Багатогранне відновлення, каталізоване комерційно доступним паладієм: погляд на реакцію із практичного досвіду

Aim. To share our experience when working with the Pd-catalyzed hydrogenation and discuss reactions occurred contrary to our expectations, as well as express our vision of the causes for such an unusual reactivity.Results and discussion. Catalysis is a key technology and among the central themes of both petrochemical and fine chemical industries. Although extremely useful and reliable, it can sometimes astonish researchers. The paper discusses 17 intriguing cases of the catalytic hydrogenation and hydrogenolysis reactions from our practice in the High-pressure Synthesis Laboratory (Enamine Ltd.). All examples presented are characterized by peculiar performance of commercially sourced heterogeneous palladium-containing catalysts (Pd/C or Pd(OH)2). Thus, some cases were characterized by reduced activity of the catalyst (or even its complete loss), meaning that reaction conditions found before to be suitable for reduction appeared to be “broken”, and we had to search for a new, often harsher reaction setup. Curiously, it is a matter of classical Pd-catalyzed hydrogenations of N+–O– and C=C fragments. Apparently, these results indicate the heterogeneity of commercially available catalysts and are related to their fine internal structure, in particular the surface morphology. Another interesting issue the article deals with is chemoselectivity of the catalytic hydrogenation. Sometimes some reactions led to astonishing results going across theoretical views and expectations. Saturation of benzene rings instead of (or accompanying) debenzylation, breaking of the common order of hydrogenation for compounds containing several aromatic parts with different resonance energies, irreproducible experiment, obtaining of different products under the same conditions, uncommon results of Pd-catalyzed reactions is the list of interesting results, which we observed and discussed in the article. Analyzing the information available in the literature and considering all the results gathered we tend to believe that the presence of impurities of noble metals (Rh, Ru, Pt) in the catalysts used to be a possible reason for these strange findings. The study supports the general idea that commercial palladium catalysts differ in efficiency, resulting in significant differences in selectivity, reaction time, and yields. Elucidating the regularities behind such empirical results is undoubtedly an interesting area of research in the field of catalysis.Experimental part. All starting compounds exposed to hydrogenation were synthesized in Enamine Ltd. and had purity of not less than 95 %. The palladium-containing catalysts used in the experiment were purchased from 6 commercial sources within 2011 – 2022. The structure and purity of the compounds synthesized were characterized by 1H NMR spectroscopy, liquid chromatography coupled with the mass spectrometry method, elemental analysis. Chromatographic experiments revealed the purity of all compounds obtained being not less than 95 %.Conclusions. In the paper we have summarized our experience with the Pd-catalyzed hydrogenation and presented cases of unusual reactivity or unexpected outcomes of the reactions encountered in our practice. In general, complications we faced were of three types: (1) irreproducibility of the procedures most likely as the result of a changeable activity of the catalysts; (2) chemoselectivity issues when two or multireducible functional groups were present in the substrate; (3) undesirable Pd-catalyzed defunctionalization reactions. In turn, these complications led to increase in production costs, loss of time and resources. Therefore, because of this variability in the efficiency of Pd catalysts, far more efforts are required to find out the key differences between commercial sources of Pd catalysts, as well as to create protocols clearly defining the catalytic activity of each batch of the catalyst allowing to identify high-quality catalysts immediately prior to the use without wasting precious time and synthetic materials.Мета. Метою статті було поділитися нашим досвідом роботи з Pd-каталізованим гідруванням і обговорити реакції, що відбувалися всупереч нашим очікуванням, а також висловити своє бачення причин такої незвичайної реакційної здатності.Результати та їх обговорення. Каталіз є ключовою технологією та однією з центральних тем як нафтохімічної, так і тонкої хімічної промисловості. Хоча він є надзвичайно корисним і надійним підходом, іноді він може дивувати дослідників. У пропонованій статті розглянуто 17 цікавих випадків реакції каталітичного гідрування з нашої практики в Лабораторії синтезів під високим тиском (НВП «Єнамін»). Усі наведені приклади характеризуються своєрідною поведінкою комерційно доступних гетерогенних паладієвмісних каталізаторів (Pd/C або Pd(OH)2). Так, деякі випадки характеризувалися зниженою активністю каталізатора (або навіть повною її втратою). Іншими словами, умови реакції, які ми раніше вважали придатними для відновлення, виявилися «зламаними», і нам довелося шукати нові, часто жорсткіші умови для проведення реакції. Цікаво, що мова йде про класичне Pd каталізоване гідрування N+–O– і C=C фрагментів. Певно, ці результати свідчать про різнорідність комерційно доступних каталізаторів і пов’язані з їхньою тонкою внутрішньою структурою, зокрема морфологією поверхні. Іншим цікавим питанням, висвітленим у статті, є хемоселективність каталітичного гідрування. Так, іноді реакція призводила до вражаючих результатів, що суперечили теоретичним поглядам і очікуванням. Насичення бензольних кілець замість дебензилювання (або разом із ним), порушення загального порядку гідрування для сполук, які містять кілька ароматичних частин з різною енергією резонансу, невідтворюваний експеримент, отримання різних продуктів за використання однакових умов, нетипові результати реакцій, каталізованих Pd, – це список тих результатів, які ми спостерігали та обговорюємо в статті. Аналізуючи наявну в літературі інформацію та враховуючи всі зібрані результати, ми схильні вважати причиною цих дивних знахідок наявність у використаних каталізаторах домішок благородних металів (Rh, Ru, Pt). Дослідження несе загальну ідею про те, що комерційні паладієві каталізатори відрізняються за ефективністю, що призводить до значних відмінностей у селективності, часі реакції та виході. З’ясування закономірностей, що стоять за такими емпіричними результатами, безсумнівно, є важливим напрямом досліджень у царині каталізу.Експериментальна частина. Усі вихідні сполуки, піддавані гідруванню, було синтезовано в ТОВ «Єнамін». Вони мали чистоту не менше 95 %. Використовувані в експерименті каталізатори з паладієм було закуплено у 6 комерційних джерел упродовж 2011 – 2022 років. Структуру та чистоту синтезованих сполук схарактеризовано методами 1Н ЯМР-спектроскопії, рідинної хроматографії в поєднанні з мас-спектрометричним методом, елементного аналізу. Хроматографічні досліди засвідчили, що чистота всіх одержаних сполук становить не менше 95 %.Висновки. У статті узагальнено досвід роботи з Pd-каталізованим гідруванням і розглянуто випадки незвичайної реактивності або неочікуваних результатів реакцій, які зустрічалися в нашій практиці. Загалом ускладнення, з якими ми зіткнулися, були трьох типів: (1) невідтворюваність процедур, найпевніше, у результаті варіативної активності каталізаторів; (2) проблеми хемоселективності, у випадку присутності в субстраті кількох функціональних груп, здатних до відновлення; (3) небажані реакції дефункціоналізації, каталізовані Pd. Своєю чергою ці ускладнення призвели до збільшення витрат на виробництво, втрати часу та ресурсів. Саме через таку варіабельність ефективності паладієвих каталізаторів потрібно значно більше зусиль, щоб з’ясувати ключові відмінності між комерційними джерелами Pd каталізаторів, а також створити протоколи, які чітко визначають каталітичну активність кожної партії каталізатора, що дозволяє ідентифікувати високоактивні Pd каталізатори безпосередньо перед використанням і не втрачати дорогоцінний час та синтетичні матеріали

A new approach towards ferromagnetic conducting materials based on TTF-containing polynuclear complexes

International audienceFive complexes containing binuclear cation [Cu2(LH)2]2+ (LH2 = 1 : 2 Schiff base of 1,3-diaminobenzene and butanedione monoxime) were prepared and characterized. Metathesis of one perchlorate anion in [Cu2(LH)2(H2O)2](ClO4)2 (1) by anionic TTF-carboxylate (TTF-CO2−) leads to the complex [Cu2(LH)2(CH3OH)2](TTF-CO2)(ClO4)*H2O (2). Reactions of 1 with substituted pyridines bipy, dpe and TTF-CH = CH-py result in formation of the complexes {[Cu2(LH)2(bipy)](ClO4)2}n*2nH2O (3), [Cu2(LH)2(dpe)2](ClO4)2*2CH3OH (4) and [Cu2(LH)2(TTF-CH = CH-py)(H2O)](ClO4)2*1.5H2O (5), where bipy = 4,4′-bipyridine, dpe = trans-(4-pyridyl)-1,2-ethylene and TTF-CH = CH-py = 1-(2-tetrathiafulvalenyl)-2-(4-pyridyl)ethylene. Whereas complex 2 is built from discrete ionic particles (with rather long Cu-S contacts), compounds 1 and 3 contain 1D polymeric chains, in which structural units are bonded through Cu-O bonds or through bridging bipy molecule, respectively. Dinuclear complexes 4 and 5 are linked though π-stacking of dpe or TTF-CH = CH-py, respectively. All complexes are characterized by dominating ferromagnetic behavior with J values in the range from +9.92(8) cm−1 to +13.4(2) cm−1 for Hamiltonian H = -JS1S2. Magnetic properties of the compounds, containing stacks of aromatic molecules in crystal structures (4 and 5), correspond to ferromagnetic intradimer and antiferromagnetic intermolecular interactions (zJ′ = −0.158(3) and −0.290(2) cm−1, respectively). It was found that TTF-CH = CH-py ligand in [Cu2(LH)2(TTF-CH = CH-py)(H2O)]2+ could be electrochemically oxidized to cation-radical form in the solution

Coordination polymers based on trinuclear heterometallic pivalates and polypyridines: Synthesis, structure, sorption and magnetic properties

International audienceIt was shown that interaction of trinuclear pivalates Fe2MO(Piv)6(Hpiv)3 (M = NiII or CoII, Piv = (CH3)3CCO2−) with pyridine-containing ligands - trans-bis-1,2-(4-pyridyl)ethylene (trans-dpe), bis-1,3-(4-pyridyl)propane (py2Pn) resulted in formation of 2D porous coordination polymers [Fe2NiO(Piv)6(trans-dpe)1.5]n (1), [Fe2CoO(Piv)6(trans-dpe)1.5]n (2) and 1D polymers [{Fe2CoO(Piv)6(cis-dpe)}2(trans-dpe)]n (3), [Fe2NiO(Piv)6(py2Pn)(DMF)]n (4), where cis-dpe is cis-bis-1,2-(4-pyridyl)ethylene, formed due to in situ isomerization of trans-dpe. Interaction of Fe2NiO(Piv)6(Hpiv)3 with bis-2,3-(4-pyridyl)-2,3-dihydroxybutane led to in situ destruction of this ligand and isolation of trinuclear complex Fe2NiO(Piv)6(pyCOCH3)3 (5). X-ray structures of all five complexes were determined; compounds 1 and 2 were found to be isostructural. It was shown that crystal structures of [Fe2MO(Piv)6(trans-dpe)1.5]n complexes significantly changed at temperature variation. Sorption capacity of 1 and 2 on N2, H2 at 78 K (total volume of pores VT less than 0.045 cm3/g) was much lower than sorption capacity on methanol and ethanol at 293 K (VT from 0.16 cm3/g to 0.37 cm3/g), which can be explained by flexibility of crystal structure of these coordination polymers. Magnetic properties of 1 and 2 were simulated taking into account exchange interactions between metal ions and zero-field splitting of NiII or CoII. Exchange coupling between trinuclear units Fe2MO(Piv)6 was negligibly small

Nickel(II), Nickel(I), and Nickel(O) Complexes with 1,8-Bis(2′-pyridyl)-3,6-dithiaoctane

Nickel complexes with 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (Pdto) are synthesized; Ni(Pdto)(H 2O) 2(ClO 4) 2 is studied by X-ray diffraction

Nickel(II) Complexes with Dithiadiiminoamine and Dithiabis(thiosemicarbazone) Ligands

4,7-Dithiadecane-2,9-dione (Dtdk) serves as a starting point for generation of multidentate nitrogen/sulfur chelating agents. Condensation with ethylenediamine or diethylenetriamine yields the neutral hexadentate ligands 1,14-diamino-4,11-dimethyl-6,9-dithia-3,12-diazatetradeca-3,11-diene (Dtdida) and 15-amino-9-methyl-4,7-dithia-10,13-diazapentadec-9-en-2-one (Dtidak) respectively, while the diketone\u27s bis(thiosemicarbazone), itself a neutral ligand, may be deprotonated to form the hexadentate dianion Dtdtz2-. Blue/violet nickel(II) complexes with these ligands have been prepared, viz. Ni(Dtdida)(CIO4)2·0.5H2O 1, Ni(Dtidak)(ClO4)2·0.5CH3CN 4, Ni(DtdtzH2)(ClO4)2 2, and Ni(Dtdtz) 3; they are all S = 1 pseudo-octahedral systems. Although diamines such as ethylenediamine or diethylenetriamine are in principle capable of forming macrocyclic ligands with Dtdk, the products obtained were acyclic. In the case of Ni(Dtidak)2+, a keto-group and a primary amine residue co-exist within the cation, entailing an unusual example of a complex with a non-conjugated ketone coordinated to nickel(II). The coordination spheres of all four complexes have parallel N2S2X2 donor sets, with the ligands similarly folded. The properties of Ni(Dtdtz) evidence significant contribution from the imino-thiolate resonance form of the thioamide moiety. One consequence of this is the relative facility of oxidation of Ni(Dtdtz) to the nickel(III) form, at +0.24 V vs. SCE. © The Royal Society of Chemistry 2000

The 1,8-bis(2′-pyridyl)-3,6-dithiaoctane Complex of Nickel(II): X-ray Crystal Structure and Borohydride Adduct Formation

The quadridentate dipyridyl-dithioether ligand 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (Pdto) forms a pseudooctahedral complex with nickel(II). Blue [Ni(Pdto)(OH2)2](ClO4)2 crystallizes in the space group P21/c, with a= 11.677(5), b= 13,255(2), c= 15.804(4) Å, β= 107.45(3)° and Z=4. The ligand is folded about the Ni(II) ion so that the water ligands are cis within an O2S2 plane and the pyridines mutually trans. Reduction by sodium amalgam yields a nickel (I) complex with an axial EPR spectrum, whereas borohydride reduction is very slow. Indeed, the pink adduct [Ni(Pdto)(BH4)]+ has substantial stability in solution. © 1998 Elsevier Science S.A. All rights reserved

Magnetocaloric Effect in 1D-Polymers Bearing 15-Metallacrown-5 {GdCu5}3+ Units and Anionic Oxalate Complexes

International audienceTwo complexes {[GdCu5(GlyHA)5(H2O)7Cr(C2O4)3]·11.02H2O}n (1) and {{[GdCu5(GlyHA)5(H2O)6]μ2-[Cu(C2O4)2(H2O)]}2μ4-[Cu(C2O4)2]·15.8H2O}n (2), were obtained as outcomes of the reactions between the cationic hexanuclear {GdCu5(GlyHA)5}3+ 15-metallacrown-5 complex (where GlyHA2- = glycinehydroxamate) and the anionic oxalate complexes K3[Cr(C2O4)3] or K2[Cu(C2O4)2]. Both 1 and 2 possess polymeric 1D-chain structures according to X-ray structural analysis. As a consequence of the geometric orientations of the donor atoms in the oxalates from [Cr(C2O4)3]3-, the Cu5 mean planes of neighboring 15-metallacrown-5 units {GdCu5(GlyHA)5}3+ are angled at 75.5° to each other, which leads to formation of a zig-zag motif in the 1D-chains of complex 1. The centrosymmetric complex 2 contains two structurally different bis(oxalato)cuprate anions μ2-[Cu(C2O4)2(H2O)]2-, for one of which, coordination to two adjacent {GdCu5(GlyHA)5}3+ units leads to formation of linear 1D-chains in 2, while the second type, μ4-[Cu(C2O4)2]2-, is coordinated to four {GdCu5(GlyHA)5}3+ units, causing the cross-linking of single 1D-chains into a double-chain 1D coordination polymer. Studies of χMT vs. T data for 1 and 2 in a 2-300 K temperature range revealed the presence of both ferromagnetic and antiferromagnetic interactions amongst paramagnetic centres. The experimental χMT vs. T data for 1 were fitted using a model which takes into account exchange interactions between adjacent copper(II) ions, the Gd-Cu exchange interactions within {GdCu5(GlyHA)5}3+ units and additionally Gd-Cr exchange interactions. Fitting of the χMT vs. T data for 2 was not possible, since coordination of μ4-[Cu(C2O4)2]2- to {GdCu5(GlyHA)5}3+ led to the non-equivalence of several Cu-Cu exchange interactions within the metallacrown units and hence a superfluity of fittable parameters. Complexes 1 and 2 are the first examples of 15-metallacrown-5 complexes demonstrating a magnetocaloric effect (-ΔSM at 13 T reaches 24.26 J K-1 kg-1 at 5 K and 19.14 J K-1 kg-1 at 4 K for 1 and 2, respectively)

Synthesis, structure, circular dichroism of a Δ(−)546-di-μ-hydroxo-tetrakis(S-prolinato)dicobalt(III) complex and NMR study of its interaction with chiral and non-chiral probes in solutions

International audienceSlow oxidation of cobalt(II) ions by aerial oxygen in the presence of S-prolinate led to isolation of a new μ-OH bridged binuclear chiral complex of cobalt(III): Co2(μ-OH)2(S-Pro)4. The X-ray structure of this compound was studied. CoIII ions are located in N2O4 donor sets containing N and O atoms of S-prolinates at trans(N), cis(O)- or cis(N), trans(O)-positions. Optical properties of Co2(μ-OH)2(S-Pro)4 were investigated by means of electronic and circular dichroism spectroscopy providing data for comparison with the corresponding mononuclear complex of S-prolinate, cis-(−)-Co(S-Pro)3, as well as with other previously reported μ-OH bridged cobalt(III) complexes. CD spectra also confirmed that no racemization of S-prolinate occurred during synthesis. The solution behaviour of Co2(μ-OH)2(S-Pro)4 in the presence of various organic acids was studied by 1H and 13C NMR techniques evidencing specific interactions between carboxylic groups of the substrate and hydrogen-bonding groups of the Co2(μ-OH)2(S-Pro)4 molecule. Relying on the NMR spectroscopy results, the most probable models of binding between Co2(μ-OH)2(S-Pro)4 and S-proline as well as N-benzoylated α-amino acids were discussed

Antiferromagnetic ordering in cobalt(II) and nickel(II) 1D coordination polymers with the dithioamide of 1,3-benzenedicarboxylic acid

International audienceA series of 1D coordination polymers [Co(m-dtab)Cl2]n (1), [Co(m-dtab)Br2]n (2) and [Ni(m-dtab)2(Br)2]n (3), where m-dtab = the dithioamide of 1,3-benzenedicarboxylic acid, were prepared. The structures of all complexes were determined by X-ray diffraction . Magnetic properties of the compounds were characterized by molecular susceptibility vs. T dependence in the temperature range from 2 to 300 K. All compounds possess antiferromagnetic exchange interactions, and antiferromagnetic ordering was found in [Co(m-dtab)Br2]n and [Ni(m-dtab)2Br2]n at TN = 2.9 K and 2.6 K, respectively. DFT calculations showed that exchange interactions in [Co(m-dtab)(Hal)2]n could be transferred through two pathways: m-dtab between metal ions or interchain π-π stacking of aromatic rings, so the systems are not 1D from the viewpoint of magnetochemistry. The results of DFT calculations are consistent with the existence of magnetic ordering