New bis-, tris- and tetrakis(pyrazolyl)borate ligands with 3-pyridyl and 4-pyridyl substituents: synthesis and coordination chemistry

The new ligands dihydrobis[3-(4-pyridyl)pyrazol-1-yl]borate [Bp(4py)]-, hydrotris[3-(4-pyridyl)pyrazol-1-yl]borate [Tp(4py)]-, tetrakis[3-(4-pyridyl)pyrazol-1-yl]borate [Tkp(4py)]-, dihydrobis[3-(3-pyridyl)pyrazol-1-yl]borate [Bp(3py)]-, hydrotris[3-(3-pyridyl)pyrazol-1-yl]borate [Tp(3py)]- and tetrakis[3-(3-pyridyl)pyrazol-1-yl]borate [Tkp(4py)]- are derivatives of the well known bis-, tris- and tetrakis-(pyrazolyl)borate cores, bearing 4-pyridyl or 3-pyridyl substituents attached to the pyrazolyl C3 positions. These pyridyl groups cannot chelate to the metal ions in the poly(pyrazolyl) cavity but are externally directed. Structural studies on a range of metal complexes show how, in many cases, coordination of these pendant pyridyl groups to the M(pyrazolyl)n core of an adjacent metal complex fragment results in formation of coordination oligomers or polymeric networks. [Tl(Bp(3py))], [Tl(Bp(4py))] and [Tl(Tp(4py))] form one-dimensional polymeric chains via coordination of one of their pendant pyridyl units to the Tl(I) centre of an adjacent complex fragment; in contrast, in [Tl(Tp(3py))] coordination of all three pendant pyridyl units to separate Tl(I) neighbours results in formation of a two-dimensional polymeric sheet. In [Tl(Tkp(3py))] and [Tl(Tkp(4py))] the Tl(I) is coordinated by two or three of the four pyrazolyl arms, respectively; bridging interactions of pendant 4-pyridyl groups with adjacent Tl(I) centres result in a two-dimensional sheet forming in each case. In Ag(Tkp(4py)) each Ag(I) ion is coordinated by two pyrazolyl rings, and two bridging pyridyl ligands from other complex units, resulting in a one-dimensional chain consisting of pairs of cross-linked zigzag chains. In contrast to these polymeric coordination networks, the structures of [Cu(Tp(4py))] and [(Tp(3py))Cd(CH3CO2)] are dimers, with a pendant pyridyl residue from the first metal centre attaching to a vacant coordination site on the second, and vice versa; these dimers are stabilised by pi-stacking interactions between sections of the two ligands. [Ni(Tp(3py))2] is monomeric, with an octahedral coordination geometry arising from two tris(pyrazolyl)borate chelates; the array of pendant 3-pyridyl groups is involved only in intramolecular hydrogen-bonding. [(Tp(4py))Re(CO)3] is also monomeric, with a facial arrangement of three pyrazolyl ligands and three carbonyls, with the pendant 4-pyridyl groups not further coordinated. [(Tp(2py))Re(CO)3], based on the related ligand hydrotris[3-(2-pyridyl)pyrazol-1-yl]borate, has a similar fac-(CO)3(pyrazolyl)3 coordination geometry.     

The Coordination Chemistry of Multidentate Isocyanide Ligands

In spite of the excellent ligation properties of isocyanides, until a few years ago there was only a small number of known multidentate ligands of this type. One of the reasons for this lack of interest, when compared to monodentate isocyanides, was the linear arrangement of the M? C?N? R group, which usually inhibits the formation of mononuclear chelate complexes and leads to the formation of multinuclear or polymeric metal complexes. In these, the multidentate ligand acts in a monodentate fashion towards each metal atom. Only recently has a series of polyisocyanides with large ligand backbones been synthesized successfully. Bidentate isocyanides can bridge two metal atoms or react to give chelates with only one metal center. Tripodal ligands form mono- or binuclear complexes, in which the largest organometallic rings observed to date occur (up to 36 atoms). This class of ligands promises to be interesting for the synthesis of stable, diagnostically important technetium complexes of the type [Tc(CNR) ₆ ]⁺. There also appear to be applications for tripodal isocyanides in catalysis. A facial, chiral Cr(CNR^*)₃ unit might be able to catalyze the hydrogenation or isomerization of prochiral double bonds. It is even possible to bind triisocyanides with suitable backbones to carbonyl trimetal clusters, thereby stabilizing them, or making selective cluster formation possible. Coordinated isocyanides can be transformed readily into carbene ligands, which, in the future, could lead to complexes with polycarbene ligation.     

Coordination chemistry of chelating nitrogen ligands with tungsten carbonyl nitriles

The reactions of a series of Schiff base ligands (1–4) prepared by condensation of pyridine-2-carboxaldehyde and 2-X-anilines (X = F, Cl, Br, OMe) with W(CO)₃(RCN)₃ results in the formation of deeply coloured complexes W(CO)₃(1–4)(NCR) which readily react with carbon monoxide to afford W(CO)₄(1–4). The ligand 5, prepared from pyridine-2-carboxaldehyde and N,N-dimethylethylenediamine, coordinates to W(CO)₃ through the conjugated pyridine—imine chelate to afford complexes with a pendant dimethylamino group which reacts with electrophiles. Of the ligands studied, only the bis-amine, pyridine ligand 8, coordinates to W(CO)₃ in a tridentate manner. These reactions provide insight into the geometric and electronic factors which influence coordination of nitrogen containing ligands at a fac-tricarbonyl metal centre.     

Copper(II) complexes of pyridyl-appended diazacycloalkanes: synthesis, characterization, and application to catalytic olefin aziridination

As part of an ongoing effort to rationally design new copper catalysts for olefin aziridination, a family of copper(II) complexes derived from new tetradentate macrocyclic ligands are synthesized, characterized both in the solid state and in solution, and screened for catalytic nitrene transfer reactivity with a representative set of olefins. The pyridylmethyl-appended diazacycloalkane ligands L6(py)2, L7(py)2, and L8(py)2 are prepared by alkylation of the appropriate diazacycloalkane (piperazine, homopiperazine, or diazacyclooctane) with picolyl chloride in the presence of triethylamine. The ligands are metalated with Cu(ClO4)(2).6H2O to provide the complexes [(L6(py)2)Cu(OClO3)]ClO4 (1), [(L7(py)2)Cu(OClO3)]ClO4 (2), and [(L8(py)2)Cu](ClO4)2 (3), which, after metathesis with NH4PF6 in CH3CN, afford [(L6(py)2)Cu(CH3CN)](PF6)2 (4), [(L7(py)2)Cu(CH3CN)](PF6)2 (5), and [(L8(py)2)Cu](PF6)2 (6). All six complexes are characterized by X-ray crystallography, which reveals that complexes supported by L6(py)2 and L7(py)2 (1, 2, 4, 5) adopt square-pyramidal geometries, while complexes 3 and 6, ligated by L8(py)2 feature tetracoordinate, distorted-square-planar copper ions. Tetragonal geometries in solution and d(x2 - y2), ground states are confirmed for the complexes by a combination of UV-visible and EPR spectroscopies. The divergent flexibility of the three supporting ligands influences the Cu(II)/Cu(I) redox potentials within the family, such that the complexes supported by the larger ligands L7(py)2 and L8(py)2 (5 and 6) exhibit quasi-reversible electron transfer processes (E1/2 approximately -0.2 V vs Ag/AgCl), while the complex supported by L6(py)2 (4), which imposes a rigid tetragonal geometry upon the central copper(II) ion, is irreversibly reduced in CH3CN solution. Complexes 4-6 are efficient catalysts (in 5 mol % amounts) for the aziridination of styrene with the iodinane PhINTs (in 80-90% yields vs PhINTs), while only 4 exhibits significant catalytic nitrene transfer reactivity with 1-hexene and cyclooctene.     

Mono- and dinuclear ruthenium complexes of bridging ligands incorporating two di-2-pyridylamine motifs: Synthesis, spectroscopy and electrochemistry

Mono- and dinuclear ruthenium(II) complexes of six bridging ligands that contain a central arene (phenyl, naphthalenyl or biphenyl) core to which are attached two di-2-pyridylamine groups have been prepared. These complexes possess six-membered chelate rings. Full assignments of their ¹H NMR spectra are described which provides insight into the comformations of the ligands in these complexes. The extent of metal–metal communication in the dinuclear complexes was probed by electrochemical measurements and related to metal–metal distances.     

Towards new organometallic wires: tetraruthenium complexes bridged by phenylenevinylene and vinylpyridine ligands

The tetranuclear complexes [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)Ru Cl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)- CH=CH-1,4)] (3 a) and [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (3b), which contain vinylpyridine ligands that connect peripheral Ru(PiPr(3))(2)(CO)Cl units to a central divinylphenylene-bridged diruthenium core, have been prepared and investigated. These complexes, in various oxidation states up to the tetracation level, have been characterized by standard electrochemical and spectroelectrochemical techniques, including IR, UV/Vis/NIR and ESR spectroscopy. A comparison with the results for the vinylpyridine-bridged dinuclear complex [PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)(CH=CHPh)] (6) and the divinylphenylene-bridged complexes [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,4)] (8a) and [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (8b), which represent the outer sections (6) or the inner core (8a,b) of complexes 3a,b, and with the mononuclear complex [(EtOOCpy)(CO)(PPh(3))(2)RuCl(CH=CHPh)] (7) indicate that every accessible oxidation process is primarily centred on one of the vinyl ligands, with smaller contributions from the metal centres. The experimental results and quantum chemical calculations indicate charge- and spin-delocalization across the central divinylphenylenediruthenium part of 3a,b or the styrylruthenium unit of 6, but not beyond. The energy gap between the higher lying styryl- or divinylphenylenediruthenium-based and the lower occupied vinylpyridineruthenium-based orbitals increases in the order 6<3 b<3 a and thus follows the conjugation within the non-heteroatom-substituted aromatic vinyl ligand.     

Syntheses of 8-quinolinolatocobalt(III) complexes containing cyclen based auxiliary ligands as models for hypoxia-activated prodrugs

New ligands H(2)L2-H(2)L6 comprise the cyclen macrocycle which is N,N'-dialkylated at the 1,7-nitrogen atoms by three- and four-carbon alkyl chains bearing terminal sulfonic (C(3) H(2)L2), phosphonic (C(3) H(2)L3, C(4) H(2)L4) or carboxylic acid (C(3) H(2)L5, C(4) H(2)L6) groups, and HL7 is N-monoalkylated by a four-carbon sulfonic acid group. The ligands were prepared by alkylation of a bridged bisaminal intermediate. The syntheses of cobalt(III) complexes containing a tetradentate cyclen, N,N'-1,7-Me(2)cyclen, cyclam or L2-L7 ligand together with the bidentate 8-quinolinato (8QO(-)) ligand, of interest as it is a model for a more potent cytotoxic analogue, were investigated. Coordination of ligands (L) cyclen, N,N'-1,7-Me(2)cyclen or cyclam to cobalt(III) was achieved using Na(3)[Co(NO(6))] to form [Co(L)(NO(2))(2)](+). HOTf (trifluoromethansulfonic acid) was used to prepare the triflato complexes [Co(L)(OTf)(2)](+), followed by substitution of the labile triflato ligands to yield [Co(L)(8QO)](ClO(4))(2) isolated as the perchlorate salts. One further example containing cyclam and the 5-hydroxymethyl-8-quinolinato ligand was also prepared by this method. Complexes containing the pendant arm ligands L2-L6 were prepared from the cobalt precursor trans-[Co(py)(4)Cl(2)](+). Reaction of this complex with H(2)L2·4HCl and 8QOH produced [Co(L2)(8QO)] in one step and contains two deprotonated sulfonato pendant arms. The reaction of H(2)L3·4HBr with [Co(py)(4)Cl(2)](+) gave [Co(L3)]Cl in which L3 acts as a hexadenate ligand with the three-carbon phosphonato side chains coordinated to cobalt. H(2)L5·4HCl bearing three-carbon carboxylic acid pendant arms gave a similar result. The four-carbon ligands were coordinated to cobalt by reaction of [Co(py)(4)Cl(2)](+) with H(2)L4·4HBr or H(2)L6·4HCl to give [Co(HL4)Cl(2)] or [Co(H(2)L6)Cl(2)]Cl, which in turn with 8QOH gave the 8QO(-) complexes [Co(L4)(8QO)] bearing anionic phosphate pendant arms or [Co(H(2)L6)(8QO)]Cl(2) containing neutral carboxylic acid side chains. The reaction of Na(3)[Co(CO(3))(3)] with the mono-N-alkylated ligand HL7·4HCl and then HOTf gave [Co(L7)(CO(3))] and then in turn [Co(L7)(OTf)(2)]. The carbonato complex [Co(L7)(CO(3))] with [8QO](2)[SO(4)] produced [Co(L7)(CO(3))]. All complexes containing L7 bear an anionic sulfonato group on the side chain. The synthesis and characterisation of the six new ligands based on N-alkylated cylen ligand and the cobalt complexes outlined above are described, along with cyclic voltammograms of the 8QO(-) complexes and the molecular structures determined by X-ray crystallography of [Co(cyclen)(H(2)O)(2)](OTf)(3) (formed by aquation of the triflato complex), [Co(cyclen)(8QO)](ClO(4))(2), Co(L2)(8QO)·2H(2)O, Co(L4)(8QO)·6H(2)O and [Co(H(2)L6)Cl(2)]Cl·H(2)O. These demonstrate the coordination of the cyclen ligand in the folded anti-O,syn-N configuration with the N-alkylated nitrogens occupying apical positions.     

[2]Catenanes Built Around Octahedral Transition‐Metal Complexes that Contain Two Intertwined Endocyclic but Non‐sterically Hindering Tridentate Ligands

Sterically hindering bidentate chelates, such as 2,9‐diphenyl‐1,10‐phenanthroline, form entwined complexes with copper(I) and other tetrahedrally coordinated transition‐metal centres. To prepare octahedral complexes containing two entwined tridentate ligands and thus apply a strategy similar to that used for making catenanes with tetrahedral metal centres, the use of the classical terpy ligand (terpy=2,2′:6′,2′′‐terpyridine) appears to be attractive. In fact, 6,6′′‐diphenyl‐2,2′:6′,2′′‐terpyridine (dp‐terpy) is not appropriate due to strong “pinching” of the organic backbone by coordination to the metal and thus stable entwined complexes with this ligand cannot be obtained. Herein, we report the synthesis and coordination properties of a new family of tridentate ligands, the main features of which are their endocyclic nature and non‐sterically hindering character. The coordinating fragment consists of two 8′‐phenylisoquinolin‐3′‐yl groups attached at the 2 and 6 positions of a pyridine nucleus. Octahedral complexes containing two such entangled ligands around an octahedral metal centre, such as Fe^II, Ru^II or Co^III, are highly stable, with no steric congestion around the metal. By using functionalised ligands bearing terminal olefins, double ring‐closing metathesis leads to [2]catenanes in good yield with Fe^II or Co^III as the templating metal centre. The X‐ray crystallography structures of the Fe^II precursor and the Fe^II catenane are also reported. These show that although significant pinching of the ligand is observed in both Fe^II complexes, the system is very open and no steric constraints can be detected.     

Kinetics and mechanism of ligand substitution reactions in [cis-M(CO)4(amine)(EPh3)] complexes (M = Mo,W; amine = pyridine,piperidine; E = As,Sb)

Group 6 metal carbonyls [cis-M(CO)₄(amine)(EPh₃)] (M = Mo, W; amine = piperidine (pip), pyridine (py); E = As, Sb) have been prepared and characterized. These complexes react thermally in chlorobenzene solutions with phosphine or phosphite ligands (= L) to give cis- and trans-M(CO)₄(L)(EPh₃) products. Kinetics of amine substitution by L in these complexes, under pseudo-first-order conditions, indicate that these reactions proceed by a rate law that is first-order in concentration of the metal complex. Rate constants and activation parameters for these reactions have been determined and are discussed. Competition studies for the [M(CO)₄(EPh₃)] intermediates show that these intermediates are highly reactive and react almost indiscriminately with various incoming nucleophiles with slight preference for more basic ones.     

Remarkable Tuning of the Coordination and Photophysical Properties of Lanthanide Ions in a Series of Tetrazole‐Based Complexes

A series of seven new tetrazole‐based ligands (L1, L3–L8) containing terpyridine or bipyridine chromophores suited to the formation of luminescent complexes of lanthanides have been synthesized. All ligands were prepared from the respective carbonitriles by thermal cycloaddition of sodium azide. The crystal structures of the homoleptic terpyridine–tetrazolate complexes [Ln(Li)₂]NHEt₃ (Ln=Nd, Eu, Tb for i=1, 2; Ln=Eu for i=3, 4) and of the monoaquo bypyridine–tetrazolate complex [Eu(H₂O)(L7)₂]NHEt₃ were determined. The tetradentate bipyridine–tetrazolate ligand forms nonhelical complexes that can contain a water molecule coordinated to the metal. Conversely, the pentadentate terpyridine–tetrazolate ligands wrap around the metal, thereby preventing solvent coordination and forming chiral double‐helical complexes similarly to the analogue terpyridine–carboxylate. Proton NMR spectroscopy studies show that the solid‐state structures of these complexes are retained in solution and indicate the kinetic stability of the hydrophobic complexes of terpyridine–tetrazolates. UV spectroscopy results suggest that terpyridine–tetrazolate complexes have a similar stability to their carboxylate analogues, which is sufficient for their isolation in aerobic conditions. The replacement of the carboxylate group with tetrazolate extends the absorption window of the corresponding terpyridine‐ (≈20 nm) and bipyridine‐based (25 nm) complexes towards the visible region (up to 440 nm). Moreover, the substitution of the terpyridine–tetrazolate system with different groups in the ligand series L3–L6 has a very important effect on both absorption spectra and luminescence efficiency of their lanthanide complexes. The tetrazole‐based ligands L1 and L3–L8 sensitize efficiently the luminescent emission of lanthanide ions in the visible and near‐IR regions with quantum yields ranging from 5 to 53 % for Eu^III complexes, 6 to 35 % for Tb^III complexes, and 0.1 to 0.3 % for Nd^III complexes, which is among the highest reported for a neodymium complex. The luminescence efficiency could be related to the energy of the ligand triplet states, which are strongly correlated to the ligand structures.     

Benzene and Its Derivatives as Bridging Ligands in Transition-Metal Complexes

Transition-metal complexes in which two or more metal atoms are bridged by one or more arene ligands led a shadowy existence in comparison to the extensive class of mononuclear arene complexes. Arene bridges can occur in a variety of coordination modes and with almost all of the transition–metal elements of the periodic table. Nowhere else are found so many forms of distorted and bent arene rings. The binuclear compounds can be divided into two classes: adducts which show relatively weak metal–arene bonding and complexes which show strong arene–metal interaction. Most of the adducts are in equilibrium with mononuclear complexes in solution or are only stable in the solid state (often as polymers). In both classes syn and anti coordination occurs; their geometries show a wide variation between the extreme cases of η¹ : η¹-bridge and η⁶ : η⁶-triple-decker structure. Metal surfaces with chemisorbed arenes can be seen as a form of multinuclear arene–metal complexes. On transition-metal surfaces, benzene can be bonded to one, two, or four surface atoms. Molecular clusters with face-capping arene ligands that are bonded to three metal atoms have until now mainly been limited to two classes. The arenes bound to {(CO)₃M}₃ (M = Ru, Os) or (CpCo)₃ clusters as μ₃-η² : η² : η² ligands show only a weak trigonal distortion towards a Kekulé structure. Detailed investigations of the molecular structure and ligand dynamics of [(CpCo)₃(μ₃-arene)] complexes considerably help the understanding of the bonding of arenes to metal clusters and to metal surfaces.     

High-nuclearity ruthenium carbonyl cluster complexes derived from 2-amino-6-methylpyridine: synthesis of nonanuclear derivatives containing mu4- and mu5-oxo ligands

Nonanuclear cluster complexes [Ru9(mu3-H)2(mu-H)(mu5-O)(mu4-ampy)(mu3-Hampy)(CO)21] (4) (H2ampy = 2-amino-6-methylpyridine), [Ru9(mu5-O)2(mu4-ampy)(mu3-Hampy)2(mu-CO)(CO)20] (5), [Ru9(mu5-O)2(mu4-ampy)(mu3-Hampy)2(mu-CO)2(CO)19] (6), and [Ru9(mu4-O)(mu5-O)(mu4-ampy)(mu3-Hampy)(mu-Hampy)(mu-CO)(CO)19] (7), together with the known hexanuclear [Ru6(mu3-H)2(mu5-ampy)(mu-CO)2(CO)14] (2) and the novel pentanuclear [Ru5(mu4-ampy)(2)(mu-CO)(CO)12] (3) complexes, are products of the thermolysis of [Ru3(mu-H)(mu3-Hampy)(CO)9] (1) in decane at 150 degrees C. Two different and very unusual quadruply bridging coordination modes have been observed for the ampy ligand. Compounds 4-7 also feature one (4) or two (5-7) bridging oxo ligands. With the exception of one of the oxo ligands of 7, which is in a distorted tetrahedral environment, the remaining oxo ligands of 4-7 are surrounded by five metal atoms. In carbonyl metal clusters, quadruply bridging oxo ligands are very unusual, whereas quintuply bridging oxo ligands are unprecedented. By using 18O-labeled water, we have unambiguously established that these oxo ligands arise from water.     

Di-2-pyridyl ketone oxime [(py)2CNOH] in manganese carboxylate chemistry: mononuclear, dinuclear and tetranuclear complexes, and partial transformation of (py)2CNOH to the gem-diolate(2-) derivative of di-2-pyridyl ketone leading to the formation of NO3-

The use of di-2-pyridyl ketone oxime, (py)2CNOH, in manganese carboxylate chemistry has been investigated. Using a variety of synthetic routes complexes [Mn(O2CPh)2{(py)2CNOH}2].0.25H2O (1.0.25H2O), Mn4(O2CPh)2{(py)2CO2}2{(py)2CNO}2Br2].MeCN (2.MeCN), [Mn4(O2CPh)2{(py)2CO2}2{(py)2CNO}2Cl(2)].2MeCN (3.2MeCN), [Mn4(O2CMe)2{(py)2CO2}2{(py)2CNO}2Br2].2MeCN (4.2MeCN), [Mn4(O2CMe)2{(py)2CO2}2{(py)2CNO}2(NO3)2].MeCN.H2O (5.MeCN.H2O) and [Mn2(O2CCF3)2(hfac)2{(py)2CNOH}2] (6) have been isolated in good yields. Remarkable features of the reactions are the in situ transformation of an amount of (py)2CNOH to yield the coordination dianion, (py)2CO2(2-), of the gem-diol derivative of di-2-pyridyl ketone in 2-5, the coordination of nitrate ligands in 5 although the starting materials are nitrate-free and the incorporation of CF3CO2- ligands 6 in which was prepared from Mn(hfac)(2).3H2O (hfac(-)= hexafluoroacetylacetonate). Complexes 2-4 have completely analogous molecular structures. The centrosymmetric tetranuclear molecule contains two MnII and two MnIII six-coordinate ions held together by four mu-oxygen atoms from the two 3.2211 (py)2CO2(2-) ligands to give the unprecedented [MnII(mu-OR)MnIII(mu-OR)2MnIII(mu-OR)MnII]6+ core consisting of a planar zig-zag array of the four metal ions. Peripheral ligation is provided by two 2.111 (py)2CNO-, two 2.11 PhCO2- and two terminal Br- ligands. The overall molecular structure 5 of is very similar to that of 2-4 except for the X- being chelating NO3-. A tentative reaction scheme was proposed that explains the observed oxime transformation and nitrate generation. The CF3CO2- ligand is one of the decomposition products of the hfac- ligand. The two Mn(II) ions are bridged by two neutral (py)2CNOH ligands which adopt the 2.0111 coordination mode. A chelating hfac- ligand and a terminal CF3CO2- ion complete a distorted octahedral geometry at each metal ion. The CV of complex reveals irreversible reduction and oxidation processes. Variable-temperature magnetic susceptibility studies in the 2-300 K range for the representative tetranuclear clusters 2 and 4 reveal weak antiferromagnetic exchange interactions, leading to non-magnetic ST = 0 ground states. Best-fit parameters obtained by means of the program CLUMAG and applying the appropriate Hamiltonian are J(Mn(II)Mn((III))=-1.7 (2), -1.5 (4) cm(-1) and J(Mn(III)Mn(III))=-3.0 (2, 4) cm(-1).     

New rare earth metal complexes with nitrogen-rich ligands: 5,5'-bitetrazolate and 1,3-bis(tetrazol-5-yl)triazenate-on the borderline between coordination and the formation of salt-like compounds

From the two nitrogen-rich ligands BT(2-) (BT=5,5'-bitetrazole) and BTT(3-) (BTT=1,3-bis(1H-tetrazol-5-yl)triazene), a series of novel rare earth metal complexes were synthesised. For the BT ligand, a vast number of these complexes could be structurally characterised by single-crystal XRD, revealing structures ranging from discrete molecular aggregates to salt-like compounds. The isomorphous complexes [La2(BT)3]14 H2O (1) and [Ce2(BT)3]14 H2O (2) reveal discrete molecules in which one BT(2-) acts as a bridging ligand and two BT groups as chelating ligands. The complexes, [M(BT)(H2O)7]2[BT] x (x) H2O (3-5), (M=Nd (3), Sm (4), and Eu (5)), are also isomorphous and consist of [M(BT)(H2O)7]+ ions in which only one BT(2-) acts as a chelate ligand for each metal centre. [Tb(H2O)8]2[BT]3 x H2O (6) and [Er(H2O)8](2)[BT](3)x H2O (7) are salt-like compounds that do not exhibit any significant metal-nitrogen contacts. In the BTT-samarium compound 9, discrete molecules were found in which BTT(3-) acts as a tridentate ligand with three Sm--N bonds.     

含NS和NNSS供电子原子的钌(Ⅱ)羰基配合物

通过[RuHCl(CO)(PPh₃)₂(B)] (B=PPh₃, 吡啶 (py), 哌啶 (pip), 吗啉 (morph))与适当的席夫碱按1∶1的物质的量的比反应，合成了二齿和四齿席夫碱钌(Ⅱ)配合物。所用席夫碱配体通过S-苄基二硫代肼基甲酸酯与2,3-丁二酮(物质的量的比分别为1∶1和1∶2)的缩合反应制得。通过元素分析和多种物理化学方法对钌(Ⅱ)配合物和其席夫碱配体进行了表征。钌(Ⅱ)配合物为六配位的反磁性物质。用三种细菌对席夫碱配体及其钌(Ⅱ)配合物的抗微生物活性进行了筛选试验。     

Spectral and structural studies of copper(II) complexes of thiosemicarbazones derived from salicylaldehyde and containing ring incorporated at N(4)-position

Mononuclear and binuclear copper(II) complexes (1-8) with two ONS donor thiosemicarbazone ligands {salicylaldehyde 3-hexamethyleneiminyl thiosemicarbazone [H2L1] and salicylaldehyde 3-tetramethyleneiminyl thiosemicarbazone [H2L2]} have been prepared and physico-chemically characterized. IR, electronic and EPR spectra of the complexes have been obtained. The thiosemicarbazones bind to metal as dianionic ONS donor ligands in all the complexes except in [Cu(HL1)2] (2) and [Cu(HL2)2] (6). In compounds 2 and 6 the ligands are coordinated as monoanionic HL- ones. The magnetic susceptibility measurements indicate that all the complexes are paramagnetic. In complex [(CuL1)2] (1), the magnetic moment value is lower than the expected spin only value. In all the complexes g(||)>g( perpendicular)>2.0023 and G values within the range 2.5-3.5 are consistent with dx2-y2 ground state. The complexes were given the formula as [(CuL1)2] (1); [Cu(HL1)2] (2); [CuL1bpy] (3); [CuL1phen] (4); [CuL1gamma-pic].2H2O (5); [Cu(HL2)2] (6); [CuL2py].3H2O (7); [CuL2bipy] (8). The structure of the compound 8 have been solved by single crystal X-ray crystallography and was found to be distorted square pyramid around copper(II) ion.     

Reactions of mu3-alkenyl triruthenium carbonyl clusters with alkynes: synthesis of trinuclear mu-//-alkyne, mu-vinylidene, and mu-dienoyl derivatives

The reactions of doubly face-capped triruthenium cluster complexes of the type [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-CO)(2)(CO)(6)] (HNNMe(2) = 1,1-dimethylhydrazide; R(2)CCHR(1) = alkenyl ligand) with terminal and internal alkynes have been studied in refluxing toluene. The following derivatives have been isolated from these reactions: [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-kappa(2)-//-HCCH)(CO)(7)] (R(1) = R(2) = H, 5; R(1) = Ph, R(2) = H, 6; R(1) = CH(2)OMe, R(2) = H, 7 a; R(1) = H, R(2) = CH(2)OMe, 7 b) from acetylene, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCPh)(CO)(7)] (11) from diphenylacetylene, and three isomers of [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCH)(CO)(7)] (14, 15 a, and 15 b) from phenylacetylene. These products result from substitution of a CO ligand by the alkyne and contain an Ru--Ru edge bridged by the alkyne ligand in a parallel manner. DFT calculations on selected isomeric products have helped to establish that the type of Ru--Ru edge bridged by the alkyne depends more on kinetic factors related to the size of the alkyne substituents than on the thermodynamic stability of the final products. The preparation of triruthenium cluster complexes with mu-//-alkyne ligands is unprecedented and seems to relate to the fact that the starting trinuclear complexes have their two triangular faces protected by capping ligands. The clusters bearing mu-//-acetylene (5-7) are thermodynamically unstable with respect to their transformation into edge-bridging vinylidene derivatives, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCHR)(mu-kappa(1)-CCH(2))(CO)(7)] (R = H, 8; Ph, 9; CH(2)OMe, 10). DFT calculations have shown that complex 8 is 11.2 kcal mol(-1) more stable than its precursor 5. The thermolysis of compound 11 leads to [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu-kappa(4)-H(2)CCHCPhCPhCO)(mu-CO)(2)(CO)(5)] (12), which contains a novel edge-bridging dienoyl ligand that arises from an unusual coupling of diphenylacetylene, carbon monoxide, and the ethenyl ligand of complex 11. A chloro-bridged dimer of trinuclear clusters, [Ru(6)(mu-Cl)(2)(mu(3)-kappa(2)-HNNMe(2))(2)(mu(3)-kappa(2)-HCCH(2))(2)(mu-kappa(2)-PhCCHPh)(2)(mu-CO)(2)(CO)(10)] (13), has been prepared by treating compound 11 with hydrogen chloride. Therefore, edge-bridging parallel alkynes are susceptible to protonation to give edge-bridging alkenyl ligands. Compound 13 is the first complex to contain two alkenyl ligands on a trinuclear cluster, one face-capping and the other edge-bridging.     

Synthesis and metal complexes of chiral c(2)-symmetric diamino-bisoxazoline ligands

A synthetic route to tetradentate chiral N(4) ligands has been developed with the aim to study the potential of corresponding iron and manganese complexes as catalysts for enantioselective epoxidation. These ligands, which contain two oxazoline rings and two trialkylamino groups as coordinating units, are readily prepared in enantiomerically pure form by the reaction of chiral 2-chloromethyloxazolines with achiral N,N'-dimethylethane-1,2-diamine or chiral (R,R)-N,N'-dimethylcyclohexane-1,2-diamine. The ligands derived from N,N'-dimethylethane-1,2-diamine reacted with anhydrous metal halides MnCl(2) and FeCl(2) in a stereoselective manner to give octahedral mononuclear complexes that have the general formula Delta-[(L)MCl(2)]. In contrast, the ligands derived from N,N'-dimethylcyclohexane-1,2-diamine formed complexes with different coordination modes depending on the diastereomer employed: in one case the metal ion was found to be pentacoordinate, in the other case a hexacoordinated complex was observed. The structure of a series of Fe and Mn complexes was determined by X-ray analysis. The coordination chemistry of these ligands was further studied by X-ray and NMR analyses of the diamagnetic isostructural complexes [(L)ZnCl(2)]. Analogous ionic complexes, which were prepared by removing chloride with silver trifluoromethanesulfonate or hexafluoroantimonate, were tested as catalysts for the epoxidation of olefins.     

Chelating properties of permethylated 6A,6D-dideoxy-6A,6D-bis(1-imidazolyl)cyclodextrins towards Pt(II) and Ru(III)

Two imidazole-coordinating groups have been successfully grafted onto the C-6^A and C-6^D positions of permethylated α- and β-cyclodextrin scaffolds. Both water-soluble ligands L1 and L2 turned out to behave as good chelators when reacted with K₂PtCl₄. In the resulting diamagnetic cis-chelate complexes, the metal cation is pending above the cavity entrance. Paramagnetic ruthenium(III) chelate complexes have also been successfully synthesised from L1 and L2. In these more sterically demanding octahedral complexes, the imidazole groups coordinate the metal centre in a trans-fashion.     

The preparation and spectral properties of the new ‘mixed’ complexes [MI2(CO)3(py)L] (M = Mo and W; L = PPh3, AsPh3 and SbPh3)

Abstract

Seven-coordinate complexes of molybdenum(II) and tungsten(II) have become increasingly important as homogeneous catalysts. For example, the complexes [MX₂(CO)₃L₂] (M = Mo and W; X = Cl and Br; L = PPh₃ and AsPh₃) have been shown to be catalysts for the ring-opening polymerisation of norbornene.¹ Although a wide variety of complexes of the type [MX₂(CO)₃L₂] (M = Mo and W; X = Cl, Br and I; L = nitrogen, phosphorus, arsenic and antimony donor ligands)² have been reported, until now no examples of the mixed complexes [MX₂(CO)₃(py)L] have been prepared. In this communication we wish to describe the synthesis of the new mixed pyridine/L compounds [MI₂(CO)₃(py)L] (M = Mo and W; L = PPh₃, AsPh₃ and SbPh₃).