Keith Vaughan

Interplay between steric and electronic factors in determining the strength of intramolecular resonance-assisted NH···O hydrogen bond in a series of β-ketoarylhydrazones

The crystal structures of six β-ketoarylhydrazones are reported: 1,(Z)-2-(2-bromophenylhydrazono)-3-oxobutanenitrile; 2, (Z)-2-(2-methylphenylhydrazono)-3-oxobutanenitrile; 3, (E)-methyl-2-(2-methoxyphenylhydrazono)-3-oxobutanoate; 4, E, methyl-2-(2-cyanophenylhydrazono)-3-oxobutanoate; 5, (Z)-methyl-2-(4-cyanophenylhydrazono)-3-oxobutanoate; 6, pentane-2,3,4-trione-3-(2-carboxyphenylhydrazone). All of them form intramolecular hydrogen bonds assisted by resonance (RAHB), with N···O distances in the range 2.541(5)–2.615(3) A. These hydrogen bonds are differently affected by the substituents at the heterodienic fragment, being strengthened by electronwithdrawing substituents in position 2 (more by 2-COMe than 2-CN substitution), and weakened in β-esterhydrazones and when the N–H forms a bifurcated hydrogen bond. The role played by the different steric and electronic properties of the substituents in strengthening the H-bond is investigated, besides X-ray crystallography, by IR and 1H NMR characterization of the NH proton, and quantum mechanical DFT calculations at the B3LYP/6-31+G(d,p) level of theory on test molecules.

4-(E)-2-[3-(3-[(E)-2-(4-cyanophenyl)-1-diazenyl]perhydrobenzo[d]imidazol-1-ylmethyl)perhydrobenzo[d]imidazol-1-yl]-1-diazenylbenzonitrile: X-ray crystal structure

Abstract4-(E)-2-[3-(3-[(E)-2-(4-Cyanophenyl)-1-diazenyl]perhydrobenzo[d]imidazol-1-ylmethyl) perhydrobenzo[d]imidazol-1-yl]-1-diazenylbenzonitrile (1) has been synthesized by reac- tion of p-cyanobenzene diazonium chloride with a mixture of formaldehyde and trans-1,2-cyclohexanediamine. The crystal structure has been determined by single crystal X-ray diffraction analysis. The bis-triazene (1) does not adopt a folded conformation, unlike previously studied ethylenediamine analogues, and there is no indication of π-stacking in the crystal packing. The dominant interaction between molecules is the van der Waals attraction between cyclohexane rings. This result establishes the structure of the product of this diazonium coupling reaction as the 1-(1-imidazolidinylmethyl)imidazolidine derivative and not the alternate tetraazabicyclo[4.4.1]undecane derivative. Crystal data: 1 C29H34N10, orthorhombic, space group Pbca, a = 17.946(1), b = 13.106(1), c = 24.108(1) Å, V = 5670.6(3) Å3, for Z = 8.

Interplay of hydrogen bonding and other molecular interactions in determining the crystal packing of a series of anti-β-ketoarylhydrazones

The crystal structures of six anti-beta-ketoarylhydrazones are reported: (a1) (E)-2-(4-cyanophenylhydrazono)-3-oxobutanenitrile; (a2) (E)-2-(4-methylphenylhydrazono)-3-oxobutanenitrile; (a3) (E)-2-(4-acetylphenylhydrazono)-3-oxobutanenitrile; (a4) (E)-2-(2-methoxy-phenylhydrazono)-3-oxobutanenitrile; (a5) (E)-2-(2-acetylphenylhydrazono)-3-oxobutanenitrile; (a6) (E)-2-(2-nitrophenylhydrazono)-3-oxobutanenitrile. All compounds contain the pi-conjugated heterodienic group HN-N=C-C=O and could form, at least in principle, chains of intermolecular N-H.O hydrogen bonds assisted by resonance (RAHB-inter). Compounds (a1) and (a2) form this kind of hydrogen bond though with rather long N.O distances of 2.948 (3) and 2.980 (2) Å, and compound (a6) undergoes the same interaction but even more weakened [N.O 3.150 (1) Å] by the intramolecular bifurcation of the hydrogen bond donated by the N-H group. The intrinsic weakness of the intermolecular RAHB makes possible the setting up of alternative packing arrangements that are controlled by an antiparallel dipole-dipole (DD) interaction between two C=O groups of the beta-ketohydrazone moiety [compounds (a4) and (a5)]. The critical factors that cause the switching between the different packings turn out to be the presence of hydrogen bonding accepting substituents on the phenyl and, most frequently, the intramolecular N-H.O bond with the O atom of the phenyl o-substituent. The crystal packing is widely determined by RAHB-inter (three cases) or DD (two cases) interactions. Only compound (a3) displays a different packing arrangement, where the DD interaction is complemented by a non-resonant hydro-gen bond between a p-acetyl phenyl substituent and the hydrazone N-H group [N.O 2.907 (2) Å]. Crystal densities range from 1.24 to 1.44 Mg m(-3) and are shown to increase with the number of intermolecular hydrogen bonds and other non-van der Waals interactions.

Crystal structures of a series of 3,8-di[-2-aryl-1-azenyl]-1,3,6,8-tetraazabicyclo[4.4.1]undecanes

The crystal and molecular structure of a series of 3,8-di[-2-aryl-1-azenyl]-1,3,6,8-tetraazabicyclo[4.4.1]undecanes (1–5) have been determined by single crystal X-ray diffraction analysis. In all five compounds, the tetraazabicycloundecane portion of the molecule assumes a cage-like, folded structure with the aryltriazene moieties aligned approximately parallel; the structure is held in the folded configuration by either intramolecular or intermolecular π–π stacking forces. Crystal data: 1 C19H22N10O4, monoclinic space group P21/c, a = 10.1846(7), b = 9.9556(7), c = 20.819(2) Å, β = 98.725(1)°, V = 2086.5 (3) Å3, Z = 4; 2 C23H28N8O4, triclinic, space group Pī, a = 6.7064(7), b = 12.9662(14), c = 14.054(2) Å, α = 94.796(2), β = 91.621(2), γ = 104.836(2)°, V = 1175.7(2) Å3, Z = 2; 3 C19H22N10O4, monoclinic, space group P21/c, a = 14.237(2), b = 13.520(2), c = 11.5805(12) Å, β = 113.514(2)°, V = 2044.0(4) Å3, Z = 4; 4 C21H22N10, monoclinic, space group C2/c, a = 54.247(3), b = 11.5531(7), c = 12.9670(7) Å, β = 95.710(1)°, V = 8086.4(8) Å3, Z = 16; 5 C25H32N8 04, monoclinic, space group P21/c, a = 10.2908(7), b = 16.5687(12), c = 15.1662(10) Å, β = 94,188(1)°, V = 2579.0(3) Å3, Z = 4.

Crystal structures of two 1,2-bis-(1-aryl-3-methyltriazene-3-yl-)ethanes with aryl substituents of opposite polarity

The crystal and molecular structure of 1,2-bis-{1-(2-cyanophenyl)-3-methyltriazen-3-yl-}ethane (1) and 1,2-bis-{1-(2-methoxyphenyl)-3-methyltriazen-3-yl-}ethane (2) have been determined by single crystal X-ray diffraction analysis. Bis-triazene (1) exists as the “staggered” conformation in the solid state, with an anti-anti configuration around the N2–N3 bond of the triazene units, whereas 2 assumes a “gauche” conformation with the syn-syn configuration in the triazene units. Crystal data: 1 C18H18N8, triclinic, space group P −1, a = 6.108(2), b = 8.118(3), c = 9.600(4)Å, α = 101.37(7)°, β = 96.47(7)°, γ = 102.71(5)°, V = 449.1(3)Å3, Z = 2; 2 C18H24N6O2, monoclinic, space group P 21/n, a = 13.119(5), b = 7.745(2), c = 19.201(2)Å, β = 96.47(7)°, V = 1910.3(9)Å3, Z = 4.

Triazines and related products. Part 27. Thermolysis of 4-anilino-1,2,3-benzotriazines

Thermolysis of 4-(4-cyanoanilino)-1,2,3-benzotriazine (1a) in morpholine affords 3-[2-amino-N-(4-cyanophenyl)benzimidoyl]-4-(4-cyanophenylimino)-3,4-dihydro-1,2,3-benzotriazine (3a) in addition to the major product 2-amino-N2-(4-cyanophenyl)-N1N1-oxydiethylenebenzamidine (2a). The yield of (3a) increases if high boiling non-nucleophilic solvents are employed as the thermolysis medium. Decomposition of (3a) in hot acetic acid affords derivatives of 4-(4-cyanophenyl)-2-phenyl-quinazoline.

Crystal structures of a series of 3,7-bis-(arylazo)-1,3,5,7-tetraazabicyclo[3.3.1]nonanes

The crystal and molecular structure of a series of 3,7-bis(arylazo)-1,3,5,7-tetraazabicyclo[3.3.1] nonanes (1a–d) have been determined by single crystal X-ray diffraction analysis. All four compounds have the same feature, that the tetraazabicyclononane unit assumes a cage-like structure with the aryltriazene moieties lying parallel to one another so that the aryl rings are held together by π – π stacking. Crystal data: 1a C17H18N10O4, triclinic, space group P − 1, a = 9.8899(10), b = 13.0845(13), c = 16.458(2) Å, α = 94.095(2)°, β = 107.004(2)°, γ = 111.027(2)°, V = 1863.5(3) Å3 and Z = 4; 1b, C19H18F6N8, orthorhombic, space group Pbca, a = 15.3210(8), b = 10.9512(6), c = 24.5698(13) Å, V = 4122.4(4) Å3 and Z = 8; 1c C19H18N10, monoclinic, space group P21/n a = 6.3742(6), b = 13.7343(13), c = 21.542(2)Å, β = 97.738(2)°, V = 1868.8(3) Å3, and Z = 4; 1d, C19H18N10, monoclinic, space group P21/c, a = 18.205(2), b = 17.398(2), c = 12.784(12) Å, β = 109.480(2)°, V = 3818.0(6) Å3, and Z = 8.

Functional-group modifications of dextran for linkage to a diazonium group. A potential vehicle for tumour targeting of antineoplastic triazenes

Several derivatives of dextran, containing a triazene side-chain, which are analogues of the antitumour agent DTIC (Dacarbazine), were prepared. The extent of triazene incorporation was measured by determination of the nitrogen content, and the presence of triazene groups was corroborated by u.v.- and n.m.r.-spectroscopic measurements. Some dextran-triazenes exhibited cytotoxic activity against M21 tumour cells in vitro.

A molecular recognition event in the reaction of a diazonium salt with N, N-dimethylethylenediamine

Diazotization of p-aminobenzonitrile and coupling of the resulting diazonium salt with N,N-dimethylethylenediamine affords a novel material that has been shown by X-ray crystallography to be a cocrystal (3) of the pentaazadiene (1) and the diaryltriazene (2). Crystal data: monoclinic, space group P21/c, a = 9.363(5), b = 21.509(3), c = 15.862(5) Å, β = 98.86(5)°, V = 3156.3(18) Å3, Z = 4, Rw = 0.035, Rint = 0.037. The pairing of the two molecules 1 and 2 appears to represent a unique molecular recognition event involving a combination of hydrogen bonding and π–π stacking. The crystal structure shows that the N–H of the triazene is within hydrogen-bonding distance of the tertiary nitrogen atom in the alkyl side-chain of the pentazadiene; furthermore, the benzene rings of the triazene and the pentazadiene are stacked off-register and separated by 3.53 Å. The formation of the components of the cocrystal is rationalised in terms of the formation and decomposition of the 1-aryl-3-alkyltriazene, Ar–N=N–NH–CH2CH2NH2.

Crystal structure of 1,3-di-2-[(4-methoxyphenyl)-1-diazenyl]imidazolidine

The crystal and molecular structure of 1,3-di-2-[(4-methoxyphenyl)-1-diazenyl]imidazolidine (1) has been determined by single crystal X-ray diffraction analysis. This novel bis-triazene assumes a close-to planar structure with the aryltriazene moieties aligned in diametrically opposed directions, unlike many other previously reported bis-triazenes, which assume a folded structure. The structure of 1 is compared with the closely related, non-cyclic bis-triazene analogue (2), and also compared with the structure of the simple mono-triazene (3). Crystal data: 1 C17H20N6O2, monoclinic, space group C2/c, a = 34.948(3), b = 5.925(5), c = 8.1225(6) Å, β = 100.8420(10)°, and V = 1652.0(2) Å3, for Z = 4.