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Michael B Hursthouse

Publications and source records attributed to Michael B Hursthouse.

At least 19 recordsLinked to original sources
PubMed2007

Self-assembly of halogenated cobaltacarborane compounds: boron-assisted C--H...X--B hydrogen bonds?

Full structural characterisation and complete synthetic procedures for three monohalogenated cobaltacarborane compounds closo-[3-Co(eta5-C5H5)-8-X-1,2-C2B9H10] (X=Cl (1), Br (2), I (3)) and the dibromo derivative closo-[3-Co(eta5-C5H5)-8,9-Br2-1,2-C2B9H9] (4) are reported. The supramolecular structures of 1, 3, and 4 reveal the existence of intermolecular C--HX--B interactions. The role of these interactions has been investigated through a CSD search and subsequent analysis of the reported crystalline compounds. The results show that halogens become reasonably good hydrogen-bond acceptors when bonded to boron and, in this respect, are comparable in strength to metal-bound halogens.

Boron↗
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

Luminescent Pt(II)(bipyridyl)(diacetylide) chromophores with pendant binding sites as energy donors for sensitised near-infrared emission from lanthanides: structures and photophysics of Pt(II)/Ln(III) assemblies.

The complexes [Pt(bipy){CC-(4-pyridyl)}(2)] (1) and [Pt(tBu(2)bipy){CC-(4-pyridyl)}(2)] (2) and [Pt(tBu(2)-bipy)(CC-phen)(2)] (3) all contain a Pt(bipy)(diacetylide) core with pendant 4-pyridyl (1 and 2) or phenanthroline (3) units which can be coordinated to {Ln(diketonate)(3)} fragments (Ln = a lanthanide) to make covalently-linked Pt(II)/Ln(III) polynuclear assemblies in which the Pt(II) chromophore, absorbing in the visible region, can be used to sensitise near-infrared luminescence from the Ln(III) centres. For 1 and 2 one-dimensional coordination polymers [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) are formed, whereas 3 forms trinuclear adducts [3{Ln(hfac)(3)}(2)] (tta=anion of thenoyl-trifluoroacetone; hfac=anion of hexafluoroacetylacetone). Complexes 1-3 show typical Pt(II)-based (3)MLCT luminescence in solution at approximately 510 nm, but in the coordination polymers [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) the presence of stacked pairs of Pt(II) units with short PtPt distances means that the chromophores have (3)MMLCT character and emit at lower energy ( approximately 630 nm). Photophysical studies in solution and in the solid state show that the (3)MMLCT luminescence in [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) in the solid state, and the (3)MLCT emission of [3{Ln(hfac)(3)}(2)] in solution and the solid state, is quenched by Pt-->Ln energy transfer when the lanthanide has low-energy f-f excited states which can act as energy acceptors (Ln=Yb, Nd, Er, Pr). This results in sensitised near-infrared luminescence from the Ln(III) units. The extent of quenching of the Pt(II)-based emission, and the Pt-->Ln energy-transfer rates, can vary over a wide range according to how effective each Ln(III) ion is at acting as an energy acceptor, with Yb(III) usually providing the least quenching (slowest Pt-->Ln energy transfer) and either Nd(III) or Er(III) providing the most (fastest Pt-->Ln energy transfer) according to which one has the best overlap of its f-f absorption manifold with the Pt(II)-based luminescence.

Binding Sites↗
PubMed2006

Five-coordinate Pd(II) orthometallated triarylphosphite complexes.

The reaction of the orthopalladated triarylphosphite complexes [{Pd(mu-Cl){kappa(2)-P,C-P(OC(6)H(2)-2,4-R(2))(OC(6)H(3)-2,4-R(2))}(2)] (R = H, (t)Bu) with bis(2-diphenylphosphinoethyl)phenylphosphine leads to a five-coordinate palladium(II) (R = H) and a mixture containing four-and five-coordinate species (R = (t)Bu). The crystal structure of the five-coordinate species [Pd{kappa(2)-P,C-(P(OC(6)H(4))(OC(6)H(5))(2)}{bis(2-diphenylphosphinoethyl)phenylphosphine}][SbF(6)] is presented. This complex reacts with hydrogen peroxide or [AuCl(tht)] to give four-coordinate complexes in which the displaced phosphine residue is either oxidised or coordinated to gold chloride; this demonstrates that the five-coordinate complexes are labile in solution. By contrast, the reactions of the dimeric precursors with 1,1,1-tris(diphenylphosphinomethyl)ethane give four-coordinate complexes in the solid state, although evidence is presented that the smaller phosphite-containing system is five-coordinate at room temperature or higher in solution.

Journal Article↗
PubMed2006

Phosphonioalkylthiosulfate zwitterions--new masked thiol ligands for the formation of cationic functionalised gold nanoparticles.

We report the synthesis and structural characterisation of a new family of stable phosphonioalkylthiosulfate zwitterions, R3P+ (CH2)nS2O3- (R = Ph or Bu, n = 3,4,6, 8 or 10) which behave as cationic masked thiolate ligands with applications in the functionalisation of gold nanoparticles, having potential as new diagnostic biorecognition systems. The ligands were prepared by treatment of omega-bromoalkylphosphonium salts with sodium thiosulfate. The crystal and molecular structures of the zwitterions (R = Ph, n = 3) and (R = Bu, n = 3) were determined. A series of phosphonioalkanethiolate-capped gold nanoparticles dispersed in water was prepared by borohydride reduction of potassium tetrachloroaurate in the presence of the zwitterions in a dichloromethane-water system. UV-visible spectroscopy and scanning transmission electron-microscopy indicated that capped nanoparticles of ca. 5 nm diameter were present.

Crystallography, X-Ray↗
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

Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles.

N-Alkylation of 4,5-dihydroimidazoles with alkene-containing bromomethyl ketones and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU gives rise to an intramolecular 1,3-dipolar cycloaddition reaction that affords (via a reaction cascade involving eliminative ring-opening, recyclisation and prototropic tautomerism) unexpected hexahydropyrrolo[1,2,3-de]quinoxaline products. Steric bulk in both the dihydroimidazole and the dipolarophile allows isolation of an imidazo[1,2-a]indole, the initial product of cycloaddition. When the bromomethyl ketone contains no other functionality, or when cycloaddition is inhibited due to steric constraints, the dihydroimidazolium ion undergoes ring-opening hydrolysis followed by recyclization of the exposed amino ketone to afford either 3-alkyl-1-formylpiperazine-2-ones or 3-aryl-1-formyl-1,4,5,6-tetrahydropyrazines.

Journal Article↗
PubMed2006

Further errors in polymorph identification: furosemide and finasteride.

Reassessment of the reported single-crystal X-ray diffraction characterization of polymorphs of furosemide and finasteride shows that, in each case, incomplete data collections have resulted in the mistaken identification of two forms that are, in fact, identical.

Crystallography, X-Ray↗
PubMed2006

Fluoride anion binding by cyclic boronic esters: influence of backbone chelate on receptor integrity.

A systematic investigation of fluoride anion binding properties as a function of chelate backbone has been carried out for ferrocene functionalised boronic esters of the types FcB(OR)2 and fc[B(OR)2]2 [Fc = ferrocenyl = (eta5-C5H5)Fe(eta5-C5H4); fc = ferrocendiyl = Fe(eta5-C5H4)2]. Cyclic boronic esters containing a saturated five- or six-membered chelate ring are readily synthesized from ferrocene, and selectively bind fluoride via Lewis acid/base chemistry in chloroform solution. The resulting complexes are characterized by relatively weak fluoride binding (e.g.K = 35.8 +/- 9.8 M(-1) for FcBO2C2H2Ph2-S,S), and by cathodic shifts in the ferrocene oxidation potential that form the basis for electrochemical or colorimetric fluoride detection. The fluoride selectivity of these systems is attributed to relatively weak Lewis acidity, resulting in weak F- binding, and essentially no binding of potentially competitive anions. By contrast, more elaborate Lewis acid frameworks based on calix[4]arene (calixH4), such as (FcB)2calix or fcB2calix, do not survive intact exposure to standard fluoride sources (e.g. [nBu4N]F.xH2O solutions in chloroform or acetonitrile). Instead B-O bond cleavage occurs yielding the parent calixarene; the differences between alkoxo- and aryloxo-functionalised derivatives can be rationalised, at least in part, by consideration of the differences in electron donating capabilities of RO- (R = alkyl, aryl).

Boronic Acids↗
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

Structural investigations of phosphorus-nitrogen compounds. 7. Relationships between physical properties, electron densities, reaction mechanisms and hydrogen-bonding motifs of N3P3Cl(6 - n)(NHBu(t))n derivatives.

A series of compounds of the N3P3Cl(6 - n)(NHBu(t))n family (where n = 0, 1, 2, 4 and 6) are presented, and their molecular parameters are related to trends in physical properties, which provides insight into a potential reaction mechanism for nucleophilic substitution. The crystal structures of N3P3Cl5(NHBu(t)) and N3P3Cl2(NHBu(t))4 have been determined at 120 K, and those of N3P3Cl6 and N3P3Cl4(NHBu(t))2 have been redetermined at 120 K. These are compared with the known structure of N3P3(NHBu(t))6 studied at 150 K. Trends in molecular parameters [phosphazene ring, P-Cl and P-N(HBu(t)) distances, PCl2 angles, and endo- and exocyclic phosphazene ring parameters] across the series are observed. Hydrogen-bonding motifs are identified, characterized and compared. Both the molecular and the hydrogen-bonding parameters are related to the electron distribution in bonds and the derived basicities of the cyclophosphazene series of compounds. These findings provide evidence for a proposed mechanism for nucleophilic substitution at a phosphorus site bearing a PCl(NHBu(t)) group.

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

The structural and stereogenic properties of pentaerythritoxy-bridged cyclotriphosphazene derivatives: spiro-spiro, spiro-ansa and ansa-ansa isomers.

Reactions of pentaerythritol with hexachlorocyclotriphosphazene, N3P3Cl6, and gem-disubstituted cyclotriphosphazene derivatives, N3P3Cl4R2 [R = Ph, NHBu(t) or (OCH2CF2CF2CH2O)0.5] gave a series of pentaerythritol-bridged derivatives linked spiro-spiro, spiro-ansa and ansa-ansa. The structures and stereogenic properties of the products were characterised by X-ray crystallography and 31P NMR spectroscopy on addition of the chiral solvating agent, (S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol. Molecules with spiro-spiro and spiro-ansa bridged gem-disubstituted cyclophosphazenes [R = Ph, NHBu(t) or (OCH2CF2CF2CH2O)0.5] are found to be chiral and exist as racemates. Molecules with ansa-ansa bridged cyclophosphazenes [R = Cl or (OCH2CF2CF2CH2O)0.5] have been characterised for the first time and are shown to have meso configurations. Analysis of crystal structure data shows that the six-membered chair form of the spiro rings and the eight-membered boat-chair form of the ansa rings in the bridged compounds are similar to analogous spiro and ansa exocyclic ring conformations of 1,3-propanedioxy-derivatives of cyclophosphazenes.

Journal Article↗
PubMed2005

Self-assembly of mercaptane-metallacarborane complexes by an unconventional cooperative effect: a C-H...S-H...H-B hydrogen/dihydrogen bond interaction.

The existence of a dihydrogen bond (S-H...H-B) and its combination with a C-H...S hydrogen bond in an unusual cooperative effect are demonstrated from a combination of experimental and theoretical methods. This cooperative effect seems to be responsible for self-assembly of mercaptane-metallacarborane complexes such as closo-[3-Ru(eta6-C6H6)-8-HS-1,2-C2B9H10] (1) and closo-[3-Co(eta5-C5H5)-8-HS-1,2-C2B9H10] (3), which present identical supramolecular two-dimensional polymeric networks. The findings, besides documenting structurally the first S-H...(H-B)2 dihydrogen bond and the unconventional cooperative ability of a boron-attached SH group, prove that substituted carboranes have the potential to serve as building blocks for assembling complex structures.

Journal Article↗