四唑负离子与脒正离子复合物稳定性的理论研究

采用密度泛函B3LYP/6-31+G(d,p) 方法和自洽反应场极化连续模型(PCM)研究四唑负离子与脒类(乙脒或苄脒)正离子形成的两种形式的复合物(末端和侧端)及甲酸根负离子与脒类(乙脒或苄脒)正离子形成的复合物在气相和二甲亚砜（DMSO）溶剂中的稳定性。在气相中,四唑-乙脒和四唑-苄脒复合物的相互作用能(∆E)末端分别比侧端的大3.56和3.72 kJ/mol,表明末端复合物稍占优势。甲酸与乙脒和苄脒的复合物的相互作用能(∆E)分别比四唑与乙脒和苄脒的复合物的大59.35和58.99 kJ/mol,表明脒与甲酸形成复合物时相互作用更强。溶剂DMSO的作用使得所有复合物的相互作用能变小,但脒与四唑的相互作用仍比脒与甲酸的弱。前者的结合常数与后者的相比只有1/315（乙脒）和1/218（苄脒）,这与实验结果相一致。     

Heterolysis of Dihydrogen by Silver Alkoxides and Fluorides

Alkoxide‐bridged disilver cations react with dihydrogen to form hydride‐bridged cations, releasing free alcohol. Hydrogenolysis of neutral silver fluorides affords hydride‐bridged disilver cations as their bifluoride salts. These reactions proceed most efficiently when the supporting ligands are expanded N‐heterocyclic carbenes (NHCs) derived from 6‐ and 7‐membered cyclic amidinium salts. Kinetics studies show that silver fluoride hydrogenolysis is first‐order in both silver and dihydrogen.     

Electronic Spectra and Protonation of 1,4-Di(arylamino)anthraquinones and Their Monodimethylformamidinium Salts in Acid Solutions

Electronic spectra of arylaminoanthraquinones and their amidinium salts in acids were studied, and experimental data on electrophilic substitution of diarylaminoanthraquinone amidinium salts in acetic and sulfuric acids of various concentrations were considered.     

Remote Sensitized Photoisomerization via Through‐Bond Triplet–Triplet Energy Transfer Mediated by a Salt Bridge in a Supramolecular Dyad

A supramolecular dyad, BP‐(amidinium‐carboxylate)‐NBD is constructed, in which benzophenone (BP) and norbornadiene (NBD) are connected via an amidinium‐carboxylate salt bridge. The photophysical and photochemical properties of the assembled BP‐(amidinium‐carboxylate)‐NBD dyad are examined. The phosphorescence of the BP chromophore is efficiently quenched by the NBD group in BP‐(amidinium‐carboxylate)‐NBD via the salt bridge. Time‐resolved spectroscopy measurements indicate that the lifetime of the BP triplet state in BP‐(amidinium‐carboxylate)‐NBD is shortened due to the quenching by the NBD group. Selective excitation of the BP chromophore results in isomerization of the NBD group to quadricyclane (QC). All of these observations suggest that the triplet–triplet energy transfer occurs efficiently in the BP‐(amidinium‐carboxylate)‐NBD salt bridge system. The triplet–triplet energy transfer process proceeds with efficiencies of approximately 0.87, 0.98 and the rate constants 1.8×10³ s^?1, and 1.3×10⁷ s^?1 at 77 K and room temperature, respectively. The mechanism for the triplet–triplet energy transfer is proposed to proceed via a “through‐bond” electron exchange process, and the non‐covalent bonds amidinium‐carboxylate salt bridge can mediate the triplet–triplet energy transfer process effectively for photochemical conversion.     

Six- and seven-membered ring carbenes: Rational synthesis of amidinium salts, generation of carbenes, synthesis of Ag(I) and Cu(I) complexes

Reactions of neat 1,3- and 1,4-dibromides with N,N′-diarylformamidines in the presence of diisopropylethylamine (DIPEA) afford corresponding amidinium salts in high yields (>80%). Six- and seven-membered ring amidinium salts bearing bulky Mes (2,4,6-Me₃C₆H₂) and Dipp (2,6-ⁱPr₂C₆H₃) aryl groups were prepared using this method. Free six-membered ring carbene 6-Dipp was generated from amidinium salt using LiHMDS as a base. NHC-Ag(I) complexes were obtained by the reactions of amidinium salts with Ag₂O. NHC complexes of Pd and Rh are not accessible by deprotonation of amidinium salts, nor by transmetallation of Ag(I) complexes. However NHC-Cu(I) complexes were obtained by transmetallation of NHC-Ag(I). Thus, transmetallation of six- and seven-membered NHC-Ag(I) complexes was documented for the first time.     

Preparation of imidazolinium salts by the Pd-catalyzed reduction of thioureas with triethylsilane and trialkylsilyl triflate

A Pd-catalyzed method for the preparation of imidazolinium salts from the corresponding thioureas that could then be used for the synthesis of imidazolium and amidinium salts is described. This method has great potential because all the required reagents are readily available and thioureas are safely converted to their corresponding precursors of NHCs under mild conditions.     

Synthesis of Pd complexes bearing an enantiomerically resolved seven-membered N-heterocyclic carbene ligand and initial studies of their use in asymmetric Wacker-type oxidative cyclization reactions

The development of enantiomerically resolved, axially-chiral seven-membered N-heterocyclic carbene (⁷NHC) ligands for palladium is described. These ⁷NHC ligands are derived from enatiomerically pure 2,2′-diamino-6,6′-dimethylbiphenyl, which is transformed via a synthetic sequence consisting of ortho-arylation, N-alkylation, and cyclization to afford seven-membered-ring amidinium salts. Synthesis of the seven-membered amidinium salts benefits from microwave irradiation, and in-situ metalation of the amidinium salts yields ⁷NHC-Pd^II complexes. The chiral ⁷NHC-Pd complexes were examined as chiral catalysts under aerobic conditions in two intramolecular oxidative amination reactions of alkenes. In one case, enantioselectivities up to 63% ee were obtained, while the other substrate underwent cyclization to afford essentially racemic products. The catalytic data compare favorably to results obtained with a Pd^II catalyst bearing a chiral five-membered-ring NHC ligand and, thereby, highlight the potential significance of this new class of chiral NHC ligands.     

A novel three-component one-pot pyrimidine synthesis based upon a coupling-isomerization sequence

[reaction: see text] 2,4,6-Tri(hetero)aryl-substituted pyrimidines can be readily synthesized in a three-component one-pot process based upon a coupling-isomerization sequence of an electron-poor (hetero)aryl halide and a terminal propargyl alcohol subsequently followed by a cyclocondensation with amidinium salts.     

Amidine als Zwischenprodukte bei Umamidierungsreaktionen. 9. Mitteilung über Umamidierungsreaktionen

Amidines as Intermediates in Transamidation Reactions By loss of water in the presence of p-toluenesulfonic acid/xylole N-aminoalkyllactames form bicyclic amidines. The corresponding N-alkylaminoalkyl-lactames' react to bicyclic amidinium salts or to transamidated products, ring-enlarged by the N-alkylamino residue, respectively (s. Scheme 1). The bicyclic amidines and amidinium salts are partially hydrolyzed by KOH/H₂O to lactames (s. Scheme 2). Which of the two possible isomeric lactames are formed is discussed.     

Organic/inorganic hybrid materials and nanocomposites based upon layered silicates modified with cyclic amidines

Various cyclic amidinium cations were used to exchange intergallery sodium cations of water‐swellable fluorohectorite in order to produce novel families of organic/inorganic hybrid materials. Oligomeric cyclic amidinium cations, such as mono(imidazolinium)‐terminated oligostyrene, oligostyrene‐co‐oligo(acrylonitrile), and oligo(methyl methacrylate) with number‐average molecular masses around 3 000 g/mol afforded effective exfoliation during melt processing. Morphology and dynamic mechanical properties were measured as a function of silicate content and silicate modification.     

Molecular structure and hydrolytic stability amidinium salts derived from triazatricyclo[5.2.1.0]decane

Five amidinium salts have been prepared from triazatricyclo[5.2.1.0^4,10]decane (tacnoa) and characterised by mass spectrometry, NMR spectroscopy and X-ray crystallography. The X-ray structures revealed a long distance between the methine carbon and the ammonium nitrogen, viz., C-N distance 1.64-1.70 Å, cf. other C-N distances of 1.40-1.50 Å. An NMR study of 1-ethyl-4,7-diaza-1-azoniatricyclo[5.2.1.0^4,10]decane and 1-benzyl-4,7-diaza-1-azoniatricyclo[5.2.1.0^4,10]decane, confirmed that these amidinium salts hydrolyse in aqueous solution, the latter 60 times faster than the former. Tacnoa, which has C-N distances typical of single bonds, showed no evidence of hydrolysis after several days at 80 °C. Molecular modeling calculations indicate that the preferred gas phase structure of the salts is one where the positive charge is delocalised over the two secondary amines and the methine carbon. The calculated distance between this carbon and the ammonium nitrogen is 0.15-0.4 Å longer than in the crystal structure. The energy difference between the preferred gas phase and solid state conformations is 2 kJ mol⁻¹ and presents little barrier to nucleophilic attack of the methine carbon. Further analysis of the methine carbon geometry (C(7)) reveals that the bond angles in the benzyl salt are closer to those expected for an sp² centre than in the ethyl salt and that this could be the origin of the faster hydrolysis rate.     

1-(N-Acylamino)alkyltriphenylphosphonium salts as synthetic equivalents of N-acylimines and new effective α-amidoalkylating agents

1-(N-Acylaminoalkyl)triphenylphosphonium salts 2a-f on reaction with DBU in MeCN are transformed into 1-(N-acylaminoalkyl)amidinium salts 3a-f. Amidinium salts 3d-f with a proton at the β-position undergo slow tautomerization into the corresponding enamides 6d-f. The same 1-(N-acylamino)alkyltriphenylphosphonium salts 2d-f in the presence of Hünig’s base are transformed directly into the corresponding enamides. Phosphonium salts 2, amidinium salts 3, and enamides 6 react with dialkyl malonates in the presence of DBU to give the corresponding amidoalkylation products. α-Amidoalkylation of dialkyl malonates is not observed in the presence of (i-Pr)₂EtN, yet proceeds well under these conditions with more acidic nucleophiles, for example, phthalimide or benzyl mercaptan.     

Synthesis and rearrangement of diphosphorus analogues of amidinium salts

Transient diphosphinocarbocations IIP are generated either by addition of phosphenium salts to the stable [bis(diisopropylamino)phosphino](silyl)carbene or by chloride abstraction from C-phosphino-P-chloro phosphorus ylides. In contrast to their nitrogen anlogues (amidinium salts) IIN, which feature a planar 3-center-4p-electron system, calculations show that IIP should exist as IIPb, in which one phosphorus is planar, while the other remains pyramidal. With small substituents at phosphorus, derivatives of type IIP rearrange by a 1,3-shift of a phosphorus substituent to the other phosphorus center to give C-phosphoniophosphaalkenes. When bulky substituents are present at phosphorus, derivatives IIP undergo ring closure, giving rise to the corresponding cyclic valence isomers IIIP, in which the carbon atom bears a negative charge. Diphosphinocarbocations IIP can be trapped by acetonitrile giving regioselectively the corresponding [2+3] cycloadduct.     

Unusually weak binding interactions in tetrazole-amidine complexes

[reaction: see text] Tetrazoles frequently replace carboxylic acids in pharmaceutical drugs. However, while the binding modes of tetrazolate and carboxylate anions in amidinium complexes turns out to be similar, the association constant of the former is 2-3 orders of magnitude smaller in DMSO. Crystal structures revealed that the N...H-N hydrogen bonds in amidinium tetrazolates are bent (162 degrees and 169 degrees ) and noticeably longer (N...N 2.96 A) than corresponding hydrogen bonds in both amidinium carboxylates and ammonium tetrazolates.     

Supramolecular porphyrin assemblies through amidinium-carboxylate salt bridges and fast intra-ensemble excited energy transfer

Well‐defined supramolecular assemblies of Zn and free‐base porphyrins are constructed through the formation of amidinium–carboxylate salt bridges. A one‐to‐one donor–acceptor pair and a four‐to‐one antenna‐type assembly are investigated. The steady‐state and time‐resolved fluorescence measurements unequivocally showed that efficient singlet–singlet excited energy transfer from the Zn–porphyrin complex to the free‐base porphyrin takes place in these assemblies. Indeed, the observed energy‐transfer rates in both types of assemblies are much faster than those the Förster mechanism would suggest, implying the involvement of an intermolecular through‐bond mechanism.     

Synthesis and alkylation of amidines of the phenanthridine series

A number of 6-aminophenanthridines have been synthesized; upon alkylation, these compounds form amidinium salts. Depending on the structure of the original amidine, the alkylation may proceed at the exocyclic (n-alkyl), phenanthridine (N-aryl), or pyridine [N-(2-pyridyl)] nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1361–1364, October, 1991.     

4,5‐Di­hydro‐3‐methyl‐5‐(4‐methyl­phenyl)‐1H‐pyrazole‐1‐carboxamidinium acetate acetone hemisolvate

The X‐ray structure analysis of the unexpected product of the reaction between 4‐(4‐methyl­phenyl)­but‐3‐en‐2‐one and amino­guanidine revealed the title compound, C₁₂H₁₇N₄⁺·C₂H₃O₂^?·0.5C₃H₆O, consisting of a protonated amidine moiety joined to a substituted pyrazoline ring at the N1 atom. The amidine group is protonated and the positive charge is delocalized over the three C—N bonds in a similar manner to that found in guanidinium salts. The amidinium moiety of the cation is linked to the acetate anions through four N—H?O hydrogen bonds, with N?O distances of 2.749 (4), 2.848 (4), 2.904 (4) and 2.911 (4) Å. The pyrazoline ring adopts a flattened envelope conformation and the substituted phenyl ring is oriented perpendicular to the attached heterocycle. The acetone solvate molecule lies across a twofold rotation axis.     

Probing the effect of the amidinium group and the phenyl ring on the thermodynamics of binding of benzamidinium chloride to trypsin

The effect of the amidinium group and the phenyl ring on the thermodynamics of binding of benzamidinium chloride to the serine proteinase trypsin has been studied using isothermal titration calorimetry. Binding studies with benzylammonium chloride, [small alpha]-methylbenzylammonium chloride and benzamide, compounds structurally related to benzamidinium chloride, showed that hydrogen bonding between the amidinium group and the enzyme is primarily enthalpy-driven. Binding of cyclohexylcarboxamidinium chloride and acetamidinium chloride showed that the hydrophobic binding of the phenyl ring in the S1 pocket is primarily entropy-driven and that a rigid, flat hydrophobic binding site for the inhibitor is favourable. The compounds that have been studied over a range of temperatures exhibit a negative change in heat capacity upon binding and enthalpy-entropy compensation, both characteristic of hydrophobic interactions.     

Amidinium salts: Towards enabling electrochemistry in non-polar media from alkanes to ionic liquids

There is little known about electrochemical behavior in non-polar media due to lack of compatible, hydrophobic salts. In this work, this difficult challenge has been overcome by following a strategy based on designing and synthesizing a novel family of organic salts with highly-delocalized cations and anions. The salts are based on the amidinium cation with highly-delocalized positive charge and long alkyl groups that enable good miscibility in heptane, an archetypical, non-polar media, while being hydrophobic, room-temperature ionic liquids. The electrolyte solutions show ionic conductivities that span the range 10^− 11–10^− 4 S cm^− 1 and electrochemical activity which enable their application as antistatic agents and also as new type of hydrophobic electrolytes in various electrochemical devices.     

7-Amino-5-imino-8(5H)-quinolones, 6-Amino-8-imino-5(8H)-quinolones and 7-Alkyl-4,6-dihydroxy-5,8-quinolinediones as potential antiprotozoal agents

Oxidation of 7-amino-8-hydroxyquinoline-5-sulfonic acid with silver oxide in dimethylformamide and in the presence of arylamines provided a series of 7-amino-5-arylimino-8(5H)-quinolones (VIIIb). Reaction of 8-dialkylamino-5,6-quinolinediones with triethyloxonium tetrafluoborate gave a series of unstable but synthetically useful enol ethers. These reacted with amines to give 6-amino-8-imino-5(8H)-quinolones, isolated and characterized as tetrafluoborate salts (XIa). Proton magnetic resonance studies showed these to be vinylogous amidinium salts, analogous to those previously obtained with 2-amino-1,4-naphthoquinone imines. 4,6-Dihydroxy-5,8-quinolinedione underwent free radical alkylation to give a 7-alkyl-4,6-dihydroxy-5,8-quinolinedione. Evaluation of the new compounds against various Plasmodium species in rodents, birds and mosquitoes revealed no significant antimalarial activity.