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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.

A novel electrochemiluminescence (ECL) biosensor for the determination of lipopolysaccharide (LPS), a biomarker of endotoxemia, was designed. The nanoprobe (Ru1@SiO2-peptide) with a specific peptide (CIGKLHSAGK) labeled with a carboxyl functionalized Ru@SiO2 (Ru1@SiO2) was prepared by the acylation reaction. The ECL peptide biosensor was obtained by the strong gold-sulfur bond between Au on the gold electrode (AuE) surface and thiol group in the peptide. In the present of LPS, the peptide on the ECL biosensor can capture effectively LPS and the LPS/peptide/AuE was fabricated. When the Ru1@SiO2-peptide nanoprobe was bound, a sandwich compound of Ru1@SiO2-peptide/LPS/peptide was formed, and Ru(bpy)32+, in the sandwich compound, will do the ECL performance. The effective ECL amplification of Ru1@SiO2 exhibited excellent analytical performance to LPS with a wide detection linear range of 1.0~500 ng mL-1 and the detection limit was 0.3 ng mL-1. The biosensor could provide an evaluate of LPS expression on the bacteria surface and guide a new path to the clinical analysis of LPS related diseases.

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 ruthenocenecarbo­nitrile mol­ecule exhibits mirror symmetry in the solid state., The mol­ecular structure of ruthenocenecarbo­nitrile, [Ru(η5-C5H4C N)(η5-C5H5)], exhibits point group symmetry m, with the mirror plane bis­ecting the mol­ecule through the C N substituent. The RuII atom is slightly shifted from the η5-C5H4 centroid towards the C N substituent. In the crystal, mol­ecules are arranged in columns parallel to [100]. One-dimensional inter­molecular π–π inter­actions [3.363 (3) Å] between the C N carbon atom and one carbon of the cyclo­penta­dienyl ring of the overlaying mol­ecule are present.

The hexagonal and heptagonal holes of B-39(-) allow its complexation with a half sandwich complex ECp*+ (E=Si, Ge, Sn, Pb). Structure and the nature of bonding of (eta(6/7)-B-39)E(eta(5)-Cp-*) are explored through the density functional theory based computation. (eta(6)-B-39)E(eta(5)-Cp-*) isomers are more stable than (eta(7)-B-39)E(eta(5)-Cp*) and the energy difference between these two isomers decreases down the group from Si to Pb. The dissociation path, (eta(6/7)-B-39)E(eta(5)-Cp-*) -> B-39(-)+ ECp*+ is studied. For all E, (eta(6/7)-B-39)E(eta(5)-Cp-*) is formed exergonically at 298 K temperature as given by the Delta G values of dissociation path [60.1(Si) to 68.3(Pb) kcal/mol for (eta(6)-B-39)E(eta(5)-Cp-*) and 58.3(Si) to 67.8(Pb) kcal/mol for (eta(7)-B-39)E(eta(5)-Cp-*)]. The adduct becomes bent around the central E atom when B-39(-) gets attached to ECp*+ and the amount of bending increases gradually down the group from Si to Pb. Bonding analysis of the stable isomer, (eta(6)-B-39)E(eta 5-Cp*) has been done by natural bonding orbital (NBO) and energy decomposition analyses (EDA). The electron density from B-39(-) is transferred to the ECp*+ moiety as revealed by the NBO analysis. All the complexes are mainly stabilized by the electrostatic and orbital interactions between B-39(-) and ECp*+ fragments as highlighted by the EDA results.

Controlled O2-oxidation of the Sm(II) sandwich compound [{EtAl(2-py)3}2Sm] (1a) gives the Sm(III)/Al(III) compound [{EtAl(2-py)3}{EtAl(2-py)2O}Sm]2 (2), containing the novel multifunctional dianionic ligand [EtAl(2-py)2O]2-. The formation of an O-bridged Al-O-Sm arrangement in the structure of 2 is potentially relevant to the catalytic epoxidation of styrene with dry air using heterobimetallic sandwich compounds like 1a.

The cocondensation of Mn atoms, I 2 and toluene at 77 K yields small quantities of [Mn(η-C 6 H 5 Me) 2 ] + I − . A single crystal X-ray structure determination shows that the manganese sits on a crystallographic inversion centre with a Mn ring steroid distance of 1.56(1) A.

The salt [Mo(η-C6H6)2][PF6] has been prepared by iodine oxidation of [Mo(η-C6H6)2] followed by metathesis with NaPF6. The cyclic voltammogram of [Mo(η-C6H6)2][PF6] in MeCN exhibits a reversible redox couple (E½) at –730 mV vs. a saturated calomel electrode (SCE). The solid-state room-temperature EPR spectrum exhibits an isotropic resonance centred at g= 1.993 which is consistent with an assignment of a 2A1g ground state for the 17-electron [Mo(η-C6H6)2]+ radical cation. The salt [Mo(η-C6H6)2][FeBr4] has been synthesised from [NEt4][FeBr4] and [Mo(η-C6H6)2][PF6]. It crystallises in the orthorhombic space group Pbca, a= 18.527(17), b= 12.521(5), c= 14.915(6)A; R and R′= 0.051 and 0.059. The salt [Mo(η-C6H6)2][FeBr4] consists of segregated chains of cations and anions. The solid-state room-temperature EPR spectrum exhibits two resonances centred at g= 1.987 and 2.008 assignable to the cation and anion respectively. The solid-state magnetic susceptibility data for [Mo(η-C6H6)2][FeBr4] can be fitted to the Curie–Weiss law between 40 and 300 K with C= 3.93 and θ=–5.4 K. Below 15 K the [FeBr4]– anion sub-lattice orders antiferromagnetically leaving a magnetic susceptibility which is dominated by the [Mo(η-C6H6)2]+ cations.

The lithium-cyclopropylethynylamidinates Li[c-C3H5-C[triple bond, length as m-dash]C-C(NR)2] (1a: R = (i)Pr, 1b: R = cyclohexyl (Cy)) have been used as precursors for the preparation of five new series of half-sandwich complexes. These complexes contain the large flat cyclooctatetraenyl ligand (C8H8(2-), commonly abbreviated as COT), and were isolated as solvated, unsolvated and inverse sandwich complexes. Treatment of the halide precursors [(COT)Pr(μ-Cl)(THF)2]2 with 1b and [(COT)Nd(μ-Cl)(THF)2]2 with 1a and 1b in THF in a 1 : 2 molar ratio, respectively, afforded (COT)Ln[μ-c-C3H5-C[triple bond, length as m-dash]C-C(NR)2]2Li(L) (2: Ln = Pr, R = Cy, L = Et2O; 3: Ln = Nd, R = (i)Pr, L = THF; 4: Ln = Nd, R = Cy, L = THF). Treatment of the dimeric cerium(iii) bis(cyclopropylethynylamidinate) complexes [{c-C3H5-C[triple bond, length as m-dash]C-C(NR)2}2Ce(μ-Cl)(THF)]2 (5: R = (i)Pr; 6: R = Cy) in situ with K2C8H8 in a 1 : 1 molar ratio in THF at room temperature afforded the inverse-sandwich complexes (μ-η(8):η(8)-COT)[Ce{c-C3H5-C[triple bond, length as m-dash]C-C(NR)2}2]2 (7: R = (i)Pr; 8: R = Cy). This reaction represents a new method for encapsulation of a planar (C8H8)(2-) ring in lanthanide complexes containing amidinate ligands in the outer decks. Novel unsolvated dinuclear lanthanide half-sandwich complexes were prepared by using the precursors 1a, 1b and COT(2-). Unlike the complexes 2-4, the reaction of [(COT)Pr(μ-Cl)(THF)2]2 with 1a afforded the unsolvated centrosymmetric complex [(COT)Pr(μ-c-C3H5-C[triple bond, length as m-dash]C-C(N(i)Pr)2)]2 (9). These dimeric structures could be also accessed by reaction of LnCl3 (Ln = Ce or Nd) with 1a or 1b and K2COT in a 1 : 1 : 1 molar ratio as a one-pot reaction to give novel [(COT)Ln(μ-c-C3H5-C[triple bond, length as m-dash]C-C(NR)2)]2 complexes (10: Ln = Ce, R = (i)Pr; 11: Ln = Ce, R = Cy; 12: Ln = Nd, R = (i)Pr). Similar treatment of HoCl3 with 1a or 1b and K2COT as three-component reactions in a 1 : 1 : 1 molar ratio afforded the solvated half-sandwich complexes (COT)Ho(c-C3H5-C[triple bond, length as m-dash]C-C(NR)2)(THF) (13: R = (i)Pr; 14: R = Cy). A unique multidecker sandwich complex [(μ-η(8):η(8)-COT){Nd(c-C3H5-C[triple bond, length as m-dash]C-C(NCy)2)(μ-Cl)}2]4 (15) was prepared by reaction of anhydrous NdCl3 with K2COT and 1b in a one-pot reaction. The solid state structure of 15 revealed the presence of an unprecedented macrocyclic sandwich compound ("giant neodymium wheel") consisting of four COT rings sandwiched between eight Nd(3+) ions, and each Nd(3+) ion is bonded to one amidinate ligand and bridged by two chlorine atoms with the neighbouring Nd(3+) ion.

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 synthesis of novel cyclobutadiene linked dimers of [η5-RCp]Co(η4-C4Ph4) was reported recently from a three-component reaction of 1,4-diphenylbutadiyne, diphenylacetylene and [η5-RCp]Co(PPh3)2 [R = H or MeOC(O)]. The chiral bis oxazoline derivative of this dimer was found to form cobalt oxazolinyl palladacycles which were excellent chiral catalysts for the Overman–Claisen rearrangement of trichloroacetimidates, similar to the well-known COP catalysts. In this paper, we report reactions carried out for identifying the intermediates in the formation of the dimeric sandwich compound {[η5-MeOC(O)Cp]Co(η4-C4Ph3)}2(1). On varying the stoichiometric ratio of the reactants of the three component reaction, two new cobalt sandwich compounds [η5-MeOC(O)Cp]Co[η4-C4Ph3(C≡CPh)] (2) and [η5-MeOC(O)Cp]Co[η4-C4-Ph2(C≡CPh)2] (3) were found to form as viscous oily liquids. The identity of 2 was ascertained by oxidizing its alkyne moiety to yield crystalline [η5-MeOC(O)Cp]Co{η4-C4Ph3[C(O)-C(O)Ph]} (4) which was structurally characterized. Further, the role of phenylethynyl derived monomeric sandwich compound 2 as a precursor to the dimeric compound 1 was established by reacting 2 with diphenylacetylene and CpCo(COD) which yielded the first example of an unsymmetrical cyclobutadiene linked dimeric cobalt sandwich compound {η5-[MeOC(O)Cp]Co(η4-C4Ph3)}[(η5-Cp)Co(η4-C4Ph3)] (5) which was also structurally characterized.

In the present research, the temperature dependence of heat capacity C p,m ∘ = f ( T ) of crystalline bis-(η6-cumene)chromium fulleride [(η6-PhCH(CH3)2)2Cr] +[C60] − has been measured between Т = (6 and 310) K in the precision adiabatic vacuum calorimeter and reported for the first time. Also, for the first time, the temperature dependence of EPR signal parameters of bis-(η6-cumene)chromium fulleride over the range from T = (120 to 290) K was investigated by electron paramagnetic resonance. In the interval from T = (196 to 240) K the reversible endothermic transformation was detected and its thermodynamic characteristics were estimated. This transformation was caused by dissociation of dimer ( C 60 - ) 2 and formation of fulleride [(η6-PhCH(CH3)2)2Cr] +[C60] − during heating. The experimental results have been used to calculate the standard (р° = 0.1 MPa) thermodynamic functions C p,m ∘ / R , Δ T 1 T 2 H m ∘ / RT , Δ T 1 T 2 S m ∘ / R , and Φ m ∘ / R = Δ T 1 T 2 S m ∘ / R - Δ T 1 T 2 H m ∘ / RT (where R is the universal gas constant) for dimeric fulleride over the range from T → (0 to 196) K and for monomeric complex [(η6-PhCH(CH3)2)2Cr] +[C60] − between Т = (240 and 310) K.

Ethylene/norbornene copolymerizations were conducted with [Ph_2C(Flu)(3-RCp)]ZrCl_2 [R: Me (1) or Me_3Si (2)], which give alternating EN copolymers. The activity of 1 in the absence of R_3Al was approximately twice that of 2 and increased further upon addition of R_3Al. Et_3Al increased the activity most effectively, and the M^^-_n of the produced polymer decreased from 100 000 to 25 000 g.mol^ . On the other hand, the M^^-_n value increased upon addition of (Bu_3Al)-Bu-i from 100 000 to 209 000 g.mol^ accompanied by an approximate to 2.5-fold increase of activity. Consequently, 1 was found to be one of the most promising complexes for the synthesis of alternating EN copolymers, of which M^^-_n value was efficiently controlled by the kind and the amount of R_3Al added.

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.

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.

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.

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.

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.

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.

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.

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.

Potassium and ammonium salts of the tungstoarsenate anion [(ReVO)3(AsW9O33)2]9– (1) have been isolated and characterized by elemental analysis, infrared and 183W NMR spectroscopy. The five-line NMR spectrum indicates a sandwich structure of C2v symmetry analogous to that found for [As2W21O69(H2O)]6–. Thermal treatment of both salts of 1 at temperatures to 900 °C leads to materials in which ~95% of the rhenium is retained, in contrast to the Keggin-derived K4PW11ReO40 which loses rhenium at ~500 °C. Based upon powder diffraction analysis, following quantitative loss of As2O3 at 420–430 °C, the following phases were identified in samples heated to 600 and 725 °C. From the potassium salt, a monoclinic K2W3O10-type bronze, and from the ammonium salt a mixture of hexagonal and tetragonal WO3 bronzes. Reflections corresponding to ReO2, ReO3, solid solutions of ReO3 in WO3, and Re2O7 were absent. The incorporation of rhenium into tungsten bronze phases suggests that technetium might behave similarly, opening a possible route to storage of 99Tc waste. To cite this article: A. Besserguenev, M.T. Pope, C. R. Chimie 8 (2005).

The synthesis and characterization of the previously unknown mixed-metal sandwich-type Wells–Dawson complexes, αββα-[(ZnIIOH2)2(FeIII)2(P2W15O56)2]14– (Zn2Fe2P4) and αββα-[(ZnIIOH2)2(FeIII)2(As2W15O56)2]14– (Zn2Fe2As4), are described. The complexes are prepared by the reaction of Zn(II) with the divacant lacunary species, αααα-[(NaOH2)2(FeIII)2(P2W15O56)2]16– and αααα-[(NaOH2)2(FeIII)2(As2W15O56)2]16–, respectively, and are characterized by X-ray crystallography, infrared and NMR spectroscopy, elemental and thermogravimetric analyses, differential scanning calorimetry, and cyclic voltammetry. Like their analogues, αββα-[(MnIIOH2)2(FeIII)2(P2W15O56)2]14– (Mn2Fe2P4) and αββα-[(MnIIOH2)2(FeIII)2(As2W15O56)2]14– (Mn2Fe2As4), the remarkable stability observed for these complexes from pH 0 to at least 6 has permitted a comprehensive evaluation of their electrocatalytic abilities toward the reduction of O2, H2O2, HNO2 and NO. A comparison of the properties of the mixed-metal Zn(II) and Mn(II) complexes is provided. To cite this article: I.M. Mbomekalle et al., C. R. Chimie 8 (2005).

Copolymerization of propene with two α-olefins (1-hexene and 1-octadecene) using iso- and syndioselective metallocene catalysts (EtInd2ZrCl2, Et(2-MeInd)2ZrCl2, Me2SiInd2ZrCl2, Ph2CFluCpZrCl2 and Me2CFluCpZrCl2) activated with methylaluminoxane (MAO) is reported. The so-called comonomer effect was seen in the catalytic activity of the Me2SiInd2ZrCl2/MAO system. Incorporation of syndiotactic copolymers was greater than that of isotactic copolymers. The molecular weight of the isotactic copolymers was not affected significantly by the presence of the comonomer, but the molecular weights of the copolymers obtained with the syndioselective catalysts decreased with increasing comonomer concentration in the medium. Tensile properties were studied. Syndiotactic copolymers with incorporation of the order of 6 mol% of 1-octadecene presented elastomeric properties.

Three alkali-metal-indium compounds K34In(92.30)Li(12.70) (I), K14Na20In(91.82)Li(13.18) (II), and K14Na20In(96.30) (III) (all Rm) have been synthesized and characterized by structural and physical property measurements and electronic structure calculations. Novel mixed In/Li anionic icosahedra and fused icosahedra form in I and II. All three contain In28 as the first triply fused In icosahedra, which are further linked into (In28)In(In28) sandwich adducts in compounds I and II and (In28)In2(In28) in III. Stabilization of these electron-poorer phases through electronic tuning occurs via two different structural (redox) perturbations, either by substitution of certain indium atoms in the clusters by electron-poorer lithium atoms or by the introduction of defects and disorder in the fused cluster (III). The preferential occurrence of either substitutions or defect formation in the clusters is consistent with extended Huckel band calculation results for both the ideal pure indium phase and the Li-substituted equivalent. Model (ideal) and experimental EF values (based on stoichiometries) fall around a pseudogap in DOS. All three compounds are metallic according to both EHTB band calculations and measured resistivities. The cations (A = K, Na) in all the three structures generate A136 clathrate-IotaIotatype networks with remarkably specific and transferable cation dispositions around the two types of anionic cluster units.

Ethylene was copolymerized with the non-conjugated diene 5,7-dimethylocta-1,6-diene by metallocene catalysts, homogenous and supported on MCM-41 mesoporous material activated by methylaluminoxane at room temperature. The employed metallocenes were (BzCp)2ZrCl2 (1), (C18H37Cp)2ZrCl2 (2), (CH3)2Si(Ind)2ZrCl2 (3) and ϕ2C(Cp,Flu)ZrCl2 (4). Diene incorporation and thermal characteristic of the polymers were determined by 13C-NMR and DSC. For the homogeneous systems, only the unbridged metallocene (1) showed a decrease in the activity as the diene content was increased. The ability for diene incorporation in the polymer chain followed the catalyst order (1)

The reaction of nickel atoms with tBuCP affords a mixture of the isomeric complexes [Ni(η3-PC2But2)(η5-P3C2tBu2)] and [Ni(η4-P2C2But2)2]. The former complex has been structurally characterised in the solid sate as its [W(CO)5] adduct, which in solution undergoes fluxional behaviour. To cite this article: F.G.N. Cloke et al., C. R. Chimie 7 (2004).

Combination of trimeric perfluoro-ortho-phenylene mercury (1) with TTF and TCNQ in a 1:1 mixture of CH2Cl2 and CS2 followed by slow evaporation of the solvent leads to the formation of orange needles of [(1)2·TTF] (2) and light yellow needles of [(1)2·TCNQ] (3), respectively. The structure of both complexes has been determined by X-ray analysis. The solid-state structure of 2 consists of centrosymmetrical supramolecules of [(1)2·TTF], in which the TTF molecule is sandwiched by two molecules of 1. This supramolecule is held by multiple Hg···S secondary interactions ranging from 3.467(5) A to 3.533(5) A. The solid state of 3 also consists of centrosymmetrical molecules of [(1)2·TCNQ]. In this case, however, the TCNQ molecule is approximately perpendicular to the neighboring molecules of 1 with which it interacts by coordination of two nitrile groups. Examination of the atomic connectivity indicates the simultaneous coordination of the coordinated nitrile nitrogen atoms to the three mercury centers of 1. The resulting Hg···N distances range from 3.102(11) to 3.134(11) A. To cite this article: M.R. Haneline et al., C. R. Chimie 7 (2004).

A molecular approach to information storage employs redox-active molecules tethered to an electroactive surface. Attachment of the molecules to electroactive surfaces requires control over the nature of the tether (linker and surface attachment group). We have synthesized a collection of redox-active molecules bearing different linkers and surface anchor groups in free or protected form (hydroxy, mercapto, S-acetylthio, and Se-acetylseleno) for attachment to surfaces such as silicon, germanium, and gold. The molecules exhibit a number of cationic oxidation states, including one (ferrocene), two [zinc(II)porphyrin], three [cobalt(II)porphyrin], or four (lanthanide triple-decker sandwich compound). Electrochemical studies of monolayers of a variety of the redox-active molecules attached to Si(100) electrodes indicate that molecules exhibit a regular mode of attachment (via a Si-X bond, X = O, S, or Se), relatively homogeneous surface organization, and robust reversible electrochemical behavior. The acetyl protecting group undergoes cleavage during the surface deposition process, enabling attachment to silicon via thio or seleno groups without handling free thiols or selenols.

To examine the effects of molecular structure on charge storage in self-assembled monolayers (SAMs), a family of redox-active molecules has been prepared wherein each molecule bears a tether composed of a tripodal linker with three protected thiol groups for surface attachment. The redox-active molecules include ferrocene, zinc porphyrin, ferrocene-zinc porphyrin, magnesium phthalocyanine, and triple-decker lanthanide sandwich coordination compounds. The tripodal tether is based on a tris[4-(S-acetylthiomethyl)phenyl]-derivatized methane. Each redox-active unit is linked to the methane vertex by a 4,4'-diphenylethyne unit. The electrochemical characteristics of each compound were examined in solution and in SAMs on Au. Redox-kinetic measurements were also performed on the SAMs (with the exception of the magnesium phthalocyanine) to probe (1) the rate of electron transfer in the presence of an applied potential and (2) the rate of charge dissipation after the applied potential is disconnected. The electrochemical studies of the SAMs indicate that the tripodal tether provides a more robust anchor to the Au surface than does a tether with a single site of attachment. However, the electron-transfer and charge-dissipation characteristics of the two tethers are generally similar. These results suggest that the tripodal tether offers superior stability characteristics without sacrificing electrochemical performance.

Kinetic studies on the syndiospecific polymerizations of propylene with i Pr(Cp)(Flu)ZrCl 2 /methylaluminoxane (MAO) were performed at 20, 40 and 70 °C and at 5 atm with various Al/Zr molar ratios. The average polymerization activity for 60 min decreased, and the time to reach a maximum activity ( t max ) decreased as Al/Zr molar ratio increased. However, at Al/Zr molar ratio of 10,000, catalytic activity decreased rapidly and became the smallest among any other Al/Zr molar ratios after 20 min of polymerization. At higher Al/Zr molar ratio, methylation and cationization progress rapidly, but its polymerization rate decayed quickly due to strong interaction between MAO and metallocene, resulting in less active species. Regardless of change in polymerization temperature, t max was maintained around 15 min. Stereoregularity was strongly dependent on the polymerization temperature, and active site isomerization was dominant source for stereoirregularity, and it was strongly influenced by polymerization temperature.

The electrochemical behaviour of the copper-substituted Keggin-type and sandwich-type polyoxotungstate anions of the compounds α-[(C4H9)4N]4H[PW11CuIIO39] and α-B-[(C4H9)4N]7H3[CuII4(H2O)2(PW9O34)2] was studied by cyclic voltammetry in acetonitrile. In both cases two copper 1-electron reduction waves were detected in the cathodic scan. The first one was due to the reduction of one CuII to CuI in the polyoxoanion and the second one to the consecutive reduction of the preformed CuI to Cu0, with the consequent deposition/adsorption of the ejected metal atom at the glassy carbon electrode surface. In the anodic scan, Cu0 was re-oxidised with regeneration of the initial copper(II) complexes, via a CuI intermediate. The observed two-step reduction of copper(II) to copper(0) and the formation of intermediate species containing copper(I) is here reported for the first time for copper substituted polyoxotungstates. The co-ordination of the acetonitrile molecules to the copper ions must play a role in the formation of the copper(I) species, which are not detected in aqueous solution. Keywords: Polyoxometalates, Keggin, Sandwich complexes, Copper, Electrochemistry, Cyclic voltammetry

m- or p-phenylenediamine and m- or p-chlorophenyl-substituted azacrown ether derivatives were synthesized through sequential nucleophilic substitution of [(eta(5)-cyclopentadienyl)(eta(6)-(m- or p-dichlorobenzene))]iron hexafluorophosphate by azacrown ethers and cyclohexaamines. Monoarylation is the main reaction for diazacrown ethers. The overall yield from the starting complex is 50-96% for multiple steps.

Sandwich-type polyoxometalates (POMs), namely [WZnM2(ZnW9O34)2]q- [M = Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], are shown to catalyze selectively the epoxidation of chiral allylic alcohols with 30% hydrogen peroxide under mild conditions (ca. 20 degrees C) in an aqueous/organic biphasic system. The transition metals M in the central ring of polyoxometalate do not affect the reactivity, chemoselectivity, or stereoselectivity of the allylic alcohol epoxidation by hydrogen peroxide. Similar selectivities, albeit in significantly lower product yields, are observed for the lacunary Keggin POM [PW11O39]7-, in which a peroxotungstate complex has been shown to be the active oxidizing species. All these features support a tungsten peroxo complex rather than a high-valent transition-metal oxo species operates as the key intermediate in the sandwich-type POM-catalyzed epoxidations. On capping of the hydroxy functionality through acetylation or methylation, no reactivity of these hydroxy-protected substrates [1a(Ac) and 1a(Me)] is observed by these POMs. A template is proposed to account for the marked enhancement of reactivity and selectivity, in which the allylic alcohol is ligated through metal-alcoholate bonding, and the H2O2 oxygen source is activated in the form of a peroxotungsten complex. 1,3-Allylic strain promotes a high preference for the threo diastereomer and 1,2-allylic strain a high preference for the erythro diastereomer, whereas tungsten-alcoholate bonding furnishes high regioselectivity for the epoxidation of the allylic double bond. The estimated dihedral angle alpha of 50-70degrees for the metal-alcoholate-bonded template of the POM/H2O2 system provides the best compromise between 1,2A and 1,3A strain during the oxygen transfer. In contrast to acyclic allylic alcohols 1, the M-POM-catalyzed oxidation of the cyclic allylic alcohols 4 by H2O2 gives significant amounts of enone.

The previously reported product from the solid-state reaction of quinolin-8-ol (oxine) with salicylic acid has been characterized using single crystal X-ray diffraction methods and confirmed as the discrete dimeric proton-transfer sandwich compound [(C9H8NO+)2(C7H5O3–)2] (1). As with similar compounds of carboxylic acids and oxine, protonation of the quinoline nitrogen occurs. However, in the case of 1, the two salicylate anions provide unusual duplex carboxylato-(O,O′) hydrogen-bonding bridges [(oxine)-N+H⋯O,O′(salicylate)⋯H′–O′-(oxine)′] which stitch together the pairs of π–π-associated oxine cations. This structure determination may provide a possible explanation of the mechanism involved in the facile solid-state reaction of oxine with salicylic acid.

Ethylene, propylene and α-olefins were homo- and copolymerized in the presence of a series of homogeneous catalytic systems consisting of methylaluminoxane (MAO) and group IV metallocenes such as Et(Ind) 2 ZrCl 2 (I), Me 2 Si(Ind) 2 ZrCl 2 (II), Et(2-Me-Ind) 2 ZrCl 2 (III), Ph 2 C(Flu)(Cp)ZrCl 2 (IV). It was found that the catalytic activity, the incorporation of comonomer in the case of copolymers, and the microstructure of the polymers depend on the catalyst's structure. For heterogeneous catalysts, several supports based on metal oxide compounds have been investigated, with special emphasis in those obtained by the sol-gel preparation technique. The homo- and copolymerization of the monomers in the homogeneous systems studied where also investigated using the same catalyst system, but in a heterogeneous medium. Comparative results from the homogeneous and heterogeneous systems are presented and discussed.

A general method for rapid construction of metallocene-based hosts is described. Treatment of polyether bridged bis(diphenylacetylenes) with a source of cyclopentadienyl cobalt at high temperature leads, via macrocyclization and capture of the intermediate cyclobutadiene, to macrocyclic systems tethered to an integral metallocene platform. Equal yields of the two possible structural isomers, the products of parallel or antiparallel cycloaddition of the precursor, are obtained. A combination of X-ray crystallography and NMR is employed to assign structures to the individual isomers and to assess the strength of lithium ion binding by the individual macrocycles.

In the title compounds, [Ru(C10H15)(C11H11)], (III), [Ru(C10H15)(C19H17)], (IV), and [Ru(C19H17)2], (V), respectively, the coordinating ring systems are planar and parallel, with the Ru atoms lying at perpendicular distances of Ru–Cp* 1.790 (1) A and Ru–indenyl 1.836 (1) A in (III), Ru–Cp* 1.791 (1) A and Ru–indenyl 1.837 (1) A in (IV), and Ru–indenyl 1.812 (1) A and 1.809 (1) A in (V) (Cp* is penta­methyl­cyclo­penta­dienyl). The ring conformations are eclipsed for (III), staggered for (IV) and intermediate for (V). All three compounds show short intermolecular contacts from C—H groups to some ring centroids; these could be regarded as C—H⋯π hydrogen bonds. The mol­ecules of each compound are thus connected via the 21 screw axis to form layers parallel to the xy plane.

Copolymerizations of ethylene with 1-decene have been carried out by using two syndiospecific metallocenes synthesized by modifying the bridge: highly syndiospecific isopropylidene(1-η 5 -cyclopentadienyl)(1-η 5 -fluorenyl)-dimethylzirconium (Me 2 C(Cp)(Flu)ZrMe 2 , 1) and less syndiospecific (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Cp)(Flu)ZrMe 2 , 2), in the presence of [Ph 3 C][B(C 6 F 5 ) 4 ] as a cocatalyst. The ethano bridged 2 compound of smaller dihedral angle showed much higher activity than 1 compound. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1-decene comonomer is present in the feed. The compound 1 showed better comonomer reactivity than 2. The properties (T m , density, and crystallinity) of copolymers seem not to be affected by the type of bridge of the metallocenes, and mainly depend on 1-decene content in the copolymer.

The cyclic voltammetry behaviours of the new Dawson heteropolyanion (HPA) octadecatungstomonoarsenate [H4AsW18O62]7− were studied as a function of pH. The electrochemistry of the fully symmetrical octadecatungstodiarsenate [As2W18O62]6− in a pH 0.3 medium is constituted mainly by four reduction steps, the first two featuring reversible one-electron processes. The comparison of the cyclic voltammetry behaviours of two complexes reveals, interestingly, that the merging of the first two waves of the monoarsenate occurs in a less acidic pH medium than for the diarsenate. The voltammograms of the two corresponding trivacant species, [H4AsW15□3O56]13− and [As2W15□3O56]12−, in which the symbol □ represents the vacancy, were also studied and compared. The comparison was extended to the Zn- and Cu-sandwich-type derivatives, with particular emphasis on the compounds of the monoarsenate series, [Zn4(H2O)2(H4AsW15O56)2]18− and [Cu4(H2O)2(H4AsW15O56)2]18−. All these species prove efficient in the electrocatalytic reduction of nitrite, but only copper-substituted derivatives are active for the electrocatalytic reduction of nitrate. To our knowledge, this observation constitutes the first example of electrocatalysis of nitrate reduction by a sandwich complex of the polyoxometalate family. Keywords: Dawson structure, Tungstoarsenate, Sandwich-type derivatives, Nitrite, Nitrate, Electrocatalysis.

In this work, the performance of the ethylene(fluorenyl)(cyclopentadienyl)zirconium dichloride/methylaluminoxane (Et(Flu)(Cp)ZrCl2/MAO) catalytic system for the polymerization of propylene was evaluated. The polymerizations were carried out at different temperatures, monomer pressures and aluminum/zirconium molar ratios ([Al]/[Zr]). The effect of these variables on the catalyst activity and on the polymer characteristics was investigated using a proposed statistical experiment planning model. Significant influences of the experimental conditions mainly on the catalyst activity, and also on the weight-average molecular weight, glass transition temperature and syndiotacticity of the produced polypropylenes, were observed.

The synthesis and characterization of 15 new, unbridged metallocene dichloride complexes of the type (L)(Ind)ZrCl2 (L=ω-phenylalkyl substituted cyclopentadienyl or 1-phenylsilyl substituted indenyl; Ind=indenyl) and (L′)(Flu)ZrCl2(L′=1-benzyl substituted indenyl or 2-benzyl substituted indenyl; Flu=fluorenyl) are reported. After activation with methyl aluminoxane (MAO), these complexes are highly active catalysts for homogeneous ethylene polymerization. The influence of various substituents on the catalyst activities and the polymer properties are discussed.

Addition of small amounts of ethylene or hydrogen leads to significant productivity increase in propylene polymerization catalyzed by fluxional bis(2-arylindenyl)zirconocenes. To test if this phenomenon is related to the reactivation of dormant species formed as a result of regioirregular propylene insertions, we have reinvestigated the regioregularity of these catalysts. Approximately 0.1–0.3 mol% of 2,1-misinsertions were found in polymers synthesized by these catalysts. The presence of these regioirregular insertions could account for the ethylene and hydrogen effects observed but does not rule out formation of other catalyst dormant sites.