Related Bis Research Articles

On the Bonding Properties of Diphosphanylmethanide Complexes with the Group-14 Elements Silicon, Germanium, Tin, and Lead in Their Divalent Oxidation States

The mono- and bidentate chelation of the main-group elements silicon, germanium, tin, and lead through the phosphorus atoms of the diphosphanylmethanide ligand has been studied by means of quantum chemical methods. In accord with experimental investigations, the species are found to adopt a psi-tbp conformation of high flexibility. The various distortional modes causing the axial and equatorial positions to become equivalent have also been investigated. In addition, the bonding situations in the electronically related bis(diamino)- and the higher element homologue bis(diarsanyl)methanide ligand systems have been studied. The bonding situation in the hitherto experimentally unknown bis(diamino)methanide Ligands is predicted to be similar to that in bis(amidinate) complexes. An analysis of the electron distributions (natural bond orbital population analysis) in these compounds reveals that the central main-group element is positively charged and weakly chelated by the surrounding ligands.

Selective solvent extraction of tetrahedrally-coordinating transition metal ions from acidic aqueous media using benzimidazole–phosphinate ligands: specificity for zinc(II) over copper(II)

The synthesis, solution complexation behaviour and solvent extraction ability of related chelating mono-and bis-(benzimidazole)phosphinate ligands 8 and 9 has been assessed. 31P NMR, fluorescence and absorption spectroscopy and electrospray mass spectrometry revealed preferential formation of 1:1 complexes with the divalent ions Zn, Co and Ni, and ML2 complex formation with the bidentate ligand. Extraction studies showed that 9 extracted Zn>CoNi with no extraction of copper(II), but avid extraction of copper(I), generated insitu, consistent with the ligand's preference for the binding of tetrahedrally-coordinating metal ions.

Intramolecular Sandwich Complexation of Light Lanthanoid Nitrates with Bis(benzo-12-crown-4)s: Enhanced Selectivity for Eu

Spectrophotometric titrations performed in anhydrous acetonitrile at 25°C give the complex stability constants (log Ks) and the Gibbs free energy changes (-ΔG° for the stoichiometric 1 : 1 intramolecular sandwich complexation of light lanthanoid (III) nitrates (La ∼ Gd) with the polymethylene-bridged bis(benzo-12-crown-4)s 1, the corresponding dioxo derivative 2 and its dihydroxy analogue 3. The complex stability sequence as a function of reciprocal ionic radius of lanthanoids showed similar profiles in stability constants (log Ks) and maximum stabilities were obtained at Eu3+ for the complexation of light lanthanoids with the three bis(benzo-12-crown-4)s 1–3. The cation binding abilities and relative selectivities for the trivalent lanthanoid ions of these structurally related bis(benzo-12-crown-4)s 1–3 are discussed according to the derivatization of the bridging.

DNA-Directed alkylating agents. 7. Synthesis, DNA interaction, and antitumor activity of bis(hydroxymethyl)- and bis(carbamate)-substituted pyrrolizines and imidazoles.

A series of bis(hydroxymethyl)-substituted imidazoles, thioimidazoles, and pyrrolizines and related bis(carbamates), linked to either 9-anilinoacridine (intercalating) or 4-(4-quinolinylamino)benzamide (minor groove binding) carriers, were synthesized and evaluated for sequence-specific DNA alkylation and cytotoxicity. The imidazole and thioimidazole analogues were prepared by initial synthesis of [(4-aminophenyl)alkyl]imidazole-, thioimidazole-, or pyrrolizine dicarboxylates, coupling of these with the desired carrier, and reduction to give the required bis(hydroxymethyl) alkylating moiety. The pyrrolizines were the most reactive alkylators, followed by the thioimidazoles, while the imidazoles were unreactive. The pyrrolizines and some of the thioimidazoles cross-linked DNA, as measured by agarose gel electrophoresis. Strand cleavage assays showed that none of the compounds reacted at purine N7 or N3 sites in the gpt region of the plasmid gpt2Eco, but the polymerase stop assay showed patterns of G-alkylation in C-rich regions. The corresponding thioimidazole bis(carbamates) were more selective than the bis(hydroxymethyl) pyrrolizines, with high-intensity bands at 5'-NCCN, 5'-NGCN and 5'-NCGN sequences in the PCR stopping assay ( indicates block sites). The data suggest that these targeted compounds, like the known thioimidazole bis(carbamate) carmethizole, alkylate exclusively at guanine residues via the 2-amino group, with little or no alkylation at N3 and N7 guanine or adenine sites. The cytotoxicities of the compounds correlated broadly with their reactivities, with the bis(hydroxymethyl)imidazoles being the least cytotoxic (IC50s >1 microM; P388 leukemia) and with the intercalator-linked analogues being more cytotoxic than the corresponding minor-groove-targeted ones. This was true also for the more reactive thioimidazole bis(carbamates) (IC50s 0.8 and 11 microM, respectively), but both were more active than the analogous "untargeted" carmethizole (IC50 20 microM). The bis(hydroxymethyl)pyrrolizine analogues were the most cytotoxic, with IC50s as low as 0.03 microM.

Tracing an organometallic early—late transition element relationship

This work explores M. E. Vol'pin's early notion that TiCp2 possesses carbenoid character, and transfers this concept to the related dicarbonyl bis(phosphorus donor)iron fragment. Similarities and differences in electronic and molecular structure of the titanium and iron fragment are elucidated based on density functional calculations. Isolobal analogies to the carbene unit are presented to rationalize the computational results. Experimental verification of analogies between TiCp2 and Fe(CO)2L2 chemistries is given.

Synthesis, structure and trypanocidal activity of dibutyltin derivatives of 2-mercaptobenzoxazole and 5-chloro-2-mercaptobenzothiazole

Single X-ray crystal structure analysis has been determined for the dibutyltin derivatives of 2-mercaptobenzoxazole 1 and 5-chloro-2-mercaptobenzothiazole 2. In both cases, the geometry at the tin atom is that of an octahedron, and it is weakly coordinated by N,S chelating ligands. Trypanocidal activity patterns are also presented, showing a large difference in behaviour between 1, 2 and the related bis (2-mercaptobenzothiazolyl) dibutyltin.

Synthesis and Structure of C2-Symmetric, Doubly Bridged Bis(indenyl)titanium and -zirconium Dichlorides

The synthesis of the new C2h-symmetric doubly bridged 1,2‘-(ethane-1,2-diyl)-2,1‘-(ethane-1,2-diyl)bis(indene) ligand 9 from 1,5-dimethyl-1,5-cyclooctadiene via a selenium-catalyzed oxidation reaction and a double Nazarov π-cyclization reaction is reported. Only one bridged C2-symmetric metallocene diastereomer was formed in the metalation of 9 because the geometry of the double bridge precluded formation of a meso isomer. The C2-symmetric [1,2‘-(ethane-1,2-diyl)-2,1‘-(ethane-1,2-diyl)bis(indenyl)]titanium and -zirconium dichlorides 10 and 11 were prepared in good (63 and 67%) yields, with no evidence of oligomeric metallocene products. The solid-state structure of 11 was determined by X-ray crystallography. The related bis(indene) 19, containing a bicyclo[3.3.1]nonane bridging moiety, was synthesized from Meerwein's diketone but could not be efficiently metalated.

Enhanced Carboxylate Binding Using Urea and Amide-Based Receptors with Internal Lewis Acid Coordination: A Cooperative Polarization Effect

A structural design strategy is described that greatly improves the acetate binding ability of neutral urea and amide-based receptors. The enhanced binding is due to a cooperative polarization effect which is induced by intramolecular coordination of the urea or amide carbonyl to a Lewis acidic boronate group. A series of boronate-ureas, 3, and a related bis(boronate-amide), 23, were prepared in two steps from 2-(aminophenyl)boronic acid and their structures elucidated using X-ray crystallography and other spectrometric methods. The abilities of the receptors to associate with tetrabutylammonium acetate in dimethyl sulfoxide solution were determined by (1)H NMR titration experiments. Association constants were calculated using nonlinear curve-fitting methods. The boronate-ureas 3 strongly bind to acetate in dimethyl sulfoxide solution with association constants as high as 6 x 10(4) M(-)(1). This is more than 150 times greater than the association constants for control urea receptors that lacked an appropriate boron substituent. Thermodynamic studies indicate that the enhanced association is due to a favorable enthalpic change. Additional NMR studies eliminated the possibility of proton transfer to the acetate during complex formation. Molecular modeling indicates that the boronate-ureas exhibit improved acetate binding because the intramolecular coordination (i) induces a larger host dipole moment which strengthens the guest/host ion-dipole interaction, and (ii) increases the positive surface potential at the urea NH residues which strengthens short range Coulombic interactions with the anionic acetate. The observed association constants correlate better with calculated host dipole moments, suggesting that for the boronate-ureas described here this is the more influential factor controlling association.

Synthesis and characterization of bis(trialkoxysilymethyl)arenes from related bis(trichlorosilylmethyl)arenes. Comparisons between some organosilicate xerogel materials derived from both

A series of bis(trialkoxysilylmethyl)aryl compounds1–17 {[(RO) 3 SiCH 2 ] 2 Ar, R=Me, Et, Pr , Bu, Ar=1,4-C 6 H 4 ; R=Et, Pr, Bu, Ar=1,4-C 6 H 2 Me 2 -2,6; R=Et, Pr, Bu, Ar=1,4-C 6 Me 4 -2,3,5,6 ; R=Et, Pr, Bu, Ar=1,3-C 6 H 4 ; R=Bu, Ar=1,2-C 6 H 4 ; R=Et, Pr, Bu, Ar=9,10-C 14 H 8 } prepared from the related bis(trichlorosilylmethyl)aryl compounds and characterised by 1 H, 13 C and 29 Si NMR and IR spectroscopy, and high resolution mass spectrometry. The X-ray crystal structures of two of the bis(trichlorosilylmethyl)aryl precursor compounds are reported. Organosilicate xerogels prepared from the precursors 2,7 and 12 are discussed. These have been studied by a combination of solid state NMR spectroscopy, scanning electron microscopy (one case) and nitrogen sorption porosimetry and their properties compared with those of xerogels derived from related bis(trichlorosilylmethyl)arenes.

Mixed bis(thiosemicarbazone) ligands for the preparation of copper radiopharmaceuticals: synthesis and evaluation of tetradentate ligands containing two dissimilar thiosemicarbazone functions.

A series of four "mixed" bis(thiosemicarbazone) keto aldehyde derivatives containing dissimilar thiosemicarbazone functions were synthesized and evaluated as ligands for preparation of radiocopper-labeled radiopharmaceuticals. The pyruvaldehyde-based mixed bis(thiosemicarbazone) ligands CH3C[=NNHC(S)NH2]CH[=NNHC(S)NHMe] (4a), CH3C[=NNHC(S)NHMe]-CH[=NNHC(S)NH2] (4b), CH3C[=NNHC(S)NH2]CH[=NNHC(S)NMe2] (4c), and CH3C[=NNHC-(S)NHMe]CH[=NNHC(S)NMe2] (4d) were obtained by reaction of thiosemicarbazide, N4-methylthiosemicarbazide, or N4,N4-dimethylthiosemicarbazide with pyruvaldehyde 2-thiosemicarbazones that had been generated by oxidative cleavage of the appropriate pyruvic aldehyde dimethyl acetal 2-thiosemicarbazone. The 67Cu-labeled complexes of ligands 4a-d were prepared and screened in a rat model to assess the potential of each chelate as a 62Cu radiopharmaceutical for imaging with positron emission tomography. In the rat model the 67Cu complexes of ligands 4a-d exhibit significant uptake into the brain and heart after intravenous injection, following trends similar to those previously reported for the related bis(thiosemicarbazone) complexes, Cu-PTS, Cu-PTSM, and Cu-PTSM2 (derived from pyruvaldehyde bis(thiosemicarbazone), pyruvaldehyde bis(N4-methylthiosemicarbazone), and pyruvaldehyde bis(N4,N4-dimethylthiosemicarbazone), respectively). Ultrafiltration studies using solutions of dog and human serum albumin reveal that the 67Cu complexes of ligands 4a-d, like the Cu(II) complex of pyruvaldehyde bis(N4-methylthiosemicarbazone), interact more strongly with human albumin than dog albumin.

Crystal structure, spectral and electrochemical properties of [TBA] 2[Ni(i-MNT) 2], [TBA][Ni(i-MNT) 2], [TBA] 2[Ni(i-MNS) 2] and related bis(1,2-dithiolene) metal complexes

The synthesis, crystal structure and physical properties of bis(1,1-dithiolene) or bis (1,1-diselenolene) metal complexes of [TBA] 2[Ni(i-MNT) 2], [TBA][Ni(i-MNT) 2] and [TBA] 2[Ni(i-MNS) 2] (i-MNT = 2,2-dicyanoethylene-1,1-dithiolate,i-MNS = 2, 2-dicyanoethylene-1, 1-diselenolate) were studied and compared to one another or to the related bis (1,2-dithiolene) metal complexes of 5,6-dihydro-1,4-dithiin-2,3-dithiolate, 1,3-dithiole-2-thione-4,5-dithiolate and 1,3-dithiole-2-one-4,5-dithiolate ligands. The structures of the complexes contain equidistant anionic stacks well separated by the counter cation sheets. The planarity and short C-S or C-Se distances in the structures indicate extensive delocalization of the π-system in the compounds. The relative low conductivities for the complexes are due to the low polarizability, large intra-and inter-stack S ··· S distances, and the relative high on-site electron-electron repulsion energy in the compounds.

Synthesis and Properties of 2‐Carboxyalkyl‐1,2‐benzisoselenazol‐3(2H)‐ones and Related Organoselenium Compounds as Nitric Oxide Synthase Inhibitors and Cytokine Inducers

AbstractA convenient synthesis of the 2‐carboxyalkyl‐1,2‐benzisoselenazol‐3(2H)‐ones 4a–k and their esters 41–p from 2‐(chloroseleno)benzoyl chloride (2) and amino acids or their carboxy esters is reported. In similar way other 2‐substituted 1,2‐benzisoselenazol‐3(2H)‐ones 4q–u were synthesized. The related bis[2‐(carbamoyl)phenyl] diselenides 5 were obtained by reductive conversion of 1,2‐benzisoselenazol‐3(2H)‐ones 4 or directly by the reaction of bis[2‐(chlorocarbonyl)phenyl] diselenide (3) with compounds having a primary amino group. It was found that some of compounds 4 and 5 are modest cytokine (TNF, IFN) inducers in human peripheral blood leucocyte cultures and block the constitutive endothelial nitric oxide synthase (ce NOS).

Determination of the antileukemic drug mitoguazone and seven other closely related bis(amidinohydrazones) in human blood serum by high-performance liquid chromatography.

A reversed-phase (C18) HPLC method with diode-array detection was developed for the separation and determination of methylglyoxal bis(amidinohydrazone) (mitoguazone) and seven closely related aliphatic analogs thereof, namely the bis(amidinohydrazones) of glyoxal, dimethylglyoxal, ethylmethylglyoxal, methylpropylglyoxal, butylmethylglyoxal, diethylglyoxal and dipropylglyoxal. The mobile phase consisted of a non-linear binary gradient of methanol and 0.03 M aqueous sodium acetate buffer (pH 4.3). Good separation of the eight congeners was achieved. On increasing the methanol content of the eluent, the bis(amidinohydrazones) eluted in the order of increasing number of carbon atoms in the side-chains. The method was also applied to the quantitative analysis of the compounds in aqueous solution and, combined with ultrafiltration, for the separation of the eight congeners in spiked human blood serum. A separate simplified method for the quantitative determination of each of the compounds in spiked human blood serum samples was also developed. The methods developed made for the first time possible the simultaneous HPLC analysis of more than one bis(amidinohydrazones). The results obtained indicate that the bis(amidinohydrazones) studied obviously have a distinct tendency to form ion associates with acetate ions and probably also other carboxylate ions in aqueous solution. This aspect may be of biochemical significance, especially concerning the intracellular binding of the compounds. Each one of the compounds studied invariably gave rise to one peak only, this result supporting the theory that the conventional synthesis of each of the compounds gives rise to one geometrical isomer only. This result is completely in agreement with the results of previous proton and carbon NMR spectroscopic as well as X-ray diffraction studies.

Marine sponge bis(indole) alkaloids that displace ligand binding to α1 adrenergic receptors

The α1 adrenergic receptor assay guided fractionation of an extract from the marine sponge Spongosorites sp. led to the isolation of topsentin-B2 (bromotopsentin) as the active compound. Topsentin-B2 and five related bis(indole) marine sponge metabolites were shown to displace ligand binding to α1a and α1b adrenergic receptors with K i values for the α1b receptor ranging from 0.08 to 1.15 μM. All six compounds show selectivity for α1b relative to α1a adrenergic receptors.

Ternary complex of cisplatin with glycine and 1-methyluracil: cis-[(NH 3) 2Pt(glyH- N)(1-MeU- N3)]ClO 4·H 2O

A mixed amino acid (glycine, glyH) nucleobase (1-methyluracilate, 1-MeU) complex of cis-(NH 3) 2Pt(II) has been prepared with the purpose of studying its behavior as a ligand for additional transition metal ions and comparing it with related bis(nucleobase) complexes. The title compound cis-[(NH 3) 2Pt(glyH- N)(1-MeU- N 3)]ClO 4·H 2O ( 3b) crystallizes in the space group P2 1/ n and has cell dimensions a = 12.832(4), b = 8.429(3), c = 16.066(5) A ̊ , β = 110.95(2)°, Z = 4 .

Atomic Proximity Due to Molecular Congestion: Rational Design of Bis(phosphite) Ligands by Restriction of Molecular Motion(1).

The synthesis and conformational analysis of the sterically congested bis(phosphite) ligand {2-{1-{3,5-(t)Bu(2)-2-[2,2'-CHCH(3)(4,6-(t)Bu(2)C(6)H(2)O)(2)PO]C(6)H(2)}Et}-4,6-(t)Bu(2)C(6)H(2)O}(PhO)(2)P (5) are reported. X-ray crystallographic, dynamic (31)P{(1)H} NMR, NOE, DNOE, CP-MAS (31)P NMR, and calculational studies of 5 as well as the structurally related bis(phosphites) 1 and 6 suggest that the conformational freedom of the molecule is severely restricted because of geometric restraints due to steric congestion. A through-space mechanism of coupling is suggested to explain the observed eight-bond P-P J coupling of 27.5 Hz in the (31)P{(1)H} NMR spectrum of 5, which is a result of the proximity of the two phosphorus atoms in 5. The results of this study support the contention that the restriction of molecular motion by steric congestion can be used to rationally design a ligand favoring a particular disposition of phosphorus atoms.

Methane activation by tris(imido) complexes: the effect of metal, ligand and d orbital occupation

An effective core potential (ECP) and molecular mechanics (MM) study of methane activation by tris(imido) complexes is presented. The effects of metal, ligand, and d-orbital occupation on the potential energy surface are determined for d 0 systems M(NH) 3 (M W), [M(NH) 3] − (M  Ta), and [M(NH) 3] + (M  Tc, Re), and for d 2 systems. The [M(NH) 3] − (M  Tc) and M(NH) 3 (M  Os). d 2 (20 electron) tris(imido) complexes are planar, while d 0 (18 electron) complexes are pyramidal, except for [Ta(=NH) 3] −, which is planar. Methane activation is more exothermic for neutral, tris(imido) complexes than related bis(imido) and mono(imido) complexes. For a series of tris(imido) complexes the reaction enthalpy is more sensitive to d orbital occupation than metal or overall charge on the complex. The enthalpic barrier to methane elimination (microscopic reverse of methane activation) is strongly dependent on the extent of π-loading in the product. Methane elimination barriers ( ΔH elim ‡ ) to form tris(imido) complexes are much higher than ΔH elim ‡ to form bis(imido) complexes and mono(imido) complexes. Activation barriers for [2 σ + 2 π] CH activation ( ΔH act ‡ ) of methane by d 2 imidos are considerably larger (≈ 50 kcal mol −1) than activation by d 0 analogues, owing primarily to overcoming a repulsive methane-complex interaction. The methane-complex interaction increases upon going from anion to cation, [Ta(=NH) 3 −] < W(=NH) 3 < [Re(=NH) 3] +, with ΔH add = −8.3, −15.6, and −26.3 kcal mol −1, respectively. For this isoelectronic series more negative ΔH add correlate with larger ΔH act ‡. A combination of ECP and MM calculations suggests that an alkane adduct of [Tc(NAr) 3] + (and its Re analogue) is a plausible experimental target.

Synthesis, spectroscopic and structural characterization of Pd II and Pt II complexes of the cyclic diselenoether 1,5-diselenacyclooctane, [8]aneSe 2

The complexes [M([8]aneSe 2)Cl 2] and [M([8]aneSe 2) 2][PF 6] 2 [M = Pd or Pt, [8]aneSe 2= ▪ have been prepared, and characterized by analysis, UV-vis and multinuclear ( 1H, 77Se{ 1H} and 195Pt) NMR spectroscopy and FAB mass spectrometry. The structures of [Pd([8]aneSe 2)Cl 2]·0.5MeNO 2 [ PdSe = 2.3647(8), 2.3693(8) A ̊ , PdCl = 2.363(2), 2.348(2) A ̊ ] and of the related bis(bidentate) diselenoether model complex [Pt{MeSe(CH 2) 3SeMe} 2][PF 6] 2·2MeCN [ PtSe = 2.414(2), 2.421(2) A ̊ ] have been determined by single-crystal X-ray analyses.

Indolocarbazoles.3. Synthesis of novel aza analogs of staurosporine and K 252a as PKC inhibitors.

Indolocarbazole 4 and arcyriaflavin A 19 reacted under basic conditions with 1-benzyl-2,6-bis (benzotriazolyl)-piperidine to give 5 and 20. As an extension of this methodology other related bis benzotriazole derivatives were synthesized and coupled with 19 to obtain a variety of aza derivatives 3. N-dbenzylation of these compounds gave novel PKC inhibitors.

Structure électronique du complexe organométallique binucléaire du biphényle (η 6 : η 6-C 12H 10)[Cr(CO) 3] 2 et de son dianion η 5: η 5-C 12H 10)[Cr(CO) 3] 22−

In their electrochemical and reactivity studies on the binuclear complex of biphenyl (η 6: η 6-C 12H 10)[Cr(CO) 3] 2 ( 2) Rieke and collaborators suggested that the bireduced species 2 2− should have a structure of the type (η 5: η 5-C 12H 10)[Cr(CO) 3] 2 2−, with a non-planar ligand exhibiting an exocyclic double bond ( i.e. chemical coupling induced by reduction). Unfortunately, no direct structural proof is up-to-date available for this and related bis- chromium complexes. However, in a recent report on related bis-iron compounds of the type (η 6 : η 6-C 12H 10)[Fe (η 5-C 5H 5)] 2 2+ ( 3 2+) it has been possible to structurally characterize a similar chemical coupling upon reduction. This coupling was rationalized on the ground of MS-SCF-Xα theoretical calculations. In this paper, we present similar calculations on the related 2 and 2 2− compounds. The molecular structures which were considered in the calculations for these molecules have been derived from the known structures of the isoelectronic species 3 2+ and 3. Our results indicate that the electronic structures of 2 and 2 2− are very similar to the ones of 3 2+ and 3, respectively. They confirm the suggestion of Rieke and collaborators about the formation of an exocyclic double bond upon reduction which stabilizes significantly the entering electron pair. Even, our calculations suggest that this coupling is likely to be stronger in the case ] of the chromium complexes.