Amidine Fragment Research Articles

Synthesis of Non-Aromatic Pyrroles Based on the Reaction of Carbonyl Derivatives of Acetylene with 3,3-Diaminoacrylonitriles.

The reaction of 3,3-diaminoacrylonitriles with DMAD and 1,2-dibenzoylacetylene was studied. It is shown that the direction of the reaction depends on the structure both of acetylene and of diaminoacrylonitrile. In the reaction of DMAD with acrylonitriles bearing a monosubstituted amidine group, 1-substituted 5-amino-2-oxo-pyrrole-3(2H)ylidenes are formed. On the other hand, a similar reaction of acrylonitriles containing the N,N-dialkylamidine group affords 1-NH-5-aminopyrroles. In both cases, pyrroles containing two exocyclic double bonds are formed in high yields. A radically different type of pyrroles containing one exocyclic C=C bond and sp3 hybrid carbon in the cycle is formed in reactions of 3,3-diaminoacrylonitriles with 1,2-diaroylacetylenes. As in reactions with DMAD, the interaction of 3,3-diaminoacrylonitriles with 1,2-dibenzoylacetylene can lead, depending on the structure of the amidine fragment, both to NH- and 1-substituted pyrroles. The formation of the obtained pyrrole derivatives is explained by the proposed mechanisms of the studied reactions.

Convenient Approach to 10‐ and 11‐Membered Azalactams

AbstractA convenient method for the synthesis of 10‐ and 11‐membered azalactams via reductive cleavage of bicyclic systems featuring an amidine fragment was studied. It was found that the ring‐expansion reaction of bicyclic dihydropyrimidones depends on the ring size of saturated fragment, substituents in the pyrimidone core and reaction conditions. A new efficient method for the synthesis of medium ring azalactams by reductive cleavage of quaternary salts of annulated dihydropyrimidones was proposed as well. The obtained medium ring azalactams with a secondary amine function were used in the synthesis of bicyclic heteroaromatic systems.

Bis(alkyl) Sc and Y Complexes Supported by Tri‐ and Tetradentate Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in α‐Olefin and Isoprene Polymerization

AbstractBis(alkyl) complexes [(2,6‐Me2C6H3)NC(tBu)N(C6H4−2‐OMe)]M(CH2C6H4−2‐NMe2)2 (M=Sc (4), Y (5)), [(2‐OMe−C6H4N)2C(tBu)]Y(CH2SiMe3)2(THF)2 (6), supported by N,N,O‐tridentate (4, 5) and N,N,O,O‐tetradentate (6) amidinate ligands were synthesized by the alkane elimination approach reacting tris(alkyl) rare‐earth species M(R)3Xn (R=Me3SiCH2, X=THF, n=2; R=CH2C6H4−2‐NMe2, n=0) with one equivalent of amidine (2,6‐Me2C6H3)N=C(tBu)−NH(C6H4−2‐OMe) (1) or (2‐MeO−C6H4)N=C(tBu)−NH(C6H4−2‐OMe) (2). The reaction of amidine 2 with equimolar amount of Y(CH2C6H4−2‐NMe2)3 in toluene unexpectedly results in the addition of N,N‐dimethylaminobenzyl group to C=N bond of one amidinate fragment, ligand disproportionation and the formation of novel bis(amide)amidinate complex [(2‐OMe−C6H4N)2C(tBu)CH2C6H4−2‐NMe2]Y[(2‐OMe−C6H4N)2C(tBu)] (7). Complexes 4–6 were evaluated as catalysts for α‐olefins and isoprene polymerization.

Influence of the amidine fragment on spectral properties of xanthene dyes

We synthesized a series of new xanthene dyes containing dimethylamidine group and investigated the influence of this fragment in the composition of xanthene dyes on their spectral characteristics. The amidine fragment mainly affects the absorption and emission maxima due to the π-conjugation of this substituent with xanthene moiety which leads to red shifts by 41–90 nm in the spectra. The most long-wavelength dye, derivative with 1,3,3-trimethyl-3H-indolium, have an absorption maximum at 661 nm, and an emission at 701 nm in methanol. The addition of a large excess of trifluoroacetic acid to the solution of this dye lead to a hypsochromic shift of absorption maximum to 585 nm, which is associated with the protonation of the amidine substituent. The absorption spectra of the corresponding compounds without amidine fragment after addition of trifluoroacetic acid remain almost identical, which proved the π-conjugation of the amidine fragment, but not only oxygen of xanthene moiety.

Different pathways in the reaction of N-(tosylmethyl)-substituted ureas, thioureas, and N′-cyanoguanidines with sodium cyanide. Synthesis of α-ureido nitriles, α-ureido amides, and hydantoin imino derivatives

Reaction of N-(tosylmethyl)-substituted ureas, thioureas, and N′-cyanoguanidines, prepared by condensation of the corresponding amides with various aldehydes and p-toluenesulfinic acid, with NaCN has been studied. The outcome of the reaction is strongly dependent on the amide nature and reaction conditions. Generally, N-(tosylmethyl)ureas afford α-ureido nitriles, N-(tosylmethyl)-N′-cyanoguanidines transform into 4-amino-2-cyanimino-1,5-dihydro-2H-imidazoles, and N-(tosylmethyl)thioureas give complex mixtures of various imidazole derivatives. The prepared α-ureido nitriles are selectively converted into the corresponding α-ureido amides by treatment with conc. HCl at room temperature. Under basic conditions, α-ureido nitriles cyclize into 4-amino-1,5-dihydro-2H-imidazole-2-ones. Treatment of 4-amino-2-cyanimino-1,5-dihydro-2H-imidazoles with conc. HCl at room temperature lead to hydrolysis of both the amidine fragment and cyano group to give hydrochlorides of 2-(carbamoylimino)imidazolidin-4-ones which are easily decarbamoylated to form hydrochlorides of 2-iminoimidazolidin-4-ones. Structure of the prepared imidazoles and some mechanistic aspects of cyanide-anion amidoalkylation with N-(tosylmethyl)ureas are discussed based on DFT calculations.

Synthesis of New Bulky Bis(amidine) with the Conformationally Rigid meta-Phenylene Bridge and Its Dilithium Derivative [1,3-C6H4{NC(Ph)N(2,6-iso-Pr2C6H3)}2]Li2(TMEDA)2

The reaction of 2,6-diisopropylaniline with m-phenylenedibenzimidoyl chloride 1,3-C6H4{N=C(Ph)Cl}2 in the presence of triethylamine in a toluene solution affords bis(amidine) 1,3-C6H4{NC(Ph)NH(2,6-iso-Pr2C6H3)}2 (H2L) in which two amidinate fragments are bound by the conformationally rigid m-phenylene linker. The metallation of bis(amidine) by n-butyllithium in the presence of tetramethylethylenediamine (TMEDA) occurs readily in a tetrahydrofuran solution at –70°С to form the corresponding lithium amidinate complex 1,3-C6H4{NC(Ph)N(2,6-iso-Pr2C6H3)}2Li2(TMEDA)2 (I). The X-ray structure analysis shows that complex I is monomeric (CIF file CCDC no. 1873201). Each amidinate fragment NCN is bound to one lithium atom via the κ2-N,N chelating mode.

AN EFFICIENT METHOD FOR THE SYNTHESIS OF 2-THIAZOLEACETIC ACID N -SULFONYL AMIDINES

A three-step method was designed and developed on the basis of retrosynthetic analysis for the synthesis of hybrid molecules containing a thiazole ring and an N-sulfonyl amidine fragment, connected by a methylene linker. The mechanism of the last step involves the formation of intermediate 1,2,3,4-thiatriazoles and their transformation into the final products as a result of the elimination of molecular nitrogen and sulfur.

Alternative (κ1-N:η6-arene vs.κ2-N,N) coordination of a sterically demanding amidinate ligand: are size and electronic structure of the Ln ion decisive factors?

The amine elimination reaction of equimolar amounts of ansa-bis(amidine) C6H4-1,2-{NC(tBu)NH(2,6-iPr2C6H3)}2 (L1H) and [(Me3Si)2N]2Yb(THF)2 affords a bis(amidinate) YbII complex [C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}2]Yb(THF) (1) in 68% yield. Complex 1 features a rather rare η1-amido:η6-arene coordination of both amidinate fragments to the YbII ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 1 by I2 regardless of the molar ratio of reagents (2 : 1 or 1 : 1) leads to the formation of the YbIII species [{(2,6-iPr2C6H3)[double bond, length as m-dash]NC(tBu)NH}-C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}]YbI2(THF)2 (2) in which only one amidinate fragment is coordinated to the ytterbium ion in κ2-N,N'-chelating coordination mode, while the second NCN fragment is protonated in the course of the reaction and is not bound to the metal ion. The outcome of the salt metathesis reaction of LaCl3 with lithium amidinates [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)}2Li2] (R = Me, iPr) is proven to be strongly affected by the substituent 2,6-R2C6H3 on the amidinate nitrogens. When R = iPr, the salt metathesis reaction occurs smoothly and results in the formation of an ate-chloro-amidinate complex [C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}2]La(μ2-Cl)Li(THF)(μ2-Cl)2Li(THF)2 (3) in which the LaIII ion is coordinated by both amidinate fragments in a "classic"κ2-N,N'-chelating fashion. In the case of R = Me, the reaction requires prolonged heating for completion. Moreover, the salt metathesis reaction is accompanied by the fragmentation of the ligand and affords a trinuclear chloro-amidinate complex [C6H4-1,2-{NC(tBu)N(2,6-Me2C6H3)}2]La{[(tBu)C(N-2,6-Me2C6H3)2]La(THF)}2(μ2-Cl)4(μ3-Cl)2 (4) containing one dianionic ansa-bis(amidinate) and two monoanionic [(tBu)C(N-2,6-Me2C6H3)2] amidinate fragments. DFT calculations are conducted to determine the factor that governs this change in coordination mode and, in particular, the effect of the metal oxidation state.

An efficient method for the synthesis of 2-thiazoleacetic acid N-sulfonyl amidines

A three-step method was designed and developed on the basis of retrosynthetic analysis for the synthesis of hybrid molecules containing a thiazole ring and an N-sulfonyl amidine fragment, connected by a methylene linker. The mechanism of the last step involves the formation of intermediate 1,2,3,4-thiatriazoles and their transformation into the final products as a result of the elimination of molecular nitrogen and sulfur.

Asymmetric Cationic Phosphines: Synthesis, Coordination Chemistry, and Reactivity.

A single enantiomer of a cationic phosphine, [α-CgPAmHMe]BF4, containing two asymmetric subunits, an amidinium group (AmH) and a phosphacycle (CgP), has been synthesized and isolated. The ligand, which is of an extremely rare class, has been coordinated to Rh(I), Au(I), Ag(I), Cu(I), and Pt(0) to enable an empirical assessment of its donor properties. Analysis of the IR stretching frequency of the carbonyl ligand in trans-[Rh(α-CgPAmHMe)2(CO)Cl](BF4)2 coupled with metric data obtained from crystal-state molecular structures of pertinent complexes confirms the strong π-accepting properties of the ligand. The integrity of the N-P bond is compromised upon addition of base to both [Cu(α-CgPAmHMe)Cl]BF4 and [Ag(α-CgPAmHMe)(OTf)]BF4 where, instead of isolating anticipated chelating and/or bridging forms of the neutral, deprotonated α-CgPAmMe derivative, decomposition products were obtained containing a phosphacycle fragment and/or amidine ligands. The fragility of the N-P bond is also evident in uncoordinated [α-CgPAmHMe]BF4 as treatment with aqueous base releases a neutral amidine fragment and generates the P-P dimer [α,α-CgPP(O)Cg]. These fortuitous observations show [α-CgPAmHMe]BF4 to be a very useful synthon for the potential production of novel asymmetric phosphines.

СПЕКТОРОФОТОМЕТРИЧНІ ТА ПРОТОЛІТИЧНІ ВЛАСТИВОСТІ КОНДЕНСОВАНИХ ЦІАНОПІРИДИНІВ

Development of new optical probes is a promising trend that has been actively implemented in recent years. A rational design of the probes should consider a number of parameters that contribute to the ability of the probe to exhibit highly selective optical response to the analyte. The obvious criteria are the chemical stability and reactivity of the probe, its photostability and the possibility of its reusable application. In this work, new probes based on fused benzothiazoles with different heterocyclic substituents were studied. The spectrophotometric characteristics of compounds in dimethylsulfoxide, acetonitrile and ethanol solutions were obtained. The probes exhibited the absorption in the near UV region and the blue part of the visible spectrum. Absorption spectra of the molecules are characterized by broad band with absorption maximum around 391–400 nm. The selected compounds demonstrated a slight positive solvatochromism. The blue shift of absorption maxima is due to the formation of protonated form of the probe in the presence of hydrochloric acid. Further, in basic conditions, the absorbance maxima of the probes are localized at longer wavelength (Δλ around 80 nm). Reversibility of compounds in the reactions of deprotonation-protonation was studied. Formal protonation constants of compounds (lgKpf) in water-organic solutions were calculated using the UV-Vis spectrophotometry titration method. Protonation constants of probes are in the range: lgKpf = 2.67–4.95. The obtained values of the protonation constants are in good agreement with the data calculated using the software ACD Labs. The presence of the amidine fragment in the structure of the chromophore core leads to an increase in its basicity, with respect to heterocyclic substituents. It was shown that the presence of a substituent more basic than benzothiazole leads to the destruction of the probe in solution with a pH 11. It occurs due to the opening of the iminopyridine cycle into its synthetic precursor. Based on the results, 2-(1,3-benzothiazol-2-yl)-3-(3-hydroxypropyl)-1-imino-1H-pyrido[2,1-b][1,3]benzothiazole-4-carbonitrile was selected for further use as sensitive pH probe.

Synthesis of 5-methylsulfonylpyrimidines and their fused derivatives

The interaction of available 2-methylsulfonyl-3-ethoxyacrylonitrile with amidine, their analogs, and aminoazoles containing amidine fragment, yielding earlier unknown 4-amino-5-methylsulfonylpyrimidines and their fused derivatives has been studied.

Conversion of a monodentate amidinate-germylene ligand into chelating imine-germanate ligands (on mononuclear manganese complexes).

The unprecedented transformation of a terminal two-electron-donor amidinate-germylene ligand into a chelating three-electron-donor κ(2)-N,Ge-imine-germanate ligand has been achieved by treating the manganese amidinate-germylene complex [MnBr{Ge((i)Pr2bzam)(t)Bu}(CO)4] (1; (i)Pr2bzam = N,N'-bis(isopropyl)benzamidinate) with LiMe or Ag[BF4]. In these reactions, which afford [Mn{κ(2)Ge,N-GeMe((i)Pr2bzam)(t)Bu}(CO)4] (2) and [Mn{κ(2)Ge,N-GeF((i)Pr2bzam)(t)Bu}(CO)4] (3), respectively, the anionic nucleophile, Me(-) or F(-), ends on the Ge atom while an arm of the amidinate fragment migrates from the Ge atom to the Mn atom. In contrast, the reaction of 1 with AgOTf (OTf = triflate) leads to [Mn(OTf){Ge((i)Pr2bzam)(t)Bu}(CO)4] (4), which maintains intact the amidinate-germylene ligand. Complex 4 is very moisture-sensitive, leading to [Mn2{μ-κ(4)Ge2,O2-Ge2(t)Bu2(OH)2O}(CO)8] (5) and [(i)Pr2bzamH2]OTf (6) in wet solvents. In 5, a novel digermanate(II) ligand, [(t)Bu(OH)GeOGe(OH)(t)Bu](2-), doubly bridges two Mn(CO)4 units. The structures of 1-6 have been characterized by spectroscopic (IR, NMR) and single-crystal X-ray diffraction methods.

Ring opening and bidentate coordination of amidinate germylenes and silylenes on carbonyl dicobalt complexes: the importance of a slight difference in ligand volume.

The reactions of [Co2 (CO)8 ] with one equiv of the benzamidinate (R2 bzam) group-14 tetrylenes [M(R2 bzam)(HMDS)] (HMDS=N(SiMe3 )2 ; 1: M=Ge, R=iPr; 2: M=Si, R=tBu; 3: M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co2 {κ(1) MM(R2 bzam)(HMDS)}(CO)7 ] (4: M=Ge, R=iPr; 5: M=Si, R=tBu; 6: M=Ge, R=tBu), which contain a terminal κ(1) M-tetrylene ligand. Whereas the Co2 Si and Co2 Ge tert-butyl derivatives 5 and 6 are stable at 20 °C, the Co2 Ge isopropyl derivative 4 evolved to the ligand-bridged derivative [Co2 {μ-κ(2) Ge,N-Ge(iPr2 bzam)(HMDS)}(μ-CO)(CO)5 ] (7), in which the Ge atom spans the CoCo bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate-tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group-14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate NR groups. The disubstituted derivatives [Co2 {κ(1) MM(R2 bzam)(HMDS)}2 (CO)6 ] (8: M=Ge, R=iPr; 9: M=Si, R=tBu; 10: M=Ge, R=tBu), which contain two terminal κ(1) M-tetrylene ligands, have been prepared by treating [Co2 (CO)8 ] with two equiv of 1-3 at 20 °C. The IR spectra of 8-10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3-diarylimidazol-2-ylidenes), whereas that of silylene 2 is even higher.

Benzonitrile Insertion into Silylarylamides – ansa‐Bis(benzamidinate) Ligand Systems with Rigid o‐ and m‐Phenylene Linkers in the Synthesis of Lithium and Rare Earth Complexes

AbstractThe reactions of the lithium silylarylamides [1,2‐C6H4(NSiMe3)2Li2]2 and [1,3‐C6H4(NSiMe3)2Li2] with two equivalents of PhCN [tetrahydrofuran (thf), room temp.] is an efficient synthetic approach to the ansa‐bis(amidinate) ligand systems [1,2‐C6H4{NC(Ph)NSiMe3}2Li2(thf)]2 and [1,3‐C6H4{NC(Ph)NSiMe3}2Li2(thf)2]2, which were isolated in 54 and 60 % yields, respectively. However, lithium silylarylamide [2,6‐C5H3N(NSiMe3)2Li2] containing a pyridine fragment does not undergo PhCN insertion even at elevated temperatures (thf, toluene), and the reaction affords the silylarylamido complex [2,6‐C5H3N{NSiMe3}2Li2]3·(C6H5CN)4, which contains a coordinated benzonitrile molecule. The different reactivity of the compounds correlates with the changes in the molecular orbital energies estimated by DFT calculations. The salt metathesis reaction of anhydrous YCl3 with lithium amidinate [1,2‐C6H4{NC(Ph)NSiMe3}2Li2(thf)]2 in 2:1 molar ratio (thf, 20 °C) afforded a neutral bis(amidinate) chloro yttrium complex [1,2‐C6H4{NC(Ph)NSiMe3}2]YCl(thf)2 in 80 % yield. With NdCl3, the analogous reaction resulted in a trinuclear neodymium chloro ate complex with a rather unusual μ‐bridging lateral coordination of the amidinate fragment [1,2‐C6H4{NC(Ph)NSiMe3}2Nd(thf)(μ‐Cl)(1,2‐C6H4{NC(Ph)NSiMe3}2Nd{μ‐Cl}2)][Li(thf)2].

Remarkably strong polarization of amidine fragment in the crystals of 1-imino-1H-isoindol-3-amine

Results of the X-ray diffraction studies of 1-imino-1H-isoindol-3-amine and its derivatives reveal unusual distribution of bond lengths within the NH2–C=N amidine fragment in the considered crystals. In the crystal phase, single C–N bond is shorter or at most has the same length as double C=N bond, while in isolated molecules both these bonds have expected lengths, according to the calculations by MP2/6-311G(d,p) and MP2/cc-pvtz methods. It is demonstrated that so unusually strong polarization of the amidine fragment is induced by polar environment in solid state. This effect stabilizes the amino-imino tautomer of 1-imino-1H-isoindol-3-amine, which becomes more stable than the diimino tautomer possessing the lowest energy in the gas phase.

2-[(1-{[3-(dimethylazaniumyl)propyl]methylamino}ethylidene)azaniumyl]nonahydro-closo-decaborate dimethyl sulfoxide disolvate

The title compound, 2-B10H9NH=C(CH3)N(CH3)CH2CH2CH2N(CH3)2H·2C2H6OS or C8H29B10N3·2C2H6OS, is zwitterionic with the negative charge localized on the deca­borate cage and the positive charge on the terminal ammonium group. Two mol­ecules of dimethyl sulfoxide (DMSO) and one mol­ecule of the title compound constitute the asymmetric unit. One DMSO mol­ecule is disordered [ratio 0.739 (3):0.261 (3)]. The bonds and angles within the deca­borate cage are within the normal ranges. The amidine fragment of the ligand, which is expected to be planar, is significantly distorted from planarity as exemplified by four torsion angles [B—N—C—C = 8.4 (3), H—N—C—N = 5(2), N—C—N—C = 7.3 (3) and C—C—N—C = 14.8 (3)°] found within this portion of the mol­ecule. The crystal packing consists of head-to-tail-arranged dimers of the title mol­ecule held together by four mol­ecules of DMSO which are attached via strong N—H⋯O and weak C—H⋯O hydrogen bonds.

High-resolution crystal structure of the intramolecular d(TpA) thymine-adenine photoadduct and its mechanistic implications

A high-resolution crystal structure is reported for d(TpA)*, the intramolecular thymine–adenine photoadduct that is produced by direct ultraviolet excitation of the dinucleoside monophosphate d(TpA). It confirms the presence of a central 1,3-diazacyclooctatriene ring linking the remnants of the T and A bases, as previously deduced from heteronuclear NMR measurements by Zhao et al. (The structure of d(TpA)*, the major photoproduct of thymidylyl-(3′-5′)-deoxyadenosine. Nucleic Acids Res., 1996, 24, 1554–1560). Within the crystal, the d(TpA)* molecules exist as zwitterions with a protonated amidine fragment of the eight-membered ring neutralizing the charge of the internucleotide phosphate monoanion. The absolute configuration at the original thymine C5 and C6 atoms is determined as 5S,6R. This is consistent with d(TpA)* arising by valence isomerization of a precursor cyclobutane photoproduct with cis–syn stereochemistry that is generated by [2 + 2] photoaddition of the thymine 5,6-double bond across the C6 and C5 positions of adenine. This mode of photoaddition should be favoured by the stacked conformation of adjacent T and A bases in B-form DNA. It is probable that the primary photoreaction is mechanistically analogous to pyrimidine dimerization despite having a much lower quantum yield.

2-Amino-5,5-bis(hydroxymethyl)-1,3-thiazol-4(5H)-one and its spirodioxane compounds in the Mannich reaction

It was found that the aminomethylation of 2-amino-5,5-bis(hydroxymethyl)-1,3-thiazol-4(5H)-one and its spiro analogs using primary amines is accompanied by cyclization at the amidine fragment of the molecule with annelation of a tetrahydrotriazine ring. When using secondary amines the aminomethylation occurs at the exocyclic nitrogen atom.

Synthesis of 3(5)-Amino-4-acylamino-5(3)-arylsulfanylpyrazoles and Their Fused Derivatives on the Basis of N-(2,2,2-Trichloro-1-hydroxyethyl)benzamides

Addition products of carboxylic acid amides and trichloroacetaldehyde are readily converted into 3-arylsulfanyl-2-acylamino-3-chloroacrylonitriles which react with hydrazine hydrate to afford 3(5)-amino-5(3)-arylsulfanyl-4-acylaminopyrazoles. The presence of an amidine fragment in the latter makes them capable of undergoing cyclocondensations with β-dicarbonyl compounds and ethyl cyanoacetate.