A simple, general route to 2-pyridylidene transition metal complexes

Pyridinium 2-carboxylates decompose thermally in the presence of a variety of late transition metal precursors to yield the corresponding 2-pyridylidene-like complexes. The mild reaction conditions and structural diversity that can be generated in the heterocyclic ring make this method an attractive alternative for the synthesis of 2-pyridylidene complexes. IR spectra of the Ir(i) carbonyl compounds [IrCl(NHC)(CO)(2)] indicate that these N-heterocyclic carbene ligands are among the strongest σ-electron donors.     

Synthesis and properties of cycloparaphenylene-2,5-pyridylidene: a nitrogen-containing carbon nanoring

The first synthesis of a nitrogen-containing cycloparaphenylene, cyclo[14]paraphenylene[4]2,5-pyridylidene ([14,4]CPPy), has been achieved. A palladium-catalyzed stepwise assembly of 2,2'-bipyridine, benzene, and L-shaped cyclohexane units, followed by NaHSO(4)/o-chloranil-mediated aromatization, successfully provided [14,4]CPPy. While the absorption and fluorescence properties of [14,4]CPPy were somewhat similar to those of cycloparaphenylenes (λ(abs) = 344 nm, ε = 7.3 × 10(4) cm(-1) M(-1), λ(em) = 427 nm, Φ(F) = 0.80), it was found that [14,4]CPPy possesses an interesting halochromic property.     

Solvent extraction and lanthanide complexation studies with new terdentate ligands containing two 1,3,5-triazine moieties

The extracting agent 2,6-bis(4,6-di-pivaloylamino-1,3,5-triazin-2-yl)-pyridine (L(5)) in n-octanol was found, in synergy with 2-bromodecanoic acid, to give D(Am)/D(Eu) separation factors (SFs) between 2.4 and 3.7 when used to extract the metal ions from 0.02-0.12 M HNO(3). Slightly higher SFs (4-6) were obtained in the absence of the synergist when the ligand was used to extract Am(III) and Eu(III) from 0.98 M HNO(3). In order to investigate the possible nature of the extracted species crystal structures of L(5) and the complex formed between Yb(III) with 2,6-bis(4,6-di-amino-1,3,5-triazin-2-yl)-pyridine (L(4)) were also determined. The structure of L(5) shows 3 methanol solvent molecules all of which form 2 or 3 hydrogen bonds with triazine nitrogen atoms, amide nitrogen or oxygen atoms, or pyridine nitrogen atoms. However, L(5) is relatively unstable in metal complexation reactions and loses amide groups to form the parent tetramine L(4). The crystal structure of Yb(L(4))(NO(3))(3) shows ytterbium in a 9-coordinate environment being bonded to three donor atoms of the ligand and three bidentate nitrate ions. The solvent extraction properties of L(4) and L(5) are far inferior to those found for the 2,6-bis-(1,2,4-triazin-3-yl)-pyridines (L(1)) which have SF values of ca. 140 and theoretical calculations have been made to compare the electronic properties of the ligands. The electronic charge distribution in L(4) and L(5) is similar to that found in other terdentate ligands such as terpyridine which have equally poor extraction properties and suggests that the unique properties of L(1) evolve from the presence of two adjacent nitrogen atoms in the triazine rings.     

2-Isoxazoline derivatives. Part I. A base-promoted fragmentation of 2-isoxazolines

The action of bases on 3-aryl (or alkyl)-5-acyl-2-isoxazolines has been shown to give rise to the corresponding aromatic (or aliphatic) nitriles and α-diketones by cleavage of the O-N and C₃? C₄ bonds of the heterocyclic ring. This fragmentation reaction has been extended to other 2-isoxazolines substituted in the 5-position with electron-attracting groups.     

1,3,5-Triaza-2-phosphapentalenes

Abstract

Refluxing a dialkylammonium 4,5-dicyano-1,3,2-diazaphospholate¹ with a dialkyl-amine in chloroform gives a 4,6-bis(dialkylamino)-1,3,5-triaza-2-phosphapentalene¹ in good yield as the only reaction product. Unsymmetrically substituted representatives are accessible this way too.     

2-nitroguanidine derivatives: X. Synthesis and nitration of 4-nitriminotetrahydro-1,3,5-oxadiazine and 2-nitriminohexahydro-1,3,5-triazine and their substituted derivatives

A new synthetic procedure was developed to obtain 1-hydroxymethyl-2-nitroguanidine from 2-nitroguanidine and formaldehyde without catalyst. Reactions of 2-nitroguanidine and its 1-methyl-and 1-phenylsubstituted derivatives with formaldehyde and urotropin under acid catalysis resulted in 4-nitriminotetrahydro-1,3,5-oxadiazine and 2-nitriminohexahydro-1,3,5-triazine and their methyl-and phenyl-substituted derivatives, whose nitration with concn. HNO₃ in the presence of acetic anhydride and concn. H₂SO₄ depending on the temperature conditions led to the formation of 4-nitrimino-3,5-dinitrotetrahydro-1,3,5-oxadiazine, 3-methyl-4-nitrimino-5-nitrotetrahydro-1,3,5-oxadiazine, 2-nitrimino-5-nitrohexahydro-1,3,5-triazine, and 1,3,5-trinitro-hexahydro-1,3,5-triazine-2-one.     

1,3,5-Triaryl-Δ2-pyrazoline

2-Iodo-3-chloro-1,3-diphenyl-1-propanones react with phenylhydrazine to yield the 1,3,5-Triaryl-Δ²-pyrazoline. The reaction proceeds with elimination of ICl to the chalcones and their reaction with an excess of phenylhydrazine.     

5-Substituted 2-alkyl- and 2-arylsulfonyliminohexahydro-1,3,5-triazines

A new procedure was developed for the preparation of previously unknown 5-substituted 2-alkyl- and 2-arylsulfonyliminohexahydro-1,3,5-triazines by cyclocondensation of sulfoguanidines with formaldehyde and primary alkyl(aryl)amines.     

Strong bicyclic guanidine base-promoted wittig and horner-wadsworth-emmons reactions

A convenient procedure to effect the Wittig and Horner-Wadsworth-Emmons reactions employs guanidine TBD and MTBD as base-promoters; mild reaction conditions, high efficiency, and facile isolation of the final products make the present methodology, at least in some cases, a practical alternative to known procedures.     

Synthesis of 1,3,5-tris(2-chloroethyl)- and 1,3,5-tris(2-iodoethyl)benzenes

A new method has been elaborated for the synthesis of 1,3,5-tris(2-chloroethyl)- and 1,3,5-tris(2-iodoethyl)benzenes based on the commercially available 1,3,5-tribromobenzene.     

Carbene-stabilized diphosphorus: bidentate complexation of BH2(+)

Reaction of carbene-stabilized diphosphorus, L:P-P:L (L: = :C{N(2,6-Pr(i)(2)C(6)H(3))CH}(2), 1), with excess BH(3)·THF affords the boronium salt [L:P(μ-BH(2))P:L](+)[B(2)H(7)](-), 2, which contains a three-membered P(2)B ring. When 2 is dissolved in THF, compounds 1 and 2 exist in a dynamic solution equilibrium.     

A study of the sensitivity and decomposition of 1,3,5-trinitro-2-oxo-1,3,5-triazacyclo-hexane

The thermal decomposition and thermal stability of 1,3,5-trinitro-2-oxo-1,3,5-triazacyclohexane (keto-RDX or K-6) was studied. The keto-RDX synthesis is described, mass spectra (electron impact (70 eV) and chemical ionization) similar to RDX spectra registered under identical conditions are presented, and mass spectroscopy fragmentation paths are proposed. The LI-MS (laser induced/mass spectroscopic) results imply that the first step in the decomposition of keto-RDX is the elimination of NO₂ or HONO and subsequent breakdown of the triazacyclohexane ring. The thermal stability, activation energy (E_a = 140 kJ mol⁻¹), and frequency factor (K₀ = 9 × 10⁹ s⁻¹) in the temperature interval 90-120°C were measured using chemiluminescence (NO detection only). The activation energy was also determined from DSC data using the ASTM method E 698-79, and was found to be 280 kJ mol⁻¹ with a frequency factor of 7.0 × 10²⁹ s⁻¹ in the temperature interval 175-200°C. Microcalorimetry, drop-weight test, friction test, and ignition temperature (Wood's metal bath) measurements were also conducted. Quantum mechanical calculations (semi-empirical method with PM3 set at the unrestricted Hartree-Fock level) were conducted to correlate the sensitivity and thermal decomposition with those of RDX. No significant differences in bond-breaking energies for RDX and keto-RDX were found. Conclusions drawn from the experiments are that the decomposition of keto-RDX is auto-catalytic, and that the sensitivity of keto-RDX is not connected with the initial bond-breaking step. More than one method for measuring the risk involved in handling an explosive is necessary since the sensitivity depends on different stages in the decomposition.     

Heterocycles from heterocycles. - III[1]. 1,3,5-trisubstituted hexahydro-1,3,5-triazines-2-ones from 1,3,5-trisubstituted hexahydro-1,3,5-triazines and organic isocyanates

1,3,5-Triscubstituted hexahydro-1,3,5-trazin-2-ones 3 are easily obtained by the reaction of 1,3,5-trisub-stituted hexahydro-1,3,5-triazines 1 with organic isocyanates 2 . The reaction is believed to occur by the sequential addition to 2 of two molecules of the monomeric N-methyleneamines in thermal equilibrium with 1. Substituent scrambling at the operating temperature (120°) was negligible. The crystal structure of 1,3,5-triphenylhexahydro-1,3,5-triazin-2-one (3a) has been determined by X-ray diffraction methods.     

1,3,5-trisubstituted 1,4-diazepin-2-ones

Six 1,3,5-trisubstituted 1,4-diazepin-2-ones were synthesized by a sequence featuring the cascade addition of vinyl Grignard to N-[Boc-aminoacyl]-N-alkyl-beta-amino esters, followed by Boc group removal and annulation by a reductive amination. Relative to the parent sequence employing N-Boc-aminoacyl beta-amino esters to make 3,5-disubstituted heterocycle, the additional N-alkyl substituent caused a noticeable acceleration and gave relatively higher yield in the 1,4-diazepin-2-one annulation.     

Synthesis of 5-alkyl-1,3,5-triazinan-2-ones and 5-alkyl-1,3,5-triazinane-2-thiones using Cu- and Sm-containing catalysts

Efficient procedures have been developed for the synthesis of 5-alkyl-1,3,5-triazinan-2-ones and 5-alkyl-1,3,5-triazinane-2-thiones by reaction of urea (thiourea) with primary alkylamines and N,N,N′,N′-tetramethylmethylenediamine and by reaction of primary amines with N,N′-bis(dimethylaminomethyl)urea(thiourea) in the presence of Cu- and Sm-containing catalysts.