PubMed Health⌕ Search

Biomedical subjects

A J Lough

Publications and source records attributed to A J Lough.

At least 19 recordsLinked to original sources
PubMed2001

C-H activation with elemental sulfur: synthesis of cyclic thioureas from formaldehyde aminals and S8.

The C-H activation of cyclic formaldehyde aminals LCH2 (L = RN-CH2CH2CH2-NR and RNCH2CH2-NR, R = Me, Et, iPr, tBu, or Ph) with S8 proceeds at unusually low temperatures (T< 160 degrees C) and results in the formation of the respective thioureas LC=S and H2S. The reaction constitutes a new, solvent-free method for the synthesis of thioureas that eliminates the toxic and highly flammable CS2. For R = tBu, the ionic carbenium thiocyanates [LCH]+ SCN- dominate the product spectrum and the respective thioureas are obtained in low yield. The reactivity of the analogous sulfur and oxygen ring systems towards S8 was investigated. 1,3-Dithiolane is cleanly converted into 1,3-dithiolane-2-thione (S8, 14 d, 190 degrees C) and resembles the cyclic formaldehyde aminals in this respect. 1,3-Dioxolane (L = OCH2CH2O) is completely inert towards sulfur even under forceful reaction conditions (190 degrees C, 14 d). The formation of thioureas from aminals was investigated at the CBS-4 and B3LYP/6-31G(d) levels of theory.

Formaldehyde↗
PubMed2001

Rhodium-catalyzed dehydrocoupling of the sterically encumbered phosphine-borane adduct tBu(2)PH.BH(3): synthesis of the linear dimers tBu(2)PH-BH(2)-tBu(2)P-BH(3) and tBu(2)PH-BH(2)-tBu(2)P-BH(2)Cl.

The dehydrocoupling of the sterically hindered phosphine-borane adduct tBu(2)PH.BH(3) above 140 degrees C is catalyzed by the rhodium complexes [Rh(1,5-cod)(2)][OTf] or Rh(6)(CO)(16) to give the four-membered chain tBu(2)PH-BH(2)-tBu(2)P-BH(3) (1), which was isolated in 60% yield and characterized by multinuclear NMR spectroscopy, mass spectrometry, and elemental analysis. Thermolysis of 1 in the temperature range 175-180 degrees C led to partial decomposition and the formation of tBu(2)PH.BH(3). When the dehydrocoupling of tBu(2)PH.BH(3) was performed in the presence of [[Rh(mu-Cl)(1,5-cod)](2)] or RhCl(3) hydrate, the chlorinated compound tBu(2)PH-BH(2)-tBu(2)P-BH(2)Cl (2) was formed which could not be obtained free of 1. The molecular structures of tBu(2)PH.BH(3), tBu(2)PH-BH(2)-tBu(2)P-BH(3) (1), and tBu(2)PH-BH(2)-tBu(2)P-BH(2)Cl (2) together with 1 were determined by single-crystal X-ray diffraction studies.

Journal Article↗
PubMed2001

Hydrogen-bonded bilayers in piperazinium(2+) bis(mandelate) bis(methanol) solvate.

In the title compound, C(4)H(12)N(2)(2+).2C(8)H(7)O(3)(-).2CH(4)O, the cations lie across centres of inversion and are disordered over two orientations with equal occupancy; there are equal numbers of (R)- and (S)-mandelate anions present (mandelate is alpha-hydroxybenzeneacetate). The anions and the neutral water molecules are linked by O-H...O hydrogen bonds [O...O 2.658 (3) and 2.682 (3) A, and O-H...O 176 and 166 degrees] into deeply folded zigzag chains. Each orientation of the cation forms two symmetry-related two-centre N-H...O hydrogen bonds [N...O 2.588 (4) and 2.678 (4) A, and N-H...O 177 and 171 degrees] and two asymmetric, but planar, three-centre N-H...(O)(2) hydrogen bonds [N...O 2.686 (4)-3.137 (4) A and N-H...O 137-147 degrees], and by means of these the cations link the anion/water chains into bilayers.

Crystallography, X-Ray↗
PubMed2001

N,N'-Dimethylpiperazinium(2+) phosphonoacetate: hydrogen-bonded anion sheets containing cation-templated R(6)(6)(28) rings.

In the title compound, C(6)H(16)N(2)(2+).2C(2)H(4)O(5)P(-), the cations lie across centres of inversion; in the anions, two of the H-atom sites have 0.50 occupancy. The anions are linked by short O-H...O hydrogen bonds [O...O 2.465 (3)-2.612 (3) A and O-H...O 165-171 degrees ] into sheets of alternating R(2)(2)(12) and R(6)(6)(28) rings, both of which are centrosymmetric; the cations lie at the centres of the larger rings linked to the anion sheet by N-H...O hydrogen bonds [N...O 2.642 (2) A and N-H...O 176 degrees ].

Journal Article↗
PubMed2001

Sodium 2-nitroethanaloximate forms a layered-framework structure.

In the title compound, [Na(C(2)H(3)N(2)O(3))], the Na(+) cation lies on a centre of inversion in space group P2(1)/m and all the atoms of the anion lie on a mirror plane. Na is octahedrally coordinated by four O and two N atoms from six different anions and each anion is coordinated to six different Na(+) cations, forming chains of confacial octahedra which link the anion layers. Within these layers, the individual anions are linked by both O-H...O and C-H...O hydrogen bonds.

Journal Article↗
PubMed2001

Hydrogen-bonded adducts of ferrocene-1,1'-diylbis(diphenylmethanol): monomeric and dimeric 1:1 adducts with 1,2-bis(4-pyridyl)ethane and 1,2-diaminoethane.

In ferrocene-1,1'-diylbis(diphenylmethanol)-4,4'-ethylenedipyridine (1/1), [Fe(C(18)H(15)O)(2)].C(12)H(12)N(2), there is an intramolecular O-H...O hydrogen bond in the ferrocenediol component and a single O-H...N hydrogen bond linking the two components into a finite monomeric adduct. Ferrocene-1,1'-diylbis(diphenylmethanol)-ethylenediamine (1/1), [Fe(C(18)H(15)O)(2)].C(2)H(8)N(2), crystallizes with Z' = 2 in space group P1, and there are two independent four-component aggregates in the structure, both of which are centrosymmetric. In the first type of aggregate, the molecular components are linked by O-H...N and N-H...O hydrogen bonds, in which both diamine N atoms participate; in the second type of aggregate, the diamine component is disordered over two sets of sites, but only one N atom is involved in the hydrogen bonding.

Journal Article↗
PubMed2001

Mu-1,4-benzenedicarboxylato-bis[trans-aqua(1,4,8,11-tetraazacyclotetradecane)nickel(II)] diperchlorate forms a three-dimensional hydrogen-bonded framework.

The title compound, [Ni2(C8H4O4)(C10H24N4)2(H2O)2](ClO4)2, contains two independent octahedral Ni(II) centres with trans-NiN4O2 chromophores. The bridging benzenedicarboxylate ligand is bonded to the two Ni atoms, each via one O atom of each carboxylate, while the other O atom participates in an intramolecular N-H...O hydrogen bond, forming an S(6) motif. The cations are linked to the perchlorate anions via O-H...O and N-H...O hydrogen bonds [O...O 2.904 (6) and 2.898 (6) A; O-H...O 158 (6) and 165 (6) degrees; N...O 3.175 (7) and 3.116 (7) A; N-H...O 168 and 166 degrees ] to form molecular ladders. These ladders are linked by further O-H...O and N-H...O hydrogen bonds [O...O 2.717 (6) and 2.730 (5) A; O-H...O 170 (4) and 163 (6) degrees; N...O 3.373 (7) and 3.253 (7) A; N-H...O 163 and 167 degrees ] to form a continuous three-dimensional framework. The perchlorate anions both participate in three hydrogen bonds, and both are thus fully ordered.

Journal Article↗
PubMed2001

Ferrocenecarboxylic acid-1,4-diazabicyclo[2.2.2]octane (2/1): sheets built from O--H...N and C--H...O hydrogen bonds.

In the title compound, 2[Fe(C5H5)(C6H5O2)].C6H12N2, the molecular components are linked into finite three-component aggregates by strong O-H...N hydrogen bonds [O.N 2.578 (4) and 2.604 (5) A; O-H...N 170 (5) and 174 (6) degrees ]; these aggregates are further linked by C-H...O hydrogen bonds [C...O 3.327 (5)-3.401 (5) A; C-H...O 149-157 degrees ] into continuous sheets in the form of (6,3) nets.

Journal Article↗
PubMed2001

Hydrated salts of 3,5-dihydroxybenzoic acid with organic diamines: hydrogen-bonded supramolecular structures in two and three dimensions.

The trigonally trisubstituted acid 3,5-dihydroxybenzoic acid forms hydrated salt-type adducts with organic diamines. In 1,4-diazabicyclo[2.2.2]octane-3,5-dihydroxybenzoic acid-water (1/1/1) (1), where Z' = 2 in P2(1)/c, the constitution is [HN(CH(2)CH(2))(3)N](+).[(HO)(2)C(6)H(3)COO](-).H(2)O: the anions and the water molecules are linked by six O-H.O hydrogen bonds to form two-dimensional sheets and each cation is linked to a single sheet by one O-H.N and one N-H.O hydrogen bond. Piperazine-3,5-dihydroxybenzoic acid-water (1/2/4) (2) and 1,2-diaminoethane-3,5-dihydroxybenzoic acid-water (1/2/2) (3) are also both salts with constitutions [H(2)N(CH(2)CH(2))(2)NH(2)](2+).2[(HO)(2)C(6)H(3)COO](-).4H(2)O and [H(3)NCH(2)CH(2)NH(3)](2+).2[(HO)(2)C(6)H(3)COO](-).2H(2)O, respectively. Both (2) and (3) have supramolecular structures which are three-dimensional: in (2) the anions and the water molecules are linked by six O-H.O hydrogen bonds to form a three-dimensional framework enclosing large centrosymmetric voids, which contain the cations that are linked to the framework by two N-H.O hydrogen bonds; in (3) the construction of the three-dimensional framework requires the participation of cations, anions and water molecules, which are linked together by four O-H.O and three N-H.O hydrogen bonds.

Journal Article↗
PubMed2001

Methoxy[meso-5,10,15,20-tetrakis-(2,6-difluorophenyl)porphyrinato]-iron(III), [Fe(TDFPP)(OCH3)].

The crystal structure of the title compound, [Fe(C(44)H(20)F(8)N(4))(CH(3)O)], has been determined. The Fe atom lies 0.485 (1) A out of the plane of the four N atoms to which it is coordinated and from the inversion centre at the origin of the unit cell. The methoxy group is axially coordinated to the Fe atom with O-Fe-N angles of 106.3 (2) and 102.4 (2) degrees, a C-O-Fe angle of 128.3 (5) degrees and an Fe-O distance of 1.788 (5) A. Difluorophenyl rings are tilted from the porphyrin (por) plane with torsion angles of -68.1 (6) and 77.7 (5) degrees across the two C(por)-C-C-C(ar) systems.

Crystallography, X-Ray↗
PubMed2001

Synthesis and reactivity of perhalogenated acyclic and metallacyclic tantalum(V) phosphoraniminato complexes: discovery of an unexpected ligand coupling reaction to form the novel phosphazenium salt.

The reaction of TaCl5 with a single equivalent of Cl3P=NSiMe3 resulted in the isolation of the perhalogenated (phosphoraniminato) tantalum(V) complex TaCl4(N=PCl3) (1). Reaction of 1 with an excess of THF and subsequent cooling produced crystals of TaCl4(N=PCl3)(THF) (1.THF), which possesses a distorted octahedral Ta center with a THF molecule coordinated trans to the phosphoraniminato ligand. The reaction of 1 with the aminophosphoranimine, (Me3Si)2NPCl2=NSiMe3, resulted in a [3 + 1] cyclocondensation reaction to form the metallacyclic complex, TaCl3(N=PCl3)[N(SiMe3)PCl2N(SiMe3)] (2), which contains a TaNPN four-membered ring and a phosphoraniminato ligand (N=PCl3). The analogous [3 + 1] cyclocondensation reaction between (Me3Si)2NPCl2=NSiMe3 and TaCl5 led to the isolation of TaCl4[N(SiMe3)PCl2N(SiMe3)] (3). An attempt to cleave the NPN ligand from the Ta center in 2 via protonolysis with HCl led to an unusual phosphoraniminato ligand coupling reaction to yield the novel phosphazenium salt [N(PCl2NH2)2][TaCl6] (4). All new compounds (1.THF and complexes 1-4) were characterized by single-crystal X-ray diffraction.

Journal Article↗
PubMed2001

Tuning the strain and polymerizability of organometallic rings: the synthesis, structure, and ring-opening polymerization behavior of [2]ferrocenophanes with C-SI, C-P, and C-S bridges.

A series of novel [2]ferrocenophanes with unsymmetrical C-E bridges has been prepared in which the covalent radius of the second-row element, E, and hence the ring strain present is varied. Species [Fe(eta-C(5)Me(4))(eta-C(5)H(4))CH(2)ER(x)] (7, ER(x) = SiMe(2); 8a, ER(x) = PPh; 8b, ER(x) = PMes; 9, ER(x) = S) were synthesized via reaction of the PMDETA (N,N,N',N' ',N' '-pentamethyldiethylenetriamine) adduct of [(eta-C(5)H(4)Li)Fe(eta-C(5)Me(4))CH(2)Li] with Cl(2)ER(x) (E = Si or P) or S(SO(2)Ph)(2). Studies of 7-9 by single-crystal X-ray diffraction confirmed the presence of ring-tilted structures: for 7, alpha (angle between the planes of the Cp rings) = 11.8(1) degrees; for 8a, alpha(average) = 14.9(3) degrees; for 8b, alpha(average) = 18.2(2) degrees; and for 9, alpha = 18.5(1) degrees. The least tilted compound, 7, was found to be resistant to thermal, anionic, and transition metal catalyzed ROP. In contrast, the significantly more tilted compounds 8a, 8b, and 9 were all found to polymerize thermally with small negative values of DeltaH(ROP) of ca. 10-20 kJ.mol(-1) determined by DSC. Whereas thermal ROP of 8a yielded the soluble high molecular weight polycarbophosphaferrocene [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)PPh](n) (11), species 9 formed the insoluble polycarbothiaferrocene [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)S](n) (14). Attempted anionic ROP of 8a and 9 with (n)BuLi was unsuccessful and treatment of 8a with CF(3)SO(3)Me resulted in the formation of the novel phosphonium salt [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)PMePh][CF(3)SO(3)] (13), which was found to be resistant to thermal ROP as a result of its less strained structure (for 13, alpha = 11.4(7) degrees ). Treatment of 9 with CF(3)SO(3)Me or BF(3).Et(2)O resulted in the first example of cationic ROP for a transition metal-containing heterocycle to yield polycarbothiaferrocene 14. In the presence of excess 2,6-di-tert-butylpyridine as a selective proton trap, ROP of 9 was only observed with CF(3)SO(3)Me, and not BF(3).Et(2)O, which indicated that Me(+) and H(+) are the probable cationic initiators, respectively. Thermal copolymerization of 9 with trimethylene sulfide resulted in the isolation of the soluble, high molecular weight, random copolymer [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)S](n)[(CH(2))(3)S](m), 15.

Journal Article↗
PubMed2001

A hydrogen-bonded adduct containing seven-component supramolecular aggregates.

The title compound is a salt, 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2(11,14)]triaconta-1(26),11(29),12,14(30),24,27-hexaene-3,5-dinitrobenzoic acid-methanol (1/4/2), C24H42N6(4+).4C7H3N2(O6)(-).2CH4O, in which the cation lies across a centre of inversion and one of the two independent anions is positionally disordered over two sets of atom sites having equal occupancy. The components are linked by four types of N-H...O hydrogen bond [N...O 2.674 (2)-2.815 (2) A; N-H.O 149-163 degrees] and one type of O-H...O hydrogen bond in which the acceptor is disordered over two closely adjacent sites [O...O 2.67 (4) and 2.75 (4) A; O-H...O 172 and 173 degrees], forming centrosymmetric seven-component aggregates.

Journal Article↗
PubMed2001

A three-dimensional hydrogen-bonded framework in 4,4'-trimethylenedipiperidinium-2,5-dicarboxybenzene-1,4-dicarboxylate-water (1/1/1).

The title compound is a salt, C13H28(N2)(2+).C10H4(O8)(2-).H2O. In the anion, there are two short intramolecular hydrogen bonds [O.O 2.395 (2) and 2.383 (2) A; O.H.O 175 and 172 degrees]. Pairs of anions and pairs of water molecules are linked by further O-H.O hydrogen bonds [O.O 2.756 (2) and 2.980 (2) A; O-H.O 171 and 175 degrees] into cyclic centrosymmetric R(6)(6)(16) aggregates; these aggregates are linked via the cations into a three-dimensional framework by means of four distinct N-H...O hydrogen bonds [N...O 2.787 (2)-3.204 (2) A; N-H...O 148-173 degrees].

Journal Article↗
PubMed2001

Hydrogen-bonded sheets in the 1:1 salt of tet-b and trimesic acid.

Tet-b (racemic 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, C(16)H(36)N(4)) and trimesic acid (1,3,5-benzenetricarboxylic acid, C(9)H(6)O(6)) form a salt partially solvated by both water and methanol, i.e. 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1,3,5-benzenetricarboxylic acid--methanol--water (1/1/0.78/1.12), C(16)H(38)N(4)(2+) x C(9)H(4)O(6)(2-) x 0.78CH(4)O x 1.12H(2)O. The anions are linked by O--H...O hydrogen bonds [O...O 2.442 (4) and 2.458 (4) A; O--H...O 170 and 171 degrees ] into zigzag chains; orientationally disordered cations are linked to the anion chains by means of N--H...O hydrogen bonds [major orientation: N...O 2.695 (3)--3.071 (4) A, N--H...O 148--179 degrees; minor orientation: N...O 2.75 (2)--3.34 (2) A, N--H...O 147--170 degrees ] and link the chains into sheets. The solvent molecules are all disordered, but appear to play no significant structural role apart from space filling.

Journal Article↗
PubMed2001

Ethane-1,2-diphosphonic acid as a building block in supramolecular chemistry; a pillared-layer framework and framework-encapsulated cations.

The 1:1 adduct of piperazine and ethane-1,2-diphosphonic acid is a salt [C(4)H(12)N(2)](2+).[C(2)H(6)O(6)P(2)](2-), in which both ions lie across centres of inversion in space group P2(1)/c. The anions are linked by a single type of O-H...O hydrogen bond [O...O, 2.562 (3) A; H...O, 1.73 A, O-H...O, 169 degrees ] into (6, 3) nets built from a single type of R(4)(4)(22) ring. The cations lie between these nets, linked to them by two types of N-H...O hydrogen bond [N...O, 2.635 (3) and 2.735 (3) A; H...O 1.72 and 1.82 A, N-H...O, 175 and 177 degrees ] such that the cations link adjacent sheets, thus forming a pillared-layer framework. The aquated adduct formed between trimethylenedipiperidine and ethane-1,2-diphosphonic acid is also a salt [C(13)H(28)N(2)](2+).[C(2)H(6)O(6)P(2)](2-).2.8[H(2)O], in which there are 12 different types of hydrogen bond, eight O-H...O and four N-H...O. The anions are linked into chains by pairs of O-H...O hydrogen bonds and these chains are linked by the water molecules into a continuous three-dimensional framework. Within the anion/water framework are large voids which contain pairs of cations, linked to the framework by N-H...O hydrogen bonds.

Journal Article↗