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Peter N Horton

Publications and source records attributed to Peter N Horton.

At least 19 recordsLinked to original sources
PubMed2006

Extended dipolar nonlinear optical chromophores based on trans-bis[1,2-phenylenebis(dimethylarsine)]chlororuthenium(II) centers.

Four new complex salts trans[RuIICl(pdma)2LA][PF6]n [pdma = 1,2-phenylenebis(dimethylarsine); LA = 1,4-bis[E-2-(4-pyridyl)ethenyl]benzene (bpvb), n = 1, 1; LA = N-methyl-1,4-bis(E-2-(4-pyridyl)ethenyl)benzene (Mebpvb+), n = 2, 2; LA = N-phenyl-1,4-bis(E-2-(4-pyridyl)ethenyl)benzene (Phbpvb+), n = 2, 3; LA = N-(2-pyrimidyl)-1,4-bis(E-2-(4-pyridyl)ethenyl)benzene (Pymbpvb+), n = 2, 4] have been prepared. The electronic absorption spectra of 1-4 display intense, visible metal-to-ligand charge-transfer (MLCT) bands, with lambda(max) values in the range 432-474 nm in acetonitrile. Intense intraligand charge-transfer (ILCT) bands due to LA are also observed, with lambda(max) values in the range 350-416 nm. Cyclic voltammetric studies in acetonitrile reveal reversible RuIII/II waves with E(1/2) values of ca. 1.05 V vs Ag/AgCl, together with LA-based reduction processes that are irreversible with the exception of 1. Salts 1-4 have been investigated by using Stark (electroabsorption) spectroscopy in butyronitrile glasses at 77 K. These studies have afforded dipole moment changes, Deltamu12, for the MLCT and ILCT transitions which have been used to calculate molecular static first hyperpolarizabilities, Beta0, according to the two-state equation Beta0 = 3Deltamu12(mu12)2/(Emax)2 (mu12 = transition dipole moment, Emax = MLCT/ILCT energy). In contrast with related RuII ammine complexes, replacement of a central E-ethylene bond with a 1,4-phenylene unit does not appear to be an especially effective strategy for combating the NLO transparency-efficiency tradeoff in these pdma complexes. Single-crystal X-ray studies with the complex salts 2 and 3 and also with the pro-ligand salt [Phbpvb+] PF6.0.5HPF6 show that these materials all adopt centrosymmetric packing structures.

Journal Article↗
PubMed2006

Synthesis and characterisation of benzyl phosphino-thioether and -thiolato Pd(II) complexes and their applications in Suzuki coupling reactions.

The synthesis of the benzyl phosphinothioether derivatives Ph(2)PCH(2)CH(Et)SR and their corresponding palladium complexes are reported, where R = CH(2)Ph, R = CH(2)-3,5-Me-C(6)H(3) and R = 1-CH(2)C(10)H(7)(5). Crystallographic data obtained for the complexes Pd(3)Cl(2) and Pd(4)Cl(2) show intra- and inter-molecular pi-pi interactions between the aromatic rings on the P and S substituents, and NOE experiments for Pd(4)Cl(2) show that these interactions persist in solution. The performance of the phosphinothioether palladium complexes in aryl-aryl cross-coupling reactions is compared with that of the corresponding complex of the parent phosphinothiolato ligand Ph(2)PCH(2)CH(Et)S(-)(1). High turnover numbers up to 2000000 are reported for the coupling of bromobenzene, using the palladium dimer [Pd(1)I](2) as the catalyst precursor. Kinetic studies show a linear dependence of the reaction on catalyst loading. The effect of other variables on the cross-coupling reaction, such as temperature, solvent and base, is also reported.

Journal Article↗
PubMed2006

Quadruply hydrogen bonded cytosine modules for supramolecular applications.

In view of the range of properties required from supramolecular materials, there is clearly a need for new strong quadruple hydrogen bonded modules, which can be used in polymer or copolymer synthesis via the self- or hetero-association of complimentary units. A cytosine-based module has been prepared for supramolecular applications using a straightforward synthetic approach. The cytosine module was designed such that it does not undergo tautomeric changes observed with ureidopyrimidinones. The cytosine module was capable of forming quadruple hydrogen bonded assemblies both in solution and in the solid state, and the structure of the dimeric self-assembled unit was confirmed by single-crystal X-ray and solution NMR techniques. The dimerization constant was estimated to be greater than 9 x 106 M-1 in deuterated benzene. The capacity of the cytosine-based module to strongly hetero-associate with the ureidopyrimidinone module was demonstrated, and a supramolecular polymer of a bifunctional unit incorporating the cytosine module and PEG-based linker was described.

Cytosine↗
PubMed2006

Practical synthesis of chiral vinylphosphine oxides by direct nucleophilic substitution. Stereodivergent synthesis of aminophosphine ligands.

[reaction: see text] A practical synthesis of optically pure alkylphenylvinylphosphine oxides is described, utilizing a nucleophilic displacement at phosphorus to install the vinyl moiety. The products were used to prepare classes of P-stereogenic aminophosphine (PN) and aminohydroxyphosphine (PNO) ligands. Stereocontrol can be exerted at various stages of the synthesis, to provide specific combinations of chirality in the final product. The effect of the stereogenic phosphorus and match-mismatch of chiralities of PNO ligands were examined in the asymmetric ruthenium-catalyzed hydrogen transfer reduction of three aryl ketones.

Journal Article↗
PubMed2006

The synthesis of new weakly coordinating diborate anions: anion stability as a function of linker structure and steric bulk.

The successive addition of KCN and Ph3CCl to B(C6F4-C6F5-2)3 (PBB) affords triphenylmethyl salts of the [NC-PBB]- anion. By contrast, the analogous reaction with sodium dicyanamide followed by treatment with Ph(3)CCl leads to the zwitterionic aminoborane H2NB(C12F9)2C12F8, via nucleophilic attack on an o-F atom, together with CPh3[F-PBB]. Whereas treatment of [NC-PBB]- with either PBB or B(C6F5)3 fails to give isolable cyano-bridged diborates, the reaction of Me3SiNC-B(C6F5)3 with PBB in the presence of Ph3CCl affords [Ph3C][PBB-NC-B(C6F5)3]. Due to steric hindrance this anion is prone to borane dissociation. The longer linking group N(CN)2- gives the very voluminous anions [N[CNB(C6F5)3]2]- and [N(CN-PBB)2]-. A comparison of propylene polymerisations with rac-Me2Si(Ind)2ZrMe2 activated with the various boranes or trityl borates gives an anion-dependent activity sequence, in the order [NC-PBB]- < [MeB(C6F5)3]- < [MePBB]- approximately [PBB-NCB(C6F5)3]- approximately [N[CNB(C6F5)3]2]- < [F-PBB]-<< [B(C6F5)4]- < [N(CN-PBB)2]-. The anion [N(CN-PBB)2]- gives a catalyst productivity about 2500 times higher than that of [NC-PBB]- and exceeds that of [B(C6F5)4]- based catalysts. The van der Waals volumes and surface areas of the anions have been calculated and provide a rationale for the observed reactivity trends in polymerisation reactions.

Journal Article↗
PubMed2006

Syntheses and quadratic optical nonlinearities of ruthenium(II) complexes with ethynyl-connected N-methylpyridinium electron acceptors.

We have prepared a number of new dipolar complexes containing ethynyl or buta-1,3-diynyl units linking electron-rich {Ru(II)(NH3)5}2+, trans-{Ru(II)(NH3)4L}+ (L = pyridine or N-methylimidazole), or trans-{Ru(II)Cl(pdma)2}+ [pdma = 1,2-phenylenebis(dimethylarsine)] centers to pyridinium electron acceptors. In acetonitrile solutions at 295 K, the new complexes display unusual blue-shifting of their metal-to-ligand charge-transfer (MLCT) bands as the conjugation is extended, in a fashion similar to that of the corresponding ethenyl systems. Hyper-Rayleigh scattering (HRS) and Stark spectroscopic measurements provide direct and indirect estimates of static first hyperpolarizabilities beta0, and both the linear and nonlinear optical (NLO) properties are temperature- and medium-dependent. Thus, at 77 K in butyronitrile glasses, the MLCT bands display more normal red shifts upon conjugation extension. While the Stark-derived beta0 values generally increase as n (the number of ethynyl units) increases from 0 to 2, the HRS data show maximization at n = 1 for two of the ammine series but an increase upon moving from n = 1 to 2 for the pdma complexes. Comparisons with the analogous ethenyl chromophores show that the latter generally display larger beta0 values, whether determined via HRS or Stark data, and the inferiority of the ethynyl systems in terms of NLO response is more pronounced when n = 2. This differing behavior is attributable primarily to larger increases in the transition dipole moment mu12 (and, hence, donor-acceptor pi-electronic coupling) on elongation in the ethenyl chromophores.

Journal Article↗
PubMed2005

Group 4 salicyloxazolines are potent polymerization catalysts.

Octahedral titanium and zirconium complexes based on salicyloxazoline ligands with sterically demanding ortho-substituents provide a new family of extremely active ethene polymerization catalysts [up to 10(8) g PE (mol bar h)(-1)] which are in some cases "single site".

Journal Article↗
PubMed2005

Intra- and intermolecular N-H...F-C hydrogen-bonding interactions in amine adducts of tris(pentafluorophenyl)borane and -alane.

The reaction between B(C(6)F(5))(3) and NH(3)(g) in light petroleum yielded the solvated adduct H(3)N.B(C(6)F(5))(3).NH(3). Treatment with a second equivalent of B(C(6)F(5))(3) afforded H(3)N.B(C(6)F(5))(3). Attempts to prepare the analogous alane adduct were unsuccessful and resulted in protolysis. Related compounds of the form R'R' 'N(H).M(C(6)F(5))(3) were synthesized from M(C(6)F(5))(3) and the corresponding primary and secondary amines (M = B, Al; R' = H, Me, CH(2)Ph; R' ' = Me, CH(2)Ph, CH(Me)(Ph); R'R' ' = cyclo-C(5)H(10)). The solid-state structures of 13 new compounds have been elucidated by single-crystal X-ray diffraction and are discussed. Each of the borane adducts has a significant bifurcated intramolecular hydrogen bond between an amino hydrogen and two o-fluorines, while N-H...F-C interactions in the alane adducts are weaker and more variable. (19)F NMR studies demonstrate that the borane adducts retain the bifurcated C-F...H...F-C hydrogen bond in solution. Compounds of the type R'R' 'N(H).M(C(6)F(5))(3) conform to Etter's rules for the prediction of hydrogen-bonding interactions.

Journal Article↗
PubMed2005

Design, synthesis, and enzymatic evaluation of N1-acyloxyalkyl- and N1-oxazolidin-2,4-dion-5-yl-substituted beta-lactams as novel inhibitors of human leukocyte elastase.

Human leukocyte elastase (HLE) is a serine protease that very efficiently degrades various tissue matrix proteins such as elastin. The imbalance between HLE and its endogenous inhibitors leads to excessive elastin proteolysis and is considered to be responsible for the onset of chronic obstructive pulmonary disease (COPD). A novel series of C-3-, C-4-, and N-1-substituted azetidin-2-ones were prepared as potential mechanism-based inhibitors of HLE to restore the protease/antiprotease imbalance. N-Acyloxyalkylazetidin-2-ones, 4, and their carbamate counterparts, 5, are weak HLE inhibitors, being 5 times less active than their bicyclic oxazolidin-2,4-dione-substituted analogues, 6, containing an electron-withdrawing substituent at C-4. Compounds 6 containing a C-4 substituent exist as two diastereomeric pairs of enantiomers, each pair presenting similar inhibitory activity against HLE. Comparative docking experiments with the C-4-substituted oxazolidin-2,4-dione inhibitors 6 suggest that only the 4R,5'S and 4S,5'S diastereomers consistently interact with the beta-lactam carbonyl carbon atom accessible to the serine hydroxyl oxygen.

Azetidines↗
PubMed2005

Conformation analyses, dynamic behavior, and amide bond distortions of medium-sized heterocycles. 2. Partially and fully reduced 1-benzazocines, benzazonines, and benzazecines.

Partially and fully reduced forms of benzo-fused eight- to ten-membered nitrogen heterocycles (1-benzazecines, 1-benzazonines and 1-benzazecines) have been prepared. Conformational features, transannular distances and dynamic behavior were studied using X-ray crystallography and VT NMR spectroscopy. The amide moiety in the nine-membered benzazonine ring 5b favors N-pyramidization, whereas the ten-membered benzazecine 5c adopts an amide twist. Molecular mechanics calculations reveals a correlation between the amide twist (tau) and ring stability. The dynamic behavior of the heterocycles in solution were also found to be dependent on the extent and nature of the amide distortion. We thus conclude that ring strain of these medium-sized heterocyclic rings is relieved through amide distortion, which leads to a more stable structure.

Amides↗
PubMed2005

Conformation analyses, dynamic behavior and amide bond distortions of medium-sized heterocycles. 1. Partially and fully reduced 1-benzazepines.

Five 1-benzazepine heterocycles were synthesized by utilizing transition-metal-catalyzed processes in key bond-forming steps. exo-Methylene and methyl substituents were introduced at position 5, as well as a unit of unsaturation between positions 3 and 4, with benzoyl or benzyl N-substituents. Solution- and solid-state structures were examined, using dynamic NMR spectroscopy and X-ray crystallography, corroborated by molecular mechanics calculations. Greater amide distortion is associated with a more stable ground-state structure, which is in turn more reluctant to undergo conformational changes.

Amides↗
PubMed2004

Mixed valence Mn(II)/Mn(III) [3 x 3] grid complexes: structural, electrochemical, spectroscopic, and magnetic properties.

Mn(II)9 grid complexes with a [Mn9(mu-O)12] core, obtained by self-assembly of a series of tritopic picolinic dihydrazone ligands with Mn(II) salts, have been oxidized by both chemical and electrochemical methods to produce mixed oxidation state systems. Examples involving [Mn(III)3Mn(II)6] and [Mn(III)4Mn(II)5] combinations have been produced. Structures are reported for [Mn9(2poap-2H)6](NO3)6.14H2O (1), [Mn9(2poap-2H)6](ClO4)10.10H2O (3), and [Mn9(Cl2poap-2H)6](ClO4)9.14H2O.3CH3CN (10). Structural studies show distinct contraction of the corner grid sites on oxidation, with overall magnetic properties consistent with the resulting changes in electron distribution. Antiferromagnetic exchange in the outer ring of eight metal centers creates a ferrimagnetic subunit, which undergoes antiferromagnetic coupling to the central metal, leading to S=1/2 (3) and S2/2 (10) ground states. Two moderately intense absorptions are observed on oxidation of the Mn(II) grids in the visible and near-infrared (1000 nm, 700 nm), associated with charge transfer transitions (LMCT, IVCT respectively). Compound 1 crystallized in the monoclinic system, space group P2 1/n, with a=21.308(2) A, b=23.611(2) A, c=32.178(3) A, beta=93.820(2) degrees . Compound 3 crystallized in the tetragonal system, space group I, with a=b=18.44410(10) A, c = 24.9935(3) A. Compound 10 crystallized in the triclinic system, space group P, with a=19.1150(10) A, b=19.7221(10) A, c=26.8334(14) A, alpha=74.7190(10) degrees, beta=77.6970(10) degrees, gamma=64.7770(10) degrees. The facile oxidation of the Mn(II)9 grids is highlighted in terms of their potential use as molecular based platforms for switching and data storage.

Journal Article↗
PubMed2004

Modeling novel radiopharmaceuticals: mono-C6-substituted PnAO ligands (PnAO = 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime).

The solid-state behavior of six novel 6-substituted PnAO (propylene amine oxime) complexes (6-11) involving Tc(V), Co(III), and Cu(II) salts is reported. Each of the Tc complexes 6-8 has the C6-substituent located equatorially in a six-membered chelate ring involving a Tc=O unit which has the expected boat geometry. The C6-substituent therefore has little effect on the conformational behavior of the PnAO complex and thus provides an attractive site for further modification. The Co(III) complex 9 has the expected octahedral geometry, while the Cu(II) complexes 10 and 11 form square-based pyramids capped by water molecules. One Cu(II) system (10) contains two unique complexes in the asymmetric unit which are associated via multiple hydrogen bonds to a BF(4) anion, the remaining BF(4) anion being loosely hydrogen bonded to a coordinating water molecule. The cobalt and copper complexes 9-11 each exhibit a chair conformation for the six-membered chelate ring.

Crystallography, X-Ray↗