, both of which are observed in the Ag complexes.

scholarly journals Effect of a SO2 Rich Atmosphere on Tempera Paint Mock-Ups. Part 2: Accelerated Aging of Azurite- and Malachite-Based Paints

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 424
Author(s):  
Jose Santiago Pozo-Antonio ◽  
Carolina Cardell ◽  
Diana Barral ◽  
Amelia Dionisio ◽  
Teresa Rivas
Keyword(s):  
Crack Formation ◽  
Accelerated Aging ◽  
Egg Yolk ◽  
Chemical Degradation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sulfate Salts ◽  
Physical Changes ◽  
Significant Chemical ◽  
Industrial Atmosphere

In order to improve our knowledge of the weathering response of tempera paints exposed to an industrial atmosphere, azurite- and malachite-based paint mock-ups prepared with either rabbit glue or egg yolk binders were artificially aged in an SO2 rich atmosphere. The aim was to identify the different alteration mechanisms and forms of degradation in the paints by observing their physical (color, gloss, reflectance, and roughness), mineralogical, chemical, and micro-textural characteristics. Superficial physical changes were evaluated by stereomicroscopy, spectrophotometry, gloss measurement, hyperspectral imaging, and roughness measurements. Chemical and mineralogical changes were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with microanalysis (SEM-EDS), which was also used to evaluate the micro-texture of the paints. The differences between the fresh temperas were due mainly to the binder (egg yolk or rabbit glue) used in the paint mixture, which also played a crucial role in the different deterioration patterns in the artificially aged paint mock-ups. Thus, the egg yolk-based paints remained physically quite intact after SO2 exposure, although they suffered more significant chemical degradation, above all in the form of copious precipitation of Cu and Ca-rich sulfate salts and the subsequent yellowing of the egg yolk binder. The SO2 aged rabbit glue-based mock-ups showed microscopically important crack formation and binder loss and fewer sulfated salts precipitated on the surface of the paints.

Non-stoichiometric chloride salts of dioxotetrakis(imidazole)rhenium(V) cations

1993 ◽  
Vol 71 (12) ◽  
pp. 2070-2078 ◽  
Author(s):  
Anne-Marie Lebuis ◽  
Jim M.C. Young ◽  
André L. Beauchamp
Keyword(s):  
Infrared Spectra ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Octahedral Structure ◽  
X Ray ◽  
Extra Peak ◽  
Protonated Species ◽  
Chloride Salts ◽  
Additional Charge ◽  
C Nmr

Orange [ReO2L4]Cl salts were prepared with L = imidazole and 2-methylimidazole. The presence of a strong Re = O stretching band in the infrared spectra near 785 cm−1 is consistent with a trans-dioxo octahedral structure. With 1,2-dimethylimidazole, red-violet solids were obtained, which were studied by X-ray diffraction. Form I (from methanol): cubic, [Formula: see text]a = 25.205 Å, R = 0.032, 986 observed reflections; form II (from ethanol-dichloromethane): cubic, [Formula: see text]a = 25.520 Å, R = 0.056, 766 observed reflections. Both materials are non-stoichiometric, containing trans-[ReO2L4]+ and protonated trans-[ReO(OH)L4]2+ in an approximate ratio of 3:1 for 1 and 2:1 for II. In both cases, the unit cell contains 1 "normal" Cl− ion and 2/3 H2O per complex. In form I, the additional charge of [ReO(OH)L4]2+ is balanced by an extra Cl− ion partly occupying the unit cell origin, where it is replaced by disordered methanol the rest of the time. In form II, ReO4− and CH2Cl2 play the corresponding roles. In the infrared spectra, besides the characteristic band for the dioxo species, both forms show an extra peak at ~932 cm−1 originating from the protonated species, whereas form II shows an additional band at 907 cm−1 for uncoordinated ReO4−. The 1H and 13C NMR spectra of both forms in D2O are identical to those of the pure [ReO2L4]+ salt, indicating that the protonated species is strongly acidic.

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