Nathaniel W. Alcock

Synthesis and resolution of 1-(2-diphenylphosphino-1-naphthyl)isoquinoline; a PN chelating ligand for asymmetric catalysis.

Abstract A multistep synthesis resulting in a good yield of the title compound has been developed based on the Pd-catalysed coupling of 1-chloroisoquinoline and 2-methoxy-1-naphthylboronic acid (5). The product is converted into the corresponding trifluoromethanesulphonate (10) by successive demethylation and treatment with (CF3CO)2O, followed by a further Pd-catalysed coupling with Ph2P(O)H. The resulting phosphine oxide (11) was cleanly reduced with HSiCl3. Resolution of the phosphinamine (4) was carried out with the Pd complex derived from (R)-(+)-dimethyl(1-(1-naphthyl)ethyl)amine and PdCl2; the diastereomers were of different stabilities and solubilities and were therefore readily separated. The resolved phosphinamine, [α]D22 ± 153 (c = 1, CHCl3), was enantiomerically stable on heating to 65°C for 24h. X-ray crystal structures of the adduct (16) and the Pd dimer (7) isolated during the initial coupling reaction are presented.

Gaining control over molecular threading: benefits of second coordination sites and aqueous–organic interfaces in rotaxane synthesis

Rotaxane synthesis is facilitated by the presence of two functional groups on the axle reagent; the yield of rotaxane is also substantially improved by reaction in a mixed aqueous–organic phase, compared to a homogeneous phase; the benefit may be associated with reaction at the interface.

Spacer Control of Directionality in Supramolecular Helicates Using an Inexpensive Approach

Careful selection of the spacer group used to separate the metal-binding domains allows control of the directionality in a helix; self-assembly leads uniquely to a double-helical cation with a head-to-tail (HT) configuration (shown schematically) in both the solid state and solution.

Stereochemistry of the 4-hydroxyisoleucine from Trigonella foenum-graecum

Abstract The stereochemistry of the 4-hydroxyisoleucine from fenugreek ( Trigonella foenum-graecum ) has been reinvestigated. The absolute configuration was shown to be (2 S ,3 R ,4 S by a combination of chemical, spectroscopic and X-ray crystallographic techniques.

Crystal structure and emission spectrum of tris(nitrato)-1,4,7,10-tetraozacyclododecane-Europium(III) ☆

Abstract The crystal and molecular structure of the title compound was determined from single crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P 2 1 /c, with Z = 4. Lattice parameters are: a = 12.121(3), b = 8.556(2), c = 15.269(4) A and β = 91.86(2)°. The structure was solved by Patterson and Fourier techniques and refined by least-squares to a final conventional R value of 0.079. The europium(III) ion is 10-coordinate, being bonded to three bidentate nitrate groups and to the four oxygen atoms of the crown ether. The EuO distances are in the range in the range 2.41–2.57 A (average: 2.49(5) A . The nitrate groups are planar with NO bond lengths between 1.21 and 1.29 A . The coordination polyhedron of Eu(III) is discussed. The effective ionic radius of the 10-coordinate Eu(III) ion is 1.178 A .

Immobilization of π-Assembled Metallo-Supramolecular Arrays in Thin Films: From Crystal-Engineered Structures to Processable Materials

Layer-by-layer deposition of π-assembled arrays of discrete metallo units with aryl tails and polystyrenesulfonate gives structurally well-defined thin films. The formation of these films, which is controlled by π-π interactions, metal-ion coordination, and electrostatic interactions, bridges the gap between supramolecular crystal engineering and design of layered materials.

Actinide structural studies. Part 7. The crystal and molecular structures of (2,2′-bipyridyl)dinitratodioxo-uranium(VI) and -neptunium(VI), and diacetato-(2,2′-bipyridyl)dioxo-uranium(VI) and -neptunium(VI)

The crystal structures of the title compounds, [MO2(bipy)(NO3)2][M = U (1) or Np (2)] and [MO2(bipy)(CH3COO)2][M = U (3) or Np (4)](bipy = 2,2′-bipyridyl) have been determined using X-ray diffraction techniques. Complexes (1) and (2) are isomorphous and isostructural crystallising in the monoclinic system, space group C2/c; (3) and (4) are also isomorphous and isostructural, crystallising in the monoclinic system, space group P21/n. All four complexes exhibit hexagonal-bipyramidal co-ordination about the central metal atom. The M–O bond lengths in the MO22+ cations are 1.763(13)(1), 1.728(7)(2), 1.770(8)(mean)(3), and 1.729(10)A(mean)(4). The bidentate oxy-anions have M–O distances of 2.472(8)–2.494(13)A in (1) and (2), and 2.429(9)–2.476(9)A in (3) and (4). For the bidentate 2,2′-bipyridyl group the M–N distances are 2.578(13)(1), 2.564(9)(2), 2.631 (10) and 2.642(9)(3), and 2.835(13) and 2.842(13)A(4). This anomalous increase in the M–N distance between complexes (3) and (4) is attributed to overcrowding around the NpO22+ ion.

Synthesis, structure, and stability in acid of copper(II) and zinc(II) complexes of cross-bridged tetraazamacrocycles

New copper(II) and zinc(II) complexes of cross-bridged tetraazamacrocyclic ligands derived from 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,4,7,10-tetraazacyclotridecane ([13]aneN4), and 1,4,7,10-tetraazacyclododecane (cyclen) have been synthesized. The X-ray crystal structures of the two cyclen-derived complexes have been determined and show both metal ions to be in distorted octahedral environments with the ligand in a cis -folded conformation. The bridged-ligand complexes are remarkably stable kinetically under harsh acidic conditions, as seen from their dissociation reactions. The electrochemical and spectroscopic properties of the Cu 2 complexes have also been investigated. # 2003 Elsevier Science B.V. All rights reserved.

SYNTHESIS OF A HIGHLY STRAINED URANACYCLE : MOLECULAR STRUCTURES OF ORGANOMETALLIC PRODUCTS ARISING FROM REDUCTION, OXIDATION AND PROTONOLYSIS

Abstract The reaction of [U(NN′ 3 )I] [NN′ 3 =N(CH 2 CH 2 NSiMe 2 Bu t ) 3 ] with Group 1 and 2 metal alkyls gives, via metalation of a methylsilyl group, a highly strained metallacycle [U( bit -NN′ 3 )] in high yield. The molecular structure of this compound shows that it has an unusually long UC bond (ca. 2.75 A) and additional CH⋯M agostic interactions. On exposure of the complex in solution to 2 H 2 the methylsilyl groups and the metallacyclic UCH 2 Si group are deuterated, leaving the tert -butyl and methylene groups intact. The analogous thorium metallacycle is prepared from the reactions of [Th(NN′ 3 )Cl], or by attempted reduction of [Th(NN′ 3 )I] with potassium metal in pentane. Attempted reduction of [U(NN′ 3 )I] in a similar manner in toluene gave a high yield of a fascinating dimeric metallacyclic anion {[K(η 6 -C 6 H 5 Me)][U( bit -NN′ 3 )]} 2 , which was characterised by X-ray crystallography. The authenticity of this compound as U(III) is established by near-IR spectroscopy, and also by its production from the reaction of the neutral uranacycle [U( bit -NN′ 3 )] with potassium. A mechanism for the formation of the anion is postulated. Its reaction with benzyl chloride led to oxidation to the parent uranacycle. Oxidation of [U( bit -NN′ 3 )] with air or oxide sources leads to formation of an oxo-bridged dimer with intermonomer metalated methylsilyl groups and pentavalent uranium centres. Reactions of [U( bit -NN′ 3 )] with a range of acids HX occur rapidly, reprotonating the previously metalated methylsilyl group and forming complexes [U(NN′ 3 )X]. For example, lutidinium hydrochloride, diethylamine and tert -butanol gave [(NN′ 3 )UCl], [(NN′ 3 )U(NEt 2 )] and [(NN′ 3 )U(OBu t )], respectively. Reactions with carbon acids were also successful. For example, β-hydropyridines gave η 2 -dehydropyridyl complexes. One of these, [U(NN′ 3 )(η 2 -NC 5 H 4 )], is shown in the first X-ray crystallographic study of such an actinide complex to contain an essentially planar U(η 2 -NC 5 H 4 ) unit. Monosubstituted alkynes react with the uranacycle in a similar manner to give η 1 -alkynyls. The molecular structure of one example shows that the UCC unit is bent (156°) in contrast to other structurally characterised non-bridging alkynyls of the f-elements.

Enantiomeric resolution of supramolecular helicates with different surface topographies

The enantiomeric resolution of an extended range of di-metallo supramolecular triple-helical molecules are reported. The ligands for all complexes are symmetric with two units containing an aryl group linked via an imine bond to a pyridine. Alkyl substituents have been attached in different positions on the ligand backbone. Previous work on the parent compound, whose molecular formula is [Fe(2)(C(25)H(20)N(4))(3)]Cl4, showed that it could be resolved into enantiomerically pure solutions using cellulose and 20 mM aqueous sodium chloride. In this work a range of mobile phases have been investigated to see if the separation and speed of elution could be increased and the amount of NaCl co-eluted with the compounds decreased. Methanol, ethanol and acetonitrile were considered, together with aqueous NaCl : organic mixtures. Effective separation was most often achieved when using 90% acetonitrile : 10% 20 mM NaCl (aq) w/v, which gives scope for scaling up to incorporate the use of HPLC. The overall most efficient (i.e. fastest) separation was generally achieved where the cellulose column was packed with 20 mM NaCl (aq) and the column first eluted with 100% acetonitrile, then with 75% ethanol : 25% 20 mM NaCl (aq) until the M enantiomer had fully eluted and finally with 90% acetonitrile : 10% 20 mM NaCl (aq) until the P enantiomer had been collected. The sequence of eluents ensured minimum NaCl accompanying the enantiomers and minimum total solvent being required to elute the enantiomers, especially the second one, from the column. No helicate with a methyl group on the imine bond could be resolved and methyl groups on the pyridine rings also have an adverse effect on resolution.