5373-55-7Relevant academic research and scientific papers
Solid Versus Solution Spin Crossover and the Importance of theFe-N - (X) Angle
Rodríguez-Jiménez, Santiago,Brooker, Sally
, p. 13697 - 13708 (2017)
A new family of mononuclear [FeII(Rdpt)2(NCE)2] complexes (E = S, Se, or BH3) is formed by 1:2 reaction of [FeII(pyridine)4(NCE)2] with the monotopic pyridyl triazole ligand 4-(4-methylphenyl)-3-(2-pyridinyl)-5-phenyl-4H-1,2,4-triazole (tolpyph). The three complexes are obtained as six different solvatomorphs: [FeII(tolpyph)2(NCS)2]·H2O (1·H2O), 1·1.5CH3OH·0.5H2O, [FeII(tolpyph)2(NCSe)2] (2), 2·1.5H2O, [FeII(tolpyph)2(NCBH3)2] (3), and 3·H2O. Single-crystal X-ray diffraction reveals that 1·1.5CH3OH·0.5H2O and 2 are high-spin (HS) at 100 K, while 3 is low-spin (LS) at 100 K and HS at 373 K. Compound 3 is the first structurally characterized example of an [FeII(Rdpt)2(NCE)2]-type complex with NCBH3 co-ligand: the crystal packing is dominated by aromatic stacking interactions. Solid-state magnetic measurements show that 1·H2O and 2·1.5H2O remain HS down to 50 K, whereas 3·H2O undergoes spin crossover (SCO) with a T1/2 of 309 K, slightly above room temperature. A literature survey of analogous trans-[FeII(Rdpt)2(NCX)2]-type complexes (53 distinct crystal structures) shows that for the complexes that are SCO active in the solid state the Fe-N - C(X) angle is usually close to straight, 162-178°, whereas it is usually lower, 142-159°, for the complexes that remain HS. UV-vis studies in CHCl3 solution show that in each case the use of a 6:1 ratio of tolpyph/Fe(II) is required to ensure the iron(II) is present in solution as [FeII(tolpyph)2(NCE)2]. Interestingly, using this ratio, all three compounds are SCO-active in CDCl3 solution-in dramatic contrast to the solid-state findings. Specifically, while compounds 1 and 2 are not SCO-active in the solid state (they remain HS), they undergo gradual SCO in CDCl3 solution, with T1/2 values of 290 and 310 K, respectively. In CDCl3 solution, compound 3 has a T1/2 value of 288 K, which is 21 K lower than in the solid state. These results highlight the differences between solid state (ligand field; crystal packing) and solution (ligand field; solvation) effects on SCO, with the latter studies revealing roomerature SCO for all three of these complexes.
A chromatography-free and aqueous waste-free process for thioamide preparation with Lawesson's reagent
Wu, Ke,Ling, Yichen,Ding, An,Jin, Liqun,Sun, Nan,Hu, Baoxiang,Shen, Zhenlu,Hu, Xinquan
, p. 805 - 812 (2021/05/03)
After completing the thio-substitution with Lawesson's reagent, ethanol was found to be effective in the decomposition of the inherent stoichiometric six-membered-ring byproduct from the Lawesson's reagent to a highly polarized diethyl thiophosphonate. The treatment significantly simplified the following chromatography purification of the desired thioamide in a small scale preparation. As scaling up the preparation of two pincer-type thioamides, we have successfully developed a convenient process with ethylene glycol to replace ethanol during the workup, including a traditional phase separation, extraction, and recrystallization. The newly developed chromatography-free procedure did not generate P-containing aqueous waste, and only organic effluents were discharged. It is believed that the optimized procedure offers the great opportunity of applying the Lawesson's reagent for various thio-substitution reactions on a large scale.
Visible-Light Carbon Nitride-Catalyzed Aerobic Cyclization of Thiobenzanilides under Ambient Air Conditions
Bai, Jin,Yan, Sijia,Zhang, Zhuxia,Guo, Zhen,Zhou, Cong-Ying
supporting information, p. 4843 - 4848 (2021/06/28)
A metal-free heterogeneous photocatalysis has been developed for the synthesis of benzothiazoles via intramolecular C-H functionalization/C-S bond formation of thiobenzanilides by inexpensive graphitic carbon nitride (g-C3N4) under visible-light irradiation. This reaction provides access to a broad range of 2-substituted benzothiazoles in high yields under an air atmosphere at room temperature without addition of a strong base or organic oxidizing reagents. In addition, the catalyst was found to be stable and reusable after five reaction cycles.
Iron-Catalyzed Regioselective Synthesis of 2-Arylbenzoxazoles and 2-Arylbenzothiazoles via Alternative Reaction Pathways
Henry, Martyn C.,Abbinante, Vincenzo Mirco,Sutherland, Andrew
supporting information, p. 2819 - 2826 (2020/04/10)
A one-pot regioselective method for the preparation of 2-arylbenzoxazoles from N-arylbenzamides has been developed using iron(III)-catalyzed bromination of the aryl ring, followed by copper(I)-catalyzed O-cyclization with the benzamide side chain. In contrast, reaction of N-arylthiobenzamides with N-bromosuccinimide and iron triflimide led directly to the isolation of the corresponding 2-arylbenzothiazoles via intramolecular C–S bond formation. Mechanistic and control experiments suggest that in this case, bromination occurs at the sulfur atom, resulting in a reactive intermediate that can undergo electrophilic aromatic substitution and S-cyclization. The scope of both processes was explored yielding a range of structural analogues, including a pharmaceutically active compound for the treatment of Duchenne muscular dystrophy and an affinity agent of the amyloid-beta protein in Alzheimer's disease.
Mild and Chemoselective Thioacylation of Amines Enabled by the Nucleophilic Activation of Elemental Sulfur
Saito, Masato,Murakami, Sho,Nanjo, Takeshi,Kobayashi, Yusuke,Takemoto, Yoshiji
supporting information, p. 8130 - 8135 (2020/05/20)
A mild and chemoselective method for the thioacylation of amines using α-keto acids and elemental sulfur has been developed. The key to the success of this transformation is the nucleophilic activation of elemental sulfur by thiols such as 1-dodecanethiol
Extension of Azine-Triazole Synthesis to Azole-Triazoles Reduces Ligand Field, Leading to Spin Crossover in Tris-L Fe(II)
Brooker, Sally,Singh, Sandhya
, (2020/02/04)
The first examples of azole-Triazole Rat ligands, bidentate L4NMeIm(3-(1-methyl-1H-imidazol-4-yl)-5-phenyl-4-(p-Tolyl)-4H-1,2,4-Triazole) and L4SIm (4-(5-phenyl-4-(p-Tolyl)-4H-1,2,4-Triazol-3-yl)thiazole), have been prepared, by extension of the general synthesis used to access many examples of azine-Triazoles. The tris-L FeII complexes of the azine-Triazoles are consistently low spin (LS). As intended, these new azole-Triazole ligands provide lower field strengths, resulting in high-spin (HS) [FeII(L4NMeIm)3](BF4)2 (1·4H2O) and spin crossover (SCO) active [FeII(L4SIm)3](BF4)2 (2·0.5H2O). Single-crystal structure determinations revealed that at 100 K 1·solvents is HS whereas 2·solvents is LS. Solid-state variable temperature magnetic studies of air-dried crystals showed that the methylimidazole-Triazole complex 1·4H2O remains HS while the thiazole-Triazole complex 2·0.5H2O undergoes a two-step gradual SCO (T1/2 approximately 275 and 350 K). Variable-Temperature Evans method NMR studies of 2, in five different solvents (CD3NO2, CD3CN, CD3COCD3, CD2Cl2, and CDCl3) gave T1/2 values in a relatively narrow range, 214-259 K. These T1/2 values did not correlate with the solvent polarity index P′ (R2 = 0.25) but did correlate with the solvent basicity parameter SB (R2 = 0.90). Variable-Temperature UV-vis studies on a golden yellow CH3CN solution of 2, with monitoring of the d-d transition at 530 nm (? = 39 L mol-1 cm-1 at 293 K) while the solution was heated from 253 to 303 K, showed that the high-spin fraction increased from 0.51 to 0.77. Cyclic voltammetry studies in CH3CN revealed a Fe(III)/Fe(II) redox process that was reversible for 1 and irreversible for 2, with significant tuning of the Epa value: The methylimidazole-Triazole complex 1 is significantly easier to oxidize (0.46 V) than the thiazole-Triazole complex 2 (0.68 V; both vs 0.01 M Ag/AgNO3).
Iron-Promoted Three-Component 2-Substituted Benzothiazole Formation via Nitroarene ortho-C-H Sulfuration with Elemental Sulfur
Xing, Qiaoyan,Ma, Yanfeng,Xie, Hao,Xiao, Fuhong,Zhang, Feng,Deng, Guo-Jun
supporting information, p. 1238 - 1246 (2019/01/21)
A three-component procedure for the preparation of 2-substituted benzothiazoles from nitroarenes, alcohols, and sulfur powder is described. The reaction showed a good functional group tolerance to provide the heterocyclic products in moderate to good yields. The sequential assembly involving nitro reduction, C-N condensation, and C-S bond formation has been realized in one pot.
Exogenous Photosensitizer-, Metal-, and Base-Free Visible-Light-Promoted C-H Thiolation via Reverse Hydrogen Atom Transfer
Xu, Ze-Ming,Li, Hong-Xi,Young, David James,Zhu, Da-Liang,Li, Hai-Yan,Lang, Jian-Ping
supporting information, p. 237 - 241 (2019/01/10)
Visible-light-driven, intramolecular C(sp2)-H thiolation has been achieved without addition of a photosensitizer, metal catalyst, or base. This reaction induces the cyclization of thiobenzanilides to benzothiazoles. The substrate absorbs visible light, and its excited state undergoes a reverse hydrogen-atom transfer (RHAT) with 2,2,6,6-tetramethylpiperidine N-oxyl to form a sulfur radical. The addition of the sulfur radical to the benzene ring gives an aryl radical, which then rearomatizes to benzothiazole via RHAT.
Functionalization of activated methylene C-H bonds with nitroarenes and sulfur for the synthesis of thioamides
Do, Nhan T.,Tran, Khoa M.,Phan, Hao T.,To, Tuong A.,Nguyen, Tung T.,Phan, Nam T. S.
supporting information, p. 8987 - 8991 (2019/10/28)
We report a method to obtain arylthioamides by the functionalization of sp3 C-H bonds in phenylacetic acids and benzyl alcohols. Reactions proceeded without the use of any solvents and were compatible with many functionalities and heterocycles. These conditions allow for a rapid synthesis of thioamides from simple, commercial substrates.
Transition metal-free α-Csp3-H oxidative sulfuration of benzyl thiosulfates with anilines to form N-aryl thioamides
Qiao, Mengjun,Zhang, Jinli,Chen, Ling,Zhou, Fengyi,Zhang, Yali,Zhou, Lingfei,Wu, Yangjie
supporting information, p. 3790 - 3796 (2019/04/17)
A metal-free approach to N-aryl thioamides from Bunte salts and anilines in DMSO has been developed. This method tolerated a wide range of functional groups on the aromatic ring, providing an ideal way to N-aryl thioamides in good to excellent yields from cheap and easily available starting materials. A plausible mechanism was also proposed based on the X-ray single crystal diffraction, NMR and MS analyses of DMSO-concerning intermediates.
