Rapid synthesis of optically active poly(amide-imide)s by direct polycondensation of aromatic dicarboxylic acid with aromatic diamines

4,4^′-(Hexafluoroisopropylidene)-N,N^′-bis(phthaloyl-l-leucine-p-amidobenzoic acid) (2) was prepared from the reaction of 4,4^′-(hexafluoroisopropylidene)-N,N^′-bis(phthaloyl-l-leucine) diacid chloride with p-aminobenzoic acid. The direct polycondensation reaction of monomer (2) with p-phenylenediamine (2a), 4,4^′-diaminodiphenylsulfone (2b), 2,4-diaminotoluene (2c), 2,6-diaminopyridine (2d), m-phenylene diamine (2e), benzidine (2f), 4,4^′-diaminodiphenylether (2g) and 4,4^′-diaminodiphenyl methane (2h) was carried out in a medium consisting of triphenyl phosphite, N-methyl-2-pyrolidone, pyridine, and calcium chloride. The homogeneous mixture was heated at 220 °C for 1 min under nitrogen. The resulting poly(amide-imide)s (PAIs) having inherent viscosities 0.27-0.78 dl/g were obtained in high yield and are optically active and thermally stable. All of the above polymers were fully characterized by IR spectroscopy, elemental analyses and specific rotation. Some structural characterization and physical properties of this new optically active PAIs are reported.     

Novel optically active poly(amide-imide)s from N,N-(4,4-carbonyldiphthaloyl)-bis-l-phenylalanine diacid chloride and aromatic diamines by microwave irradiation

3,3^′,4,4^′-benzophenonetetracarboxylic dianhydride (4,4^′-carbonyldiphthalic anhydride) (1) was reacted with l-phenylalanine (2) in a mixture of acetic acid and pyridine (3:2) and the resulting imide-acid [N,N^′-(4,4^′-carbonyldiphthaloyl)-bis-l-phenylalanine diacid] (4) was obtained in high yield. The compound (4) was converted to the N,N^′-(4,4^′-carbonyldiphthaloyl)-bis-l-phenylalanine diacid chloride (5) by reaction with thionyl chloride. A new facile and rapid polycondensation reaction of this diacid chloride (5) with several aromatic diamines such as 4,4^′-diaminodiphenyl methane (6a), 2,4-diaminotoluene (6b), 4,4^′-sulfonyldianiline (6c), p-phenylenediamine (6d), 4,4^′-diaminodiphenylether (6e), m-phenylenediamine (6f), benzidine (6g) and 2,6-diaminopyridine (6h) was developed by using a domestic microwave oven in the presence of a small amount of a polar organic medium such as o-cresol. The polymerization reactions proceeded rapidly, compared with the conventional solution polycondensation, and was completed within 7 min, producing a series of optically active poly(amide-imide)s with high yield and inherent viscosity of 0.22-0.52 dl/g. All of the above polymers were fully characterized by IR, elemental analyses and specific rotation. Some structural characterization and physical properties of this optically active poly(amide-imide)s are reported.     

An approach to the synthesis of chemically modified bisazocalix[4]arenes and their extraction properties

Bisazocalix[4]arenes [N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)benzene (1), N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)biphenyl (2) and N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)-2,2′-dinitro biphenyl (3)] have been synthesized from 25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene by diazocoupling with the corresponding aromatic diamines (p-phenylenediamine, 4,4′-diamino biphenyl and 4,4′-diamino-2,2′-dinitrobiphenyl). Extraction studies of bisazocalix[4]arenes 1, 2, and 3 show no difference in their extraction behavior and selectivity, whereas azocalix[4]arenes are a poor extractant for heavy metal cations. The absorption spectra of the prepared bisazocalix[4]arenes are discussed, both the effect of varying pH and solvent upon the absorption ability of bisazocalix[4]arenes.     

Diisocyanate route as a convenient method for the preparation of novel optically active poly(amide-imide)s based on N-trimellitylimido-S-valine

A new class of optically active poly(amide-imide)s based on an α-amino acid was synthesized via direct polycondensation reaction of different diisocyanates with a chiral diacid monomer. The step-growth polymerization reactions of N-trimellitylimido-S-valine (TISV) (1) with 4,4′-methylene-bis(4-phenylisocyanate) (MDI) (2) was performed under microwave irradiation, as well as solution polymerization under graduate heating and reflux conditions. The optimized polymerization conditions for each method were performed with tolylene-2,4-diisocyanate (TDI) (3), hexamethylene diisocyanate (HDI) (4), and isophorone diisocyanate (IPDI) (5) to produce optically active poly(amide-imide)s via diisocyanate route. The resulting polymers have inherent viscosities in the range of 0.02-1.10 dL/g. Decomposition temperatures for 5% weight loss (T₅) occurred above 300 °C (by TGA) in nitrogen atmospheres. These polymers are optically active, thermally stable and soluble in amide-type solvents. Some structural characterization and physical properties of this new optically active poly(amide-imide)s are reported.     

Further studies of tetrakis(N,N′-dialkylbenzamidinato)diruthenium(III) chloro and alkynyl compounds: molecular engineering of metallayne monomers

Three diruthenium(III) compounds Ru₂(L)₄Cl₂, where L is mMeODMBA (N,N′-dimethyl-3-methoxybenzamidinate, 1a), DiMeODMBA (N,N′-dimethyl-3,5-dimethoxy benzamidinate, 1b), or DEBA (N,N′-diethylbenzamidinate, 1c), were prepared from the reactions between Ru₂(OAc)₄Cl and respective HL under reflux conditions. Metathesis reactions between 1 and LiC₂Y resulted in bis-alkynyl derivatives Ru₂(L)₄(C₂Y)₂ [Y=Ph (2), SiMe₃ (3), SiⁱPr₃ (4) and C₂SiMe₃ (5)]. The parent compounds 1 are paramagnetic (S=1), while bis-alkynyl derivatives 2-5 are diamagnetic and display well-solved ¹H- and ¹³C-NMR spectra. Molecular structures of compounds 1b, 1c, 2c, 3c and 4b were established through single crystal X-ray diffraction studies, which revealed RuRu bond lengths of ca. 2.32 Å for parent compounds 1 and 2.45 Å for bis-alkynyl derivatives. Cyclic voltammograms of all compounds feature three one-electron couples: an oxidation and two reductions, while the reversibility of observed couples depends on the nature of axial ligands.     

Synthesis and structural characterization of novel ruthenium(II) complexes featuring an N,N,O-scorpionate ligand: A versatile synthetic precursor for open-face scorpionatoruthenium(II) complexes

The syntheses and characterization of novel ruthenium(II) complexes containing bis(3,5-dimethylpyrazol-1-yl)acetato (bdmpza), a new class of scorpionate ligands, are reported herein. [RuCl(bdmpza)(η⁴-1,5-cyclooctadiene)] (1) was found to be a versatile precursor to synthesize a wide range of new ruthenium(II) complexes with the bdmpza ligand. The treatment of 1 with pyridine (py), diphenylphosphinoethane (dppe), 2,2′-bipyridyl (bpy), 1,10-phenanethroline (phen), or bispicolylamine (Hbpica) in refluxing N,N-dimethylformamide resulted in displacement of the 1,5-cyclooctadiene ligand to afford [RuCl(bdmpza)(py)₂] (2), [RuCl(bdmpza)(dppe)] (3), [RuCl(bdmpza)(bpy)] (4), [RuCl(bdmpza)(phen)] (5), and [Ru(bdmpza)(Hbpica)]Cl (6Cl) in good yields, respectively. The structures of 1–4, and 6 were determined by X-ray structure analyses.     

Acyclic tertiary diamines and 1,4,7,10-tetraazacyclododecane with fluorine-containing β-diketones: Leading to low melting ionic adducts

N,N,N′,N′-Tetramethylmethanediamine (1a), N,N,N′,N′-tetramethylethanediamine (1b), N,N,N′,N′-tetramethyl-1,3-propanediamine (1c), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (1d) were reacted at 25 °C with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2a), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (2b), 2-thenoyltrifluoroacetone (2c), and 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (2d) to form the ionic adducts 3-18. 1,4,7,10-Tetraazacyclododecane (1e) reacted at 25 °C with β-diketones (2a-d) and 1,1,1-trifluoro-2,4-pentanedione (2e) to give ionic solids 19-23 in good yields. Some of the products are liquid at 25 °C and are thermally stable over long liquid ranges as determined by thermal gravimetric analyses. Single-crystal X-ray structure determinations show that compounds 9 and 21 crystallize in the monoclinic space groups P2(1)/c and P2(1)/n, respectively. All the new compounds were characterized by ¹H, ¹⁹F and ¹³C NMR, electrospray MS and/or elemental analyses.     

Microwave-promoted synthesis of new optically active poly(ester-imide)s derived from N,N-(pyromellitoyl)-bis-l-leucine diacid chloride and aromatic diols

Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) was reacted with l-leucine (2) in a mixture of acetic acid and pyridine (3:2) and the resulting imide-acid [N,N^′-(pyromellitoyl)-bis-l-leucine diacid] (4) was obtained in quantitative yield. The compound (4) was converted to the N,N^′-(pyromellitoyl)-bis-l-leucine diacid chloride (5) by reaction with thionyl chloride. A new facile and rapid polycondensation reaction of this diacid chloride (5) with several aromatic diols such as phenol phthalein (6a), bisphenol-A (6b), 4,4^′-hydroquinone (6c), 1,8-dihydroxyanthraquinone (6d), 1,5-dihydroxy naphthalene (6e), 4,4-dihydroxy biphenyl (6f), and 2,4-dihydroxyacetophenone (6g) was developed by using a domestic microwave oven in the presence of a small amount of a polar organic medium such as o-cresol. The polymerization reactions proceeded rapidly and are completed within 10 min, producing a series of optically active poly(ester-imide)s (PEIs) with good yield and moderate inherent viscosity of 0.10-0.27 dl/g. All of the above polymers were fully characterized by IR, elemental analyses and specific rotation. Some structural characterization and physical properties of these optically active PEIs are reported.     

Synthesis of N,N′-bis and N,N,N′,N′-tetra-[(3,5-di-substituted-1-pyrazolyl)methyl]para-phenylenediamines: new candidate ligands for metal complex wires

A series of tridentate ligands N,N-bis-[(di-substituted-1-pyrazolyl)methyl]arylamines 2-3a,b and benzylamine 4a,b, tetradentate N,N′-bis-[(di-substituted-1-pyrazolyl)methyl]para-phenylenediamines 7a,b and hexadentate N,N,N′,N′-tetra-[(di-substituted-1-pyrazolyl)methyl]para-phenylenediamines 8a,b has been prepared in good yield by condensation of arylamines, benzylamine or para-phenylenediamine with N-hydroxymethyl disubstituted pyrazoles 1a,b. The synthesis and characterisation of these various polydentate ligands are described.     

Synthesis and characterisation of six Fe(II or III), Co(II) or Zr(IV) complexes containing the ligand [CH(SiMe2R)P(Ph)2NSiMe3] (R = Me, NEt2) and of [Co{N(SiMe3)C(Ph)C(H)P(Ph)2NSiMe3}2]

The C,N-(trimethylsilyliminodiphenylphosphoranyl)silylmethylmetal complexes [Fe(L)₂] (3), [Co(L)₂] (4), [ZrCl₃(L)]·0.83CH₂Cl₂ (5), [Fe(L)₃] (6), [Fe(L′)₂] (7) and [Co(L′)₂] (8) have been prepared from the lithium compound Li[CH(SiMe₂R)P(Ph)₂NSiMe₃] [1a, (R = Me) {≡ Li(L)}; 1b, (R = NEt₂) {≡ Li(L′)}] and the appropriate metal chloride (or for 7, FeCl₃). From Li[N(SiMe₃)C(Ph)C(H)P(Ph)₂NSiMe₃] [≡ Li(L″)] (2), prepared in situ from Li(L) (1a) and PhCN, and CoCl₂ there was obtained bis(3-trimethylsilylimino- diphenylphosphoranyl-2-phenyl-N-trimethylsilyl-1-azaallyl-N,N′)cobalt(II) (9). These crystalline complexes 3-9 were characterised by their mass spectra, microanalyses, high spin magnetic moments (not 5) and for 5 multinuclear NMR solution spectra. The X-ray structure of 3 showed it to be a pseudotetrahedral bis(chelate), the iron atom at the spiro junction.     

Complexes derived from the copper(II)/succinamic acid/N,N′,N″-chelate tertiary reaction systems: Synthesis,structural and spectroscopic studies

The use of succinamic acid (H₂sucm) in Cu^II/N,N′,N″-donor [2,2′:6′,2″-terpyridine (terpy), 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine (dmbppy)] reaction mixtures yielded compounds [Cu(Hsucm)(terpy)]_n(ClO₄)_n (1), [Cu(Hsucm)(terpy)(MeOH)](ClO₄) (2), [Cu₂(Hsucm)₂(terpy)₂](ClO₄)₂ (3), [Cu(ClO₄)₂(terpy)(MeOH)] (4), [Cu(Hsucm)(dmbppy)]_n(NO₃)_n·3nH₂O (5^.3nH₂O), and [CuCl₂(dmbppy)]·H₂O (6·H₂O). The succinamate(−1) ligand exists in four different coordination modes in the structures of 1–3 and 5, i.e., the μ₂-κO:κO′:κO″ in 1 and 5 which involves asymmetric chelating coordination of the carboxylato group and ligation of the amide O-atom leading to 1D coordination polymers, the μ₂-κ²O:κO′ in 3 which involves asymmetric chelating and bridging coordination of the carboxylato group, and the asymmetric chelating mode in 2. The primary amide group, either coordinated in 1 and 5, or uncoordinated in 2 and 3, participate in hydrogen bonding interactions, leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of complex 5·3nH₂O was monitored by TG/DTG and DTA measurements.     

Novel thermally stable and chiral poly(amide-imide)s bearing from N,N′-(4,4′-diphthaloyl)-bis-l-isoleucine diacid: Synthesis and characterization

Novel optically active aromatic poly(amide-imide)s (PAIs) were prepared from newly synthesized N,N′-(4,4′-diphthaloyl)-bis-l-isoleucine diacid (3) via polycondensation with various diamines. The diacid was synthesized by the condensation reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (1) with l-isoleucine (2) in a mixture of acetic acid and pyridine (3:2 v/v). All the polymers were obtained in quantitative yields with inherent viscosities of 0.20-0.43 dL g⁻¹. All the polymers were highly organosoluble in solvents like N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran, γ-butyrolactone, cyclohexanone and chloroform at room temperature or upon heating. These poly(amide-imide)s had glass transition temperatures between 198 and 231 °C, and their 10% weight-loss temperatures were ranging from 368 to 398 °C and 353 to 375 °C under nitrogen and air, respectively. The polyimide films had tensile strengths in the range of 63-88 MPa and tensile moduli in the range of 0.8-1.4 GPa. These poly(amide-imide)s possessed chiral properties and the specific rotations were in the range of −3.10° to −72.92°.     

Reactivity of M(en)Cl2 (M = Pd/Pt,en = 1,2-diaminoethane) with N,N′-bis(salicylidene)-p-phenylenediamine: Binding with hexafluorobenzene

Schiff base N,N′-bis(salicylidene)-p-phenylenediamine (LH₂) complexed with Pt(en)Cl₂ and Pd(en)Cl₂ provided [Pt(en)L]₂ · 4PF₆ (1) and Pd(Salen) (2) (Salen = N,N′-bis(salicylidene)-ethylenediamine), respectively, which were characterized by their elemental analysis, spectroscopic data and X-ray data. A solid complex obtained by the reaction of hexafluorobenzene (hfb) with the representative complex 1 has been isolated and characterized as 3 (1 · hfb) using UV–Vis, NMR (¹H, ¹³C and ¹⁹F) data. A solid complex of hfb with a reported Zn-cyclophane 4 has also been prepared and characterized 5 (4 · hfb) for comparison with complex 3. The association of hfb with 1 and 4 has also been monitored using UV–Vis and luminescence data.     

Microwave-assisted rapid synthesis of novel optically active poly(amide-imide)s containing hydantoins and thiohydantoins in main chain

Rapid and highly efficient synthesis of novel optically active poly(amide-imide)s (PAIs) 6(a-f) was achieved using microwave irradiation. These were made from the polycondensation reactions of 4,4^′-carbonyl-bis(phthaloyl-l-alanine) diacid chloride [N,N^′-(4,4^′-carbonyldiphthaloyl)] bisalanine diacid chloride 5 with six different derivatives of hydantoin and thiohydantoin compounds 4(a-f) in the presence of a small amount of a nonpolar organic medium that acts as a primary microwave absorber. Hydantoin and thiohydantoin derivatives 4(a-e) were synthesis from the reactions between benzil or benzil derivatives 3(a-e) with urea and thiourea. 5,5-Dimethylhydantoin 4f was synthesis from the reactions between acetone cyanohydrin 3f and ammonium carbonate. The polycondensation proceeded rapidly, and was completed within 10 min giving a series of PAIs with an inherent viscosity about 0.25-0.45 dL/g. The resulting PAIs 6(a-f) were obtained in a high yield and were optically active and thermally stable. All of the above compounds were fully characterized by means of Fourier transform infrared spectroscopy, elemental analyses, inherent viscosity (η_inh), solubility tests and specific rotation. Thermal properties of the PAIs 6(a-f) were investigated using thermal gravimetric analysis.     

An improved synthesis of 2-(1,2,4-thiadiazol-5-yl)pyridine by interception of an intermediate involved in a competing cyclisation reaction

Reaction of thiopicolinamide with N,N′-dimethylformamide dimethyl acetal leads to the formation of 3-(dimethylamino)-1-methylthioimidazo[1,5-a]pyridine (3). However, the course of the reaction can be diverted to produce the title compound (1) in good yield by timely interception of the intermediate thioacylamidine (2).     

Synthesis, characterization and Schlenk equilibrium studies of methylmagnesium compounds with O- and N-donor ligands - the unexpected behavior of [MgMeBr(pmdta)] (pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine)

MgMe₂ (1) was found to react with 1,4-diazabicyclo[2.2.2]octane (dabco) in tetrahydrofuran (thf) yielding a binuclear complex [{MgMe₂(thf)}₂(μ-dabco)] (2). Furthermore, from reactions of MgMeBr with diglyme (diethylene glycol dimethyl ether), NEt₃, and tmeda (N,N,N′,N′-tetramethylethylenediamine) in etheral solvents compounds MgMeBr(L), (L = diglyme (5); NEt₃ (6); tmeda (7)) were obtained as highly air- and moisture-sensitive white powders. From a thf solution of 7 crystals of [MgMeBr(thf)(tmeda)] (8) were obtained. Reactions of MgMeBr with pmdta (N,N,N′,N″,N″-pentamethyldiethylenetriamine) in thf resulted in formation of [MgMeBr(pmdta)] (9) in nearly quantitative yield. On the other hand, the same reaction in diethyl ether gave MgMeBr(pmdta) · MgBr₂(pmdta) (10) and [{MgMe₂(pmdta)}₇{MgMeBr(pmdta)}] (11) in 24% and 2% yield, respectively, as well as [MgMe₂(pmdta)] (12) as colorless needle-like crystals in about 26% yield. The synthesized methylmagnesium compounds were characterized by microanalysis and ¹H and ¹³C NMR spectroscopy. The coordination-induced shifts of the ¹H and ¹³C nuclei of the ligands are small; the largest ones were found in the tmeda and pmdta complexes. Single-crystal X-ray diffraction analyses revealed in 2 a tetrahedral environment of the Mg atoms with a bridging dabco ligand and in 8 a trigonal-bipyramidal coordination of the Mg atom. The single-crystal X-ray diffraction analyses of [MgMe₂(pmdta)] (12) and [MgBr₂(pmdta)] (13) showed them to be monomeric with five-coordinate Mg atoms. The square-pyramidal coordination polyhedra are built up of three N and two C atoms in 12 and three N and two Br atoms in 13. The apical positions are occupied by methyl and bromo ligands, respectively. Temperature-dependent ¹H NMR spectroscopic measurements (from 27 to −80 °C) of methylmagnesium bromide complexes MgMeBr(L) (L = thf (4); diglyme (5); NEt₃ (6); tmeda (7)) in thf-d₈ solutions indicated that the deeper the temperature the more the Schlenk equilibria are shifted to the dimethylmagnesium/dibromomagnesium species. Furthermore, at −80 °C the dimethylmagnesium compounds are predominant in the solutions of Grignard compounds 4-6 whereas in the case of the tmeda complex7 the equilibrium constant was roughly estimated to be 0.25. In contrast, [MgMeBr(pmdta)] (9) in thf-d₈ revealed no dismutation into [MgMe₂(pmdta)] (12) and [MgBr₂(pmdta)] (13) even up to −100 °C. In accordance with this unexpected behavior, 1:1 mixtures of 12 and 13 were found to react in thf at room temperature yielding quantitatively the corresponding Grignard compound 9. Moreover, the structures of [MgMeBr(pmdta)] (9c), [MgMe₂(pmdta)] (12c), and [MgBr₂(pmdta)] (13c) were calculated on the DFT level of theory. The calculated structures 12c and 13c are in a good agreement with the experimentally observed structures 12 and 13. The equilibrium constant of the Schlenk equilibrium (2 9c ? 12c + 13c) was calculated to be K_gas = 2.0 × 10⁻³ (298 K) in the gas phase. Considering the solvent effects of both thf and diethyl ether using a polarized continuum model (PCM) the corresponding equilibrium constants were calculated to be K_thf = 1.2 × 10⁻³ and K_ether = 3.2 × 10⁻³ (298 K), respectively.     

Aigialomycins and related polyketide metabolites from the mangrove fungus Aigialus parvus BCC 5311

Reinvestigation of the secondary metabolites from the marine mangrove fungus Aigialus parvus BCC 5311 led to the isolation of six new nonaketide metabolites, aigialomycins F (4) and G (5a/5b), 7′,8′-dihydroaigialospirol (7), 4′-deoxy-7′,8′-dihydroaigialospirol (8), and rearranged macrolides 9 and 10, along with six previously described compounds, hypothemycin (1), aigialomycins A (2) and B (3), aigialospirol (6), 4-O-demethylhypothemycin (11), and aigialone (12). The structures of the new compounds were elucidated by analyses of the NMR spectroscopic and mass spectrometry data in combination with chemical means.     

Solvent-free reactions of N,N′-thiocarbonyldiimidazole with ferrocenylcarbinols

The efficient and simple routes for the synthesis of various ferrocenyl derivatives from ferrocenylcarbinols and N,N′-thiocarbonyldiimidazole (TCDI) are described. It involves grinding the two substrates in a Pyrex tube with a glass rod at room temperature. The reaction of ferrocenylmethanol (1a) provided S,S-bis(ferrocenylmethyl)dithiocarbonate (1b), whose crystal structure and a plausible mechanism for its formation are also reported. The reaction of 1-ferrocenyl-1-phenylmethanol (2a) and 1-ferrocenylbutanol (2b) gave the products 2c and 2d, respectively. The reaction of ω-ferrocenyl alcohols 4-ferrocenylphenol (3a) and 6-ferrocenylhexan-1-ol (3b) yielded the products 3c and 3d, respectively. Reaction of 1,1′-ferrocenedimethanol (3e) afforded 3f in moderate yield, and by contrast, it was not similar to 1b. Reaction of [4-(trifluoromethyl)phenyl]methanol (4a) provided the thiocarbonate 4b in good yield.     

Dimolybdenum complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo₂(O₂CCH₃)₄ with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo₂(O₂CCH₃)(L1)₂(L2) (1) trans-Mo₂(L1)₂(L2)₂ (2) cis-Mo₂(L1)₂(L2)₂ (3) and Mo₂(L2)₄ (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.