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Bromination of (AsPh2)2S leads to cleavage of the sulfide bridge to give AsPh2Br when 1 mol of bromine is used but with 2 mols the product is the polybromide, [AsPh2Br2]2[Br8], containing the previously unknown [AsPh2Br2]+ cation and a rare [(Br3)−…(Br2)…(Br3)−] ensemble whose short (yet not covalent) Br2…Br3 contacts have previously supported tentative description as an octabromide Br82− anion. X-ray crystallography shows that the compound has a three dimensional supramolecular structure based on cooperativity of weak intermolecular Csingle bondH…π, Csingle bondH…Br hydrogen bonds and secondary Br…Br interactions in the solid state. The electronic structure and the stability of the [AsPh2Br2]2[Br8] are rationalized using DFT and HF calculations and molecular orbital considerations.

With an exceptional portfolio of properties such as high water content and cross-linked nature, hydrogels can provide an ideal and compatible environment not only to encapsulate but also to control the delivery of biological therapeutics. However, uncontrollable degradation, release and especially swelling impose limitations on our ability to engineer these gels. Herein a zirconium metallogel is proposed that utilizes zirconyl tetramers as the metal component in conjunction with a nucleic acid (adenine). The variable gel-formation temperature as a simple step of gel formation allows the tuning of gel formation and properties by controlling the adenine-nucleobase interactions. Reconstitution, entrapment, degradation, cytotoxicity, and release of bovine serum albumin (BSA) as a negatively charged macromolecular therapeutic agent were investigated. The controllable and sustained release of BSA, offers a route to new tailorable protein delivery applications.

The phosphinimine, trimethylsilyl-substituted BIPM ligand [BIPM = bis(iminophosphorano)methanide] has been used to stabilise CH(Ph2PNSiMe3)2MgFe(η5-C5H5)(CO)2 (1), which is a structurally authenticated complex exhibiting a direct, unsupported bond between an alkaline earth metal and a transition metal. The FTIR-measured carbonyl stretching frequencies for this complex suggest that there is a polarisation of charge from the transition metal fragment to the magnesium centre. The presence of a polar metal-metal bond in 1 is confirmed by DFT calculations, which suggest that the Mg−Fe bond is predominantly ionic in nature.

In two binuclear complexes of formula [Cu 2 (AnthenMe 2 ) 2 (μ 1,3 -SCN) 2 (NCS) 2 ] ( 1 ) and [Cu 2 (AnthenMe 2 ) 2 (μ 1,1 -N 3 ) 2 (N 3 ) 2 ] ( 2 ), where AnthenMe 2 is the bidentate N , N -donor Schiff base formed by anthracene-9-aldehyde and N , N -dimethylethylenediamine, each Cu(II) center adopts a square pyramidal geometry with N 4 S and N 5 coordination environments for 1 and 2 , respectively. In spite of the very different Cu⋯Cu separations in these two complexes (5.141 A in 1 and 3.4744 A in 2 ), the molecules show very similar catalytic efficiency for the aerial oxidation of 3,5-ditertiarybutyl catechol (DTBCH 2 ) to the corresponding quinone (DTBQ), probably because similar mononuclear complexes are involved in the catalytic reaction in both the cases. The k cat and k cat / K M values of 1.53(0.20) × 10 4 h −1 and 5.71(0.15) × 10 7 M −1 h −1 for 1 and 1.56(0.12) × 10 4 h −1 and 5.61(0.12) × 10 7 M −1 h −1 for 2 are comparable to the best values reported in the literature for Cu(II) model complexes of catecholase.

The Co(III) and Ni(II) complexes [Co(L2)2(bpy)]Cl (1) and [Ni(L2)2(phen)] (2) (where L2 is a monoanionic bidentate hydrazone ligand and bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been synthesized and characterized by infra-red, UV–Vis, ESI-MS spectroscopies and elemental analyses. Complexes 1 and 2 were structurally characterized by single crystal X-ray diffraction. Structural analysis reveals a distorted octahedral coordination environment around the metal center with an MN4O2 chromophore [M = Co(III) and Ni(II)], with the hydrazone ligand acting as a monoanionic bidentate N,O-donor. Binding of complexes 1 and 2 with calf thymus DNA (CT-DNA) was investigated by UV–Vis absorption, fluorescence spectroscopy and viscosity measurements. Complex 1 shows excellent catecholase mimicking activity with 3,5-di-tert-butylcatechol (3,5-DTBCH2) as the substrate. Kinetic measurements suggest the rate of catechol oxidation follows saturation kinetics with respect to the substrate and the kcat value was found to be quite high, with a value of 1.00 × 105 h−1.

Over recent decades, the rapid development of lanthanide-based coordination polymers (Ln-based CPs) has been made possible by the implementation of crystal engineering concepts in the design of materials with desired properties. Because of the effects of lanthanide ions on properties of Ln-based CPs, it is essential to understand the ability of the Ln ion to bind to donors. This ultimately leads to the construction of architectures with unique characteristics and applications. Within the great variety of functional groups, carboxylate type ligands are of interest in the construction of various architectures that not only depend on carboxylate coordination modes but are also influenced by their spatial arrangement. This study will concisely summarises the various architectures of Ce(III)-based CPs resulting from molecular self-assembly of Ce(III) and O/N-donor polydentate organic ligands. Furthermore, advanced applications of Ce(III)-based CPs in simultaneous luminescent sensing and detection of metal ions and radical organic species (ROS), and also the utilization of Ce(III)-based CPs as effective precursors for ceria (CeO2) are reviewed. This review covers research conducted on Ce(III)-based CPs after the year 2000.

Two square planar Ni(II) complexes of general formula NiL2 and an octahedral Ni(II) complex of formula Ni(LH)2Cl2 have been synthesized and characterized, where LH and L are protonated and deprotonated forms of bidentate hydrazone ligands. The spectroscopic and cyclic voltammetric studies of these complexes are also reported. X-ray crystal structure determination of the three complexes show that in two of the complexes Ni(II) have a N2O2 donor environment in a square planar geometry, while in the remaining one Ni(II) is in a distorted octahedral coordination environment of N2O2Cl2 donor atoms. The role of H-bonding interactions in determining the octahedral versus square planar geometry of Ni(II) is discussed. DFT calculations are used to understand the nature of the frontier orbitals.

The Schiff base 2-[(E)-(quinolin-3-ylimino)methyl]phenol (H-QMP) was crystallized in Pc space group and complexed with Ni(II) and Co(II) in [M(QMP)2] and Cu(II) and Zn(II) in [M(QMP)(CH3COO)]H2O compositions. Elemental analyses, mass spectrometry, IR, UV–vis spectroscopy, conductance study and magnetic susceptibilities were used to characterize the complexes. The thermograms obtained in the range of 30–1000 °C were used for kinetic and thermodynamic calculations. The activation energies and order of pyrolysis were calculated using Horowitz–Metzger method. The calculated activation energies were subsequently used for the calculations of thermodynamic parameters including ΔS*, ΔH* and ΔG*. It was found that the thermal stability and activation energy follow the order Cu(II) > Ni(II) > Co(II) > Zn(II) and E Ni * > E Cu * > E Co * > E Zn * , respectively. All the compounds were also studied for their urease and α-chymotrypsin inhibition, showing medium to moderate activities for both the enzymes except nickel complex. Nickel complex shows IC50 = 9.9 ± 0.124 μM ± SEM, and the activity was rationalized by carrying out molecular modeling studies.

Two-step reductive removal of the chiral template from optically active pyrroloimidazoles, available from 1,3-dipolar cycloaddition of homochiral 4,5-dihydroimidazolium ylides, gives optically active substituted pyrrolidines. Selective manipulation of the substituents affords, e.g., naturally occurring and other optically active proline derivatives, and optically active pyrrolizidines and indolizidines.

The use of the 2,6-diphenoxyphenyl ligand has facilitated the stabilisation of lithium, silane and stannane complexes. The ortho-metallation reaction between 1,3-(PhO)2C6H4 and nBuLi yields 2,6-(PhO)2C6H3Li (1); the crystallographically characterised dimer [2,6-(PhO)2C6H3Li(OEt2)]2 ([1.Et2O]2) can be obtained by the crystallisation of 1 from diethyl ether. The reaction between 1 and Me3ECl gives rise to the structurally authenticated complexes 2,6-(PhO)2C6H3EMe3 [E = Si, 2; E = Sn, 3].

The solution chemistry and solid-state structures of two new uraniumVI metal–organic compounds, (tataH)2[(UO2)2(pdtc)2(μ-OH)2]·2H2O (1) and (AcrH)2[(UO2)(pydc)2] (2), [where tata = 1,3,5-triazine-2,4,6-triamine, Acr = acridine, pydc = pyridine-2,6-dicarboxylate and pdtc = pyridine-2,6-bis(monothiocarboxylate)] have been investigated. These compounds were obtained via proton-transfer methodology by reacting UO22+ with the preformed proton-transfer systems (tataH)2(pdtc) and (AcrH)2(pydc), respectively, in aqueous solution, after evaporation of the solvent. Our results show that noncovalent interactions such as hydrogen bonds, sulfur···sulfur, and π···π interactions, when acting cooperatively, are driving forces for the selection of different structures. The protonation constants of Acr, tata, pdtcH2, and pydcH2, the building blocks of the proton-transfer systems (tataH)2(pdtc) and (AcrH)2(pydc), and the stability constants of these systems were determined by potentiometric studies in a dioxane/H2O (1:1 v/v) mixture. The stoichiometry and the formation stability constants of complexes formed on reacting pydcH2/Acr or pdtcH2/tata 1:1 molar mixtures with the UO22+ ion in dioxane/H2O (1:1 v/v) were investigated by potentiometric pH titration methods. The stoichiometries of the complex species formed in solution were compared with those observed for the crystalline metal ion complexes 1 and 2.

Reaction of 2-(2',6'-diethylphenylazo)-4-methylphenol (L 2 ) with [Ir(PPh 3 ) 3 Cl] afforded two organoiridium complexes 3 and 4 via C-H bond activation of an ethyl group in the arylazo fragment of the L 2 ligand. In both the complexes the azo ligand binds to iridium as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride (in the case of complex 3) or chloride (in the case of complex 4) are also coordinated to the metal center. A similar reaction of [Ir(PPh 3 ) 3 Cl] with 2-(2',6'-diisopropylphenylazo)-4-methylphenol (L 3 ) yielded another organoiridium complex 5, where migration of one iso-propyl group from its original location (say, the 2' position) to the corresponding third position (say, the 4' position) took place through C-C bond activation. In this complex the modified azo ligand binds to iridium as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride are also coordinated to the metal center. The structures of complexes 3 and 4 have been optimized through DFT calculations. The structure of complex 5 has been determined by X-ray crystallography. All the complexes show characteristic 1 H NMR signals and intense transitions in the visible region. Cyclic voltammetry on all the complexes shows an oxidation within 0.66-1.10 V vs SCE, followed by a second oxidation within 1.15-1.33 V vs SCE and a reduction within -0.96 to -1.07 V vs SCE.

The sterically demanding pyridines 2,6-Ar2C6H3N [Ar = 2,4,6-Me3C6H2 (1) or 2,4,6-Pri3C6H2 (2)] were prepared by a palladium catalysed Kumada C–C coupling reaction in high yield. Pyridine 1 reacted with one equivalent of GaCl3 to afford the tetra-chloro gallate–pyridinium ion pair complex [GaCl4]−[2,6-(2,4,6-Me3C6H2)2C6H3NH]+ (3). Contrastingly, pyridine 2 reacted with one equivalent of GaCl3 to afford the anticipated donor-acceptor complex [GaCl3{2,6-(2,4,6-Pri3C6H2)2C6H3N}] (4). Complexes 1–4 have been characterised variously by single crystal X-ray diffraction, NMR, CHN, and mass spectrometry.

Transition-metal carbene X–H insertion reactions (X=N or O) have been employed in the simple conversion of anilines and phenols into indoles and benzofurans, respectively. Thus copper(II) catalyzed N–H insertion reactions of α-diazo-β-ketoesters with N-methylanilines followed by treatment with acidic ion-exchange resin gives indoles. In a similar manner, dirhodium(II) catalyzed O–H insertion reactions of α-diazo-β-ketoesters with phenols followed by treatment with PPA gives benzofurans.

A study of copper-phosphoramidite-catalysed ZnR2 and AlR3 additions to 1,1′-dicarbonyl-activated cyclic Michael acceptors has revealed high enantioselectivities for AlR3 (R = Me, Et) 1,4-addition to a range of 3-acylcoumarins (85–98% ee, trans:cis ∼90:10) using commercial or readily available ligands. Large substituents at the 6-position, and to some extent at the 5-position, of the coumarin are less well tolerated, nor is truncation of the coumarin motif to a comparable 2-acylcyclohexenone (ee values up to 78%).

Reaction of N-(4-R-phenyl)picolinamide (R = OCH3, CH3, H, Cl and NO2) with [Ir(PPh3)3Cl] in refluxing ethanol in the presence of a base (NEt3) affords two yellow complexes (1-R and 2-R). The 1-R complexes contain an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphines, a chloride and a hydride. The 2-R complexes contain an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphines and two hydrides. Similar reaction of N-(naphthyl)picolinamide with [Ir(PPh3)3Cl] affords two organometallic complexes, 3 and 4. In complex 3 the amide ligand is coordinated to the metal center, via C–H activation of the naphthyl ring at the 8-position, as a dianionic tridentate N,N,C donor, along with two triphenylphosphines and one chloride. Complex 4 is similar to complex 3, except a hydride is bonded to iridium instead of the chloride. Structures of the 1-OCH3, 2-Cl and 4 complexes have been determined by X-ray crystallography. All the complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a IrIII–IrIV oxidation within 0.50–1.16 V vs. SCE and a reduction of the coordinated amide ligand within −1.02 to −1.25 V vs. SCE.

The substitution of symmetrical N-protected diketopiperazines (DKPs) via enolate intermediates has been studied. The enolate reactions were highly diastereocontrolled, leading to enantiopure DKP products if chiral amino acid precursors were employed, and giving racemic products, starting with centrosymmetric DKPs, even when a chiral lithium amide base was used to generate the lithium enolate. With unsymmetrical DKPs derived from proline and either alanine, phenylalanine or valine, the enolate substitution occurred with high regio- and stereoselectivity on the proline residue. This enabled the synthesis of substituted DKPs that could be cyclised via cationic processes to give the bicyclo[2.2.2]diazaoctane core structure present in paraherquamide and stephacidin natural products.

Oxidation of the indolo[2,3-a]carbazole 16, readily obtained in six steps from indigo, followed by deprotection results in formation of the indolo[3,2-j]phenanthridine quinone alkaloid calothrixin B 2, demonstrating the viability of the proposed biosynthetic route to this unique ring system.

Four ruthenium (II) complexes of general formula Ru(PPh 3 ) 2 (L) 2 have been synthesized and characterized. The spectroscopic and cyclic voltammetric studies of these complexes are also reported. X-ray crystal structure determination of two of the complexes reveal that Ru(II) occupies trans , trans , trans -( t , t , t ) N 2 O 2 P 2 centrosymmetric octahedral environments, with the ligand pair occupying the equatorial plane. 31 P NMR confirms the presence of two trans -PPh 3 groups in all the complexes. The transformation of the complexes in dichloromethane solution is studied by spectrophotometry and 31 P NMR spectroscopy.

Reaction of 2-(2'-hydroxyphenylazo)phenol with [Rh(PPh3)(3)Cl] in refluxing benzene in presence of triethylamine afforded a red complex in which the ligand is coordinated to rhodium as a tridentate O,N,O-donor. However, similar reaction of [Rh(PPh3)(3)Cl] with 2-(2'carboxyphenylazo)-4-methylphenol yielded two complexes, viz. a blue one and a green one. In both the complexes the ligand is coordinated as C,N,O-donor. However, in the blue complex orthometallation takes place from the ortho-carbon atom, which bears -COOH group via decarboxylation and in green one orthometallation occurs from the other ortho-carbon. Structures of all the three complexes were determined by X-ray crystallography. In all the three complexes rhodium is sharing the equatorial plane with the tridentate ligand and a chloride, and the two triphenylphosphines are axially disposed. All of the complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE and a reduction of the coordinated azophenolate ligand on the negative side. (c) 2006 Elsevier B.V. All rights reserved.

The use of a Schiff-base calixpyrrole (L) as a dinucleating ligand for early transition metals is described. Salt elimination reactions between the crystallographically-characterised [K4(THF)3(PhMe)(L)] and titanium(III) and vanadium(III) halides form the new dinuclear complexes [(MCl)2(L)] (M = Ti, V). Adventitious, and partial, oxidation of [(VCl)2(L)] resulted in the formation of the unusual mixed-valence vanadyl complexes [(V O)(S)(VCl)(L)] (S = THF or pyridine), which both adopt desired Pacman geometries in the solid state in which the oxo ligand is accommodated within the dinuclear molecular cleft.

In the discussion that follows some of the more recent progress in the area of anion binding by synthetic polyamine receptors is presented, with emphasis given to work undertaken by the authors’ groups. A continuing theme in these studies has been the relationship between receptor structure and its anion extraction properties. Systematic solvent extraction and structural studies for halide and perrhenate complexes with polyamines of tripodal, macrocyclic and macrobicyclic architecture that contain both aromatic moieties and four to eight amine functions have been performed in order to derive relevant structure-binding/extractability relationships. The results demonstrate that the binding and extraction behaviour of the polyamines towards halides and perrhenate is a complex function of their structural features, degree of protonation and lipophilic properties. The extraction is characterized by the preferred formation of mono- and diprotonated amine species in the organic phase. X-ray structure studies of iodide and perrhenate complexes with open-chain tetraamino derivatives and octaamino cryptands in different protonation states lead to the conclusion that in the first case only limited chelation of the anion occurs and in the second only highly protonated species are able to encapsulate the anion. The structural patterns observed are strongly influenced by the presence of water molecules in the crystals.

The one-pot bromo- and chloro-methylation of various 5-substituted salicylaldehydes with paraformaldehyde and hydrobromic or hydrochloric acid has been achieved. This approach establishes a convenient and flexible method to attach functional arms to salicylaldehydes for further applications in organic and coordination chemistry. Examples are described using 3-bromomethyl-5-t-butylsalicylaldehyde in the synthesis of piperazine-containing heteroditopic ligands as receptors for metal salts.

Regioselective enolate formation, followed by stereoselective electrophilic quenching of unsymmetrical proline-derived diketopiperazines (DKPs), enabled the synthesis of variously substituted DKPs, including one substrate which could be further substituted and cyclised to give the bicyclo[2.2.2]diazaoctane core structure present in paraherquamide and stephacidin natural products.

Ferrocene reacts with hexafluoroacetone trihydrate in refluxing octane to afford >80% yields of [CpFe(η5-C5H4C(CF3)2OH)] (X-ray), carrying out the reactions at 180 °C gives an additional 5% yield of [Fe(η5-C5H4C(CF3)2OH)2] (X-ray).The mono alcohol is lithiated with ButOK/BunLi/TMEDA affording partial conversion to mixtures of [CpFe(1,2-η5-C5H3C(CF3)2OH)(X)] and [Fe(η5-C5H4X)(1,2-η5-C5H3C(CF3)2OH)(X)] (X = SMe, CPh2OH) upon reaction with Me2S2 or O CPh2.For X = CPh2OH both structures are crystallographically characterised.Enantiopure [CpFe(1,2-η5-C5H3C(CF3)2OH)(SMe)] can be prepared from (R)-[CpFe(η5-C5H4S(O)C6H4Me)] via [CpFe(1,2-η5-C5H3S(O)C6H4Me)(C(CF3)2OH)] (X-ray) or [CpFe(1,2-η5-C5H3S(O)C6H4Me)(SMe)].Related procedures allow the preparation of [CpFe(1,2-η5-C5H3CPh2OH)(Y)] (Y = SMe, CHO (X-ray), C(CF3)2OH) and[CpFe(1,2-η5-C5H3C(CF3)2OH)(CHO)].

A series of azathia- and azaoxathiacrown ether macrocycles have been prepared in good yields via the use of N-boc-bis(2-chloroethyl)amine as a precursor, which minimises undesirable side reactions and facilitates subsequent deprotection to the free cyclic amine. The mono-aza macrocycles, [12]aneNS3, [12]aneNOS2, [15]aneNS4, [15]aneNO2S2 and [16]aneNS4 have been prepared via this route. The single-crystal X-ray structure of [12]aneNS3 · HBr · 2H2O confirms the macrocycle to be distorted quadrangular with the S-centres lying along the edges and six out of 12 torsion angles less than 90°. The synthesis of di-aza macrocycles utilising the diamide precursors, N,N′-bis(chloroacetyl)-1,2-diaminoethane and N,N′-bis(chloroacetyl)-1,3-diaminopropane, affords the free macrocycles [12]aneN2S2, [15]aneN2S3, [15]aneN2OS2, [16]aneN2S3 and [19]aneN2S4 after reduction of the intermediate cyclic amides. Reaction of 3,6-dioxa-1,8-octanediamine with the dimethyl ester of thiadiglycolic acid followed by reduction affords [15]aneN2O2S, while the hydroxy-substituted macrocycles [20]aneS6(OH)2, [13]aneS4(OH), and [26]aneS8(OH)2 have been prepared by reaction of 1,3-dichloro-2-hydroxypropane with the appropriate dithiol. The crystal structure of [20]aneS6(OH)2 shows two endo- and four exo-dentate S-centres as observed in the parent [18]aneS6. The N-aryl substituted macrocycles N-4-NO2Ph-[12]aneNS3 (N-4-nitrophenyl-7-aza-1,4,10-trithiacyclododecane) and N-4-NH2COPh-[12]aneNS3 (N-4-benzamido-7-aza-1,4,10-trithiacyclododecane) have been prepared by reaction of 4-substituted bis-tosylated N,N-bis(2-hydroxyethyl)aniline with 3-thia-1,5-pentanedithiol.

Silver(I) complexes of heterobidentate ligands that incorporate one or two N-heterocyclic carbene moieties coupled with an alcohol or amine group have been made by direct deprotonation of ligands of the form [HOCR1R2CH2(1-HC{NCHCHNR})][X], H2L1X (X = Br, I), [H2NR1CHR2CHR2(1-HC{NCHCHNR})][Br]2 H3L2X2 (X = Cl, Br), and [H2N{CH2CH2(1-HC[NCHCHNMes])}2][X]3 H4L3X3 (X = Cl, Br). Silver(I) oxide is sufficiently basic to deprotonate both the imidazolium and the alcohol functional groups of all but one of the L1 ligand precursors, to afford rare examples of silver alkoxide complexes [Ag(L1)], stabilised by the soft donor carbene. Another complex of L1 is characterised as the carbene alcohol adduct [Ag(HL1)2I]. The analogous reactions of silver(I) oxide with the amino imidazolium precursors afford silver amino-carbenes [Ag(HL2)Br] with the potentially bidentate L2 ligand, and [Ag(HL3)X] (X = Cl, Br) with the potentially tridentate L3 ligand. A single crystal X-ray diffraction study of the latter complex confirms that the neutral amine of the potentially tridentate L3 ligand is unco-ordinated; instead the structure contains discrete chains of T-shaped silver bis(carbene) halide moieties that bridge to form a zig-zag 2-connected polymer. Protonolysis of two of the silver alkoxide and amino adducts, [Ag(L1a)] and [Ag(HL2a)Br], affords imidazolium complexes salts [H2L1a][AgCl2] and [Ag(H2L2a)Br][AgBr2] that retain the Ag(I) centre as complex counterions. The single crystal X-ray structures of these salts have been determined and show the silver(I) cations are now incorporated into ladders or chains as silver(I) halo-anions, and a silver amine dative bond is present in the latter complex.

A synthesis of model DEF-rings of the polyketide anti tumor natural products FR182877 and hexacyclinic acid has been achieved. The key steps in the synthesis are an intramolecular Pd(0) catalyzed allylic substitution reaction, which was used to generate a 9-membered carbocycle, and a novel transannular iodocyclization reaction which furnished the DF-rings of both natural products.

Enantioselective symmetrising–desymmetrising allylic oxidation of racemic bridged bicyclic alkenes using an asymmetric copper-catalysed Kharasch–Sosnovsky reaction has been explored. Good yields and reasonable levels of induction (up to 70% ee) have been obtained using carbocyclic systems as substrates.

A range of reactions of cyclic lactam systems is described in which an atropisomeric C–N axis controls the stereochemical outcome of ring substitution or addition. In the case of enantiopure menthol adducts, substitution via N -acyliminium intermediates occurred with essentially complete control. However, the range of nucleophiles that participate in the reaction is very limited and at present the removal of the N -aryl substituent is problematic. A six-membered enamide is of moderate configurational stability and the axis exerts synthetically useful levels of control over enolate alkylations of the system. A novel Lewis acid mediated enamide arylation process was identified.

An array of neutral oxomolybdenum(IV) complexes with potentially pentadentate ONSNO donor Schiff bases in the form of thiocarbodihydrazone of salicylaldehyde and substituted salicylaldehydes actually acting as tridentate ONS donor ligands (H3L) were synthesized through oxo abstraction of the corresponding cis-dioxomolybdenum(VI) complexes. Oxomolybdenum(IV) complexes with similar ONS main ligands but different N–N donor coligands were also obtained by one-pot synthesis from the corresponding cis-dioxomolybdenum(VI) precursors. The complexes are found to be of the form [MoO(LH)]n and [MoO(LH)(N–N)], where N–N=bipy (2,2′-bipyridine), ophen (1,10-phenanthroline) and diacetyldihydrazones. In this work diacetyldihydrazones were used as N–N coligands for the first time in molybdenum chemistry. The complexes were characterized by elemental analyses, UV–Vis and IR spectroscopy, magnetic susceptibility measurement at room temperature in the solid state, molar conductivity in solution and by cyclic voltammetry. One of the complexes, [MoO(LH)(o-phen)] is structurally characterized by X-ray crystallography. The structure reveals that the molybdenum acceptor centre is present in a distorted octahedral N3O2S donor environment. The N–N coligand was found to occupy a plane perpendicular to that taken up by the ONS ligand. It is to be noted that structurally characterized oxomolybdenum(IV) complexes are quite scarce.

The synthesis of a range of thiazole containing cyclic peptides using cyclooligomerisation reactions of amino acid substituted thiazole monomers and by macrolactamisation procedures is reported. The synthetic approaches lead to high yields of novel 18- and 24-membered ring analogues of the naturally occurring Lissoclinum families of cyclic peptides found in marine organisms and algae.

The development of some new lanthanide chemistry of aryloxide-based ligands is presented. The use of chelating, dianionic aryloxide ligand sets, such as sterically encumbered binolates, to allow a degree of geometrical control over the reaction chemistry of these large metal cations, is reviewed. We show how the development of potentially tridentate, dianionie, sulfur-bridged biphenolate and binaphtholate [OSO] ligands has allowed us to make new Ln(III) aryloxide complexes such as [Sm{1,1'-S(2-OC 6 H 2 Bu'-3,-Me-5) 2 }(OC 6 H 3 Bu t 2 -2,6)(THF)] and [Sm{1,1'-S(2-OC 10 H 4 Bu t 2 -3,6) 2 }(OC 6 H 3 Bu t 2 -2,6)(THF)]. Unusually, both symmetric and asymmetric derivatives of the [OSO] ligands may be prepared; reasons for this observation are suggested. Reactivity studies of these Sm(III) derivatives have shown them to be selective Lewis acid catalysts for the one-step monoacylation of 1,2-diols. Oxidation products of the sulfur-bridged binaphtholate ligand have been crystallographically characterized.

The mixed oxa-aza macrocycle [15]aneN 3 O 2 with cyanomethyl pendant arms on all three N-centres, 1,4,7-tris(cyanomethyl)-1,4,7 triaza-10,13-dioxacyclopentadecane (L), and its complexes with Cu(II), Ni(II), Zn(II), Cd(II) and Pb(II) have been prepared. The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 metal:ligand complexes with Cu(II), Zn(II), Cd(II) and Pb(II) have been investigated by means of potentiometric measurements in aqueous solutions. These metal ions form only mononuclear complexes with unusually low stability constants, compared with those found for other cyclic or acyclic triamine compounds due to the relatively poor σ-donating properties of tertiary nitrogens and to the stiffening of the macrocyclic framework imposed by the cyanomethyl side arms, which are unable to co-ordinate to the metal ion sitting within the macrocyclic cavity. The single crystal X-ray structures of 1:1 complexes with Cu(II), Ni(II), Cd(II) and Pb(II) have been determined. The structures of [Cu(L)(CH 3 CN)](ClO 4 ) 2 and [Ni(L)(CH 3 CN)](ClO 4 ) 2 show slightly distorted octahedral co-ordination geometries with the metal cation bound to all the donor atoms of the macrocyclic ring and to a MeCN molecule. The structure of [Cd(L)(NO 3 ) 2 ] confirms binding of all the donor atoms of the ring, but in this case the metal ion is also co-ordinated to two nitrate anions, one of them in a bidentate fashion. In the case of Cu(II), Ni(II) and Cd(II) complexes, the nitrile arms do not take part in co-ordination to the metal ion and are directed away from its co-ordination sphere. Interestingly, the structure of the Pb(II) complex [Pb(L)(ClO 4 )] 2 2 + confirms the formation of a binuclear species with binding of a nitrile pendant arm from an adjacent molecule. Two ClO 4 - anions bridge within the binuclear units in a bidentate fashion. NMR spectroscopic studies on the Zn(II), Cd(II) and Pb(II) complexes have revealed a rigidity in the complexes which is lost on increasing temperature.

The enantioselective deprotonation of 1,2,5-triphenylphospholane oxide with a chiral base, followed by electrophilic quenching, gives a range of chiral products in good yield and in ca. 85% ee. The absolute and relative configuration of two of the products was determined by X-ray crystallography. A number of the chiral phospholane oxides were subjected to further transformations, in particular reduction to give enantiomerically pure phospholanes.

The enantioselective deprotonation of several ring-fused imides with a chiral base, followed by electrophilic quenching, gives a range of chiral products in good yield and in ≥91% ee. The absolute stereochemistry of two of the products was determined by X-ray crystallography. A number of the imide products were subjected to further, highly regioselective, transformations, including enolate substitution, reduction and thionation.

Alkenyl-substituted six- and seven-membered cyclic enol ethers, which are potential building blocks for the synthesis of marine polyether natural products, can be prepared in high yield (70–97%) from alkynyl ethers by ruthenium-catalysed ring-closing enyne metathesis. The carbene-bearing ruthenium complex 9 is generally the most efficient catalyst for the reaction.

The aggregates {[Zn(L1)]H2O}∞ and {[Y(L2)]4Na3(H2O)2(MeOH)1.2}(NO3)3·2H2O·5.6MeOH have been assembled from complexes of imino–phosphonate monoester ligands [L1]2− {CH2[CH2NC(CH3)PO2(OMe)]2}2− and [L2]3− {N[CH2CH2NC(CH3)PO2(OMe)]3}3−, the topology of these materials differing from that of their imino–carboxylate analogues.

4,7-Phenanthroline (L) acts as a hydrogen-bond acceptor in the compounds {[M(NO3)2(H2O)4].L2} (M=Mn, Co, Ni, Zn) forming square-grid hydrogen-bonded structures which are linked into an α-Po three-dimensional structure via supplementary hydrogen bonding and π–π interactions.

Crystallisation of cobalt(II) nitrate from solutions containing 4,4′-bipyridine (4,4′-bipy) yields, depending on the conditions, 4,4′-bipyridine cobalt(II) nitrate networks with 4,4′-bipy:Co molar ratios of 3:2 {[{Co(O2NO)2}(μ-4,4′-bipy)1.5]·Et2O}∞, 3:1 {[{Co(ONO2)2(4,4′-bipy)2}(μ-4,4′-bipy)]·2.5MeOH}∞, 1, 4:1 {[{Co(H2O)2}(μ-4,4′-bipy)2][NO3]2·2(4,4′-bipy)·2H2O}∞, 2, or 5:1 {[{Co(H2O)2(4,4′-bipy)2}(μ-4,4′-bipy)]·1.5[NO3]·0.5OH·2(4,4′-bipy)·2.5H2O}∞, 3. Whereas the purple 3:2 product is based on a pentagonal pyramidal CoO4N3 co-ordination sphere, the other three orange products (1–3) are all based on octahedral CoO2N4 centres. Although analogues of the purple product, the extended structure of which adopts a 1-D ladder motif, have been reported previously, the orange products, the extended structures of which are based on 2-D sheets of (4,4) topology, are unprecedented. These products, however, differ in the construction of the (4,4) sheets. In 2, all four of the 4,4′-bipy molecules bridge cobalt(II) centres to generate an almost square (4,4) grid, while in 1 and 3, only two of the four 4,4′-bipy molecules bridge cobalt(II) centres to generate either a zig-zag chain (in 1) or a linear chain (in 3). The two terminal 4,4′-bipy ligands in 1 and 3 are involved in π–π stacking interactions and in hydrogen-bonding interactions, respectively, to form rhombic (4,4) grids. In 2, however, an unprecedented sequence of co-ordinate, hydrogen-bonding and π–π stacking interactions links cobalt(II) centres from parallel {[Co(μ-4,4′-bipy)2]2+}∞ square grids via two water and two 4,4′-bipy molecules to generate a doubly-interpenetrated ReO3-type network structure.

This review discusses the design and structure of coordination polymers derived from Ag(I) with N-donor ligands and their role in the investigation of weak non-covalent interactions in the solid state. These forces include arene–arene, metal–anion, metal–arene and metal–metal interactions. The main purpose of this review is to classify and discuss the supramolecular forces which define the overall observed structure (topology, geometry and packing arrangement) of coordination polymers by comparison of a series of structurally related compounds when one parameter of the multi-component system (choice of anion, ligand or solvent) is varied. Design criteria for one-dimensional polymers are given and discussed with respect to the fundamental importance of these compounds for understanding and further development of supramolecular synthetic strategies.

The reaction of silylketenes with thiophenol, mediated by cinchona alkaloid catalysts, proceeds to give α-silylthioester products in good chemical yield and with enantiomeric excess values in the range 79–93%. The absolute configuration of one of the thioester products was determined by X-ray diffraction.

The AB ring system found in the manzamine A and related alkaloids has been prepared from (−)-quinine by a short enantioselective route. The key step in the sequence is a ruthenium-catalysed ring-closing enyne metathesis re action which delivers a bicyclic diene in good yield. The functionality required for further elaboration of the AB system has been installed by sequential regioselective hydroboration and stereoselective catalytic aminohydroxylation.

Two-dimensional structures are an emerging class of materials within nitride chemistry. We report here our systematic studies of two groups of these layered compounds: 1 Lithium transition metal compounds, Li3-x-y□yMxN (M = Co, Ni, Cu, □ = Li vacancy) and 2 ternary transition metal nitrides of general formulation AMN2 (A = alkaline earth metal, M = Ti, Zr, Hf). Compounds in class 1 are based on the hexagonal Li3N structure, unique to nitrides. Compounds in group 2, by contrast, crystallise with oxide structures (α-NaFeO2 or KCoO2). Specific and unusual synthetic methods have been developed to reproducibly prepare these compounds. Compounds in series 1 contain ordered or disordered Li vacancies at increased levels relative to the parent Li3N, itself a Li+ fast ion conductor. Nitrides in series 2 should be nominally diamagnetic (S = 0), yet magnetic measurements reveal behaviour seemingly inconsistent with this assumption. © 2001 Elsevier Science B.V.

Reaction of cuprates derived from R3MgBr/CuI/LiBr (R3 = n-alkyl) with R1C CCH(O2CR2)2 (R1 = sp2 hybridised substituent, R2 = mainly Me, alkyl, Ph) provides access to allenyl esters R1R3C C CH(O2CR2) (51–88%). Such species are not accessible via rearrangement of precursor propargylic R1R3C(O2CR2)C CH.

The syntheses of the 1,3,5-trimethyl- and tri-tert-butyl-1,3,5-triazacyclohexane-supported imido complexes [M(NR)(R′ 3tach)Cl 2] (M = Ti or Zr (NMR only); R = Bu t or 2,6-C 6H 3Pr i2; R′ = Me or Bu t) are reported, along with that of the thermally robust dibenzyl derivative [Ti(NBu t)(Me 3tach)(CH 2Ph) 2]. The tert-butylimido ligand in [Ti(NBu t)(Me 3tach)Cl 2] undergoes exchange with ArNH 2 (Ar = 4-C 6H 4Me or 2,6-C 6H 4Me or 2,6-C 6H 3Pr i2) to form the corresponding arylimides [Ti(NAr)(Me 3tach)Cl 2]. The Me 3tach ring in [Ti(NR)(Me 3tach)Cl 2] undergoes slow exchange with Bu t3tach or Me 3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) to give the ring-exchanged products [Ti(NR)(Bu t3tach)Cl 2] and [Ti(NR)(Me 3tacn)Cl 2], respectively. The complexes [Ti(NR)(Me 3tach)X 2] (R = Bu t or 2,6-C 6H 3Pr i2; X = Cl or CH 2Ph) exhibit room-temperature dynamic NMR behaviour via an unusual trigonal twist of the facially coordinated Me 3tach ligand, and the activation parameters for these processes have been measured and are discussed. The X-ray structures of [Ti(NR)(Bu t3tach)Cl 2] (R = Bu t or 2,6-C 6H 3Pr i2) and [Ti(NBu t)(Me 3tach)(X) 2] [X= Cl or CH 2Ph) are reported. Me 3tach and Bu t3tach = 1,3,5-trimethyl- and tri-tert-butyl-1,3,5-triazacyclohexane, respectively. © 2000 Elsevier Science S.A. All rights reserved.

Rh2(cod)2(μ2-dppm)(μ2-Cl)]BF4 (1) rearranges under carbon monoxide to give [Rh3(μ2-dppm)2(μ2-CO)3(K1-CO)3]BF4 (2). Complex 2 has been structurally characterized by single crystal X-ray crystallography. The hydroformylation activities of 1 and 2 were compared for substrates styrene and 1-hexene and the activity of 2 found to be unexpectedly high.

Pd(II) and Pt(II) complexes of [16]aneS4 and Pd(II) complexes of cis-(HO)2[14]aneS4 and [9]aneS3 have been used as templates for the self-assembly of polyiodide ions. The complexes {[M([16]aneS4)]2I}I11 (M = Pd, Pt), [Pd(cis-(HO)2[14]aneS4)](I3)2, [Pd([9]aneS3)2](Ix)2 (x = 3, 5) have been synthesized and structurally characterized. In {[M([16]aneS4)]2I}I11, the polyiodide network consists of fused 14-member polyanion rings made up of interacting “L”-shaped I5− and I− units; binuclear [([16]aneS4)M–I–M([16]aneS4)]3+ complex cations featuring a highly unusual linear and symmetric M–I–M moiety are each surrounded by one of these 14-member polyiodide rings in a belt-like fashion. The structures of [Pd(cis-(HO)2[14]aneS4)](I3)2 and [Pd([9]aneS3)2](I3)2 both feature tri-iodides as counter-anions. In [Pd(cis-(HO)2[14]aneS4)](I3)2, quite asymmetric I3− ions form sinusoidal infinite chains via head-to-tail I3−⋯I3− interactions; these chains run along the (001) direction and are stacked along the (100) direction to form highly puckered anionic layers via I⋯I weak interactions that cross-link the chains. In [Pd([9]aneS3)2](I3)2, [Pd([9]aneS3)2]2+ cations are bridged on each side by pairs of symmetric I3− ions through long-range S⋯I contacts to form discrete infinite ribbons that run parallel to the a axis. By contrast, the structure of [Pd([9]aneS3)2](I5)2 consists of highly puckered polyanionic layers featuring fused 18-member polyiodide rings made up of I5− ions. Two of these layers related by an inversion center are stacked along the b axis and interact with each other to form large cavities within which the complex cations sit. In these complex arrays the cation can be regarded as a template around which polyanion networks can be structured. The solid state FT-Raman spectra of the reported polyiodides are discussed on the basis of their crystal structures.

Reaction of copper(I) iodide with a range of bridging bidentate N-donor ligands is reported. CuI reacts with L [L = pyrazine (pyz) 1, 1,2-trans-(4-pyridyl)ethene (bpe) 2, quinoxaline (quin) 3, 4,4′-bipyridyl (4,4′-bipy) 4, pyrimidine (pym) 5, 4,7-phenanthroline (4,7-phen) 6] in MeCN to afford insoluble yellow powders of stoichiometry [(CuI)2(L)]∞ 1–6, respectively. Single crystal structure determinations on compounds 1–3, 5, and 6 confirm constructions based on (CuI)∞ staircase ladders linked by bridging ligands to afford two-dimensional sheets. The separation of the (CuI)∞ ladders can be controlled by simple variation of the length of the ligands. In 5 and 6 the two-dimensional sheets undulate due to the angle between the N-donors of the ligand. [(CuI)(diaz)]∞ 7 (diaz = 2,7-diazapyrene), formed by reaction of CuI with diaz in PhCN and CH2Cl2, has a split-staircase motif for the (CuI)∞ moiety, while [(CuI)(4,4′-bipy)]∞ 8, formed by the reaction of CuI with the ligand in DMSO and CH2Cl2, shows rhomboid dimers of (CuI)2 linked by bridging ligands to give honeycomb sheets that are perpendicularly interpenetrated.

The influence of solvent and anion on the formation of coordination polymers between silver(I) and 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3′-pytz), a bridging ligand that can adopt both cisoid and transoidconformations, is reported. Reaction of AgPF6 in MeCN with 3,3′-pytz in CH2Cl2 gives ([{Ag(NCMe)2}(μ-3,3′-pytz)][PF6]·MeCN)∞, 1, of AgPF6 in MeNO2 and 3,3′-pytz in CH2Cl2 gives ([{Ag2(μ-3,3′-pytz)2}(μ-3,3′-pytz)][PF6]2·4MeNO2)∞, 2, and of AgCF3SO3 in MeCN and 3,3′-pytz in CH2Cl2 gives {[Ag(μ-3,3′-pytz)]CF3SO3}∞, 3. These cationic coordination polymers exclusively form chain structural motifs. That in 1, ([{Ag(NCMe)2}(μ-3,3′-pytz)]+)∞, has a castellated construction with each tetrahedral silver(I) center coordinated by two solvent molecules as well as two linking transoid-oriented 3,3′-pytz bridges (Ag⋯Ag 13.210 A) in a 1:1 polymeric chain. That in 2, ([{Ag2(μ-3,3′-pytz)2}(μ-3,3′-pytz)]2+)∞, is novel. It is the first coordination polymer to exhibit both cisoid and transoid conformations of a bridging ligand coordinated to the same metal center. Pairs of silver(I) centers are linked by pairs of cisoid-oriented 3,3′-pytz molecules (Ag⋯Ag = 11.695 A) to form [Ag2(μ-3,3′-pytz)2] motifs, which are bridged, in turn, by transoid-oriented 3,3′-pytz molecules (Ag⋯Ag = 13.318 A) to form a 3:2 ligand:metal infinite polymeric zigzag chain. That in 3, {[Ag(μ-3,3′-pytz)]+}∞, has a zigzag architecture despite being based on linear silver(I) centers. Transoid-oriented 3,3′-pytz molecules link silver(I) centers (Ag⋯Ag 13.225 A) to give a 1:1 ligand:metal infinite polymeric zigzag chain. The chains aggregate in parallel pairs linked by weak Ag⋯Ag contacts (Ag⋯Ag = 3.220 A), which are supported by (μ2-κO,κO′) bridging CF3SO3− anions.