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Biomedical subjects

Ian Manners

Publications and source records attributed to Ian Manners.

At least 55 records · Page 3Linked to original sources
PubMed2004

Linear hybrid aminoborane/phosphinoborane chains: synthesis, proton-hydride interactions, and thermolysis behavior.

The reaction of the lithiated phosphine-borane adducts Li[PPhR.BH(3)] or Li[CH(2)-PR(2).BH(3)] with Me(2)NH.BH(2)Cl afforded the hybrid linear species Me(2)NH-BH(2)-PPhR-BH(3) (1, R = Ph; 2, R = H) or Me(2)NH-BH(2)-CH(2)-PR(2)-BH(3) (3, R = Ph; 4, R = Me). Single-crystal X-ray diffraction studies on 1 and 3, the first for linear hybrid aminoborane/phosphinoborane adducts, confirmed the expected four-coordinate N-B-P-B and N-B-C-P-B frameworks. In addition, interactions between the protic N-H and hydridic B-H hydrogen atoms resulted in short intermolecular H...H contacts for 1, whereas 3 was found to possess an exceptionally short intramolecular H...H distance of 1.95 A. Solution and solid state infrared studies on 3 and 4 also suggest that these dihydrogen interactions were maintained even in dilute solution. Hydrogen bond strengths in the range of 7.9 to 10.9 kJ mol(-1) indicate the presence of a relatively weak interaction. The thermal and catalytic dehydrocoupling reactivities of 1-4 were also investigated. Chain cleavage reactions were observed for 1 and 2 upon thermolysis at 130 degrees C to afford species such as Me(2)NH.BH(3), [Me(2)N-BH(2)](2), PhPRH.BH(3) (R = Ph, H), PhPRH (R = Ph, H), Ph(2)PH-BH(2)-PPh(2)-BH(3), and also the low molecular weight polyphosphinoborane [PhPH-BH(2)](n) (M(w) approximately 5000). Similar products were observed for the attempted catalytic dehydrocoupling reactions but under milder reaction conditions (50 degrees C). Thermolysis of 3 at 130 degrees C yielded the six-membered ring [BH(2)-CH(2)-PPh(2)](2) (5), which presumably results from the dissociation of Me(2)NH.BH(3) from 3. Thermolysis of 4 at 90 degrees C afforded Me(2)NH.BH(3) and Me(3)P.BH(3), in addition to a product tentatively assigned as [BH(2)-CH(2)-PMe(2)](2) (6).

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PubMed2004

Synthesis of linear and cyclic carbophosphazenes via an oxidative chlorination strategy.

The use of a mild, oxidative chlorination route for the synthesis of linear and cyclic carbophosphazenes is described. For example, chlorination of the linear PNCN chain Ph(2)P-N=C(Ph)-N(SiMe(3))(2) (1) with C(2)Cl(6) led to the clean formation of the previously known 8- and 6-membered rings [Ph(2)PNC(Ph)N](2) (2) and [Ph(2)PNC(Ph)NP(Ph)(2)N] (3), respectively. In a similar fashion, the N-alkyl-substituted PNCN derivatives, Ph(2)P-N=C(Ph)-N((t)Bu)SiMe(3) (4) and Ph(2)P-N=C(Ph)-N(i)Pr(2) (7) were readily converted by C(2)Cl(6) into the halogenated derivatives ClPh(2)P=N-C(Ph)=N(t)Bu (5) and [ClPh(2)P=N=C(Ph)-N(i)Pr(2)]Cl (8), respectively. Protonation of 5 was accomplished using HCl and gave the carbophosphazenium salt [ClPh(2)P=N-C(Ph)=N((t)Bu)H]Cl (6). In addition, the isolation of a rare 8-membered P(2)N(4)C(2) heterocycle [(Cl(3)P=N)ClPNC(Ph)NP(Cl)(2)NC(Ph)N] (9) from the reaction of PCl(5) and Li[PhC(NSiMe(3))(2)] is reported. Treatment of 9 with one equivalent of GaCl(3) led to the discovery of an unusual Lewis acid-induced ring contraction reaction whereby the (PNCN)(2) ring in 9 is converted into the novel 6-membered P(2)N(3)C heterocyclic adduct [(Cl(3)P=N)ClPNP(Cl)(2)NC(Ph)N].GaCl(3) (10) with concomitant release of PhCN. Structural characterization of compounds 1, 5, 6, and 8-10 by single-crystal X-ray diffraction is also provided.

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PubMed2003

Shell cross-linked cylinders of polyisoprene-b-ferrocenyldimethylsilane: formation of magnetic ceramic replicas and microfluidic channel alignment and patterning.

Stable organometallic cylindrical nanostructures have been prepared by shell cross-linking of PI320-b-PFS53 wormlike micelles in hexane through metal-catalyzed hydrosilylation at 23 degrees C. The cross-linked structures permit the formation of cylindrical ceramic replicas containing size- and separation-tunable arrays of Fe nanoclusters. In addition, microfluidic alignment of the cross-linked cylinders was possible.

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PubMed2003

A reversible tube-to-rod transition in a block copolymer micelle.

A remarkable morphology transition occurs with a change in temperature for a diblock copolymer [poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS40-b-PDMS480, PDI = 1.01)] in n-decane solution. This polymer, which forms nanotubes at 25 degrees C, rearranges to form short dense rods when the solution is heated to 50 degrees C. When the solution is cooled to 25 degrees C, the system evolves back to nanotubes. These experiments demonstrate that both structures are dynamic and represent equilibrium states of the material. Contrast matching static light-scattering measurements on the short dense rods show that the insoluble PFS core is rigid and has a length distribution similar to that seen in electron microscopy images.

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PubMed2003

Transition metal-catalyzed formation of boron-nitrogen bonds: catalytic dehydrocoupling of amine-borane adducts to form aminoboranes and borazines.

A mild, catalytic dehydrocoupling route to aminoboranes and borazine derivatives from either primary or secondary amine-borane adducts has been developed using late transition metal complexes as precatalysts. The adduct Me(2)NH.BH(3) thermally eliminates hydrogen at 130 degrees C in the condensed phase to afford [Me(2)N-BH(2)](2) (1). Evidence for an intermolecular process, rather than an intramolecular reaction to form Me(2)N=BH(2) as an intermediate, was forthcoming from "hot tube" experiments where no appreciable dehydrocoupling of gaseous Me(2)NH.BH(3) was detected in the range 150-450 degrees C. The dehydrocoupling of Me(2)NH.BH(3) was found to be catalyzed by 0.5 mol % [Rh(1,5-cod)(mu-Cl)](2) in solution at 25 degrees C to give 1 quantitatively after ca. 8 h. The rate of dehydrocoupling was significantly enhanced if the temperature was raised or if the catalyst loading was increased. The catalytic activity of various other transition metal complexes (Ir, Ru, Pd) for the dehydrocoupling of Me(2)NH.BH(3) was also demonstrated. This new catalytic method was extended to other secondary adducts RR'NH.BH(3) which afforded the dimeric species [(1,4-C(4)H(8))N-BH(2)](2) (2) and [PhCH(2)(Me)N-BH(2)](2) (3) or the monomeric aminoborane (i)Pr(2)N=BH(2) (4) under mild conditions. A new synthetic approach to the linear compounds R(2)NH-BH(2)-NR(2)-BH(3) (5: R = Me; 6: R = 1,4-C(4)H(8)) was developed and subsequent catalytic dehydrocoupling of these species yielded the cyclics 1 and 2. The species 5 and 6 are postulated to be intermediates in the formation of 1 and 2 directly from the catalytic dehydrocoupling of the adducts R(2)NH.BH(3). The catalytic dehydrocoupling of NH(3).BH(3), MeNH(2).BH(3), and PhNH(2).BH(3) at 45 degrees C to give the borazine derivatives [RN-BH](3) (10: R = H; 11: R = Me; 12: R = Ph) was demonstrated. TEM analysis of the contents of the reaction solution for the [Rh(1,5-cod)(mu-Cl)](2) catalyzed dehydrocoupling of Me(2)NH.BH(3) together with Hg poisoning experiments suggested a heterogeneous catalytic process involving Rh(0) colloids.

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PubMed2003

Bulk microphase segregation of an asymmetric organometallic-inorganic diblock copolymer: a remarkable example of concentric cylinders.

We report that an asymmetric diblock copolymer, poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS90-b-PDMS900, PDI = 1.01, volume fraction PFS = 0.20), self-assembles in the bulk state to form a hexagonal periodic structure with a remarkable morphology. Part of the major component forms the core of concentric cylinders with a mean diameter of 35.5 nm surrounded by a 7 nm thick shell of PFS. The remaining PDMS fills the interstitial spaces. The morphology was elucidated by small-angle X-ray scattering, as well as by scanning and conventional transmission electron microscopy.

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PubMed2003

Chemistry of phosphine-borane adducts at platinum centers: synthesis and reactivity of PtII complexes with phosphinoborane ligands.

Reaction of [Pt(PEt(3))(3)] with the primary and secondary phosphine-borane adducts PhRPH x BH(3) (R=H, Ph) resulted in oxidative addition of a P-H bond at the Pt(0) center to afford the complexes trans-[PtH(PPhR x BH(3))(PEt(3))(2)] (1: R=H; 2: R=Ph). The products 1 and 2 were characterized by (1)H, (11)B, (13)C, (31)P, and (195)Pt NMR spectroscopy, and the molecular structures were verified by X-ray crystallography. In both cases, a trans arrangement of the hydride ligand with respect to the phosphidoborane ligand was observed. When 2 was treated with PhPH(2) x BH(3), a novel phosphidoborane ligand-exchange reaction occurred which yielded 1 and Ph(2)PH x BH(3). Treatment of 2 with one equivalent of depe (depe=1,2-bis(diethylphosphino)ethane) resulted in the formation of the complex cis-[PtH(PPh(2) x BH(3))(depe)] (3), in which the hydride ligand and the phosphidoborane ligand are in a cis arrangement. Treatment of 3 with PhPH(2) x BH(3) was found to result in an exchange of the phosphidoborane ligands to give the complex cis-[PtH(PPhH x BH(3))(depe)] (4) and Ph(2)PH x BH(3). Complex 4 was found to undergo further reaction in the presence of PhPH(2) x BH(3) to give meso-cis-[Pt(PPhH x BH(3))(2)(depe)] (5) and rac-cis-[Pt(PPhH x BH(3))(2)(depe)] (6).

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PubMed2002

Polyferrocenylsilane microspheres: synthesis, mechanism of formation, size and charge tunability, electrostatic self-assembly, and pyrolysis to spherical magnetic ceramic particles.

Pt(0)-catalyzed ring-opening precipitation copolymerization of [1]silaferrocenophanes fcSiMe(2) (3) and the spirocyclic cross-linker fcSi(CH(2))(3) (4) (fc = Fe(eta(5)-C(5)H(4))(2)) was used to prepare polyferrocenylsilane microspheres (PFSMSs) under mild conditions. By varying the reaction conditions, a wide variety of other morphologies was obtained. The effects of temperature, monomer ratio, solvent composition, catalyst concentration, and time on the observed morphology were investigated and interpreted in terms of a mechanism for microsphere formation. The most well-defined particles were formed using equimolar amounts of 3 and 4, in a 50:50 mixture of xylenes and decane at 60 degrees C with gentle agitation. Chemical oxidation of the polymeric microspheres led to positively charged particles (OPFSMSs) which underwent electrostatically driven self-assembly with negatively charged silica microspheres to form core-corona composite particles. Redox titration with controlled amounts of the one-electron oxidant [N(C(6)H(4)Br-p)(3)][PF(6)] in acetonitrile led to the oxidation of the outer 0.15 microm (ca. 32%) of the PFSMSs. The resulting OPFSMSs were reduced back to their neutral form by reaction with hydrazine in methanol. Pyrolysis of the PFSMSs led to spherical magnetic ceramic replicas with tunable magnetic properties that organize into ordered 2-D arrays at the air-water interface under the influence of a magnetic field.

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PubMed2002

Metallochain cluster complexes and metallomacrocyclic triangles based on coordination bonds between palladium or platinum and diphosphinoacetylene ligands.

To explore the potential of the coordination chemistry of Pd and Pt halides with phosphinoacetylene ligands for the generation of novel, highly metallated organometallic coordination polymers, investigations on model compounds [MX2(PPh2 C identical to CPh)2] that exhibit trans-configured Pd centers and cis-configured Pt centers have been performed. The molecular structure of the trans-Pd complexes 2 (M = Pd, X = Br) and 5 (M = Pd, X = I) appeared suitable for the generation of linear materials, whereas the cis-Pt complex 6 (M = Pt, X = I) suggested the prospective formation of ring systems. The presence of acetylene moieties allowed for further increase of metal concentration by cluster formation with [Co2(CO)8]. Two novel bimetal cluster complexes 7 and 8 were obtained from 5 and 6, respectively, and these exhibit a bridging iodine ligand as an interesting structural motif leading to heterocyclic systems with M-I-Co-C-P skeletons (M = Pd or Pt). A similar approach with [Fe2(CO)9] led to the formation of several products, including an unusual Pd-Fe cluster-containing compound 10. The extension of the coordination strategy to rigid bis(phosphinoacetylene) ligands gave rise to strained ring systems. Surprisingly, for the cis-configured PtCl2 center, a rarely observed triangular structure 12 was obtained exclusively. The corresponding PtI2 analog, 13a rearranged over time to form a "ring-fused" system 13b with an extended BINAP-like ligand.

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PubMed2002

Nanotubes from the self-assembly of asymmetric crystalline-coil poly(ferrocenylsilane-siloxane) block copolymers.

Block copolymers with a high asymmetry normally give spherical starlike micelles in a solvent selective for the longer block. We have discovered that samples of poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS-b-PDMS) with block ratios of 1:12 form nanotubes in n-hexane and n-decane, which are poor solvents for PFS. Two block copolymer samples PFS(40)-b-PDMS(480) (M(n) = 45 300, PDI = 1.01) and PFS(80)-b-PDMS(960) (M(n) = 90 500, PDI = 1.01) were synthesized by sequential anionic polymerization. When self-assembly occurs, the PFS blocks aggregate and crystallize to form a shell with a cavity in the middle of the tube, while the PDMS blocks form the corona. The nature of these structures was elucidated by conventional transmission electron microscopy and dark-field scanning transmission electron microscopy. Time- and temperature-dependence studies revealed that a variety of morphologies are formed initially depending on the conditions of sample preparation, but most of them eventually rearrange to form nanotubules. The lengths of the tubes can be varied with time and with the choice of solvents. We have been able to grow nanotubes with lengths reaching 0.1 mm. The presence of the hollow core was confirmed by trapping tetrabutyllead in the cavity and performing energy-dispersive X-ray measurements on the resulting structure.

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PubMed2002

Nucleophilically assisted and cationic ring-opening polymerization of tin-bridged [1]ferrocenophanes.

To obtain mechanistic insight, detailed studies of the intriguing "spontaneous" ambient temperature ring-opening polymerization (ROP) of tin-bridged [1]ferrocenophanes Fe(eta-C(5)H(4))(2)SnR(2) 3a (R = t-Bu) and 3b (R = Mes) in solution have been performed. The investigations explored the influence of non-nucleophilic additives such as radicals and radical traps, neutral and anionic nucleophiles, Lewis acids, protic species, and other cationic electrophiles. Significantly, two novel methodologies and mechanisms for the ROP of strained [1]ferrocenophanes are proposed based on this study. First, as the addition of amine nucleophiles such as pyridine was found to strongly accelerate the polymerization rate in solution, a new nucleophilicallyassisted ROP methodology was proposed. This operates at ambient temperature in solution even in the presence of chlorosilanes but, unlike the anionic polymerization of ferrocenophanes, does not involve cyclopentadienyl anions. Second, the addition of small quantities of the electrophilic species H(+) and Bu(3)Sn(+) was found to lead to a cationic ROP process. These studies suggest that the "spontaneous" ROP of tin-bridged [1]ferrocenophanes may be a consequence of the presence of spurious, trace quantities of Lewis basic or acidic impurities. The new ROP mechanisms reported are likely to be of general significance for the ROP of other metallocenophanes (e.g., for thermal ROP in the melt) and for other metallacycles containing group 14 elements.

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PubMed2002

Bis(trichlorophosphine)iminium salts, [Cl3P=N=PCl3]+, with transition metal halide counter-ions.

The structures of four bis(trichlorophosphine)iminium [[Cl(3)P=N=PCl(3)](+); systematic name: trichloro[(trichlorophosphoranylidene)iminio]phosphorus(V)] salts, namely bis(trichlorophosphine)iminium hexachloroniobate, (Cl(6)NP(2))[NbCl(6)], (I), bis(trichlorophosphine)iminium hexachlorotantalate, (Cl(6)NP(2))[TaCl(6)], (II), bis(trichlorophosphine)iminium tri-micro-chloro-bis[trichlorotitanium(IV)], (Cl(6)NP(2))[Ti(2)Cl(9)], (III), and bis[bis(trichlorophosphine)iminium] di-micro-chloro-bis[tetrachlorozirconium(IV)], (Cl(6)NP(2))(2)[Zr(2)Cl(10)], (IV), have been determined. The P=N distances in the discrete [Cl(3)P=N=PCl(3)](+) moieties in structures (I), (II) and (IV) range from 1.5460 (14) to 1.5554 (16) A, and the P=N=P angles range from 136.8 (3) to 143.4 (4) degrees. The [Cl(3)P=N=PCl(3)](+) cation in (III) is disordered and the calculated geometries for the cation are therefore less reliable. Compounds (I) and (II) are isostructural and the metal anions have slightly distorted octahedral geometries. The anion in compound (III) consists of two distorted octahedral Ti centres linked by three micro (2)-Cl atoms, while in compound (IV), the dianion is derived from two distorted edge-shared ZrCl(6) octahedra.

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PubMed2002

Reversible skeletal substitution reactions involving group 13 heterophosphazenes.

The cyclic boratophosphazene, N(PCl2NMe)2BCl2 1, reacts with two equivalents of AlMe3 to give the aluminatophosphazene heterocycle, N(PCl2NMe)2AlClMe 4. The unprecedented reverse skeletal substitution (Al for B) was accomplished by treating 4 with Ag[BF4] to form the fluorinated boratophosphazene N(PCl2NMe)2BF2 5.

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