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The Supramolecular Architecture of Arene Complexes of Bis(polyfluorophenyl)mercurials
The 1:1 (arene)mercury complexes [HgR2(arene)] [R = C6F4-o-NO2, C6F4-m-NO2, C6F4-o-H, C6F5; arene = TMB (1,2,4,5-tetramethylbenzene), PMB (1,2,3,4,5-pentamethylbenzene)] are readily formed when mixtures of the mercurial and arene are crystallised from CH2Cl2 or CH2Cl2/hexane. Analogous 1:1 complexes are also formed from Hg(C6F5)2 and PhMe, whereas novel 1:2 complexes [HgR2(arene)2] result from Hg(C6F4-o-NO2)2 and PhMe or TMO (1,2,4-trimethoxybenzene) and from Hg(C6F5)2 and TMO. In the crystalline state, the 1:1 [HgR2(arene)] complexes exist as canted columns of alternating planar HgR2 and arene layers linked by weak (Hg···C 3.2-3.5 Å) [eta]1 or [eta]2 [pi]-arene-mercury interactions. For the TMB (R = C6F4-o-NO2, C6F4-o-H, C6F5) and PhMe (R = C6F5) complexes, the packing of neighbouring columns shows aligned, alternating fluoroarene and arene ring planes resulting in a 2D brick-wall motif with potential supramolecular components (fluoroarene-fluoroarene and fluoroarene-arene stacking). For the TMB complex with R = C6F4-m-NO2 the 2D array is distorted into a herringbone motif by weak C-H···O interactions. The 1:2 complex [Hg(C6F4-o-NO2)2(PhMe)2] has an analogous mercury environment to the 1:1 complexes, and the packing shows a distinct layer structure of alternating rows of PhMe and HgR2 with two PhMe units per HgR2 unit but with no inter-stack interactions. The TMO complexes have long Hg···O contacts (3.2 Å) rather than Hg···C and similarly show a layered structure, but in this case, with a single column of alternating HgR2 and pairs of TMO. Theoretical calculations for the 1:2 [HgR2(TMB)2] complexes (R = C6F4-o-NO2, C6F4-m-NO2) are consistent with the findings from the observed crystal structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Dimethyltin(IV) Bis(3,5-diphenylpyrazolate) as a Synthetic Reagent in the Preparation of Rare-Earth Pyrazolate Complexes
Reaction of SnMe2Cl2 with [Li(Ph2pz)] (Ph2pz = 3,5-diphenylpyrazolate) in diethyl ether in a 1:2 ratio afforded the new transmetallation reagent [SnMe2(Ph2pz)2]. Treatment of [SnMe2(Ph2pz)2] with Ln metals in either 1,2-dimethoxyethane (dme) or tetrahydrofuran (thf) provided a new route to the divalent [Ln(Ph2pz)2(dme)2] (Ln = Sm, Eu, Yb) and the trivalent [La(Ph2pz)3(dme)2] and [Yb(Ph2pz)3(thf)2] complexes in comparable yields to those from alternative methods. These reactions enabled isolation of the highly reactive [Sm(Ph2pz)2(dme)2] complex in good yield, in addition to the new cis isomer of [Eu(Ph2pz)2(dme)2], thereby establishing a rare case of geometric isomerism in lanthanoid chemistry. 1H and 119Sn NMR spectral studies and EDAX measurements were performed on the reaction mixture and/or residue to identify the tin-containing products and suggest formation of SnMe4, Sn2Me6, tin metal and two other SnMe3 species, which plausibly result from decomposition of unstable "SnMe2". Treatment of [Yb(Ph2pz)2(dme)2] with [SnMe2(Ph2pz)2] or [Tl(Ph2pz)] resulted in the isolation of [Yb(Ph2pz)3(thf)2]·2C6D6 and [Yb(Ph2pz)3(dme)]·0.5dme complexes, the structures of which have eight-coordinate Yb atoms and contrast nine-coordination observed for previous [Ln(Ph2pz)3(thf or dme)n] complexes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Bioactive fragments synergically involved in the design of new generation Pt(ii) and Pd(ii)-based anticancer compounds
Daniela Pucci, Anna Bellusci, Sergio Bernardini, Rossana Bloise, Alessandra Crispini, Giorgio Federici, Paola Liguori, Maria Fatima Lucas, Nino Russo, Alessandra Valentini
Soft-Soft Interactions Involving Iodoselenophosphonium Cations: Supramolecular Structures of Iodine Adducts of Bulky Trialkylphosphane Selenides
The reactions of trialkylphosphane selenides tBuniPr3-nPSe (n = 3: 1a; n = 2: 1b; n = 1: 1c; n = 0: 1d) with iodine are studied with the help of heteronuclear NMR spectroscopy, vibrational spectroscopy, and X-ray crystal structure determinations. The reaction of 1a with one equivalent of iodine provides, after crystallization from dichloromethane/pentane, solid 2a, which consists of pairs of molecular adducts tBu3PSe-I-I, together with chains of alternating [(tBu3PSe)2I]+ and I3- ions. The addition of iodine to 1b, 1c, and 1d in a 1:1 molar ratio furnishes ionic solids with the formulation [(tBuniPr3-nPSe)2I]+[I3]- (n = 2: 2b; n = 1: 2c; n = 0: 2d). Compounds 2a-2d exhibit supramolecular structures based on various kinds of weak Se···I and Se···Se interactions. In 2a, the uncharged molecules form dimers through Se···Se contacts, while the anions and cations assemble to form chains through linear P-Se···Ianion contacts. The ionic compounds 2b and 2d consist of the same type of chains, although they are not isotypic to each other. The two independent formula units of 2c are topologically different; one forms cation-anion chains analogous to those of 2b and 2d, whereas the other forms cation chains through Se···Se contacts. Se···I contacts between the latter chains and triiodide anions are very long but seem to be structurally significant; for such contacts, at well above the sum of the van der Waals radii, we propose the term tertiary contacts. On using more than one equivalent of I2, compounds corresponding to the formulation tBuniPr3-nPSeIx (x = 3, n = 3: 3a; x = 4, n = 1: 4c; x = 7, n = 2 and 0: 5b and 5d) were isolated as single crystals. Ionic 3a contains pairs of cations [(tBu3PSe)2I]+, connected by Se···Se contacts, located between corrugated layers of polymeric I5- anions. Compound 4c consists of two independent formula units tBuiPr2PSeI2·I2, which could, however, be regarded as tBuiPr2PSeI+·I-·I2 because of the long I-I distance adjacent to Se. To a fair approximation, the packing of the two units is independent; unit 1 forms dimers (···Se-I-I···I-I···)2, whereas the same motif in unit 2 forms chains. The structural subunits are linked through further contacts involving terminal iodine atoms from tBuiPr2PSeI···I units, which thereby form [mu]3-bridging units, and by additional I-I···Se contacts. In 5b,iodide-bridged cations [tBu2iPrPSeI···I···ISePiPrtBu2]+ are anchored to a polyiodide network of formal composition I11-[= (I-)(I2)5] through I···I contacts. Except for one I···I contact, the polyiodide is two-dimensional, although highly puckered. In 5d, [iPr3PSeI]+ cations and I2 molecules exhibit weak I···I interactions with I- units from puckered square-net-like polyiodide layers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Lewis Base Adducts of Heavier Group 13 Halohydrides - Not Just Aspiring Trihydrides!
The chemistries of the heavier group 13 halohydrides have been scarcely studied relative to those of their trihydride and trihalide counterparts. This short review summarises the literature concerning these compounds and seeks to highlight their distinct reactivities such that they may find increasing application in other fields of science. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Synthesis, Characterization, and In Vitro Antitumor Activity of New Amidineplatinum(II) Complexes Obtained by Addition of Ammonia to Coordinated Acetonitrile
New cis- and trans-dichloridoplatinum(II) complexes, which contain two amidine ligands or one amidine and one ammine ligand, cis- and trans-[PtCl2{(Z)-HN=C(NH2)CH3}2] (1) and cis- and trans-[PtCl2(NH3){(Z)-HN=C(NH2)CH3}] (2), have been prepared from the corresponding nitrile complexes by amminolysis in thf solution. All synthesized compounds were characterized by elemental analysis, ESI-MS, and IR and NMR spectroscopy. Amidines are isosters of iminoethers and ketimines. The trans isomers of the platinum complexes of the latter are endowed with an unexpectedly high antitumor activity. An important feature of complexes 1 and 2, as compared to iminoethers, is the exclusive preference for the Z configuration of the amidine ligand(s). The tumor cell growth inhibitory potency of the amidine compounds was tested towards a pair of human ovarian tumor cell lines A2780 (cancer cells sensitive to cisplatin) and A2780cisR (cancer cells with acquired resistance to cisplatin), and compared to that of cisplatin. From the obtained results it appears that the resistance factor is lower for cis-amidine complexes as compared to cisplatin, and for trans compounds it is lower as compared to cis compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
HP-NMR Study of the Pd-Catalyzed Methoxycarbonylation of Styrene Using Monodentate and Bidentate Phosphane-Modified Systems
Catalytically active palladium systems bearing the monodentate phosphetane ligand 1 and diphosphane 2 were studied by multinuclear NMR and HP-NMR spectroscopy under methoxycarbonylation conditions. The reaction of the complex [PdCl2(1)2] (1a) with pTsOH yields the dimeric complex [PdCl([mu]-Cl)(1)]2 (1b), which was characterized by multinuclear NMR spectroscopy and X-ray crystallography. The isolated complex 1b was tested as a precursor in the methoxycarbonylation of styrene, providing poor activity and enantioselectivity. Evidences for the protonation of ligand 1 under catalytic conditions were obtained. When complex [Pd(OTs)(OH2)(R,R-bdpp)][OTs] (2b) was used as the catalyst precursor evidences for both hydride and methoxycarbonylation mechanisms were achieved. Two isomeric forms of [Pd([pi]-methylbenzyl)(R,R-bdpp)], 2h and 2i, were characterized by multinuclear NMR spectroscopy and DFT calculations. The results obtained by DFT calculations showed that the two most stable isomers contain the ligand bdpp in the "chair" conformation and that both isomers have very similar energies. The hydrido-carbonyl-bridged complex [Pd2([mu]-H)([mu]-CO)(R,R-bdpp)2][OTs] (2e) was also detected under catalytic conditions. Deuterium labeling experiments using [D4]MeOH and GC-MS analysis of the unconverted substrate and products were performed and the results indicate that the styrene insertion step into the Pd-H bond of the catalyst is irreversible when the phosphetane containing system is used, whereas this step is reversible when the diphosphane precursor is used as the incorporation of deuterium was only observed in the latter case.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Terpyridineplatinum(II) Incorporation in N-Methylpyrrole-Based Polyamides by Solid Phase Techniques
The incorporation of terpyridineplatinum(II) centres into sequence-selective polyamides has been explored in this study, with the aim of producing cytotoxic molecules that display DNA sequence specificity. To facilitate this a terpyridineplatinum(II)-based metallointercalator has been developed, which can be incorporated into sequence-selective polyamides using standard machine-assisted peptide coupling techniques. A novel N-methylpyrrole-based metallopolyamide, containing the new terpyridineplatinum(II) moiety, was also synthesised to validate this new method of incorporation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
A4Ge9 (A = K, Rb) as Precursors for Hg-Substituted Clathrate-I Synthesis: Crystal Structure of A8Hg3Ge43
The Hg-substituted type-I clathrates A8Hg3+xGe43-x (A = K, Rb) were obtained by solid-state reactions from the corresponding Zintl phases A4Ge9 and Hg or HgO. The crystal structures of the compounds were determined by single-crystal and powder X-ray diffraction methods. They crystallize in the space group Pmn, with a = 10.849(1) Å and x = 0.19(5) for K8Hg3+xGe43-x (1) and a = 10.875(1) Å and x = 0.03(7) for Rb8Hg3+xGe43-x (2). Specific atomic positions (6c site) of the Ge framework are partially substituted by Hg atoms, whereas the alkali-metal atoms reside at the center of the cavities. Both compounds exceed the electron-counting rule for Zintl phases. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Flux Synthesis, Crystal Structures, and Luminescence Properties of Salt-Inclusion Lanthanide Silicates: [K9F2][Ln3Si12O32] (Ln = Sm, Eu, Gd)
Ming-Feng Tang, Pei-Yun Chiang, Yu-Han Su, Yu-Chi Jung, Guang-Yi Hou, Bor-Chen Chang, and Kwang-Hwa Lii
The Binary Ph2PCl/GaCl3 System: A Room-Temperature Molten Medium for P-P Bond Formation
An equimolar reaction mixture of Ph2PCl and GaCl3 at room temperature results in the formation of a melt M consisting of the donor-acceptor complex Ph2PCl[rarr]GaCl3 (1a), the chloro(diphenylphosphanyl)diphenylphosphonium cation (2a), and the counteranions [GanCl3n+1]- (n = 1, 2, 3). The melt has been characterized by Raman and NMR spectroscopy and is compared with the reaction mixture of Ph2PCl and GaCl3 observed in solution (CH2Cl2). The melt provides a facile and reactive source of the diphenylphosphenium cation, as demonstrated with use for P-P bond insertion into (PhP)5, to give the 2,3,4,5-tetraphosphanyl-1,4-diphosphonium dication (3), and reductive coupling with gallium metal to give the diadduct Cl3GaPPh2PPh2GaCl3 (5).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Cu2+-Mediated Nucleophilic Addition of Different Nucleophiles to Dicyanamide - Synthesis, Structures, and Magnetic Properties of a Family of Mononuclear, Trinuclear, Hexanuclear, and Polymeric Copper(II) Complexes
Five new copper(II) complexes have been isolated from the reaction system of CuII/N(CN)2-/HNu (HNu = pyrazole or MeOH) by Cu2+-mediated in situ nucleophilic additions of methanol or pyrazole to dicyanamide; they are [Cu(HdcadMeOH)2](ClO4)2·2H2O (3), [Cu(dca)2(3-nic)2]n·(HdcaMeOH)2n (4), [Cu(dcapz)(dcadMeOH)] (5), [Cu3(dcadpz)2(Hpz)2(MeCN)2](ClO4)2(NO3)2 (6), and [Cu6(dcadpz-2H)2([mu]-pz)6] (7) [HdcadMeOH = bis(methoxycarbimido)amine, HdcaMeOH = (methoxycarbimido)cyanoamine, dcadMeOH- = bis(methoxycarbimido)aminato, dcapz- = (pyrazolecarbimido)cyanoaminato, dcadpz- = bis(pyrazolecarbimido)aminato, Hpz = pyrazole, 3-nic = nicotinamide]. X-ray crystallography revealed that 3 and 5 are mononuclear complexes, 6 is a trinuclear complex, 7 is a cyclic hexanuclear cluster, whereas 4 is composed of neutral one-dimensional [Cu([mu]1,5-dca)2(3-nic)2]n coordination chains with HdcaMeOH guest molecules located between these chains. In the five complexes, the 1:1 and 1:2 nucleophilic addition reactions occurred between dca- and methanol or pyrazole molecules under controlled conditions. In complexes 3, 5, 6, and 7, the addition products generated in situ act as bridging or chelating ligands, whereas in compound 4 the addition product acts as the guest molecule. The magnetic properties of complexes 6 and 7 were studied by variable-temperature magnetic susceptibility and magnetization measurements. In 6, significant ferromagnetic coupling exists between the three S = 1/2 spins within the Cu3 unit through the dcadpz- bridges, whereas in 7, strong antiferromagnetic couplings exist between the neighboring copper ions through the [dcadpz-2H]3- and pz- bridges with an intratrimer exchange interaction of -250.6 K and an intertrimer coupling interaction of -69.1 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Probing the Effect of Binding Site and Metal Centre Variation in Pentadentate Oligopyridylimine-Bearing Bimetallic (Fe2, Co2, Ni2) Ethylene Oligomerisation Catalysts
The symmetrical and unsymmetrical pentaaza 2,6-oligopyridylimines, 6,6[Prime]-[(2,6-iPr2C6H3)N=CMe]2-2,2[prime]:6[prime],2[Prime]-C15H9N3 (L1) and 6-[(2,6-iPr2C6H3)N=CMe]-2,2[prime]:6[prime],2[Prime]:6[Prime],2[Prime][prime]-C20H13N4 (L2), have been prepared in good yield using a combination of palladium(0)-mediated cross-coupling and condensation strategies. Treatment of L1 or L2 with two equivalents of MX2 in nBuOH at elevated temperatures affords the paramagnetic bimetallic complexes [(L1)M2X4] [M = Fe, X = Cl (1); M = Co, X = Cl (2a); M = Co, X = Br (2b); M = Ni, X = Br (3)] and [(L2)M2X4] [M = Fe, X = Cl (4); M = Co, X = Cl (5a); M = Co, X = Br (5b); M = Ni, X = Br (6)] in high yield, respectively. The molecular structures of 2a along with the acetonitrile adduct of 5b, [5b(NCMe)], have been determined and reveal that L1 and L2 compartmentalise the MX2 units into mixed pyridylimine/dipyridylimine (2a) and pyridylimine/terpyridine [5b(NCMe)] binding sites. Unexpectedly during crystallisation of 6 from acetonitrile, the salt [(L2)Ni2Br2([mu]-Br)(NCMe)2]2[NiBr4] (7) was obtained as the only crystalline product. On activation with MAO (methylaluminoxane), 4-6 show only low activities for ethylene oligomerisation (6/MAO > 5/MAO) or are inactive (4/MAO). On the other hand, 1-3 are considerably more active (3/MAO > 2/MAO > 1/MAO) with the most productive system, dinickel-based 3/MAO (450 g mmol-1 h-1 bar-1), yielding methyl-branched waxes composed of mostly internal unsaturation along with lower levels of [alpha]-olefins; conversely the diiron (1/MAO) and dicobalt (2/MAO) systems give uniquely linear [alpha]-olefins. For purposes of comparison the synthesis, structure and catalytic activity of mono-nickel [(6-{(2,6-iPr2C6H3)N=CMe}-2,2[prime]-C10H7N2)NiBr2] (8) are also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Facile, Ambient Temperature, Double Sn-C Bond Cleavage: Synthesis, Structure, and Electrochemistry of Organotin and Organotellurium Ferrocenecarboxylates
The reaction of organotin halides R3SnCl (R = Me or benzyl) with ferrocenecarboxylic acid (FcCOOH) in the presence of triethylamine affords Me3SnO2CFc (1) or Bn3SnO2CFc (2) (Bn = benzyl). The latter undergoes a facile ambient temperature double Sn-C bond cleavage to give the monoorganostannoxane, [BnSn(O)O2CFc]6 (3). Compound 3 is also formed by a single Sn-C bond cleavage reaction in the reaction between Bn2SnCl2 and FcCOOH. In contrast, the reaction of Me2SnCl2 with FcCOOH affords Me2Sn(O2CFc)2 (4), where the Sn-C bonds are robust. Organotellurium ferrocene carboxylates [(4-OMe-Ph)2Te(O2CFc)2] (5) and [(4-NMe2-Ph)2Te(O2CFc)2] (6) are obtained in the reaction of the corresponding diorganotellurium oxides/halides with FcCOOH. Whereas 1 is a zig-zag one-dimensional coordination polymer with a square-wave architecture, the structures of 3-6 are molecular. Compound 3 is a hexameric cage and possesses a drum-type structure, whereas 4 is mononuclear and contains a six-coordinate tin with a skewed trapezoidal geometry. In compounds 5 and 6 the lone pairs on tellurium are stereochemically active thereby conferring see-saw geometries. Compounds 1, 2, 4, and 5 show single quasireversible peaks at +0.62, +0.72, +0.66, and +0.64 V, respectively with respect to the Ag/AgCl electrode. Compound 3, which contains six ferrocene arms, shows a single redox event along with a stripping peak. Compound 6 shows quasireversible and irreversible redox events at +0.62 and +1.17 V, respectively. The latter is due to a ligand-centered oxidation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Broad HOMO-LUMO gap tuning through the coordination of a single phosphine, aminophosphine or phosphite onto a Ru(tpy)(bpy)2+ core
Isabelle M. Dixon, Emilie Lebon, Gilles Loustau, Pierre Sutra, Laure Vendier, Alain Igau, Alberto Juris
Novel ruthenium(ii) complexes containing the N-phosphorylated iminophosphorane-phosphine ligand Ph2PCH2P{[double bond, length as m-dash]NP([double bond, length as m-dash]O)(OEt)2}Ph2: a new coordination mode of its methanide anion
Victorio Cadierno, Josefina Diez, Joaquin Garcia-Alvarez, Jose Gimeno, Javier Rubio-Garcia
Unprecedented NaI-CuII-LnIII heterometallic coordination polymers based on 3,5-pyrazoledicarboxylate with both infinite cationic and anionic chains
Yan Wang, You Song, Zhao-Rui Pan, Ying-Zhong Shen, Zheng Hu, Zi-Jian Guo, He-Gen Zheng
Inorganic Chemistry
Inorganic Chemistry , Volume 47 Issue 17 (September 1, 2008) is now available
Spin canting in an unprecedented three-dimensional pyrophosphate- and 2,2[prime or minute]-bipyrimidine-bridged cobalt(ii) framework
Nadia Marino, Teresa F. Mastropietro, Donatella Armentano, Giovanni De Munno, Robert P. Doyle, Francesc Lloret, Miguel Julve
Monocyclopentadienyl Phenoxido-Amino and Phenoxido-Amido Titanium Complexes: Synthesis, Characterisation, and Reactivity of Asymmetric Metal Centre Derivatives
Reduction of phenol-imine derivatives R[prime]N=CH(3,5-R2C6H2-2-OH) (R = tBu; R[prime] = C6H5 1a, p-MeC6H4 1b, Cy 1c, tBu 1d, 2,6-Me2C6H3 1e; R = H; R[prime] = p-MeC6H4 1f; Cy = cyclohexyl) with MBH4 (M = Li, Na) or AlLiH4 in ethyl ether or thf at room temperature affords the phenol-amine compounds R[prime]NHCH2(3,5-R2C6H2-2-OH) 2a-c and 2e,f. The N-R-[2,4-di-tert-butyl]benzo-1-oxa-3-azine species (R = tBu 2d1, 2,6-Me2C6H3 2e1) are obtained by Mannich reaction of 2,4-di-tert-butylphenol with RNH2 in refluxing methanol. Intermediate 2d1 is converted in ethanol at room temperature into N-tert-butyl[2-hydroxy-3,5-di-tert-butyl]benzylamine (2d), whereas 2e is not obtained from 2e1 by using this procedure.N-alkyl,N-tert-butyl[2-hydroxy-3,5-di-tert-butyl]benzylaminecompounds tBuN(R)CH2(3,5-tBu2C6H2-2-OH) (R = Me 2g, Et 2h, nPr 2i, CH2Ph 2j) are also prepared by the appropriate synthetic method. Treatment of 2a-c with 1 equiv. of TiCpCl3 in the presence of 2.5 equiv. of NEt3 in hexane at room temperature gives the monocyclopentadienyl phenoxido-amido monochloride complexes TiCp[R[prime]NCH2(3,5-tBu2C6H2-2-O)]Cl (R[prime] = C6H5 3a, R[prime] = p-MeC6H4 3b, R[prime] = Cy 3c). The analogous complex Ti([eta]5-C5H4SiMe2Cl)[C6H5NCH2(3,5-tBu2C6H2-2-O)]Cl (4a) results from the reaction of 2a with Ti([eta]5-C5H4SiMe2Cl)Cl3. Nevertheless, 2d reacts with TiCpCl3 in hexane in the presence of NEt3 at room temperature yielding the monocyclopentadienyl phenoxido dichloride compound TiCp[tBuNHCH2(3,5-tBu2C6H2-2-O)]Cl2 (5), whereas in ethyl ether and in the absence of NEt3 adduct 5·HCl is obtained, which is further converted into TiCp[tBuNCH2(3,5-tBu2C6H2-2-O)]Cl (3d) by addition of a NEt3/ethyl ether solution. The reaction of TiCpCl3 with 2a in the presence of 2.5 equiv. of NEt3 in a polar solvent (thf, CH2Cl2 or toluene) at room temperature affords TiCp[Ph(H)NCH2(3,5-tBu2C6H2-2-O)]Cl (6a) as a mixture of two stereoisomers. All the reported compounds were characterised by the usual analytical and spectroscopic methods and the molecular structures of 2a, 2d, 2e and 3d were determined by X-ray diffraction analysis from suitable single crystals. Preliminary studies of catalytic activity for ethylene polymerisation by using solid methylaluminoxane as cocatalyst were performed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Rational Assembly of High-Spin Polynuclear Magnetic Complexes into Coordination Networks: the Case of a [Mn4] Single-Molecule Magnet Building Block
The synthesis of transition-metal high-spin complexes and of infinite coordination networks of these high-spin carriers now represents a recognized subdiscipline of coordination chemistry. This new research trend has been particularly encouraged by the discoveries that molecular and one-dimensional coordination aggregates may behave as nanomagnets, as illustrated by the so-called single-molecule magnets (SMMs) and single-chain magnets (SCMs). While the synthesis of isolated polynuclear high-spin complexes still rely mostly on serendipitous assembly with appropriate ligands, the synthesis of SCMs or extended networks of high-spin complexes demands a more designed and controlled bottom-up assembly of precursor complexes and bridging species selected for their coordination abilities. In this context, the case of a [Mn4] SMM is unique in the literature, as one-, two-, and three-dimensional networks have been rationally designed by using this SMM unit as a building block, giving rise to original magnetic properties. This review gathers all reported systems that we know of, having the corresponding [Mn4O6] core, either in isolated complexes or in frameworks. Their structures and, when relevant, the synthetic strategy and magnetic properties are described. The demonstrated and potential outcomes, in terms of physical properties, of such coordination assemblies of high-spin complexes are then discussed. These are highlighted through examples with other building blocks, to broaden the scope of possible strategies and building blocks, and thus provide a basis for the further development of this promising area. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Variable Coordination Modes of Benzaldehyde Thiosemicarbazones - Synthesis, Structure, and Electrochemical Properties of Some Ruthenium Complexes
Reaction of benzaldehyde thiosemicarbazones [H2LR, where H2 stands for the two protons, the hydrazinic proton, and the phenyl proton at the ortho position, with respect to the imine function and R (R = OCH3, CH3, H, Cl, and NO2) for the para substituent] with [Ru(PPh3)2(CO)2Cl2], carried out in refluxing ethanol, afforded monomeric complexes of type [Ru(PPh3)2(CO)(HLR)(H)]. The crystal structure of the [Ru(PPh3)2(CO)(HLNO2)(H)] complex was determined. The thiosemicarbazone ligand is coordinated to the ruthenium center as a bidentate N,S-donor ligand forming a four-membered chelate ring. When the reaction of the thiosemicarbazones with [Ru(PPh3)2(CO)2Cl2] was carried out in refluxing toluene, a family of dimeric complexes of type [Ru2(PPh3)2(CO)2(LR)2] were obtained. The crystal structure of [Ru2(PPh3)2(CO)2(LCl)2] was determined. Each thiosemicarbazone ligand is coordinated to one ruthenium atom, by dissociation of the two protons, as a dianionic tridentate C,N,S-donor ligand, and at the same time the sulfur atom is also bonded to the second ruthenium center. 1H NMR spectra of the complexes of both types are in excellent agreement with their compositions. All the dimeric and monomeric complexes are diamagnetic (low-spin d6, S = 0) and show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry of the [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes show the ruthenium(II)-ruthenium(III) oxidation within 0.48-0.73 V vs. SCE followed by a ruthenium(III)-ruthenium(IV) oxidation within 1.09-1.47 V vs. SCE. Potentials of both the oxidations are found to correlate linearly with the electron-withdrawing character of the substituent R. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
A Ferrocene-Peptide Conjugate as a Hydrogenase Model System
This work introduces a bis(cysteine) ligand to build a small peptidic model system of hydrogenase enzymes. Fe(C5H4CO-Cys-OMe)2 (LH2) has been employed as a chelate for an iron-carbonyl complex, which mimics two essential structural properties of the hydrogenase class of enzymes, namely the coordination of the iron-carbonyl core to peptide ligands and the presence of an electrochemical relay in spatial proximity. The treatment of LH2 with Fe3(CO)12 yields LFe2(CO)6 (3a), which is the first peptide-coordinated iron hydrogenase active-site model complex. Compound 3a was fully characterized spectroscopically (1H NMR, 13C NMR, IR and Mössbauer spectroscopy, mass spectrometry and elemental analysis). A single-crystal X-ray analysis confirms the proposed structure and reveals a staggered conformation of the Fe2(CO)6S2 core. Fourier transform infrared (FTIR) spectroelectrochemistry reveals an electronic interaction between the peptide backbone and the iron-carbonyl cluster, but not with the ferrocene subsite. The introduction of this peptidic cysteine-based ligand into hydrogenase model chemistry helps to confirm the proposed cofactor biosynthesis and understand the electronic interplay between the metal-carbonyl active site and the protein environment in this important class of enzymes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Tetranuclear and Octanuclear Cobalt(II) Citrate Cluster Single Molecule Magnets
In a follow-up study of the cobalt(II) member 1 of a family of isostructural cubane clusters of type [C(NH2)3]8[MII4(cit)4]·8H2O (cit = citrate, M = Mg, Mn, Fe, Co, Ni, Zn) by measuring AC magnetic susceptibilities, as a function of frequency, this compound clearly displays behaviour typical of magnetization reversal and slow magnetic relaxation ([Delta]E = 13.1 K, [tau]o = 8.4 × 10-7 s). A related octanuclear cluster [Co8(C4O7)4(H2O)12]·24H2O (2) that contains a [Co4(C4O7)4] cubane moiety, behaves likewise ([Delta]E = 20.5 K, [tau]o = 1.0 × 10-7 s).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
A Theoretical Study on the Reactivity of a Rhenium Hydroxo-Carbonyl Complex Towards [beta]-Lactams
The mechanism of the reaction between the complex [Re(OH)(CO)3(N2C2H4)] and azetidin-2-one or 3-formylamino-N-sulfonatoazetidin-2-one was investigated by using the B3LYP density functional theory methodology in conjunction with the PCM-UAHF model to take into account solvent effects. According to our calculations, the rate-determining energy barrier for the azetidin-2-one case of 38.8 kcal mol-1, becomes 25.7 kcal mol-1 in the case of the 3-formylamino-N-sulfonatoazetidin-2-one species. The presence of the sulfonato group is crucial for the cleavage of the [beta]-lactam N1-C2 bond by the Re complex thanks to the interaction of the sulfonato group with the hydroxy and bidentate ligands of the complex. This could be of interest for the synthesis of [beta]-amino acids and their derivatives from [beta]-lactams under mild conditions and in solvents of low polarity promoted by organometallic complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
From Single-Molecule Precursors to Coupled Ag2S/TiO2 Nanocomposites
A single-source approach using mild temperatures was applied to prepare morphological well-defined and coupled TiO2/metal-sulfide nanocomposites. Metal N-alkyldithiocarbamates were used as the precursors to the metal-sulfide nanophases and, in particular, Ag2S nanostructures were investigated in more detail. These were observed as nano-islands at the surface of TiO2 (anatase) particles, which were used as substrates. To explain the formation of these nanocomposite particulates, a tentative mechanism has been proposed which involves the controlled release of sulfide ions from an intermediate coordination compound. Because the growth of the metal sulfide can be controlled at the surface of a photoactive substrate, we anticipate the potential of this synthetic method to chemical design reasonable amounts of semiconductor-sensitized TiO2, such as Ag2S/TiO2 nanocomposites. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
The structure of Fe(iii) ions in strongly alkaline aqueous solutions from EXAFS and Mossbauer spectroscopy
Pal Sipos, Dalma Zeller, Erno Kuzmann, Attila Vertes, Zoltan Homonnay, Monika Walczak, Sophie E. Canton
Synthesis, Structures, and Oxidation of Iridium(III) Alkyl Compounds Containing Thiolate and Dithiolate Ligands
Treatment of [Ir(dtbpy){CH2CMe2Cc6H4(Ir-Cc)}(C6H4tBu-2)] (1) (dtbpy = 4,4[prime]-di-tert-butyl-2,2[prime]-bipyridyl) with the dichalcogenides R2Q2 in refluxing toluene afforded the chalcogenolate-bridged dinuclear complexes [Ir(dtbpy) {CH2CMe2Cc6H4(Ir-Cc)}]2([mu]-QR)2 [RQ = pTolS (2), PhSe (3)]. Similarly, heating a solution of [Rh(dtbpy){CH2CMe2Cc6H4(Ir-Cc)}(CH2CMe2Ph)] and p-tolyl sulfide in toluene at reflux gave [Rh(dtbpy){CH2CMe2Cc6H4(Ir-Cc)}]2([mu]-SpTol)2 (4). Treatment of [Ir(dtbpy)(CH2CMe2Ph)Cl]2([mu]-Cl)2 with Na(Sxyl) (xyl = 2,6-dimethylphenyl) and Na2(S[and]S) afforded [Ir(dtbpy)(CH2CMe2Ph)(Sxyl)2]2 (5) and [Ir(dtbpy)(CH2CMe2Ph)(S[and]S)]2 {S[and]S2- = maleonitriledithiolate (6), toluene-3,4-dithiolate (7), benzene-1,2-dithiolate (8)}. Oxidation of compound 8 with AgOTf (OTf- = triflate) resulted in dimerization of the bdt2- ligand by S-S bond formation and the isolation of [Ir2(dtbpy)2(CH2Me2Ph)2{(bdt)2}][OTf]2 (9). The solid-state structures of compounds 2, 3, 4, 7, and 9 were determined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
