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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.

Homogeneous metallocene and CGC catalyzed copolymerizations of ethene (E) and various substituted styrenes are examined. It is found that those with p-tert-butylstyrene (TBS) occur with dramatically higher degrees of incorporation and overall productivity than those observed under the same conditions with styrene. It is argued that that the sigma-donating effect of the tert-butyl substituent is responsible for this performance, effecting a destabilization of an otherwise dormant benzylic species following 2,1-insertion of the styrene. It was found possible to produce what is essentially TBS-alt-E (44% TBS with no sequential TBS units) using a standard constrained geometry catalyst at impressively high productivity 1.1.5 x 10(6) g/(mol(Ti).bar(E).h)] and unusually low concentration of TBS (0.7 M). (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 31,11-3117, 2009

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 exo-substituted η 4 -cyclopentadiene CpCo(I) complexes were found to be the actual catalyst for the cobaltocene-catalyzed ATRP. Cobaltocene is just a precatalyst, which can be converted to the catalyst by the reaction with halide initiator. As a new kind of ATRP catalyst, the exo-substituted η 4 -cyclopentadiene CpCo(I) complexes can catalyze the living radical polymerization of MMA, styrene, and the block copolymerization of MMA with styrene.

Statistical copolymers of tetradecene-1 and octene-1 with 1-tert-butyl-dimethylsilyloxy-10-undecene were synthesized by metallocene catalyzed copolymerization. The C s -symmetry hafnium metallocene [(p-Et 3 Si)Ph] 2 C(2,7-di-tert-BuFlu) (Cp)Hf(CH 3 ) 2 and tetrakis(pentafluorophenyl) borate dimethylanilinium salt ([B(C 6 F 5 ) 4 ] - [Me 2 NHPh] + ) were employed as the catalytic system, in the presence of trioctylaluminum (TOA) as a scavenger. The monomer reactivity ratios were calculated using the Finemann-Ross, inverted Finemann-Ross, and Kelen-Tudos graphical methods. The structural parameters of the different copolymers were obtained from the calculation of the dyad monomer sequence fractions and the mean sequence lengths derived via the reactivity ratios.

The near-edge X-ray absorption fine structure (NEXAFS) spectra of poly(phenyl thioether) polymers with pendant Fe(Cp) iron moieties have been recorded at the carbon 1s, iron 2p, and phosphorus 1s and 2p edges. This study shows that solution photofragmentation of the organometallic polymer causes the removal of iron moieties and the preparation of the corresponding organic polymer: poly(phenyl thioether). Spectroscopic characterization of poly(phenyl thioether) prepared in this manner indicates the presence of iron oxide, likely Fe2O3, and hexafluorophosphate counterion trapped in the demetalated polymer matrix. A photolytic examination of the solid phase poly(phenyl thioether)−Fe(Cp) organometallic polymer shows that irradiation of this polymer in air leads to the formation of poly(phenyl thioether) and Fe2O3, while irradiation in vacuum leads to formation of iron species with a lower oxidation state. The ability to probe the oxidation state of this metal species is relevant to understanding how demetalat...

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.

The reaction of the iodide complex [(η5-C9H2Me5)RhI2]2 (1) or the acetonitrile complex [(η5-C9H2Me5)Rh(MeCN)3]2+ with Tl[Tl(η-7,8-C2B9H11)] afforded rhodacarborane (η5-C9H2Me5)Rh(7,8-C2B9H11) (2). The cationic triple-decker complex with the bridging boratabenzene ligand [Cp*Fe(μ-η:η-C5H3Me2BMe)Rh(η5-C9H2Me5)]2+ (3) was synthesized by the reaction of the nitromethane solvate [(η5-C9H2Me5)Rh(MeNO2)3]2+ with the sandwich compound Cp*Fe(η-C5H3Me2BMe). The structure of 2 was established by X-ray diffraction.

Extrapolation from ferrocene and dibenzenechromium suggests the currently unknown 18-electron sandwich compound (η 7 -C 7 H 7 ) 2 Ti as a possible stable molecule. However, density functional theory (DFT) methods using the B3LYP and BP86 functionals predict (η 7 -C 7 H 7 ) 2 Ti to distort by ring slippage to give a singlet 16-electron complex (η 7 -C 7 H 7 )-Ti(η 5 -C 7 H 7 ) having an uncomplexed C=C double bond in one of the C 7 H 7 rings but otherwise closely related to the known (η 7 -C7H7)Ti(η 5 -C5H5). The situation is similar with (C 7 H 7 ) 2 V except that the corresponding structures have doublet spin multiplicity. However, an analogous (η 7 -C 7 H 7 )-Cr(η 5 -C 7 H 7 ) structure is not found for chromium. Instead the most stable (C 7 H 7 ) 2 Cr structure is a singlet d° six-coordinate formally Cr VI complex with two tridentate cyclopropyldivinyl C 7 H 7 ligands. The latter rearrangement of the C 7 H 7 rings bonded to chromium can involve initially a (η 6 -C 7 H 7 ) 2 Cr diradical sandwich compound followed by a bis(η 5 -norcaradienyl)Cr intermediate. For the later first-row transition metals the lowest energy (C 7 H 7 ) 2 M structures are predicted to be doublet (η 7 -C 7 H 7 )Mn(η 3 -C 7 H 7 ) rather than (η 5 -C 7 H 7 ) 2 Mn for manganese, singlet cis and trans structures (η 5 -C 7 H 7 ) 2 Fe for iron, doublet (η 3 -C 7 H 7 ) 2 Co for cobalt, and two singlet (η 3 -C 7 H 7 ) 2 Ni stereoisomers for nickel.

Cationic 30 VE triple-decker complexes [Cp*Ru(μ-η 7 :η 7 -C 5 B 2 Me 6 H)ML] + [ML = Co(C 4 Me 4 ) (3a), RuCp* (4a), Rh(cod) (7a), and Ir(cod) (8a)] with a bridging hexamethyl-4-borataborepine ligand were obtained by electrophilic stacking of the sandwich compound Cp*Ru(η 7 -C 5 B 2 Me 6 H) (2a) with [ML] + complex fragments. The reaction of the phenyl-substituted derivative Cp*Ru(η 7 -7-PhC 5 B 2 Me 5 H) (2b) with [(C 4 Me 4 )Co(MeCN) 3 ] + selectively affords the triple-decker complex [Cp*Ru(μ-η 7 :η 7 -7-PhC 5 B 2 Me 5 H)Co(C 4 Me 4 )] + (3b), whereas a similar reaction with [Cp*RuCl] 4 /TlBF 4 produces a 1:3 mixture of cations, the triple-decker [Cp*Ru(μ-η 7 η 7 -7-PhC5B2Me5H)RuCp*] + (4b) and the arene-coordinated [Cp*Ru(μ-η 6 :η 7 -7-PhC5B2Me5H)RuCp*] + (5). Stacking of Cp*Ru(η 7 -7-PhCH 2 C 5 B 2 Me 5 H) (2c) with [CpRu(MeCN) 3 ] + selectively gives the triple-decker complex [Cp*Ru(μ-η 7 :η 7 -7-PhCH2C5B2Me5H)RuCp]+ (6c). The dinuclear cations 3-8 were isolated as deep-colored air-stable salts with [BF 4 ] - or [PF 6 ] - anions in moderate to high yields. Structures of 3bPF 6 , 4aBF 4 , 7aBF 4 , and 8aBF 4 were confirmed by X-ray diffraction studies. Energy decomposition analysis of complexes CpRu(ring) and [CpRu(ring)RuCp] + (ring = Cp, C 5 BH 6 , C 5 B 2 H 7 ) revealed that the insertion of BH units makes the bonding between [ring]- and [RuCp] + more covalent. According to Mulliken population analysis, weakening of it-donation and strengthening of 8-back donation occur in the same order. The electrostatic character of the bond and the contribution of σ-donation to the covalent bonding are higher in the case of bifacially bonded rings. The boron-containing triple-decker complexes are considerably more stable than the cyclopentadienyl analog.

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.

The copolymerization of ethylene and norbornene (N) was carried out with iPr(Cp)(Flu)ZrCl 2 catalyst and modified methylaluminoxane (MMAO) cocatalyst. The catalytic activity was dependent on the structure of MMAO, i.e., MMAO-4 exhibited higher catalyst activity than MMAO-3A containing more i-butyl groups. The glass transition temperature (T← 1 g) and the composition of the produced copolymer were not affected by MMAO type. With styrene derivatives as 3 r monomer, T g of copolymer increased while the catalytic activity decreased. With the addition of 3 rd monomer, not only the content of 3 rd monomer but also the content of N increased.

New double silylene-bridged binuclear zirconium complexes [(η5-RC5H4)ZrCl2]2[μ,μ-(SiMe2)2(η5-C5H3)2] [R = H (1), Me (2), nPr (3), iPr (4), nBu (5), allyl (6), 3-butenyl (7), benzyl (8), PhCH2CH2 (9), MeOCH2CH2 (10)] were synthesized by the reaction of (η5-RC5H4)ZrCl3·DME with [μ,μ-(SiMe2)2(η5-C5H3)2]2− (L2−) in THF, and they were all well characterized by 1H NMR, MS, IR, and EA. The binuclear structure of Complex 3 was further confirmed by X-ray diffraction, where the two zirconium centers are located trans relative to the bridging [μ,μ-(SiMe2)2(η5-C5H3)2] moiety. When activated with methylaluminoxane (MAO), this series of zirconium complexes are highly active catalysts for the polymerization of ethylene even under very low molar ratio of Al/Zr (Complex 7, 5.41 × 105g-PE/mol-Zr·h, Al/Zr = 50) and linear polyethylenes (PEs) with broad molecular weight distribution (MWD, Mw/Mn = 7.31–27.6) was obtained. The copolymerization experiments indicate that these complexes are also very efficient in the incorporation of 1-hexene into the growing PE chain in the presence of MAO (Complex 6, 3.59 × 106g-PE/mol-Zr·h; 1-hexene content, 3.65%). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4901–4913, 2007

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.

Copolymers of propylene with higher α-olefins (4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene) have been synthesized at 0 °C using the syndioselective catalysts Me2C(η5-C5H4)(η5-C13H8)ZrCl2 (...

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.

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.

The electronic properties of nine different hexaarylbenzene molecules substituted by sandwich compounds have been studied by applying density functional theory. Different structures and the particular electron donor power of these systems have been considered in order to analyze their oxidant capacity, using bis(ciclopentadienyl) scandium, ferrocene, and bis(benzene)chromium as sandwich compounds. Both monometallic and bimetallic combinations are investigated. According to the ionization energies and electron affinities, compounds with Cr are nucleophiles and represent the best electron donors, whereas compounds with Sc are electrophiles and represent the best electron acceptors. The worse electron donor or acceptor is hexakis(4-ferrocenyl phenyl) benzene. This is very significant, as it implies that the very well-known electronic properties of hexakis(4-ferrocenyl phenyl) benzene can be improved by substituting with other metals, such as Sc and Cr. This suggests several possible applications for these compounds.

Irradiation of Cp*(OC) 2 FeSiMe 2 ER n (ER n = NPh 2 , NMe 2 , OMe) in the presence of pyridine affords Cp*(OC)(C 5 H 5 N)FeSiMe 2 ER n , which are converted to Cp*(OC)Fe{η 3 (C,C,C)-C 5 H 5 NSiMe 2 ER n } upon mild heating via insertion of pyridine into the iron-silicon bond. This type of pyridine insertion does not proceed in the thermal reactions of Cp*(OC)(C5H5N)FeSiMe2R (R = Cl, Me) and the germanium analogues, Cp*(OC)(C 5 H 5 N)FeGeMe 2 ER n (ER n = NPh 2 , NMe 2 , Me), even under more severe conditions. Treatment of Cp*(OC)(C 5 H 5 N)RuMe with HSiMe 2 NPh 2 at room temperature gives a 5:4 equilibrium mixture of Cp*(OC)(C 5 H 5 N)RuSiMe 2 NPh2 and Cp*(OC)HRu{κ 2 (Si,C)-SiMe 2 N(o-C 6 H 4 )(Ph)}. Heating the mixture at 100 °C does not afford an analogous insertion product, although the equilibrium is shifted to the side of the orthometalated compound. These results indicate that the insertion of pyridine is specific for the heteroatom-substituted silyliron(II) system. The insertion reaction is considered to proceed via the mechanism that involves the initial formation of an η 2 (N,C)-pyridine complex. Migratory insertion of pyridine into the iron-silicon bond accompanied by coordination of the terminal heteroatom then results in a congested transition state, leading to the formation of an η 1 -allyl intermediate, Cp*(OC)Fe-{κ 2 (C,E)-C 5 H 5 NSiMe 2 ER 2 }. The formation of such a transition state is supported by kinetic analysis of the thermal conversion of Cp*(OC)(C 5 H 5 N)FeSiMe 2 NPh 2 to Cp*(OC)Fe{η 3 (C,C,C)-C 5 H 5 NSiMe 2 NPh 2 }, giving activation parameters of ΔH ‡ = 93(2) kJ mol -1 , ΔS ‡ = -53(6) J mol -1 K -1 , and ΔG ‡ 298 K = 109(3) kJ mol -1 . The η 3 -allyl complex is finally formed through dissociation of the amino part. Irradiation of Cp*(OC)Fe{η 3 (C,C,C)-C 5 H 5 NSiMe 2 NPh 2 } causes dissociation of a carbonyl ligand to produce a new type of sandwich compound, Cp*Fe(η 5 -C 5 H 5 NSiMe 2 NPh 2 ).

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.

Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane‐activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac‐ethylenebis(indenyl)ZrCl2 (1). Propene copolymerizations were further studied with Cs‐symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl2 (2), C1‐symmetric ethylene(1‐indenyl‐2‐phenyl‐2‐fluorenyl)ZrCl2 (3), and “meso”‐dimethylsilyl[3‐benzylindenyl)(2‐methylbenz[e]indenyl)]ZrCl2 (4). Catalyst 1 produced a random ethene–VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene‐co‐vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4, respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4, respectively). Catalysts 2 and 3, both bearing a fluorenyl moiety, gave propene–VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low‐molar‐mass isotactic polyvinylcyclohexane with a low activity was obtained.

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.

A chiral self-assembled supramolecular M(4)L(6) assembly has been shown to be a suitable host for a series of reactive monocationic half-sandwich iridium guests 1, 3, and 4 that are capable of activating C-H bonds. Upon encapsulation, selective C-H bond activation of organic substrates occurs. Precise size and shape selectivity are observed in the C-H bond activation of aldehydes and ether substrates. The reactions exhibit significant kinetic diastereoselectivities. Thermodynamic studies have shown that the iridium starting materials and products are bound strongly by the host assembly. The encapsulation process is largely entropy-driven. Kinetic investigations with water-soluble phosphine traps and added salts have provided evidence for a unique stepwise mechanism of guest dissociation for [4 subset Ga(4)L(6)]. Iridium guest 4 first dissociates from the host cavity to form an ion pair with the host exterior. This species then fully dissociates from the host exterior into the bulk solution. Model ion pair intermediates were characterized directly with (1)H NMR NOESY techniques. The rate of iridium guest dissociation is slower than the rate observed for the C-H bond activation processes, indicating that the selective C-H bond activation reactivity occurs within the cavity of the supramolecular host.

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.

The reaction of [Pd(2)(CH(3)CN)(6)][BF(4)](2) (1) with 1,3,5-hexatriene, 1,6-diphenyl-1,3,5-hexatriene (DPHT), or 2,2,9,9-tetramethyl-3,5,7-decatriene (DBHT) afforded bi-eta(3)-allyldipalladium complexes 3, 4, or 5. The reaction of 1 and DBHT proceeded in a stereospecific (syn) manner when the reaction was carried out in CD(2)Cl(2) under aerobic conditions, while a mixture of two diastereomers was formed under N(2) atmosphere. The two diastereomers (5-E,Z,E-antifacial and 5-E,E,E-antifacial) formed from DBHT were isolated, and the structure of 5-E,Z,E-antifacial, which was kinetically formed from the reaction of 1 and (E,E,E)-DBHT, was determined by X-ray diffraction analysis. Addition of phosphine ligands (PPh(3) or dppm) to the dinuclear adduct 5-E,Z,E-antifacial or 5-E,E,E-antifacial in acetonitrile resulted in the stereospecific (syn) elimination of [Pd(2)(PPh(3))(2)(CH(3)CN)(4)][BF(4)](2) (2) or [Pd(2)(dppm)(2)(CH(3)CN)(2)][BF(4)](2) (6). During the PPh(3)-induced dinuclear elimination, the phosphine adducts 7 that retain bi-eta(3)-allyldipalladium structure were observed initially. The phosphine adduct generated from 5-E,E,E-antifacial was isolated and structurally characterized by X-ray diffraction analysis. The reaction of 1 and DPHT in CH(2)Cl(2) afforded unique dipalladium sandwich compounds [Pd(2)(mu-eta(3):eta(3)-DPHT)(2)][BF(4)](2) (8). Interconversion between the sandwich complexes and half-sandwich complexes occurred in a stereoretentive manner. The structure of the sandwich complex 8-E,Z,E formed from 4-E,E,E-antifacial and (E,Z,E)-DPHT was determined by X-ray diffraction analysis. Transfer of the dipalladium moiety [Pd(2)(CH(3)CN)(4)](2+) from DPHT ligand of 4-E,E,E-antifacial onto DBHT ligand proceeded in a stereoretentive manner. The observed stereoretentive dinuclear process is featured by the pairwise behavior of two palladium atoms sitting on the triene pi-plane. In the dinuclear elimination, the two Pd atoms that are initially in the divalent state and bound on the opposite faces (antifacial) come to the synfacial positions to form a Pd-Pd bond prior to dissociation. These results represent the unique property of conjugated olefin as the multidentate ligands for metal-metal moieties.

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.

All relevant 13C NMR signals of two series of seven homogeneous ethylene–propylene copolymers were used to fit the second-order Markov reactivity ratios of the catalysts and the theoretical feeds. The copolymers cover a very broad range of comonomer incorporations, from about 10 to 93%, and show only primary (1,2) insertions. For both series, solutions are found with reliabilities >>99.5%. The reactivity ratios, r112 = 2.54, r121 = 0.12, r212 = 2.05, and r221 = 0.29 for the used Zirconocone and r112 = 1.69, r121 = 0.32, r212 = 1.56, and r221 = 0.51 for the hafnocene, provide direct information about the metallocenes, the kinetics, and the chain microstructure. With these results, the direct peak method demonstrates that the use of all relevant 13C NMR peaks enables accurate second-order Markov modeling, revealing subtle differences between copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 747–755, 2006

The copolymerization of propylene and disubstituted diallylsilanes [(CH2 CHCH2)2R2Si (R = CH3 or C6H5)] was investigated with isoselective and syndioselective zirconocene catalysts with methylaluminoxane as a cocatalyst. The syndioselective catalyst showed a higher reactivity for disubstituted diallylsilanes than the isoselective catalysts. Diallyldimethylsilane was incorporated into the polymer chain via cyclization insertion preferentially and formed 3,5-disubstituted dimethylsilacyclohexane units in the polypropylene main chain. In the copolymerization with diallyldiphenylsilane, diallyldiphenylsilane was copolymerized via both cyclization insertion and 1,2-insertion, which formed a pendant allyl group. The structures of isolated silacyclohexane units, determined by 13C NMR and distortionless enhancement by polarization transfer spectroscopy, proved that the 1,2-insertion of diallylsilanes proceeded with enantiomorphic site control; however, the diastereoselectivity of the cyclization reaction was independent of the stereoselectivity of the catalysts used, and cis-silacyclohexane units were mainly formed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6083–6093, 2006

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.

The copolymerization of ethylene and norbornene by catalytic systems composed of i-Pr-[(Cp)(Flu)]ZrCl2 (1) and methylaluminoxane was investigated. Ethylene-norbornene (E-N) copolymers with 40.2 mol % of norbornene are highly alternating (NENE 50 mol %) and contain a significant amount of racemic ENNE (8 mol %) and no ENNN sequences. The microstructural analysis by 13C NMR of such copolymers was completely obtained at the tetrad level by a methodology that exploits all the peak areas of the spectra and accounts for the stoichoimetric requirements of the copolymer chain. The analysis at the tetrad level allowed us to test the statistical model best describing E-N copolymerization with Cs-symmetric catalyst 1 and to study the polymerization mechanism. The root-mean-square deviations between experimental and calculated tetrads demonstrate that the first-order Markov model is sufficient to describe the microstructure of E-N copolymers with 1. It is concluded that in E-N copolymerizations with this catalyst both N and E are inserted according to a Cossee's migratory insertion, and backskips of the copolymer chain to its original position occur, causing the formation of both meso and racemic NEN sequences. The probability of chain backskip is relatively high with respect to that observed in syndiotactic propylene polymerization under the same polymerization conditions. This effect seems to be due to norbornene strong coordinating ability which can influence the competition between site epimerization and chain propagation

Nucleophilic aromatic substitution reactions of chloroarene cyclopentadienyliron complexes were utilized to prepare new classes of oligomers and polymers containing both neutral and cationic organoiron complexes in their structures. Photolysis of these polymers resulted in the removal of the cationic cyclopentadienyliron moieties, while the neutral organoiron complexes remained intact within the polymer structures. The weight-average molecular weights of these polymers after photolysis ranged from 8700 to 56 200 with polydispersities from 1.1 to 3.1. Thermal analysis established that the cationic polymers possess higher glass transition temperatures, but lower thermal stability than the neutral ferrocene-based polymers. The glass transition temperatures of the cationic polymers ranged from 65 to 161 °C, while the Tgs of the neutral polymers ranged from 10 to 92 °C. Electrochemical studies showed that the iron centers in the neutral complexes were oxidized, while the cationic complexes were reduced. Viscos...

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.

Propene-ethene copolymers with low to moderate amounts of ethene were synthesised with two C s -symmetric metallocene complexes, [(p-CH 3 OPh)2C(2,7-di- t BuFlu)-(Cp)]ZrCl 2 (I) and [(p-CH 3 OPh)2C(2,7-di- t BuFlu)(Cp)]HfCl2 (Ia). Methylalumoxane (MAO), N,N-dimethylanilinium tetra-(pentafluorophenyl)borate {[Me 2 HNPh][B(C 6 F 5 ) 4 ]}, trityl tetra(pentafluorophenyl)borate {[Ph3C][B(C6F5)4]) and tris-(pentafluorophenyl)borane [B(C 6 F 5 ) 3 ] were used as cocatalysts in the polymerisations. The differences in polymerisation activity, ethene incorporation rate and molecular weight as well as the microstructure and the thermal behaviour of the homo-and copolymers were studied. The different cocatalysts have a strong influence on the polymerisation activity and the syndiotacticity of the polymers, but only a minor influence on the ethene incorporation rate and the molecular weight. At 30 °C, the incorporation rate of ethene is ca. 25 times faster for complex I and ca. 16 times faster for complex Ia than the incorporation rate of propene. The thermal behaviour of the homo- and copolymers is dependent of the polymerisation temperature and the cocatalyst. I/MAO produces homo- and copolymers at 30 °C with more regular microstructure than I/[Me 2 HNPh][B(C 6 F 5 ) 4 ], I/ [Ph 3 C][B(C 6 F 5 ) 4 ] and I/B(C 6 F 5 ) 3 leading to homo- and copolymers with higher melting and crystallisation temperatures. On the contrary, at 0 °C I/[Me 2 HNPh][B(C 6 F 5 ) 4 ] and I/[Ph 3 C][B(C 6 F 5 ) 4 ] produce copolymers with higher propene sequence syndiotacticity and higher melting and crystallisation temperatures than I/MAO. The influence of the cocatalyst on the catalyst coordination environment is temperature-dependent and thereby the structure of the forming homo- or copolymers varies.

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.

Addition of principally sigma-donating ligands such as THF, chelating diethers, or 1,2-bis(dimethyl)phosphinoethane to eta(9),eta(5)-bis(indenyl)zirconium sandwich complexes, (eta(9)-C(9)H(5)-1,3-R(2))(eta(5)-C(9)H(5)-1,3-R(2))Zr (R = alkyl or silyl), induces haptotropic rearrangement to afford (eta(6)-C(9)H(5)-1,3-R(2))(eta(5)-C(9)H(5)-1,3-R(2))ZrL adducts. Examples where L = THF and DME have been characterized by X-ray diffraction and revealed significant buckling of the eta(6) benzo ring, consistent with reduction of the arene, and highlight the importance of the zirconium(IV) canonical form. For the THF-induced haptotropic rearrangements, the thermodynamic driving force for ring migration has been measured as a function of indenyl substituent and demonstrates silylated sandwiches favor THF coordination and the eta(6),eta(5) bonding motif over their alkylated counterparts. In the case of chelating diethers, measurement of the corresponding equilibrium constants establish more stable eta(6),eta(5) adducts with five- over four-membered chelates and with smaller oxygen and carbon backbone substituents. Kinetic studies on both THF and DME addition to (eta(9)-C(9)H(5)-1,3-(SiMe(3))(2))(eta(5)-C(9)H(5)-1,3-(SiMe(3))(2))Zr established a first-order dependence on the incoming ligand, consistent with a mechanism involving direct attack of the incoming nucleophile on the eta(9),eta(5) sandwich. These results further highlight the ability of the indenyl ligand to smoothly adjust hapticity to meet the electronic requirements of the metal center.