Sigrid Wocadlo

Vanadium(V) Complexes of O,N,O-Donor Tridentate Ligands Containing the {VVO(OMe)}2+ Unit: Syntheses, Structures and Properties

Abstract Syntheses, characterisation and properties of two complexes containing the oxovanadium(V) methoxide unit have been described. Deprotonated benzoylhydrazones of 2–hydroxy–5–methoxy‐benzaldehyde (H2bhsOMe) and 2–hydroxy–5–chlorobenzaldehyde (H2bhsCl) were used as coligands. Crystal structures of both the complexes were determined. In solid state one of them is a dinuclear species [VO(bhsOMe)(OMe)]2 (1) whereas the other one is a mononuclear complex [VO(bhsCl)(OMe)(HOMe)](2). The dinegative ligands coordinate the metal ions via phenolate–O, imine–N and deprotonated amide–O atoms. In 1, the metal ions of two square pyramidal VO(bhsOMe)(OMe) units share the methoxide groups to form a dinuclear species. The oxygen of a methanol molecule completes the hexacoordination of the metal centre in 2. In each of the two distorted octahedral VO5N moieties of 1 the bridging methoxide oxygen and in that of 2 the methanol oxygen is trans to the corresponding oxo group. Both the complexes are redox active. The VO3+ to VO2+ reduction potentials (vs Ag/AgCl) of 1 and 2 are observed at −0.25 and −0.04 V, respectively. The band positions in the electronic spectra and the redox potentials reflect the influence of the substituents present on the ligands.

Half-sandwich complexes of titanium and zirconium with pendant phenyl substituents. The influence of ansa-aryl coordination on the polymerisation activity of half-sandwich catalysts

Abstract Benzyl-substituted Group 4 half-sandwich complexes (η5-C5H4R)TiCl3 (1a, R=CMe2Ph; 2a, R=CMe2CH2Ph; 4a, R=SiMe2Ph; 5a, R=CHPh2) are readily accessible from C5H4(R)SiMe3 and TiCl4, while the reaction of C5H4(CMe2CH2Ph)SiMe3 with ZrCl4(SMe2)2 affords (C5H4CMe2CH2Ph)ZrCl3·dme (3a). The structures of 1a, 4a and 5a have been determined by X-ray diffraction; the compounds are monomeric in the solid state. Alkylation readily affords the corresponding trimethyl and tribenzyl derivatives; the crystal structure of (η5-C5H4CHPh2)Ti(CH2Ph)3 (5b) has been determined. Treatment of (η5-C5H4R)MMe3 with [Ph3C]+[B(C6F5)4]− in dichloromethane at low temperatures generates cationic [(η5-C5H4R)MMe2]+ complexes; the complexes are stabilised by π-coordination to the phenyl ring to give ansa-arene complexes with one- and two-carbon linkages. The complexes catalyse the polymerisation of propene. Compared to the system Cp*TiMe3/B(C6F5)3 the ansa complexes show reduced catalytic activity and enhanced chain termination.

Synthesis and characterisation of uranyl substituted malonato complexes: Part I. Structural diversity with dimethylmalonate and different counter-cations

Abstract Uranyl dimethylmalonato complexes with different metal to ligand ratios and connectivity, 1:2 monomeric, dimeric and 2:3, 3:4 infinite chain structures have been prepared and characterised by elemental analysis, thermal analysis, IR and 13C CPMAS NMR spectroscopy, and X-ray crystallography. The different structural types are isolated by the use of different counter-cations. Two new kinds of binding mode of malonate with uranyl have been identified, tridentate (μ2 1,3-bidentate and 1,5-bidentate) and tetradentate (1,3-bidentate with both carboxylate groups). A basis for the prediction of structural type from the results of 13C CPMAS NMR spectroscopy is proposed. The structures of the crystallographically characterised products can be rationalised in terms of templating by the counter-cations, which appears to be influenced by the size of the counter-cations and the tendency to maximise hydrogen bonding in the lattice.

Synthesis, spectroscopic, and X-ray crystallographic characterisation of thorium(IV) and uranium(IV) malonato and substituted malonato compounds

Abstract With doubly protonated piperazine or ethylenediamine as cations, eight Th(IV) malonato or substituted malonato complexes have been prepared and characterised by elemental analysis, thermal analysis, IR and 13C CPMAS NMR spectroscopy. One polymeric U(IV) malonato complex has also been prepared and characterised by elemental analysis, thermal analysis and IR spectroscopy. (C4H12N2)2[Th(C3H2O4)4]·H2O (2), (C2H10N2)2[Th(C3H2O4)4(H2O)] (3), (C4H12N2)2[Th(C4H4O4)4]·2H2O (4), (C2H10N2)2[Th(C5H6O4)4]·5H2O (6) and [U(C3H2O4)2(H2O)3]n (9) have been further characterised by single-crystal X-ray diffraction. Two types of monomeric anion structure are identified in the Th compounds: four 1,5-bidentate ligands in a distorted square antiprismatic geometry, giving coordination number (CN) 8; and four 1,5-bidentate ligands and a coordinated H2O molecule in a capped square antiprismatic geometry, giving CN 9. The U compound has a 3D polymeric structure, with U in an approximately capped square antiprismatic geometry, achieving CN 9 from two 1,5-bidentate ligands, each of which also bridges through a carbonyl oxygen to an adjacent U centre, and three H2O molecules. In the crystallographically-characterised Th compounds, the Thue5f8O and Cue5f8O distances are correlated with the carbonyl resonance positions in the 13C CPMAS NMR spectra, allowing prediction of structural types in the non-crystalline compounds.

Dinuclear iron(III)–metal(II) complexes as structural core models for purple acid phosphatases†

A series of mixed-valent iron and mixed-metal FeIII–MII (Mxa0=xa0Zn, Cu, Ni or Co) complexes of the phenolate-hinged dinucleating ligand 2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-tert-butylphenolato(1–), bpbp– have been prepared and characterized. Both exogenous bidentate bridging groups and different terminal ligands bound to each different metal ion at the exogenous site were identified. The structure of the mixed-valence complex [(bpbp)Fe2(F)2(H2O)2][BF4]2 confirms that it is a rare example of a dimetallic complex of a single-atom hinged acyclic dinucleating ligand with a ‘non-bridged’ arrangement at the exogenous bridging site. Mossbauer spectroscopy indicates valence trapping in this complex with the parameters, ΔEQ 3.242 mm s–1, δ 1.169 mm s–1 and ΔEQ 0.221 mm s–1, δ 0.460 mm s–1, respectively for the high spin Fe2+ and high spin Fe3+ ions. Crystals of [(bpbp)Fe2(F)2(H2O)2][BF4]2·4H2O are triclinic, space group P (no. 2), with axa0=xa012.695(1), bxa0=xa019.197(2), cxa0=xa010.202(1) A, αxa0=xa0102.95(1), βxa0=xa097.61(1), γxa0=xa093.76(1)°, Zxa0=xa02. The structure was refined to Rxa0=xa00.1009 on F using 4338 reflections with Ixa0>xa02σ(I) (wR2 on all data and F n 2xa0=xa00.3522). The FeII and FeIII atoms are bridged asymmetrically by the phenolic oxygen atom of bpbp– with FeII–O 2.175(6) A and FeIII–O 2.033(6) A with a FeIIIxa0·xa0·xa0·xa0FeII distance of 3.726(2) A. The two terminal fluoride ions are bound to the FeIII atom and strongly hydrogen bonded to two water molecules bound to the adjacent FeII atom. This complex may model the mode in which fluoride ions bind to the active site of the purple acid phosphatases (PAPs) thereby inhibiting the activity of these enzymes. Tetrahedral oxo anions are known also to inhibit PAPs and to mimic this inhibition a FeIII–ZnII complex incorporating molybdate bridging groups was prepared. Crystals of [(bpbp)FeZn(MoO4)2]·C3H7OH· 2H2O are monoclinic, space group P21/n with axa0=xa011.773(13), bxa0=xa021.394(7), cxa0=xa017.001(11) A and βxa0=xa090.98(7)°, Zxa0=xa04. The structure was refined to Rxa0=xa00.0434 on F using 3758 reflections with Ixa0>xa02σ(I) (wR2 on all data and F n 2xa0=xa00.1339). The FeIIIxa0·xa0·xa0·xa0ZnII distance is 3.819(4) A. A series of acetate-bridged complexes were prepared by the novel method of diffusing ethyl acetate or isopropyl acetate into mixtures of Hbpbp and iron perchlorate in the presence and absence of a second type of metal ion. The acetate bridging groups are the result of the hydrolysis of the alkyl acetate. These complexes have the general formulation [(bpbp)FeM(CH3CO2)2][ClO4]2. Crystals of [(bpbp)FeCu(CH3CO2)2][ClO4]2·0.5CH3OH are monoclinic, space group P21/n

Spin frustration and concealed asymmetry: structure and magnetic spectrum of [Fe3O(O2CPh)6(py)3]ClO4·py

The oxo-centred trinuclear complex [Fe3O(O2CPh)6(py)3]ClO4·py and its fully deuteriated analogue have been synthesized. X-Ray crystallography at Txa0=xa0233 K shows that the complex has threefold symmetry, space group P63/m. Incoherent inelastic neutron scattering spectra at Txa0=xa01.5 K however show the presence of two inequivalent sets of molecules, one a static “isosceles” coupled system, with two J values for the three metal–metal interactions, the other a dynamic system, with rapid pseudorotation between equivalent isosceles geometries. Combining infrared and neutron scattering data, the distortion of the cluster has been estimated.

Anion dependent deprotection of a thioether group in Schiff base NS2 ligands results in new mononuclear and dinuclear thiolato nickel complexes

The synthesis and characterisation of three Schiff base compounds of nickel with NS2 donor groups is described as part of our research in structural modelling of nickel hydrogenase enzymes. 2-Aminothiophenol and 2-tert-butylthiobenzaldehyde reacted in ethanol to form a benzothiazolidine derivative, which is isolated as a yellow solid. The benzothiazolidine ring opens upon reaction with nickel acetate in ethanol to form a mononuclear complex, [Ni(tBuL1)2], 1, which crystallises in the monoclinic space group P21/n with cell dimensions, axa0=xa014.665(4), bxa0=xa014.800(7), cxa0=xa014.923(6) A, βxa0=xa094.45(3)°. Compound 1 is mononuclear with a cis N2S2 chromophore, which is square planar, but slightly distorted towards tetrahedral, and which shows weak interactions with two hydrogens of the ligands (Ni–H distances of 2.52 and 2.58 A). These C–H·xa0·xa0·Ni interactions are retained in solution as reflected in the 1H NMR spectra of 1. With other nickel salts, the same benzothiazolidine ligand reacts in ethanol to form dinuclear species [Ni(L1)]2 2, after loss of the protecting tertiary butyl group. Complex 2 crystallises in the monoclinic space group P21/c with cell dimensions, axa0=xa011.753(3), bxa0=xa011.977(3), cxa0=xa020.275(4) A, βxa0=xa0123.67(1)°. An analogous ligand, synthesised from 2-aminoethanethiol and 2-tert-butylthiobenzaldehyde, was not isolated, but was used in a template reaction with nickel salts in ethanol to form the dinuclear compound [Ni(L2)]2 3. Complex 3 crystallises in the monoclinic space group P21/c with cell dimensions axa0=xa015.049(4), bxa0=xa010.554(2), cxa0=xa012.921(4) A, βxa0=xa0108.68(2)°. Compounds 2 and 3 are dinuclear, in a ‘butterfly’ shape, with bridging thiolates. The nickel ions in these two dinuclear complexes are in a NS3 chromophore with a square planar geometry.

Cationic zirconocene complexes with benzyl and Si(SiMe3)3 substituted cyclopentadienyl ligands

Alkyl zirconocenes [Zr(η-C5H4R)2X2] (where Rxa0=xa0CH2Ph, Xxa0=xa0Cl 1a or Me 1b; Rxa0=xa0CHPh2, Xxa0=xa0Cl 2a or Me 2b; Rxa0=xa0Si(SiMe3)3, Xxa0=xa0Cl 4a or Me 4b) and for comparison [Zr(η-C5H5)(η-C5H4CH2Ph)Cl2] 3a were prepared and characterised. The reactions of these compounds with the methide abstracting reagents B(C6F5)3, B(o-C6F5C6F4)3 and [Ph3C]+[B(C6F5)4]– were investigated by low temperature NMR spectroscopy. Compound 1b reacts with [Ph3C]+[B(C6F5)4]– to form the homodinuclear complex [{Zr(η-C5H4CH2Ph)2Me}2(µ-Me)]+[B(C6F5)4]–. The related compound [{Zr(C5H4CH2Ph)2Me}2(µ-Me)]+[MeB(C6F5)3]– 5a was formed from the reaction of 1b with 0.5 equivalent of B(C6F5)3. Reaction between 1b and 1 equivalent B(C6F5)3 gave [Me(η-C5H4CH2Ph)2Zr(µ-Me)B(C6F5)3] 6a and the ion pair [Zr(η-C5H4CH2Ph)2Me][MeB(C6F5)3] 6b which are in equilibrium with each other. A similar observation was made when 2b was used instead of 1b. The sterically more demanding 4b does not show this behaviour. The role of the ligands in ethylene polymerisation was investigated.

Structural characterisation and bioconjugation of an active ester containing oxorhenium(V) complex incorporating a thioether donor

A simple new 2,3,5,6-tetrafluorophenyl ester containing diamide–thioether–thiol bifunctional chelating agent LH3, HS(CH2)2SCH2C(O)NHCH2C(O)NH(CH2)3C(O)OC6HF4, has been synthesised. The key intermediates were prepared using standard peptide chemistry procedures. Reaction of LH3 with [Bu4N][ReOCl4] formed an uncharged oxorhenium(V) complex, which was characterised by X-ray structural analysis. The five-co-ordinate complex showed approximately square-pyramidal geometry with an apical oxo group and a basal ligand set comprising a deprotonated thiol group, two deprotonated amide groups, and a thioether group. A second complex of stoichiometry [ReO(LH2)2]Cl was formed by reaction of LH3 with a rhenium(V) gluconate intermediate in water at pH 4.7. The 1∶1 complex [ReOL] was conjugated with the small protein N-TIMP-2 by aminolysis at a lysine residue, to form a 1∶1 adduct as established by electrospray mass spectrometry.