David Hughes

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Papers by David Hughes

An Eta-2-Allene Complex Of Rhenium Formed From An Alkyne - X-Ray Structure Of Recl(Eta-2-H2c-C=Chph)(Ph2pch2ch2pph2)2

ABSTRACT

Influence Of Ligand Environment On The Protonation Reactions Of Hydrazido(2-) Complexes Of Molybdenum And Tungsten - X-Ray Structures Of M(8-Quin)(Nnh2)(Pme2ph)3 I(M=Mo Or W - 8-Quin=Quinolin-8-Olate)

ABSTRACT The complexes [MX2(NNH2)(PMe2Ph)3] (M = Mo or W; X = Cl, Br or I) give ammonia with H2SO... more ABSTRACT The complexes [MX2(NNH2)(PMe2Ph)3] (M = Mo or W; X = Cl, Br or I) give ammonia with H2SO4/MeOH, the yield depending upon X. Ammonia is also obtained from [Mo(8-quin)(NNH2)(PMe2Ph)3]I (M = Mo, 8-quin = quinolin-8-olate) but the tungsten analogue gives hydrazine only. Crystal structures of the 8-quin molybdenum and tungsten complexes are reported.

Alkali-metal complexes. Part VII. Crystal and molecular structures of the o-nitrophenolatobis(1,10-phenanthroline) complexes of sodium and rubidium

The structures of the title complexes have been determined by X-ray analysis from diffractometer ... more The structures of the title complexes have been determined by X-ray analysis from diffractometer data. The sodium complex has triclinic crystals, a= 10·436(6), b= 10·062(6), c= 14·867(7)A, α= 96·98(2), β= 104·02(1), γ= 119·12(4)°, and its structure was determined by direct methods. The rubidium complex, isostructural with the corresponding potassium and caesium complexes, is also triclinic, a= 11·413(6), b= 13·214(6), c= 10·068(15)A, α= 99·06(5)β= 114·80(5), γ= 101·78(3)°; this structure was determined from Patterson and electron-density maps. The structures were refined by least-squares methods to R 0·074 (Na complex, 1371 observed reflections) and 0·051 (Rb complex, 2107 observed reflections).In the sodium complex, the cation is six-co-ordinate, interacting with the three chelating ligands in pseudo 32 symmetry, and the crystal structure of this complex is of monomeric units. The rubidium complex has a similar pseudo-three-fold symmetry of the chelating ligands but, with a larger co-ordination sphere, the cation also accepts co-ordination with a second o-nitrophenolate ion, which thus bridges cations about a centre of symmetry. Dimeric units, bound by van der Waals' forces, form the crystal structure. The packing arrangements in both complexes appear to depend on the interactions of overlapping phenanthroline molecules about centres of symmetry.The phenanthroline molecules in both complexes have similar dimensions: all are non-planar, but there is no characteristic pattern of bending or twisting. The cations are displaced from the mean planes of the phenanthroline molecules by up to 0·63 A. In the o-nitrophenolate ions, the variations in bond lengths and angles in the ions are significant and are explained in terms of resonance structure and second-order hybridisation effects. The nitro-groups are rotated about the C–N bonds by 18·6 (Na) and 14·5°(Rb).

Preparation and crystal structure of [{W(N2)2(PEt2Ph)3}2(µ-N2)]

Preparation of potential macroligands for alkali-metal ions using open-chain polyether carboxylic-acids and tricarbonylbis(triphenylphosphine)ruthenium - X-ray crystal-structure of dicarbonylbis 1-(ortho-carboxymethoxyphenoxy)-2-(ortho-hydroxyphenoxy)et hanato(1-) bis-(triphenylphosphine)rutheniu...

The preparation and X-ray crystal structure of the title compound is described. The compound crys... more The preparation and X-ray crystal structure of the title compound is described. The compound crystallizes in the triclinic space group P(no. 2) with unit-cell dimensions a= 9.677(2), b= 23.161 (6), c= 15.432(5)A, α= 92.91 (2), β= 91.29(4), γ= 102.16(3), and Z= 2. The structure was refined to a final R factor of 0.094 for 4 681 reflections. The ruthenium ion is octahedrally co-ordinated by two mutually cis carbonyl ligands, two mutually trans phosphine ligands, and two mutually cis L ligands, [1-(o-carboxymethoxyphenoxy)-2-(o-hydroxyphenoxy)ethanato(1–)] each bound to ruthenium by one oxygen of the carboxylate group. The benzene rings of the phosphine ligands are staggered, and prevent close approach of the two L ligands required to form an oxygen cavity suitable for complexation with alkali metals.

A tris-dinitrogne complex. Preparation and crystal structure of mer-[Mo(N2)3(PPrn2Ph)3]

Early Transition Metal Complexes Bearing a C-Capped Tris(phenolate) Ligand Incorporating a Pendant Imine Arm: Synthesis, Structure, and Ethylene Polymerization Behavior

The ligand 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-(2,6-diisop... more The ligand 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-(2,6-diisopropyl)phenylimine] (L 1 H3) was reacted with MCl4 (M = Ti, Zr) or MCl5 (M = Nb, Ta) to give complexes of the type [MCl2( L 1 H2)2] (M = Ti ( 1 ); Zr ( 2 )), [NbCl3( L 1 H)] ( 3 ), or [TaCl4( L 1 H2)] ( 4 ), respectively. Single crystal X-ray diffraction of 1 - 4 revealed common “iminium” species resulting in zwitterionic complexes. Reaction of [V(Np-tol)(On-Pr)3] with L 1 H3 afforded [{(VNp-tol)( L 1 H)}2(µ-On-Pr)2] ( 5 ), and a second complex [(VO)2(µ-O)( L 3 H)2] ( 6 ) ( L 3H being derived from 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-p-tolylimine]). The condensation reaction between 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2-hydroxybenzaldehyde] ( L 0 H3) and o-phenylenediamine (1,2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-bis-3-[2,2'-methylenebis(4,6-di-tert-butyl...

Combining two-directional synthesis and tandem reactions. Part 4: A concise approach to the spirocyclic core of halichlorine and the pinnaic acids

A synthesis of the spirocyclic core structure of halichlorine, an inhibitor of the induced expres... more A synthesis of the spirocyclic core structure of halichlorine, an inhibitor of the induced expression of VCAM-1 and the pinnaic acids, inhibitors of PLA 2 , is presented. A two-directional strategy is employed, in conjunction with a tandem oxime formation/Michael addition/cycloaddition to form the key azaspirocyclic skeleton in a very direct manner.

Structural Variation and Magneto-Structural Correlation in Two New Dinuclear Bis(µ2-Phenoxo)-Bridged Cu(II) Schiff-Base Complexes: Catalytic Potential for the Peroxidative Oxidation of Cycloalkanes

Synthesis and crystal structure determination of copper(II) and iron(III) complexes of 2-(2-pyridyl)benzothiazole

ABSTRACT Two complexes [CuII(pbt)(dmf)Cl2] and [FeIII(pbt)Cl3], where pbt is 2-(2-pyridyl)benzoth... more ABSTRACT Two complexes [CuII(pbt)(dmf)Cl2] and [FeIII(pbt)Cl3], where pbt is 2-(2-pyridyl)benzothiazole, and dmf is dimethylformamide, were prepared by the reaction of metal chlorides with pbt solutions. The structures of the products were identified by elemental analysis, usual spectroscopic methods and X-ray diffraction analysis. The crystal data revealed penta-coordination around both metal ions, with trigonal bipyramidal geometries. 2-(2-pyridyl)benzothiazole binds to both CuII and FeIII in the N,N-chelation manner and leaves the S atom uncoordinated.

Ferrocenyloxazoline-Derived Planar Chiral Palladacycles: C–H Activation, Transmetalation, and Reversal of Diastereoselectivity

Reinvestigation of the palladation of (S)-2-ferrocenyl-4-(methylethyl)oxazoline with Pd(OAc)2 in ... more Reinvestigation of the palladation of (S)-2-ferrocenyl-4-(methylethyl)oxazoline with Pd(OAc)2 in CH2Cl2 was found to proceed with a dr of 3.6:1 in favor of the resulting S,Sp palladacycle. A similar 4:1 dr was obtained using Na2PdCl4 in MeOH. As an alternative approach, highly diastereoselective lithiation (dr >100:1) and transmetalation were investigated. Addition of PdX2(COD) (X = Cl, Br) to (S,Rp)-2-lithio-1-(2′-(4′-methylethyl)oxazolinyl)ferrocene resulted in double halide substitution and formation of cis-(S,S,Sp,Sp)-bis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-N]palladium(II) (42% from X = Cl, 50% from X = Br). Selective monoprotodepalladation with HCl gave an S,Sp palladacycle containing a removable ferrocenyloxazoline ligand. Addition of PdCl2(MeCN)2 to mercuracycles in acetonitrile, themselves generated from Li–Hg transmetalation, followed by a brine wash gave (S,Sp)-di-μ-chlorobis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-N]dipalladium(II) as a single d...

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Synthesis of Meso‐Substituted Subphthalocyanine–Subporphyrin Hybrids: Boron Subtribenzodiazaporphyrins

The first syntheses of hybrid structures that lie between SubPhthalocyanines and SubPorphyrins ar... more The first syntheses of hybrid structures that lie between SubPhthalocyanines and SubPorphyrins are reported. The versatile, single-step synthetic protocol uses a preformed aminoisoindolene to provide the bridging methine unit and its substituent, while trialkoxyborates simultaneously act as Lewis acid/template and provider of the apical substituent. Selection of each component therefore allows controlled formation of diverse, differentially functionalised systems. The new hybrids are isolated as robust, pure materials that display intense absorption and emission in the mid-visible region. They are further characterised in solution and solid state by variable temperature NMR spectroscopy and X-ray crystallography respectivel

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Indirect approach to C-3 branched 1,2-cis-glycofuranosides: synthesis of aceric acid glycoside analogues

Aceric acid (3-C-carboxy-5-deoxy-alpha-l-xylofuranose) residues are present in pectic polysacchar... more Aceric acid (3-C-carboxy-5-deoxy-alpha-l-xylofuranose) residues are present in pectic polysaccharide rhamnogalacturonan II (RG II) in the form of synthetically challenging 1,2-cis-glycofuranosides. To access synthetic fragments of RG II incorporating aceric acid, a four-step procedure based on C-2 epimerisation of initially prepared 1,2-trans-glycofuranoside was developed. Readily available derivatives of branched-chain l-lyxofuranose bearing a 3-C-vinyl group as a masked 3-C-carboxyl group were investigated as potential precursors of aceric acid units. In the first step of the procedure, installation of a participating group at C-2 of the furanose ring ensured stereocontrol of the O-glycosylation, which was carried out with the thioglycoside of 2-O-acetyl-3,5-di-O-benzyl-3-C-vinyl-L-lyxofuranose. After the glycosylation step, the 2-O-acetyl group was removed, the free 2-OH group was oxidised and the resulting ketone was finally reduced to form the C-3-vinyl-L-xylofuranoside. The use of L-Selectride in the key reduction reaction was essential to achieve the required stereoselectivity to generate 1,2-cis-furanoside.

The synthesis, structure and ethene polymerisation catalysis of mono(salicylaldiminato) titanium and zirconium complexes

The silyl ethers 3- Bu-t - 2- ( OSiMe3) C6H3CH = NR ( 2a- e) have been prepared by deprotonation ... more The silyl ethers 3- Bu-t - 2- ( OSiMe3) C6H3CH = NR ( 2a- e) have been prepared by deprotonation of the known iminophenols ( 1a - e) and treatment with SiClMe3 ( a, R = C6H5; b, R = 2,6- Pr-i 2C6H3; c, R = 2,4,6- Me3C6H2; d, R = 2- C6H5C6H4; e, R = C6F5). 2a - c react with TiCl4 in hydrocarbon solvents to give the binuclear complexes [ Ti {3- Bu-t - 2-( O) C6H3CH = N( R)} Cl( mu - Cl-3) TiCl3] ( 3a - c). The pentafluorophenyl species 2e reacts with TiCl4 to give the known complex Ti {3- Bu-t - 2- ( O) C6H3CH = N( R)} Cl-2(2). The mononuclear five- coordinate complex, Ti {3- Bu-t - 2- ( O) C6H3CH = N( 2,4,6- Me3C6H2)} Cl-3 ( 4c), was isolated after repeated recrystallisation of 3c. Performing the dehalosilylation reaction in the presence of tetrahydrofuran yields the octahedral, mononuclear complexes Ti {3- Bu-t - 2- ( O) C6H3CH = N( R)} Cl-3( THF) ( 5a - e). The reaction with ZrCl4( THF) (2) proceeds similarly to give complexes Zr {3- Bu-t - 2- ( O) C6H3CH = N( R)} Cl-3( THF) ( 6b -...

Arylzinc Complexes as New Initiator Systems for the Production of Isobutene Copolymers with High Isoprene Content