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Magnesium cobaltates (Arnacnac)MgCo(COD)2 (1–3) were synthesised by reacting (Arnacnac)MgI(OEt2) with K[Co(η4-COD)2] (COD = 1,5-cyclooctadiene) [Arnacnac = CH(ArNCMe)2; Ar = 2,4,6-Me3-C6H2 (Mes), 2,6-Et2-C6H3 (Dep), 2,6-iPr2-C6H3Mes (Dipp)]. Compounds 1–3 form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of 2 with tert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [(Depnacnac)MgCo(P2C2tBu2)]2 (4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [(Depnacnac)Mg(THF)3][Co(P2C2tBu2)2] (5) is obtained in THF. Complex 4 is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in 4 by white phosphorus (P4) enabled the synthesis of the phosphorus-rich sandwich compound [(Depnacnac)MgCoP4(P2C2tBu2)]2 (6). The heterobimetallic complex (Cp*NiP2C2tBu2)Co(COD) (7) was isolated after treatment of 4 with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate)., Ion-pairing strongly influence the reactivity of low-oxidation state transition metalate anions, enabling the synthesis of novel phosphaorganometallic compounds.

Sandwich-type clusters with the planar fragment containing a heterometallic sheet have remained elusive. In this work, we introduce the [K(2,2,2-crypt)]4{(Ge9)2[η6-Ge(PdPPh3)3]} complex that contains a heterometallic sandwich fragment. The title compound is structurally characterized by means of single-crystal X-ray diffraction, which reveals the presence of an unusual heteroatomic metal planar fragment Ge@Pd3. The planar fragment contains a rare formal zerovalent germanium core and a peculiar bonding mode of sp2-Ge@(PdPPh3)3 trigonal planar structure, whereas the nonagermanide fragments act as capping ligands. The chemical bonding pattern of the planar fragment consists of three 2c-2e Pd-Ge σ-bonds attaching Pd atoms to the core Ge atom, while the binding between the planar fragment and the aromatic Ge9 ligands is provided by six 2c-2e Pd-Ge σ-bonds and two delocalized 4c-2e σ-bonds. The synthesized cluster represents a rare example of a sandwich compound with the heteroatomic metal planar fragment and inorganic aromatic capping ligands.

The scandium Cp/COT hybrid sandwich compound [(η 5-C 5H 5)Sc(η 8-C 8H 8)] is resistant to metallation via conventional alkyllithium and lithium amide bases. In this work, clean, selective, stoichiometric and high-yielding mono- and dimetallation is accomplished using tandem trans-metal-trapping (TMT) involving LiTMP and iBu 2AlTMP with deprotonation occurring selectively at the Cp and Cp/COT rings respectively, providing the first examples of selective metallation of a sandwich complex featuring a group 3 element.

The known sandwich compound [η5-(CH2)3N2(BPh)2CMe]2Fe in which adjacent C2 units are replaced by isoelectronic BN units can be considered as a boraza analogues of ferrocene similar to borazine, B3N3H6, considered as a boraza analogue of benzene. In this connection, the related bis(1,2,3,5-tetramethyl-1,2-diaza-3,5-diborolyl) derivatives (Me4B2N2CH)2M (M = Ti, V, Cr, Mn, Fe, Co, Ni) for all of the first row transition metals have been optimized using density functional theory for comparison with the isoelectronic tetramethylcyclopentadienyl derivatives (Me4C5H)2M. Low-energy sandwich structures having parallel B2N2C rings in a trans orientation are found for all seven metals. The 1,2-diaza-3,5-diborolyl ligand appears to be a weaker field ligand than the isoelectronic cyclopentadienyl ligand as indicated by higher spin ground states for some (η5-Me4B2N2CH)2M sandwich compounds relative to the corresponding metallocenes (η5-Me4C5H)2M. Thus (η5-Me4B2N2CH)2Cr has a quintet ground state in contrast to the triplet ground state of (η5-Me4C5H)2Cr. Similarly, the sextet ground state of (η5-Me4B2N2CH)2Mn lies ∼18 kcal mol−1 below the quartet state in contrast to the doublet ground state of the isoelectronic (Me4C5H)2Mn. These sandwich compounds are potentially accessible by reaction of 1,2-diaza-3,5-diborolide anions with metal halides analogous to the synthesis of [η5-(CH2)3N2(BPh)2CMe]2Fe.

An improved, one-pot synthesis of the linear sandwich compound [Sc(η5 -C5 H5 )(η8 -C8 H8 )] is presented. The synthetic procedure is amenable to boryl- and silyl-substituted cyclopentadienyl and cyclooctatetraenyl ligands, thereby yielding the first functionalized derivatives. We found that the synthesis of the silyl-substituted mixed sandwich complexes produces higher yields when the ligand exchange is carried out stepwise, by isolating the intermediate trimethylsilylated half-sandwich complex [Sc(η8 -C8 H7 SiMe3 )Cl(THF)] (THF=tetrahydrofuran). The molecular structures of the parent complex, as well as of its mono-boryl-substituted derivatives, have been determined by single-crystal X-ray diffraction. In addition, the optical and electrochemical properties of the mixed sandwich complexes are reported.

Palladium catalyzed bis-arylations, -alkylations, and -allylations on the Cp ring of iron and cobalt sandwich compounds have been achieved using the bidentate picolinamide directing group. This directing group along with catalytic Pd(OAc)2 was found to be highly efficient for C–H functionalization, giving up to 87% yields. The palladacyclic intermediate for the C–H activation of the Cp ring has been isolated and structurally characterized for the cobalt sandwich compound [η5-C5H5]Co(η4-C4Ph4). Attempted C–H annulation reactions using picolinamide-derived sandwich compounds did not yield the expected annulated products and instead oxidized the Cp- and picolinamide-bound CH2 unit to aldehydes. Detailed studies on this novel and unprecedented oxidation indicated that this happens only with the assistance of the picolinamide directing group. We have also shown that the sp2 C–H functionalization and the sp3 C–H oxidation can be effectively carried out as a one-pot reaction.

A covalent organic helical cage (COHC) with D3 symmetry bearing two 1,3,5-trimethylphenyl cores and six di-tert-butyldiethynylallene moieties was synthesized and fully characterized. This molecular structure cage, unlike a previously reported one, favors inclusion-complex formation with organometallic sandwich compounds due to the presence of methyl groups on the aryl rings. The strong chiroptical responses of these COHCs, along with their ability to entrap guest molecules, enabled the detection of a ruthenium sandwich compound by means of electronic circular dichroism (ECD) spectroscopy.

We investigated the coordination behavior of AgI towards three polycondensed aromatic hydrocarbons (PAHs) in solution, in the solid state, and theoretically. Silver(I) trifluoromethanesulfonate (AgTfl) coordinates to fluorene to yield crystals of the composition {[(µ-η2:η2-fluorene)Ag2(Tfl)2]}n (1), the fluorene derivative 5,12-diphenyl-5,6;11,12-di-o-phenylene-5,12-dihydrotetracene (pseudorubrene) reacts with silver(I) perchlorate to yield crystals of the composition bis[(η2-pseudorubrene)(η2-toluene)AgClO4]·toluenesolv (2), and the formation of the crystalline dimeric AgI sandwich compound [(µ-η2:η2-truxene)2(η1-toluene)(µ-H2O)Ag2(ClO4)2] (3) is accomplished by π-coordination of the PAH truxene. In complexes 1–3, it is eminent from their crystal structures that the anionic silver moieties act as linking units between the PAH molecules. Theoretical calculations based on DFT methods of the aromatic bridging ring ligands substantiate the experimentally observed selective AgI coordination for each of the three PAH molecules fluorene, pseudorubrene, and truxene.

A comprehensive review on the synthesis, reactions and applications centered on the highly stable and sterically hindered cobalt sandwich compound (η5-Cp)Co(η4-C4Ph4) is presented. The derivatization of the cyclopentadienyl and cyclobutadiene rings, reactions, structural properties and applications, particularly in the field of asymmetric catalysis of (η5-Cp)Co(η4-C4Ph4) and its derivatives and analogues are discussed. The chemistry of this cobalt sandwich compound is also compared with analogous derivatives of ferrocene.

Recently an all-metal aromatic sandwich compound of a [Sb3Au3Sb3](3-) ion has been synthesized and characterized experimentally, which indicates that there might exist a variety of stable all-metal sandwich complexes. The intralayer and interlayer chemical bonding interaction in this system plays significant roles in their stability, chemical properties and functionalities. Here we report a systematic theoretical study on the geometries, electronic structures, and chemical bonding of the [Sb3Au3Sb3](3-) ion and its congeners of [X3Au3X3](3-) (X = N, P, As, Sb, Bi, Uup) as well as [X3M3X3](3-) (M, X = Cu, As; Ag, Bi; Au, Sb; Rg, Uup) to understand the special stabilities of these species. Additional studies are also performed on the oligomers [Sb3(Au3Sb3)n](3-) (n = 1-4) to explore whether the sandwich compound can form stable extended systems. Through extensive theoretical analyses, we have shown that among the [Au3X6](3-) (X = N, P, As, Sb, Bi, Uup) species, [Sb3Au3Sb3](3-) is most stable due to superb matching of Sb3 and Au3 in both geometric size and fragment orbital energies. The significant stability of the [Au3Sb6](3-) ion is determined by the interlayer (p-d-p)σ interactions between the vertical Au 5d6s hybrid orbitals of Au3 and Sb 5pπ orbitals of the Sb3 rings. Each Sb3 ring demonstrates unique σ aromaticity, which remains when the complex is extended to oligomers. The results suggest that it is likely that there might exist other stable [ApMpAp](x-) (M = transition metals, A = main group elements, p = 3, 4, 5, …) sandwich ions and oligomers.

DFT B3LYP/6-31G(d) calculations were performed to examine the feasibility of graphene-like C42H18 and starbenzene C6(BeH)6 (SBz) polymers as ligands of 3D-extensible sandwich compounds (3D-ESCs) with uninterrupted sandwich arrays. The results revealed that sandwich compounds with three or more C42H18 ligands were not feasible. The possible reason may be the localization of π electrons on certain C6 hexagons due to π-metal interactions, which makes the whole ligand lose its electronic structure basis (higher degree of π electron delocalization) to maintain the planar structure. For comparison, with the aid of benzene (Bz) molecules, the SBz polymers can be feasible ligands for designing 3D-ESCs because the C-Be interactions in individual SBz are largely ionic, which will deter the π electrons on one C6 ring from connecting to those on neighbouring C6 rings. This means that high degree of π electron delocalization is not necessary for maintaining the planarity of SBz polymers. Such a locally delocalized π electron structure is desirable for the ligands of 3D-ESCs. Remarkably, the formation of a sandwich compound with SBz is thermodynamically more favourable than that found for bis(Bz)chromium. The assembly of 3D-ESCs is largely exothermic, which will facilitate future experimental synthesis. The different variation trends on the HOMO-LUMO gaps in different directions (relative to the sandwich axes) suggest that they can be developed to form directional conductors or semiconductors, which may be useful in the production of electronic devices.

The dicarboxylic diester of the cyclobutadiene linked dimeric cobalt sandwich compound, {[η5-C5H4(C(O)OMe)]Co(η4-C4Ph3)}2 on controlled reduction with LiAlH4 gave the bis(hydroxymethyl) compound {[η5-C5H4(CH2OH)]Co(η4-C4Ph3)}2 1 in 98% yield. The diester was also reduced to the dimethyl derivative {[η5-C5H4(Me)]Co(η4-C4Ph3)}2 2 using LiAlH4 and AlCl3. Compound 1 was reacted with NaN3 in acetic acid at 50 °C to get the diazido methyl derivative {[η5-C5H4(CH2N3)]Co(η4-C4Ph3)}2 3 whereas the bis (2-acetoxy methyl) derivative {[η5-C5H4(CH2OC(O)Me]Co(η4-C4Ph3)}2 4 was obtained in almost quantitative yield by heating compound 1 with acetic acid at 80–85 °C. Click reaction of compound 3 with phenylacetylene resulted in the bis triazole derivative {[η5-C5H4(CH2N3C2HPh)]Co(η4-C4Ph3)}2 5 whereas reduction of 3 with LiAlH4 gave the bis (aminomethyl) compound {[η5-C5H4(CH2NH2)]Co(η4-C4Ph3)}2 6. The diacetyl derivative [{η5-C5H4[C(O)Me]}Co(η4-C4Ph3)}]2 7 was prepared by the reaction of in-situ generated {η5-C5H4[C(O)Me]}Co(PPh3)2, diphenyl acetylene and diphenyl diacetylene in 2:1:3 molar ratio in 42% yield. A novel dimeric derivative having two different functional groups on the cyclopentadienyl rings [{η5-C5H4[C(O)OMe]}Co(η4-C4Ph3)][{η5-C5H4[C(O)Me]}Co(η4-C4Ph3)] 8 was synthesized in 52% yield by reacting the ethynyl ester {η5-C5H4[C(O)OMe]}Co[η4-C4Ph3(C CPh)] with {η5-C5H4[C(O)Me]}Co(PPh3)2 and diphenyl acetylene in 1:2:3 molar ratio. Structural studies on compounds 1–4, 7 and 8 indicated that the two cobalt sandwich units were oriented almost anti to each other whereas compound 3 had the two cyclobutadiene rings oriented at an angle of 55.7(1)° to each other. The identity of compounds 5 and 6 was confirmed by 1H NMR, 13C NMR, IR and mass spectrometry.

The existence of the bis(borole) nickel sandwich compound (η 5 -C 4 H 4 BCH 3 ) 2 Ni suggests the possibility of mixed methylborole nickel carbonyls. The structures and thermochemistry of the binuclear methylborole nickel carbonyls (C 4 H 4 BCH 3 ) 2 Ni 2 (CO) n ( n = 3, 2, 1) have been compared with those of the isoelectronic cyclopentadienylcobalt derivatives (C 5 H 5 ) 2 Co 2 (CO) n and cyclobutadiene nickel derivatives (C 4 H 4 ) 2 Ni 2 (CO) 3 . For the tricarbonyls ( n = 3) the lowest energy structures in all three systems have two terminal carbonyl groups, one bridging carbonyl group, and metal–metal single bonds. However, for the unsaturated derivatives (C 4 H 4 BCH 3 ) 2 Ni 2 (CO) n ( n = 2, 1) the pendant methyl groups are not “innocent bystanders”. Instead structures with one of the methyl hydrogens functioning as an agostic hydrogen to the nickel atom are competitive in energy with structures analogous to those of the (C 5 H 5 ) 2 Co 2 (CO) n and (C 4 H 4 ) 2 Ni 2 (CO) n analogues. Thus for (C 4 H 4 BCH 3 ) 2 Ni 2 (CO) 2 a structure with two bridging carbonyl groups and a formal Ni Ni double bond of length ∼2.37 A and a structure with one bridging carbonyl group, one terminal carbonyl group, a C–H–Ni agostic hydrogen atom, and a Ni–Ni single bond of length ∼2.48 A have essentially the same energies. For (C 4 H 4 BCH 3 ) 2 Ni 2 (CO) the two lowest energy structures also have agostic C–H–Ni hydrogen atoms and Ni–Ni single bonds. The thermochemistry for the synthesis of (C 4 H 4 BCH 3 ) 2 Ni 2 (CO) n derivatives from Ni(CO) 4 + (η 5 -C 4 H 4 BCH 3 ) 2 Ni is not favorable since such reactions are endothermic requiring, for example, 13 kcal/mol of energy for the reaction Ni(CO) 4 + (η 5 -C 4 H 4 BCH 3 ) 2 Ni → (C 4 H 4 BCH 3 ) 2 Ni 2 (CO) 3 + CO.

The trivacant triruthenium substituted polyoxometalate a K 6Na[{Ru3O3(H2O)Cl 2}(SiW9O34)]·17H2O (1) and two sandwich type Co and Ni containing silicotungstates K11Na 1[M4(H2O)2(SiW9O 34)2]·nH2O (M = Co2+ Ni 2+) (2 3) based on the same Keggin type building block were obtained through variation of a solution based protocol. All compounds were investigated with respect to their performance as visible light driven water oxidation catalysts (WOCs). Analytical characterizations and photocatalytic reactivity of (1) are correlated with results of B97D/Def2 TZVP computation. The WOC activity of (1) and (2) was found to arise from their immobilization into a recyclable POM photosensitizer complex (POM PS). These POM PS complexes are formed in the initial phase of the reaction and they prevent POM decomposition into colloidal oxide catalysts. This journal is © The Royal Society of Chemistry.

The work in the present investigation reports the syntheses, crystal structures and supramolecular topologies of 11 copper(II)–main group metal ion complexes [CuIILNaI(NO3)(H2O)]·2CH3CN (1), [CuIILNaI(N3)(CH3OH)]·CH3OH (2), [CuIILNaI(ClO4)(CH3CN)]·0.5CH3CN (3), [CuIILNaI(BF4)(CH3OH)]·H2O (4), [{CuIILNaI(H2O)}2(CuIIL)](BPh4)2 (5), [CuIILKI(ClO4)(CH3COCH3)] (6), [CuIILCaII(ClO4)2(H2O)] (7), [{CuIILCaII(NO3)(μ-NO3)(H2O)}(CuIIL)]·H2O·CH3COCH3 (8), [(CuIIL)2BaII(NO3)2]·CH3OH (9), [CuIILPbII(NO3)2]·CH3OH (10) and [CuIILBiIII(NO3)3]·CH3COCH3 (11), where H2L = N,N′-o-phenylenebis(3-ethoxysalicylaldimine). Among these, eight (1–4, 6, 7, 10 and 11) are dinuclear compounds, one (9) is trinuclear double-decker sandwich compound, one (8) is a [2 × 1 + 1 × 1] trimetallic cocrystal of a dinuclear and a mononuclear units and the remaining (5) is a [2 × 2 + 1 × 1] pentametallic cocrystal of two dinuclear and one mononuclear units. All the 11 compounds 1–11 contain one or more deprotonated ligand, L2−, the salen type N2O2 compartment of each of which is occupied by a CuII ion to result in the formation of a [CuIIL] moiety. On the other hand, the larger and open O(phenoxo)2O(ethoxy)2 compartment of the ligand in one or more [CuIIL] moieties interact (s) with the metal ions NaI (1–5)/KI (6)/CaII (7 and 8)/BaII (9)/PbII (10)/BiIII (11) to produce the title compounds. It has been observed that the neighbouring di/trinuclear units in 1/3/4/6/9/10/11 are self-assembled to one-/two-dimensional topologies as a result of one or more C H⋯O/O H⋯O hydrogen bonding interaction (s). Following self-assemblies are observed: one-dimensional in 4, one-dimensional helical in 1, one-dimensional double-chain (ladder) in 3, 6 and 10, two-dimensional in 9 and 11.

The reaction of 3,4-dichlorotetragermetene derivative 2 with Na(2)[Fe(CO)(4)] in THF produced a (tetragermacyclobutadiene)tricarbonyliron complex, [{η(4)-((t)Bu(2)MeSi)(4)Ge(4)}]Fe(CO)(3)4, which has a slightly folded Ge(4) ring perhaptocoordinated to the Fe center. Structural and spectral characteristics of 4 show a remarkable π-donating ability of the tetragermacyclobutadiene ligand toward the transition metal, surpassing that of tetrasilacyclobutadiene and cyclobutadiene ligands. Reduction of 2 with KC(8) resulted in exclusive formation of the dipotassium salt of the tetragermacyclobutadiene dianion derivative 3(2-)·[K(+)(thf)(2)](2), representing a rare example of a 6π-electron compound that, on the basis of its structural and magnetic properties, was recognized as a nonaromatic species. Reaction of 3(2-)·[K(+)(thf)(2)](2) with CpCoI(2)(PPh(3)) produced a (cyclopentadienyl)(tetragermacyclobutadiene)cobalt complex, [{η(4)-((t)Bu(2)MeSi)(4)Ge(4)}]CoCp 7, as the first example of a sandwich compound featuring an all-germanium-containing cyclic polyene ligand.

Coordination of dicobalt hexacarbonyl to the alkyne moiety of norbornene complexes containing either ferrocene or η(6) -chlorobenzene-η(5) -cyclopentadienyliron hexafluorophosphate, gave two unique trimetallic complexes available for ROMP. Polymerization of each monomer using Grubbs second generation catalyst gave organoiron/organocobalt polynorbornenes with weight average molecular weights between 55 300 and 69 000 with PDIs between 1.2 and 1.9. Cyclic voltammetric studies of the monomers and polymers at -40 °C showed a reversible reduction for cationic complexes containing η(6) -benzene-η(5) -cyclopentadienyliron and for the dicobalt hexacarbonyl moieties while, a reversible oxidation for the ferrocene containing complex was observed. Thermal analysis showed that the cobalt carbonyl moiety of the polymers degraded near 130 °C; however, the polymeric backbone was stable up to 350 °C. Scanning electron microscopy (SEM) and SEM-EDS indicated that the polymers possessed a fine globular morphology and that the distribution of iron and cobalt atoms was homogenous on the macro-scale.

A new class of metal-nonmetal-metal sandwich structures M3-CO3-M3' (M, M' = Li, Na, K) with all real frequencies is obtained at the second-order Möller-Plesset theory (MP2) method with the 6-311+G (2d) basis set. Because the sandwich molecule M3-CO3-M3' is composed of superatoms (M3, CO3, and M3'), it is a sandwich "superomolecule". The superatoms M3 and M3' are electron donors and CO3 is the acceptor, and then there is a strong charge transfer between M3 (or M3') and CO3 superatom, so M3-CO3-M3' can be denoted as M3(+)CO3(2-)M3'(+). Owing to the CO3(2-) anion in the middle repulsing the valence electrons of two metal rings (M3 and M3') forming a pair of excess electrons, the compound with excess electrons is also a novel electride. In metal-nonmetal-metal sandwich compound M3(+)CO3(2-)M3'(+), superatom units M3(+) and M3'(+) exhibit unusual sigma-aromaticity: the maximum negative nucleus-independent chemical shift (NICSmax) value of each aromatic ring (M3(+) and M3'(+)) does not locate at the center of the ring plane but locates outside the ring plane. The distance value from the center of the M3(+) or M3'(+) ring plane to the point with NICSmax ranges from 0.8 to 1.9 A. This shows a notable out-of-plane sigma-aromaticity for these sandwich compounds. What is the reason? We find that the out-of-plane sigma-aromaticity of M3(+) (or M3'(+)) results from the action of CO3(2-)M3'(+) (or M3(+)CO3(2-)). For electric property, on account of excess electrons, the sandwich electride M3-CO3-M3' without the central symmetry can exhibit large static first hyperpolarizability (beta0). For Na3-CO3-K3, the beta0 value is close to 56,000 au.

Lithium 2-vinyl-1,2-azaboratabenzene 1b has been prepared by a multistep synthesis from 2,2-dibutyl-2,5-dihydro-1-trimethylsilyl-1 H -1,2-azastannole 6 . The reaction of 1b with one equivalent of [Cp ∗ RuCl] 4 gave the very labile sandwich compound 11 . However, the reaction of 1b with 2 equiv. of [Cp ∗ RuCl] 4 afforded the stable diruthenium complex 12. The X-ray structure of 12 shows that the first Cp ∗ Ru moiety is π-bound to the 1,2-azaboratabenzene ring while the second is bound to Cl and to the nitrogen and the pendant B-vinyl of the 1,2-azaboratabenzene group.

Four differently substituted mixed ligand sandwich complexes CpRu(p-BrC6H4)Tp (3), CpRu(p-BrC6H4)TpMe (4), Cp∗Ru(p-BrC6H4)Tp (5), CpiPrRu(p-BrC6H4)Tp (6), incorporating cyclopentadienyl (Cp) and functionalized tris(pyrazolyl)borate (Tp) ligands, have been synthesized and characterized. Air-stable 6 has been converted to benzoic acid-functionalized CpiPrRu(p-(CO2H)C6H4)Tp (7), which has been structurally characterized in the solid state by X-ray diffraction. Compound 7 may be readily coupled to biomolecules as exemplified by the coupling to phenylalanine-methylester to give CpiPrRu(p-(CO-Phe-OMe)C6H4Tp) (8). In a solid phase peptide synthesis (SPPS), 7 has been coupled to the pentapeptide Enkephalin, to provide CpiPrRu(p-(CO-Tyr-Gly-Gly-Phe-Leu-OH)C6H4Tp) (9) as the first example of a mixed ligand sandwich ruthenium bioconjugate.

The synthesis of ethylene-co-5,7-dimethylocta-1,6-diene copolymers (CEDMO) with different molar DMO contents has been performed to incorporate double bonds in the lateral and make easier the development of crosslinkings in the resulting polymer material after application of electron-beam irradiation. The gel content as well as a comprehensive evaluation of the changes in the crystalline characteristics have been carried out. Both features are strongly dependent on DMO composition and irradiation doses. Variation in the mechanical response of the different specimens has been checked by microhardness measurements.

The reaction of the pentalene salt C8H4{(SiPr3)-Pr-i-1,4}(2)[K](2) with [SmCp*(mu-I)(THF)(2)](2) yields not the expected Sm(II) pentalene-bridged dimer but the Sm(III) sandwich complexes [Sm(eta(8)-C8H4{(SiPr3)-Pr-i-1,4}(2))(eta(5)-Cp*)] (1) and [Sm(eta(8)-C8H4{(SiPr3)-Pr-i-1,4}(2))(eta(5)-C8H5{(SiPr3)-Pr-i-1,4}(2))] (2) and the mixed-valence cluster [Cp*Sm-6(6)(OMe)(8)O][K(THF)(6)] (3) via solvent activation of THF. The samarium(III) sandwich compound 2 incorporates an eta(8)-pentalene ligand and an eta(5)-hydropentalenyl ligand. X-ray crystallography shows the Sm(II)/Sm(III) mixed-valence cluster compound 3 to contain a centrosymmetric hexanuclear array of Cp*Sm units, bridged by face-centered mu(3)-methoxy groups, with a central oxo unit.

9 pages; International audience; Five new heteropolyoxotungstates K2Na2Mn2(H2O)12[Mn2(H2O)10Mn4(H2O)2(XW9O34)2] 18H2O (X ¼ Ge, 1; X ¼ Si, 2), Na4[Mn4 (H2O)18Mn4(H2O)2(XW9O34)2] 22H2O (X ¼ Ge, 3; X ¼ Si, 4) and K3Na5[Mn2(H2O)6Mn4(H2O)2(SiW9O34)2] 23.5H2O (5) have been obtained by the routine synthetic reactions in aqueous solution. In 1 and 2, two isolated Mn2+ ions are covalently linked to the sandwich-type polyoxoanions [Mn4(H2O)2(B-a-XW9O34)2]12 (X ¼ Ge or Si) by two m2-oxygen atoms resulting in the disupporting sandwich-type polyoxometalates (POMs). Compounds 3 and 4 are built from the disupporting sandwich-type polyoxoanions 1 and 2, linked by additional four Mn2+ ions to construct a 1D ladder-like chain-like structure, which is rarely observed in the POM chemistry. Compound 5 represents the first example of the 2D structure consisting of the sandwich-type polyoxoanion [Mn4(H2O)2(SiW9O34)2]12 and the binuclear {Mn2(H2O)6}4+ group. The magnetic studies of compounds 1, 4 and 5 indicate that the antiferromagnetic interactions are predominant in the three compounds between Mn(II) metal ions.

Propylene and norbornene were copolymerized by metallocene/MAO catalysts. The organometallic compounds rac -[Me 2 C(Ind) 2 ]ZrCl 2 ( 1 ) and [Me 2 C(Cp)(Flu)]ZrCl 2 ( 2 ), [Ph 2 C(Cp)(2,7-di t BuFlu)]ZrCl 2 ( 3 ) and [Me 2 Si(3- t BuCp)(N t Bu)]TiCl 2 ( 4 ) were used to catalyze polymerization series, in which the influence of the molar fraction of norbornene in the feed and of the polymerization temperature were investigated in detail. The obtained polymers, which exhibit a wide range of properties with glass transition temperatures above 200 °C, were characterized by 13 C NMR spectroscopy, differential scanning calorimetry and gel permeation chromatography techniques. In this article, the emphasis is placed on the copolymerization behaviour of the catalysts and the properties of the obtained polymers, while other articles concentrate on NMR investigations of propylene/norbornene copolymers.

Reaction of the new cyanoscorpionate ligand, hydrotris(4-cyano-3-phenyl)pyrazolylborate (Tp(Ph),(4CN)) with Co(II), Mn(II), and Fe(II) unexpectedly results in the isolation only of crystals containing sandwich complexes in which the ligands have been isomerized to produce the heterocyanoscorpionate hydrobis(4-cyano-3-phenylpyrazolyl)(4-cyano-5-phenylpyrazolyl)borate (Tp(Ph),(4CN*)). The three complexes have been characterized crystallographically and are isostructural, with each ligand acting in a tridentate manner toward the metal. The isomerization of the ligand appears to be more facile than that of the analogous non-cyano ligand, Tp(Ph), with which crystals of the unisomerized sandwich compound have been isolated for Mn(II) and Fe(II).

The synthesis of ethene/propene macromers with a high amount of sterically unhindered vinyl groups is described. These macromers are incorporated as long-chain branches into polyethylene (PE). The remaining low molecular fractions were removed by Soxhlet extraction. Up to 60 wt.-% macromer was included, which leads to comb-like molecular topographies that distinctly affect the rheological behavior. The thermal activation energy increased significantly and the zero shear-rate viscosity enhancement factor η 0 /η lin 0 was also changed noticeably.

Substituted cis-bicyclo[3.3.0]octenyllithium prepared by addition of t-BuLi to 3-methylene-1,4-cyclooctadiene in the presence of TMEDA crystallizes as a dimer with one unsolvated Li(+) sandwiched between the external faces of two allyl anions in a triple ion, and external to it the second Li(+) is bidentately complexed to TMEDA, 8. Within each allyl unit, the allyl bonds have different lengths, and all four rings deviate from coplanarity which relieves strain in the rings despite introducing partial localization of the allyl anions. A similar structure prevails in solution as shown by (7)Li NMR and the results of (7)Li{(1)H} HOESY and (1)H, (1)H NOESY experiments. Carbon-13 NMR line shape changes indicate that the system undergoes a fast allyl bond shift concerted with conformation shifts of the out of plane carbons, ca. DeltaG = 9 kcal x mol(-1). Cyclopentyllithium prepared by CH(3)Li cleavage of the trimethylstannyl derivative slowly undergoes an allowed ring opening to pentadienyllithium as well as deprotonating the solvent. The different behavior of dienylic lithium species is attributed to the relative separation of their termini.

1,9-Decadiene/propylene copolymers were obtained with isolated metallocenes and with a binary metallocene catalyst system activated by methylaluminoxane. The metallocenes under investigation were syndiospecific diphenylmethyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (1) and isospecific rac-dimethylsilylbis(4-tert-butyl-2-methyl-cyclopentadienyl)zirconium dichloride (2). A copolymer structure, in which 1,9-decadiene linked isotactic and syndiotactic polymer chains, was obtained when copolymerisation was started with catalyst 2 at 80 °C followed by injection of catalyst 1 and instantaneous lowering of polymerisation temperature to 40 °C after 15 min of polymerisation. The copolymer was also shown to work as a compatibiliser in a blend of syndiotactic and isotactic polypropylene. We propose that catalyst 2 incorporates 1,9-decadiene into the isotactic main chain without any significant crosslinking within the first 15 min of polymerisation at 80 °C and the produced isotactic macromonomers are further incorporated at 40 °C into the syndiotactic main chain in polymerisation with catalyst 1.

The synthesis and characterisation of several functionalised polyethylenes, obtained by direct copolymerisation of ethylene with 10-undecenoic acid (UA), have been carried out. Two metallocene complexes of C s symmetry with different bridges were used: a dimethylsilyl bridge complex Me 2 Si(Cp)(Flu)ZrCl 2 and a phenylidene bridge complex Ph 2 C(Cp)(Flu)ZrCl 2 . For comparison, results obtained with the Cp 2 ZrCl 2 / MAO system are also reported. The copolymerisation activity depends strongly on the metallocene complex and on the added amount of the UA comonomer. High incorporation levels of up to 7.3 mol-% are achieved when using the phenylidene bridged catalyst presenting a rigid structure and a wide bite angle. The effect of comonomer content and catalyst geometry on the crystalline structure and mechanical behaviour of the different copolymers are comprehensively discussed.

Six (Cp)(4-phenyl-indenyl)MCl2 (A) and four (Cp)(1-phenyl-indenyl)MCl2 (C) (M=Zr/Hf) based complexes were tested in ethene homo- and copolymerisation under different conditions to explain how the differences in the complex structure affect the polymerisation process and the formed polymer. Polymerisation experiments reveal that hafnocene catalysts need a higher amount of MAO to reach the maximum activity than zirconocenes. Hafnocenes also incorporate better 1-hexene. Catalysts with the Cp* or 1,2,4-Me 3 Cp ligand show higher activity, and work well with [HNMe2Ph][B(C6F5)4]/TIBA as cocatalyst, but produce polymers with lower M n than the corresponding catalyst with a plain Cp ligand. The Cp* ligand seems to prevent 1-hexene incorporation. A methyl group in the 2-position of (Cp)(4-PhInd)ZrCl 2 decreases the activity and M n but favours 1-hexene insertion. Polymerisation activity is higher with catalysts with a 1-PhInd-ligand than with a 4-PhInd-ligand.

Two benzene centered tri- and tetracyclopentadienyl ligands C6H3(CH2C5H5)3-1,3,5 (1) and C6H2(CH2C5H5)4-1,2,4,5 (2) and their titanium complexes C6H3[CH2C5H4Ti(C5H5)Cl2]3-1,3,5 (3), C6H3[CH2C5H4Ti(C5H4CH3)Cl2]3-1,3,5 (4), as well as C6H2[CH2C5H4Ti(C5H5)Cl2]4-1,2,4,5 (5) were synthesized and characterized by mass and 1H NMR spectra. In the presence of methylaluminoxane (MAO), 3, 4 and 5 are efficient catalysts for ethylene polymerization in toluene. The influence of the polymerization conditions such as catalyst concentration, MAO/Ti molar ratio, polymerization time and temperature were investigated in detail. 3, 4 and 5 produce linear polyethylene (PE) with broad molecular weight distributions (MWD) and a little lower molecular weight.

Parallel displaced and sandwich configurations of hexafluorobenzene-substituted benzene dimers are studied by ab initio molecular orbital methods up to the MP2(full)/aug-cc-pVDZ level of theory to reveal how substituents influence pi-pi interactions. Two minimum energy configurations are found, one with the substituent group away from the pi-face of the hexafluorobenzene ring (2a-f) and the other with the substituent group on top of the pi-face of the hexafluorobenzene (3a-f). Higher binding energies are predicted for dimers with the substituent on the pi-face (3a-f). All sandwich dimers (4a-e) are found to be saddle points on the potential energy surfaces. A parallel-displaced minimum energy configuration is also predicted for the parent complex, C6F6-C6H6, which is in contrast to predictions based on quadrupole moments of benzene and hexafuorobenzene. The preference for the parallel displaced, rather than the sandwich configuration, is rationalized based on the smaller interplanar distance in the former. The closeness of contact in the parallel-displaced dimers leads to greater binding energies. The shape of the electron density isosurface of the monomers is suggested to provide a guide for the prediction of how arenes stack with one another. A large difference in binding energy between the C6F6 complex of aniline (3e) and N,N-dimethylaniline (3f) is calculated, and charge-transfer interactions are suggested to play a role in the latter.

Copolymers of propylene and hexacosene (C n = 26-28) were synthesized in the presence of three different metallocene catalysts activated by methylaluminoxane. The poly(propylene) copolymers were prepared with iso-, syndio-, and atactic backbone microstructures by using different symmetric metallocenes such as rac-{Me2Si[2-Me-4-(1-Naph)Ind]2}ZrCl2 (1), [Ph2C(Cp)(Flu)]ZrCl2 (2), and [(H3C)2Si(9-Flu)2]ZrCl2 (3) and up to 46.6 mol-% comonomer content in the feed. The influence of the incorporated linear, ethylene-based side chains into the poly(propylene) backbone were investigated by DSC, GPC, and 13 C NMR. Generally, a decreasing content of comonomer in the feed enhances the activity of metallocene based catalysts. The determination of the branched microstructure by 13 C NMR of the copolymers allows a smart identification of the amount of inserted hexacosene because of the separated backbone and side chain signals. Moreover, the relationship between the population of the side chains and the melting behavior of resulting copolymers were discussed. The melting point of the syndiotactic and isotactic poly(propylene) backbone decreases with increasing hexacosene content. When the inserted comonomer content exceeds 2 mol-%, a second melting point of the crystallized ethylene based side chains can be observed which increases with an increasing amount of hexacosene.

In the present work, the temperature dependence of heat capacity C p , m ∘ = f ( T ) of crystalline bis-(η6-diphenyl)chromium (I) fulleride [(η6-Ph2)2Cr]+[C60] − has been measured by precision adiabatic vacuum calorimetry between T = (6 and 360) K with an uncertainty of ±0.2%. In this temperature interval, the transformations were detected and their thermodynamic characteristics were estimated. The experimental data were used for calculating standard (po = 0.1 MPa) thermodynamic functions C p , m ∘ / R , Δ 0 T H m ∘ / RT , Δ 0 T S m ∘ / R and Φ m ∘ / R = Δ 0 T S m ∘ / R - Δ 0 T H m ∘ / RT (where R is the universal gas constant) in the range T → (0 to 360) K.

To understand the charge transport ability of the metal coordinated cyclobutadiene, a series of cyclobutadiene cobalt cyclopentadiene (CbCoCp) complexes containing electrochemically polymerizable thiophene units were synthesized. The complexes were electrochemically polymerized and the resulting polymers were characterized by cyclic voltammetry, in situ conductivity and UV–vis spectroelectrochemistry. Several different derivatives of the CbCoCp complexes and a model study suggested that if the oxidation of the organic fragment was above Co I/II redox couple of the CbCoCp complex, detrimental side reactions occured. Side reactions did not occurred if the oxidation of the organic fragment was below the metal oxidation.

The Cadiot-Chodkiewicz coupling of cis-1,4-diethynyl-1,4- dimethoxycyclohexa-2,5-diene and the corresponding ethynyl bromide gave a mixture of acetyenic macrocycles ranging from dimer to octamer in good isolable yields. The trimeric and tetrameric macrocycles have been structurally characterized by single-crystal X-ray crystallography. In the crystal structure of the trimeric macrocycle a molecule of benzene is sandwiched between a pair of macrocyles. The tetrameric macrocycle exhibited a tub-shaped conformation and encapsulated a molecule of ethyl acetate inside the tub. � 2006 American Chemical Society.

The products obtained in the reaction of cobalt atoms in neat benzene or in a benzene/argon mixture at low temperature have been reinvestigated. At least three cobalt-containing species were detected by IR, namely, Co(C(6)H(6)), Co(C(6)H(6))(2), and Co(x)(C(6)H(6)), x1. The IR bands were assigned to these complexes by monitoring their behavior as a function of (a) Co and C(6)H(6) concentration, (b) isotopic substitution, and (c) photoirradiation. We were able to analyze the sample in neat benzene by both electron paramagnetic resonance (EPR) and IR spectroscopy and to determine the magnetic parameters (g tensor and Co hyperfine interaction) for the Co(C(6)H(6))(2) sandwich compound. The large number of fundamental bands observed in the IR spectrum of Co(C(6)H(6))(2), the absorption pattern observed in the Co-ring stretching region of the IR spectrum of the mixed complex, Co(C(6)H(6))(C(6)D(6)) and the orthorhombic g-values extracted from the EPR spectrum are most consistent with nonequivalent benzene ligands in Co(C(6)H(6))(2), i.e., C(s) symmetry. A bonding scheme consistent with both the EPR and IR data for Co(C(6)H(6))(2) is discussed.

Syndiotactic propylene–ethylene copolymers have been synthesized with a single-center Cs-symmetric syndiospecific metallocene catalyst. A study of the effect of the presence of ethylene comonomeric units on the polymorphic behavior of syndiotactic polypropylene (sPP) and on the structural transitions occurring during stretching is reported. For copolymer samples with low ethylene contents, in the range 2–7 mol%, crystals of the helical form I, present in the melt-crystallized samples, transform into the trans-planar form III by stretching at high deformation. Form III transforms in part into the helical form II by releasing the tension, as it occurs for sPP. Samples with ethylene contents in the range 8–10 mol% are crystallized from the melt as a mixture of crystals of helical form I and form II. Both helical forms transform by stretching at low values of deformation (lower than 300%) into the trans-planar mesomorphic form, which transforms into the trans-planar form III by further stretching at higher deformations (higher than 500%). For these samples form III transforms back into the mesomorphic form, rather than into the helical forms, by releasing the tension. Unoriented samples of copolymers with ethylene content in the range 13–18 mol% are mainly crystallized in the helical form II, which transforms into the trans-planar mesomorphic form by stretching. Upon releasing the tension the mesomorphic form remains stable and no polymorphic transition is observed. The presence of ethylene comonomeric units stabilizes the trans-planar forms in fibers of the copolymer samples. This has been confirmed by the result that for high ethylene contents the trans-planar form III and the mesomorphic form do not transform in helical forms by annealing of fibers stretched at high deformations.

Different highly substituted C 1 symmetric metallocenes have been investigated for the copolymerization of ethene and norbornene. The influence of the feed ratio and the polymerization temperature were varied to characterize the polymer by means of microstructure, thermal properties and catalysts activity. The bulky structured ligands of the catalysts lead to highly stereoregular copolymers with semi-crystalline phases even at low norbornene incorporation. Two different allyl ethers (allyl ethyl and allyl propyl ether) have been used to copolymerize with ethene using metallocene catalyst system (roc-[Me 2 Si(2-Me-4-(i-Ph)Ind) 2 ]ZrCl 2 /MAO). In order to investigate the influence to ether incorporation to polymer properties, we have performed experiments varying comonomers concentration in feed, polymerization temperature and ratio AI (MAO) /Zr. The higher comonomer incorporation was followed by loss of cristallinity of the produced polymer. Additionally, the catalytic activity and melting point of the polymers also decrease with increase in comonomer concentration in feed.

Propylene was polymerised at varying trimethylaluminium (TMA) concentration with two metallocenes activated by methylaluminoxane (MAO) in an attempt to better understand the effect of TMA on the activation process, catalyst activity and termination reactions. A chemical treatment of MAO solution with 2,6-di-tert-butyl-p-cresol was used to obtain TMA-free polymerisation conditions. The metallocene precursors under investigation were diphenylmethyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (1) and rac-dimethylsilylbis(4-tert-butyl-2-methyl-cyclopentadienyl)zirconium dichloride (2). Chain transfer to aluminium was the dominating termination route for 1/MAO accompanied with β-H/β-CH 3 transfer to Zr and β-H transfer to monomer. It was found that β-H/β-CH 3 transfer to Zr was favoured over the β-H transfer to monomer at elevated temperatures, and that polymerisation and β-H transfer to monomer depended on the same critical reaction. For 2/MAO the detected termination routes were β-H transfer to Zr and chain transfer to aluminium. A strong activity dependency on TMA concentration was observed. With 1/MAO high TMA concentration decreased and stabilised the activity, whereas TMA free polymerisation conditions at 40 °C increased markedly the activity, indicating that TMA coordinated to the active site of 1/MAO. Surprisingly, with more sterically hindered 2/MAO, high TMA concentration increased the activity and nearly complete activity loss occurred at TMA-free polymerisation conditions at 40 °C.

Propene homopolymers and propene–ethene copolymers with small amount of ethene were synthesized using three catalyst systems [p-CH3OPh2C(2,7-di-tertBuFlu)(Cp)]ZrCl2/Me2HNPh][B(C6F5)4] (Cat I), [p-CH3OPh2C(2,7-di-tertBuFlu)(Cp)]ZrCl2/[Ph3C][B(C6F5)4] (Cat II) and [p-CH3OPh2C(2,7-di-tertBuFlu)(Cp)]ZrCl2/MAO (Cat III) in propene bulk phase. The activity of the catalyst was dependent on the formed ion pair: Cat I showed the highest activity, up to 96,000 kgpol/molZr h, at the used polymerization conditions. The produced homo- and copolymers have high molecular weights, between 400 and 600 kg/mol. The ethene incorporation rate was nearly the same with the different catalyst systems; the amount of ethene in the copolymer was increasing linearly with the amount of ethene in feed. The syndiotacticity of the homopolymer was highest, [rrrr]>90%, with Cat I when it was 81.4 with Cat II and 80.8 with Cat III. The small amount of ethene in the copolymer allows the control of the melting and crystallization behavior. Also the crystallization temperatures of the copolymers were found to depend on the used catalyst system.

The photoinitiated cationic polymerization of 1-cyclopropyl-1-phenyl-ethylene, 1 -cyclopropyl-1-(p-methoxyphenyl)ethylene and 1-cyclopropyl-1-(p-fluorophenyl)ethylene at ambient temperatures in bulk and in solution was investigated using (η 5 -2,4-cyclopentadiene-1-yl)[l,2,3,4,5, 6-η] (1-(methylethyl) benzene)iron(I) hexafluorophosphate (Irgacure 261,I-1) and ditolyliodonium hexafluorophosphate (I-2). In contrast to our results in the polymerization of 2-cyclopropyl-4-methylene-1,3-dioxolanes, partial ring-opening of the cyclopropane ring could be detected. A volume shrinkage of about 11% was found.

Copolymerizations of ethylene and disubstituted diallylsilanes (CH 2 =CH-CH 2 -) 2 R 2 Si (R = CH 3 , C 6 H 5 ) have been investigated with various zirconocene catalysts using methylaluminoxane as a cocatalyst. The bridged stereospecific catalysts showed a higher reactivity for disubstituted diallylsilanes than the non-bridged aspecific catalysts. Disubstituted diallylsilanes were incorporated into the polymer chain via cyclization insertion preferentially, and formed 3,5-disubstituted silacyclohexane units in the polyethylene main chain. A zirconocene catalyst, dimethylsilylenebis(indenyl)-zirconium dichloride, produced a copolymer containing pendant allyl groups derived from the 1,2-insertion of diallyldiphenylsilane without cyclization.

Thymidine conjugates containing metallacarborane, {8-[5-( N 3 -thymidine)-3-oxa-pentoxy]-3-cobalt bis(1,2-dicarbollide)} − ( 5 ) and {8-[5-( O 4 -thymidine)-3-oxa-pentoxy]-3-cobalt bis(1,2-dicarbollide)} − ( 6 ) ions and several simple [3-cobalt bis(1,2-dicarbollide)] − ion ( 1 ) derivatives have been studied as potential boron carriers for BNCT. Compound 6 and some nonnucleoside derivatives of 1 were not toxic above 100 μM. The partition coefficient for both metallacarborane bearing thymidine conjugates 5 and 6 was more than 500 times higher than that of unmodified nucleoside. The cellular uptake studies showed accumulation of compounds 6 in V79 Chinese hamster cells but not of compound 5 . The low toxicity of conjugate type of 6 together with its high partition coefficient suggest that judicially designed derivatives of metallacarboranes can be considered as potential boron carriers for BNCT.