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The synthesis and polymerization behavior of a new C1-symmetric bridged indenyl−fluorenyl zirconocene dimethylsilylene [9-fluorenyl][(2,4,7-trimethyl)indenyl]zirconium dichloride (5) is reported. The complex when activated by MAO was found to polymerize ethylene and propylene, although the activity and stereoselectivity of 5 for propylene were found to be lower than for the previously prepared ethylene-bridged analogue 4 and several other ethylene-bridged precursors. It has been found that, depending on both the substitution patterns on the indenyl ligand and the nature of the bridge in this series of asymmetric zirconocenes, polypropylenes with varying microstructures from aspecific to highly isospecific are obtained. The propylene polymerization behavior of the new complexes has been studied in detail, and the mechanistic aspects of polymerization are discussed.

Copolymerization of ethylene and 1-hexene was carried out with different catalysts: homogeneous Et[Ind] 2 ZrCl 2 , Cp 2 HfCl 2 and [(C 5 Me 4 )SiMe 2 N(tert-Bu)]TiCl 2 , the corresponding in-situ supported metallocenes and combined in-situ supported metallocene catalysts (mixtures of Et[Ind] 2 ZrCl 2 and Cp 2 HfCl 2 , and Et[Ind] 2 ZrCl 2 and (C 5 Me 4 )SiMe 2 N(tert-Bu)]TiCl 4 ). Carbon 13 nuclear magnetic resonance spectroscopy ( 31 C NMR), gel permeation chromatography (GPC) and crystallization analysis fractionation (CRYSTAF) studies showed that, compared is the corresponding homogeneous metallocenes, in-situ supported metallocenes produces polymers having different 1-hexene fractions, molecular weight distributions (MWD) and short chain branching distributions (SCBD). It was also demonstrated that polymers with broader MWD and SCBD can be produced by combining two different in-situ supported metallocenes.

Reaction between chromium and 2-trimethyl-silyl-3-methylphosphobenzene {C5PH3[Si (CH3)3](CH3)} vapours using metal vapour synthesis techniques produces an extremely air-sensitive yellow oil at room temperature; after sublimation and characterization by mass spectrometry and 1H and 31P NMR spectroscopy this oil proves to be a mixture of two isomers, which various techniques failed to separate. With the impossibility of obtaining crystal structures, we have used evidence from the NMR data that one of the isomers shows a long-distance P-P interaction, and extended Huckel calculations, to access the conformations of the two isomers. The calculations show that absolute minima occur for stereochemical reasons when both trimethylsilyl groups are pointing in opposite directions.

A study has focused on finding intrinsic properties of Hafnocenes and methylalumoxane (MAO) based catalysts. The researchers have evaluated more carefully the behavior of HF-based homologues 3 and 4 with yield polymers with much higher average molecular masses rate, in propene polymerization with different activators. Analysts have used MAO or [Ph3C] [B(C 6F5)4]/Al(iso-butyl)3 (TrB/TIBA). TIBA was considered for its role as a scavenger and also as a convenient alkylating agent of metallocene dichlorides. The observation presented in the study highlighted a hidden layer of complexity underneath the seemingly straightforward picture of propene polymerization mediated by group 4 metallocene catalysts. Proposed structure demonstrated that catalyst behavior is strongly idiosyntcratic and that changing the transition metal from Zr(IV) to Hf(IV) in an otherwise identical ligand framework can change dramatically.

The norbornadiene/ethylene copolymerization was studied using [Ph 2 C(Ind)(Cp)ZrCl 2 ] and [Cp 2 ZrCl 2 ] catalysts in the presence of methylaluminoxane as a cocatalyst. The polymerizations were carried out using a semiflow method, and the comonomer was charged batchwise into the reactor. Polymerizations were run at 60 °C at an ethylene pressure of 2.5 bar. The activities of both catalysts decreased when the norbornadiene/ethylene ratio in the reaction increased. The structural characterization of the copolymer was performed by DEPT and 1 H- 13 C 2D NMR experiments. The copolymerization of norbornadiene was shown to occur via both double bonds of norbornadiene. The polymers with high norbornadiene content were amorphous and transparent.

Ethylene polymerization was carried out with diphenylmethylidene-(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph2C(Cp)(Flu)ZrCl2) activated with various activators such as methylaluminoxane (MAO), tetrakis(pentafluorophenyl)borates (R·B(C6F5)4, R=Me2PhNH, Ph3C, C7H7, H(Et2O)n), dimethylanilinium tetrakis(pentafluorophenyl)aluminate (Me2PhNH·Al(C6F5)4) and tris(pentafluorophenyl)borane (B(C6F5)3) to study the correlation between catalyst performance for ethylene polymerization and cocatalysts at high temperature. R·B(C6F5)4-activated catalysts showed relatively high activity but Al(C6F5)4-activated catalyst showed very low activity, presumably due to the low thermal stability. B(C6F5)3-activated catalyst also indicated low activity. This activity difference reflected the relative coordinative abilities of the anions and tightness of the ion-pairing. MAO-activated catalyst was comparable in activity and copolymerization reactivity with Me2PhNH·B(C6F5)4-activated catalyst and these two catalyst produced high molecular weight ethylene/1-hexene copolymers in a high pressure process.

The homoleptic bis(phthalocyaninato) cerium(IV) sandwiches Ce(Pc*)2 [Pc* = Pc(C7H15)8, Pc(OC5H11)8, Pc] have been prepared and characterized by UV-vis, near IR, IR, mass spectrometries, CV and differential-pulse voltammetry (DP).

A new mechanism is proposed to explain the occurrence of primary-growing-chain-end epimerization, and the structure and frequency of olefinic end groups arising from primary β-hydride transfer, in low molecular weight isotactic polypropylenes produced with C 2 -symmetric zirconocenes. This mechanism, based on the reversible formation of a zirconocene allyl dihydrogen complex, accounts for both loss of catalyst stereospecificity and decrease of polypropylene molecular weights observed by lowering [propylene], and accommodates a number of previous and new experimental observations. Inter alia: (i) the formation of internal vinylidene unsaturations; (ii) the increase of catalyst activity induced by H 2 addition; (iii) the observed deuterium scrambling in the [I-D]propylene and [2-D]propylene polymerizations recently reported by Brintzinger. This new mechanism is discussed in the light of the polymerization results from two MAO-activated catalysts: rac-C 2 H 4 (Ind) 2 ZrCl 2 and the novel, highly regiospecific rac-Me 2 C(3-t-Bu-Ind) 2 ZrCl 2 .

Redox electrochemistry of tetra-iron substituted sandwich-type heteropolyoxometalates with the formula of Na 12 [Fe III 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ]·58H 2 O has been studied in acid buffer solutions using polarography and cyclic voltammetry. This new transition metal-substituted heteropolyoxometalate is one of the trivacant Dawson derivatives. It exhibited a one-electron couple associated with the Fe(III) center followed by two steps of four- and two-electron redox waves attributed to redox processes of the tungstenoxo framework. The new catalyst showed an electrocatalytic effect on the reduction of H 2 O 2 and NO 2 − . The tetra-iron-based heteropolytungstate was not degraded by repeated cycling between its oxidized and reduced states, which was attributed to its capacity to store and deliver multiple electrons to a bound substrate.

Metallocene complexes of Group 4 metals are playing an increasingly important role in olefin polymerisation catalysis. This contribution surveys several aspects of the chemistry of metallocene catalysts that are being pursued in our laboratory at present, namely the application of half-sandwich complexes as catalysts for high-molecular weight elastomeric polypropene, unusual C–H activation reactions of zirconium half-sandwich complexes, the development of 14-electron borole complexes as neutral analogues of cationic [Cp 2 ZrR] + catalysts, and the heterogenisation of MAO-free zirconocene catalysts on borate-functionalised silica.

Propylene polymerization was conducted with Ph 2 C(R-Cp)(Flu)ZrCl 2 [R = Me, i-Pr, PhCH 2 , Me 3 Si] catalysts in combination with methylaluminoxane (MAO) and dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH. B(C 6 F 5 ) 4 ) as cocatalyst; the dependence of the stereoregularity of poly(propylene) on cocatalysts and bulkiness of the substituents in β-position of the cyclopentadienyl ligand was studied. Methyl and i-propyl substituted metallocene catalysts produce hemi-isotactic poly(propylene). These results are in good agreement with the results of the isopropylidene bridged metallocene analogue. The benzyl substituted metallocene catalyst produces syndiotactic poly(propylene) regardless of the cocatalyst. This means that this substituent group does not affect migration insertion of propylene. Stereoregularity of poly(propylene) obtained with diphenylmethylidene(3-trimethylsilylcyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Me 3 SiCp)(Flu)ZrCl 2 ) as a catalyst was significantly influenced by the cocatalyst. Me 2 PhNH. B(C 6 F 5 ) 4 /triisobutylaluminium(i-Bu 3 Al) produces poly(propylene) with 65% racemic and 23% meso pentads at 40°C, whereas the MAO activated catalyst produces isotactic rich poly(propylene). Fractionation experiments indicated that Me 2 PhNH. B(C 6 F 5 ) 4 /i-Bu 3 Al forms two active sites, one of them being the same as that of the MAO activated catalyst, the other one producing syndiotactic rich poly(propylene).

Lithiophorite with a sandwich layered structure, which consists of stacked MnO6 octahedral sheets and LiAl2(OH)6 octahedral sheets, was prepared from a birnessite-type sodium manganese oxide with a...

Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: highly syndiospecific isopropylidene(1-η5-cyclopentadienyl)(1-η5-fluorenyl)-dimethylzirconium (Me2C(Flu)(Cp)ZrMe2, 1) and less syndiospecific (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Flu)(Cp)ZrMe2, 2), in the presence of [Ph3C][B(C6F5)4] as a cocatalyst. The effect of different types of bridges on the catalytic activity and comonomer reactivity was reported. The ethano bridged 2 compound of a smaller dihedral angle showed much higher activity than the 1 compound in the ethylene homo- and copolymerizations. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1-hexene comonomer is present in the feed. The copolymerization of ethylene with 1-hexene revealed a noticeable influence of the type of bridge on the relative reactivity of the 1-hexene. 13C-NMR analysis of copolymers showed that compound 1 is characterized by lower rE, taken as an index of ethylene reactivity, and higher reactivity of 1-hexene. The bridge also affects the distribution of the 1-hexene along the copolymer chain, investigated through their product of reactivity ratios, rErH. The thermal properties and the density of copolymers were not affected by the type of bridge of the metallocenes, but mainly depended on 1-hexene content in the copolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2763–2772, 1999

Polymerization of 1,7-octadiene was conducted with isospecific rac-dimethylsilylenebis(indenyl)zirconium dichloride (1), syndiospecific diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (2) and aspecific bis(cyclopentadienyl)zirconium dichloride (3) metallocene catalysts combined with methylaluminoxane. The microstructure of the poly(1,7-octadiene)s produced was characterized by means of 'H NMR, 13 C NMR and DEPT (distortionless enhancement by polarization transfer) spectroscopy. A portion of monomeric units in poly(1,7-octadiene)s is saturated as a result of cycloaddition. The fraction of the saturated units (cyclization selectivity) decreases in the following order: 1 > 3 > 2. The effect of polymerization temperature was studied, and the cyclization selectivity was found to decrease with lowering the polymerization temperature. The monomer concentration affects the microstructure of poly(1,7-octadiene), and the cyclization selectivity is drastically decreased with increasing monomer concentration.

Ethylene homo- and copolymerization with 1-hexene were performed in the presence of diphenylmethylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Cp)(Flu)ZrCl 2 ) derivatives activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH.(C 6 F 5 )4)/triisobutylaluminium (i-Bu 3 Al) or methylaluminoxane (MAO) to study the role of the substituent on activity, comonomer incorporation and molecular weight. C 1 symmetric metallocenes which have several substituents in β-position of the cyclopentadienyl ligand produce lower molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst at 200 °C, whereas the copolymerization reactivity is significantly influenced by the volume of the substituent: the trimethylsilyl substituted derivative produces ethylene/1-hexene copolymers with a broad chemical composition distribution. Polyethylene obtained with the diphenylmethylidene(cyclopentadienyl)(indenyl)zirconium dichloride (Ph 2 C(Cp)(Ind)ZrCl 2 ) based catalyst is branched, and the molecular weight distribution and the chemical composition distribution are significantly affected by the cocatalyst. C s symmetric metallocenes which have alkyl substituents in 2,7 position of the fluorenyl ligand produce higher molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst with equal copolymerization reactivity.

The olefin polymerization catalytic system iPr(CpFluo)ZrCl 2 /MAO was investigated by UV/ visible absorption spectroscopy in solvents of various polarity at 20°C. It was shown that the UV/visible main absorption band of the zirconocene, which can be related to the Ligand to Metal Charge Transfer bands (LMCT), varies greatly upon incremental addition of MAO or AlMe 3 . For low [AlMe 3 ]/[Zr] or [MAO]/[Zr] ratios (Al:Zr 1000) with this system is attributed to a reduction of active species concentration, as indicated by the intensity decrease of their UV/visible absorption band. This reveals the low stability of active species formed from iPr(CpFluo)ZrCl 2 compared to those from rac-Et(Ind) 2 ZrCl 2 .

With six different metallocenes, namely iPr[CpFlu]ZrCl2I, iPr[3-MeCpFlu]ZrCl2II, iPr[3-EtCpFlu]ZrCl2III, iPr[3-iPrCpFlu]ZrCl2IV, iPr[IndFlu]ZrCl2V and iPr[3-tBuCpFlu]ZrCl2VI propene polymerizations were carried out at different polymerization temperatures. MAO was used as a cocatalyst for all polymerizations. In case of metallocenes II, III and IV an increase in isotacticity with increasing polymerization temperature was observed. This is due to the increased rotation and, as a consequence, to the increased steric demand of the substituent at the cyclopentadienyl residue. With metallocene V a catalyst of in principle the same type was synthesized, but rotation of the substituent is not possible. Here, in the contrary, the assumed effect was observed, that the stereospecificity of the metallocene decreases, while raising the polymerization temperature. In metallocene I there is no rotatory substituent at the cyclopentadienyl residue and therefore a more stereoirregular polymer is formed at higher polymerization temperatures. Metallocene VI produces poly(propylene) with slightly increased isotacticity at higher polymerization temperature.

The reactions of [MCp * (η 6 -C 6 Me 6 )][PF 6 ], M = Fe: 1 , Ru: 2 , Cp * = η 5 -C 5 Me 5 , with KOH (in DME) or tert -BuOK (in THF) and methyl iodide, allyl bromide or benzyl bromide are regioselective on the arene ligand only for 2 , giving the complexes [RuCp * {η 6 -C 6 (CH 2 R) 6 }][PF 6 ], R = methyl ( 3 ), allyl ( 4 ) or benzyl ( 5 ), although some formations of C-C bonds also occur on the Cp * ligand in the case of the reactions of allyl and benzyl bromides. This contrasts with the complete lack of regioselectivity formerly observed with the iron analogue 1 , and is best taken into account by the difference of steric effects which are less marked in 2 than in 1 .

Regioregular organocobalt polyethers ( 3 and 4 ) and polyesters ( 5 – 8 ) have been prepared by the polycondensation of regioisomerically pure (η 4 -tetraarylcyclobutadiene)cobalt-containing bis-phenols ( 9 and 10 ) with aliphatic or aromatic comonomers. The diols ( 9 ) offered rigid-rod p -terphenyl-like structural units, while their isomers ( 10 ) led to 90° kinks in polymeric backbones. The polymers ( 3 , 5 and 7 =`odd' series) were derived from the bis-phenols ( 9 ), while their isomers ( 4 , 6 and 8 =`even' series) resulted from 10 . Most of the polymers ( 3 – 8 ) exhibited good solubilities in common organic solvents. In the case of the isomeric polyesters with aromatic backbones ( 7 and 8 ), the latter were more soluble, indicative of their higher configuration entropies. Glass transition temperatures of the `odd' and `even' isomers were similar, irrelative to the kinks in their backbones, but they showed good correlation with aliphatic-to-aromatic mass ratios and rigidities of the main chains. The polymers of the `odd' series exhibited crystalline and liquid crystalline (polyesters, 7 ) phases, while their `even' isomers remained amorphous. Correlations between mesomorphic properties and the structure of the repeating units have been discussed.

The sodium/lithium compounds closo-exo-Li(THF)-1-Na(THF)-2-(SiMe3)-3-(R)-2,3-C2B4H4 (R = SiMe3, Me, H), were found to react with several different hafnium reagents to produce half- and full-sandwich and mixed-ligand chlorohafnacarboranes in good yields. The reaction of the sodium/lithium compounds with HfCl4 in 2:1 molar ratios produced the full-sandwich complexes 1-Cl-1-(THF)-2,2‘-(SiMe3)2-3,3‘-(R)2-4‘,5,5‘,6-Li(THF)n-[1,1‘-commo-Hf(2,3-C2B4H4)2] (R = SiMe3, n = 2 (I); R = Me, n = 1 (II); R = H, n = 1 (III)) in yields of 77%, 65%, and 71%, respectively. When R = SiMe3, a 1:1 molar ratio of carborane to HfCl4 gave the half-sandwich species [Li(THF)2][1,1,1-(Cl)3-closo-1-Hf-2,3-(SiMe3)2-2,3-C2B4H4] (V) in 77% yield. On the other hand, both 2:1 and 1:1 reaction ratios of carborane (R = Me) to Cp*HfCl3 gave only the mixed-ligand sandwich compound 1,1‘-(Cl)2-2-(SiMe3)-3-(Me)-4,5-Li(THF)-1,1‘-commo-Hf[(η5-C5Me5)(η5-2,3-C2B4H4)] (IV) in 82% yield. All compounds were characterized by infrared spectroscopy, 1H, 1...

1,4-Dihydro-1,1-dimethyl-1-stannanaphthalene (10) has been prepared by a multistep synthesis starting from α,2-dibromotoluene (6). The reaction of 10 with MeBBr2 followed by LDA afforded lithium 1-methyl-1-boratanaphthalene (2a). The reaction of 10 with BCl3, followed by diisopropylamine and subsequent treatment with LDA, gave lithium N,N-diisopropyl-1-amino-1-boratanaphthalene (2c). The boratanaphthalenes have been characterized using 1H NMR, 11B NMR, and 13C NMR spectroscopy. The pKa of the conjugate acid of 2c is close to that of indene. 2a reacts with [Cp*RuCl]4 to form Ru sandwich compound 4a, in which the boratanaphthalene is η6 bound to Ru. 2c reacts with Cp*ZrCl3 to form a Cp*ZrCl2 adduct 5c, in which the boratanaphthalene unit is unsymmetrically bound to Zr.

The isolation and characterization of [CpRu(9S3)](O3SCF3), where 9S3 = 1,4,7-trithiacyclononane, is reported. The title compound crystallizes in the orthorhombic space group Pbca: a = 10.2542(18), b = 14.8991(13), c = 22.4832(18) A, and Z = 8. The Ru atom is sandwiched between the π-bound cyclopentadienyl ligand and the 9S3 ligand, bonding to all three of the sulfur atoms in the 9S3. The Ru—S distances are 2.2991(10), 2.2979(11), and 2.3055(10) A. The C—S distances range from 1.819(4) to 1.852(5) A in the trithiacyclononane ring.

Exchange couplings between two Fe layers have been investigated in polycrystalline Fe/Al/Fe/Ni-Fe/NiO and Fe/Al/Fe/Ni-Fe sandwiches. Linear exchange couplings between the two Fe layers were strong and ferromagnetic when the thickness of the Al spacer was between 0.7 and 2.2 nm. We observed biquadratic exchange couplings (90 degree couplings) when the thickness of the Al spacer was between 2.5 and 4.0 nm.

Synthesis of a family of monomeric, base-free bis(cyclopentadienyl)titanium oxide complexes, (η5-C5Me4R)2TiO (R = iPr, SiMe3, SiMe2Ph), has been accomplished by deoxygenation of styrene oxide by the corresponding sandwich compound. One example, (η5-C5Me4SiMe2Ph)2TiO, was characterized by X-ray diffraction. All three complexes undergo clean and facile hydrogenation at 23 °C, yielding the titanocene hydroxy hydride complexes (η5-C5Me4R)2Ti(OH)H. For (η5-C5Me4SiMe3)2TiO, the kinetics of hydrogenation were first-order in dihydrogen and exhibited a normal, primary kinetic isotope effect of 2.7(3) at 23 °C consistent with a 1,2-addition pathway. Isotope effects of the same direction but smaller magnitudes were determined for silane addition.

The norbornene/ethylene copolymerization was studied using C 2v - and C s -symmetric metallocene catalysts in the presence of methylaluminoxane as a cocatalyst. The batch reactions were carried out at four different temperatures copolymerizing a constant amount of ethylene with the appropriate amount of norbornene. The activity decreases for the Cp 2 ZrCl 2 catalyst and increases to a constant level for the [Ph 2 C(Flu)(Cp)]ZrCl 2 catalyst when the norbornene/ethylene ratio in the reaction increased. The highest activities and the highest norbornene contents in the copolymers were achieved using the [Ph 2 C(Flu)(Cp)]ZrCl 2 . The microstructure of the copolymer determined with 13 C NMR was observed to depend on catalyst, temperature and monomer ratio. Cp 2 ZrCl 2 produces more norbornene blocks as a function of norbornene content in the copolymer and longer norbornene sequences than [Ph 2 C(Flu)(Cp)]ZrCl 2 . The correlation between the increasing norbornene content in the copolymer and the increasing glass transition temperature is more obvious for [Ph 2 C(Flu)(Cp)]ZrCl 2 .

The gadolinium(III) complexes with polyoxometalates were studied using X-band Electron Paramagnetic Resonance (EPR) spectroscopy. We selected the following sandwiched complexes: Gd(SiW 11 O 39 ) 2 13− [ I ], GdW 10 O 36 9− [ II ], Gd(P 2 W 17 O 61 ) 2 17− [ III ], and encrypted [GdSb 9 W 17 O 86 ] 16− [ IV ], [GdP 5 W 30 O 110 ] 12− [ V ]. The EPR spectra obtained for the compounds I – III and IV – V differ markedly from the U-spectrum characteristic for Gd(III) in glasses. The values of the zero-field splitting parameter D for both kind of complexes studied have been estimated. Taking into account the spin-hamiltonian calculations, the existence of Gd(III) ion in two different surroundings, in a strong crystal field of rhombic symmetry and in a weak crystal field, is observed. The differences observed between the case I – III and IV – V seems to be related to a various coordination of the Gd(III) ion and its hydration degree. Our study shows a relation between the presence of particular g -values of the spectral lines and the number of the inner-sphere water molecules as well as the type of the Gd(III) complex (sandwiched and/or encrypted) in solid.

The structure of a mono-substituted ferrocene derivative of which the flexible spacer is located between the ferrocenyl and mesogenic groups, ω-[4-(4-methoxyphenoxycarbonyl)phenoxycarbonyl]propyl 4-ferrocenylbenzoate was determined by the X-ray diffraction method. It was found that the two cyclopentadienyl rings in the ferrocene and the—C3H6—chain introduced as a flexible spacer exhibited a very interesting conformation. The two cyclopentadienyl rings are a staggered conformation rather than an eclipsed one. This staggered conformation is an unusual structure in mono-substituted ferrocene derivatives, in general. Also, the—C3H6—chain includes two gauche conformations and makes a bent molecular feature rather than a rod-like one. As a result, the title compound does not exhibit liquid crystallinity.

The Fe-57 Mossbauer Effect was used to study a solution (0.2% by Weight) of 1,1′-diacetylferrocene (DAF) in the liquid crystalline material p-n-hexyloxy-benzylidene-p-toluidine (HBT). The DAF contained enriched Fe-57. The Mossbauer Effect parameters were determined for the temperature range 100–300K in the crystalline solid phase and 100–200K in the cold smectic s phase of HBT. Here “cold” means the smectic glass and the supercoded smectic phase. The Ln recoil-free intensity (f) vs T data exhibited linear Debye behavior for the solid phase over the entire temperature range. The low temperature (T < 190) portion of the cold smectic Inf vs T data also exhibited Debye behavior, and the smectic glass gave a Mossbauer-Debye temperature (θ lc ) about 30 K. lower than the crystalline phase. The smectic glass-super cooled smectic transition was determined to be Tg = 190 K from the deviation of the Inf vs T data from linear behavior. Above Tg , the deviation from linear Debye behavior followed a (T-Tg)2 d...

Phenyl- and 1,2-diphenyl-1,2-dicarba-closo-dodecaborane have been synthesized and deboronated to yield [7-C6H5-7,8-C2B9H11]– and [7,8-(C6H5)2-7,8-C2B9H10]–. Reaction of the monophenyl with KOBut and CoCl2 in 1,2-dimethoxyethane (dme) led to [3,3′-Co(1-C6H5-1,2-C2B9H10)2]– 1–. This has been fully characterized by X-ray analysis. A similar reaction with [7,8-(C6H5)2-7,8-C2B9H10]– did not yield the expected sandwich compound. On the contrary, reaction of [7,9-(C6H5)2-7,8-C2B9H10]– with KOBut and CoCl2 in a mixture of dme and diethylene glycol dimethyl ether led to [3,3′-Co{1,7-(C6H5)2-1,7-C2B9H9}2] 2–. The two sandwich complexes were tested for liquid–liquid extraction and transport through supported liquid membranes of 137Cs, 90Sr and 152Eu. Extractions for 137Cs were very good at pH 3 but decreased considerably at pH 1 for H[1], while H[2] showed good efficiency even at this pH. The extraction of 90Sr was performed with the incorporation of a synergistic linear polyether and was good at pH 3 and 1. For the extraction of 152Eu, compound H[2] displayed good efficiency. Transport experiments of Cs using supported liquid membranes were performed with H[1] and H[2] and o-nitrophenyl hexyl ether as the membrane solvent. The permeability of 137Cs for compound H[2] was 30.9 cm h–1 while for H[1] it was 7.95 cm h–1. These permeabilities are much higher than those of usual carriers under comparable conditions.

A theoretical approach to the mechanical coupling between phases in metal/ polymer/metal sandwich composites is developed assuming perfect interfaces. Comparisons between experimental dynamic mechanical spectroscopy and theoretical results are made with special attention to the geometrical characteristics. Unexpected results concerning the dependence on the width of the specimen are explained using the strain energy method. The polymer thickness influence is explained only by structural effects instead of the interface effects often found in the literature. The temperature of the sandwich loss factor peak is revealed to greatly depend on the specimen dimensions.

A series of diynes bearing flexible aliphatic, electron-donating, or electron-withdrawing groups between the acetylenes moieties or as lateral groups was prepared and subjected to the polymerization with (η 5 -cyclopentadienyl)bis(triphenylphosphine)cobalt (1). As a result, organocobalt polymers bearing various substituents in the side or the main chain were obtained in high yields. From the detailed structural elucidation of polymers or from the model experiments, some of the organocobalt polymers were found to be contaminated with (η 5 -cyclopentadienyl)(η 4 -cyclobutadiene)cobalt units. The regiochemistry of the main chain of the obtained polymers was also studied from the model experiments, from which 2,5-linkage of the main chain was found to be predominant in the case of diynes bearing less sterically hindered lateral substituents. The polymer obtained from 1 and a diyne having electron-withdrawing groups between the acetylenes and lateral aliphatic moieties (i.e., 1,4-bis(1-oxo-2-undecynyl)-benzene, 2I) was found to have 100% of the cobaltacyclopentadiene moieties in the repeating units and the 2,5-selective (ca. 90%) main chain linkage.

Polymerization of propene was conducted at 40°C under reduced pressure (0.35-1.0 atm) using the C 1 -symmetric threo- i Pr(3- t BuCp)(3- t BuInd)ZrCl 2 /MAO and TiCl 4 /MgCl 2 /Al( t Bu) 3 catalyst systems and the effect of propene pressure on the microstructure of the resulting isotactic polypropene was investigated. In the case of C 1 -symmetric metallocene, the [mmmm]-pentad fraction decreased moderately with decreasing propene pressure, but the magnitude of decrease was much smaller than those reported by Busico et al. using typical C 2 -symmetric metallocenes. Whereas, the [mmmm]-pentad fraction of isotactic polypropene obtained with the conventional Ziegler-Natta catalyst did not change so much in the pressure range. Thus, epimerization of the growing polymer chain was found to be drastically dependent upon the catalyst system.

We present measurements of the current-voltage Characteristics of metal/Nis 2 - x Se x /metal structures. Due to the unusual metal-insulator phase transition in NiS 2 -xSe x , in which the low-temperature phase is metallic-like, whereas above the transition temperature the material is a semiconductor, we observed N-type current-voltage characteristics. The switching time for NiS2-xse i ; thin films is estimated to be roughly 10- 8 s, which is sufficiently short to be of interest for applications.

Arene–iron chemistry was applied in the synthesis of a novel liquid crystalline polymer. The chemistry, which is based on iron cyclopentadienyl (FeCp) arene complexes, allows sequential nucleophilic substitution of the chlorides from 1,3-dichlorobenzene–FeCp complex and photolytic decomplexation of the products to afford asymmetrical aryl ethers. This methodology provides easy access to novel polyether-esters, and is potentially useful in the synthesis of various functional polyarylates. © 1997 John Wiley & Sons, Inc.

Synthesis, spectral, and structural studies of the first examples of porphyrins substituted at the meso positions with sterically hindered η(5)-CpCo(η(4)-C4Ph4) cobalt sandwich units are described. The novel dipyrromethane derived cobalt sandwich compound {η(5)-[(C4H4N)2CH]C5H4}Co(η(4)-C4Ph4) 1, as well as its parent aldehyde, η(5)-[C5H4(CHO)]Co(η(4)-C4Ph4), were used in the synthesis of porphyrins having one or two η(5)-CpCo(η(4)-C4Ph4) groups at their meso positions. 1,9-Diformyldipyrromethane derived η(5)-CpCo(η(4)-C4Ph4) 2 was synthesized using dipyrromethane 1 under Vilsmeier conditions. A reaction of 2 with unsubstituted dipyrromethane under basic conditions in the presence of Pd(C6H5CN)2Cl2 yielded an A-type palladium coordinated porphyrin 3 [where A = η(5)-CpCo(η(4)-C4Ph4)]. A similar reaction of 2 with meso aryl and ferrocenyl-substituted dipyrromethanes yielded trans-AB type palladium coordinated porphyrins 4-6 [where A = η(5)-CpCo(η(4)-C4Ph4) and B = 4-tert-butylphenyl 4, ferrocenyl 5, and pentafluorophenyl 6]. Reactions of 2 with 5-ferrocenyl dipyrromethane under the same reaction conditions in the presence of Ni(acac)2 and Zn(OAc)2 gave the trimetallic nickel(II) and zinc(II) complexed trans-AB type porphyrins 7 and 8 having both cobalt and iron sandwich units at the meso positions. Crystal structure of the Pd(II) porphyrin 5 and nickel(II) porphyrin 7 showed nonplanar structures having distinct ruffle type distortion of the porphyrin ring. Demetalation of the zinc(II) trans-AB type porphyrin 8 in the presence of trifluoroacetic acid gave the metal free base porphyrin 9. Reactions of the cobalt sandwich aldehyde [(η(5)-C5H4(CHO)]Co(η(4)-C4Ph4) with sterically hindered dipyrromethane derivatives under acid-catalyzed condensation reactions gave trans-A2B2 type porphyrins [where A = η(5)-CpCo(η(4)-C4Ph4) and B = pentafluorophenyl, 10 mesityl 11]. In contrast, reactions of [η(5)-C5H4(CHO)]Co(η(4)-C4Ph4) with sterically unhindered meso-4-tert-butylphenyl dipyrromethane resulted in both AB3 12 and cis-A2B2 13 type porphyrins [where A = η(5)-CpCo(η(4)-C4Ph4) and B = (4-tert-butylphenyl] as a result of scrambling. The new porphyrin derivatives have been structurally characterized, and their spectral and electrochemical features were determined.

A new BiLi porphyrin sandwich compound, LiBi(TPP)2 has been synthesized and characterized (TPP=tetraphenylporphyrin). The unique molecular structure of LiBi(TPP)2 is such that the Bi sits between the porphyrins and is directed towards the Li. This complex was shown to remain intact in solution by temperature-dependent 2D NMR spectroscopy. In order to investigate the potential interaction between these two metals, DFT calculations were used and showed a Bi 6s orbital polarized towards Li which could be indicative of a BiLi dative bond. This bond is remarkably short, 2.87 A, and is among the shortest BiLi distances seen in a small molecule.

Molecules of ferrocene-1,1′-diylbis(2-phenylethanedione), [Fe(C13H9O2)2], lie across twofold rotation axes. One of the oxygen atoms in each diketone unit acts as a bis-acceptor of inter­molecular C-H⋯O hydrogen bonds. Hydrogen bonds employing cyclopentadienyl C-H bonds as donors generate spirals of molecules around 31 axes, while those employing phenyl C-H bonds as donors generate two-dimensional sheets.

The title compound, tetra-μ-iodo-bis[(η5-pentamethylcyclopentadienyl)molybdenum](Mo-Mo) tetraiodoferrate(III) di-μ-iodo-μ-oxo-bis[iodo(η5-pentamethylcyclopentadienyl)molybdenum](Mo-Mo), forms as a by-product of the thermal decarbonylation of [(η5-C5Me5)MoI3(CO)2] in tetrahydrofuran. The source of the iron is an impurity in the [(η5-C5Me5)2Mo2(CO)3]2 starting material used to make the triiodide compound. The structure consists of three independent species, namely a [(η5-C5Me5)2Mo2(μ-I)4]+ cation with two pentamethylcyclopentadienylmolybdenum moieties bridged by four iodide ligands, a tetrahedral [FeI4]− anion and a neutral dinuclear species comprising two pentamethylcyclopentadienyliodomolybdenum units bridged by two iodide and an oxo ligand. All three fragments sit on crystallographic mirror planes in the monoclinic space group P21/m.

Symmetric deformation analysis of sandwich plates with symmetric and balanced laminated faces and an orthotropic core is presented here. The transverse shear and normal strain and stress effects on symmetric deformation of such sandwich plates are considered. A set of twelfth-order governing equations and consistent boundary conditions are given from a mixed variational theorem. The symmetric deformation of square sandwich plates with fully simple supports subjected to symmetric sinusoidal loading on both surfaces is evaluated. The numerical results are compared with elasticity solutions. The present theory is found to agree approximately with three-dimensional elasticity solutions.

The syntheses of the η-lutidine(η-allyl)molybdenum compounds [Mo(2,6-lutidine)(η-C3H5)Cl]2 1, Mo(η-2,6-lutidine)(η-C3H5)(η2-O2CR)] (2: R = CH3, 3: R = C(CH3)3) and [Mo(η-2,6-lutidine)(η-C3H5)2] 4 are described. The sandwich compound [Mo(η-2,6-lutidine)2] undergoes facile ligand displacement giving zero-valent compounds MoL6, where L = CO, CNR, and Mo(diene)3, where diene = 2,3-dimethyl-1,3-butadiene. The crystal structure of compound 1 has been determined.

Transition-metal sandwich complexes incorporating bifacially coordinated C 2 B 3 planar carborane rings form a large and varied family of generally air-stable, highly robust compounds that feature multidecker stacking. As a group, these complexes offer a number of advantages that are potentially of interest in the development of new electronic, magnetic and/or optical materials. They are remarkably versatile, accommodating a wide range of metals and organic substituents ; they are soluble in organic solvents and are typically resistant to air and moisture ; they can be reversibly oxidized and reduced ; in many cases they are paramagnetic, exhibiting substantial electron delocalization of the unpaired electrons between metal centers. Moreover, the small carborane starting materials can now be prepared in large (ca 100 g) quantities, making the complexes readily accessible. A brief overview of this area is presented with emphasis on the systematic utilization of metallacarborane sandwich complexes in the construction of large multimetallic systems and studies of their electronic and molecular structures.

The crystal structure of neptunocene, [Np(C8H8)2], has been determined by single-crystal X-ray diffraction and is isostructural with thorocene and uranocene. A number of crystallographic and geometric parameters of these three compounds are compared.

The vinylidene structures in polypropylenes produced by ethylenebis(indenyl)zirconiumdichloride (En(Ind) 2 ZrCl 2 ), 1 , and isopropyl(cyclopentadienyl)(fluorenyl)zirconiumdichloride (iPr(Cp)(Flu)ZrCl 2 ), 2 , were analyzed by 1 H NMR. The vinylidene group adjacent to the chain end was clearly distinguished from other internal vinylidene structures for the first time using 1,2-dichlorobenzene as solvent. The polypropylene produced by 2 had much internal vinylidene groups compared with one by 1 .

A sandwich compound of cyclooctatetraendiyl (COT)2− samarium-potassium was synthesized and analyzed using a flexible calix[4]arene dianion. This compound, [p-tBu-calix[4]-(OMe)2(O)2]arenediyl-samarium-(η8-cyclooctatetraendiyl)-potassium (tetrahydrofurane)3, is constructed as a linear sequence L-Sm--K-, where L, , and are specific ligands with L = O,O-dimethyl-calix[4]arene2−, = cyclo-octatetraendiyl, and = tetrahydrofurane templates.

Metal Atom Synthesis, Properties, and Structure of μ2(η3,η3-Toluene)bis[(η6-toluene)iron](Fe-Fe) Metal atom cocondensation of iron atoms and toluene produces the mononuclear iron sandwich compound [(η6-toluene)(η4-toluene)Fe] 1. Complex 1 reacts with a palette of N-containing ligands such as primary, secondary, and tertiary amines as well as pyridine, pyrrolidine, and tmeda to form highly reactive instable intermediates. In the temperature range from -80 to -30°C, the proposed intermediates react with toluene to form the first homoleptic Fe/toluene complex μ2-(η3η3-toluene)-bis[(η6-toluene)iron](Fe-Fe) (3) regardless which N-containing ligand is used. Additionally, 3 is also formed when ethanol is used instead of N-containing base ligands. Black thermolabile 3 was characterized by low-temperature 1H-, 13C-, and Moβbauer spectroscopy as well as by an X-ray structure analysis (-173°C). The X-ray structure determination reveals a μ-η3η3-briding toluene ligand capping two {(η6-toluene)Fe} units which are connected by an Fe-Fe bond [2.746(1) A]. However, in solution up to -30°C all three toluene ligands are fluxional according to 1H- and 13C-NMR data. At -10°C 3 reacts with CO with decomposition to form Fe metal. With 2,2-bipyridine and ethene no reaction is observed up to room temperature.

The reactivity of the organosamarium(II) indenyl complex (C 9 H 7 ) 2 Sm(THF) x , 1, has been compared with that of (C 5 Me 5 ) 2 Sm(THF) 2 , 2, and (C 5 Me 5 ) 2 Sm, 3, by examination of characteristic organosamarium(II) reactions which form trivalent oxide, iodide, cyclooctatetraenyl and azobenzene complexes. Complex 1 reacts with excess N 2 O to form [(C 9 H 7 ) 2 Sm(THF)] 2 (μ-O), 4, and (C 9 H 7 ) 3 Sm(THF), 5, as the major products. Two equivalents of 1 react with one equivalent of 1,2-diiodoethane in THF to give (C 9 H 7 )SmI 2 (THF) 2 , 6, as well as 5. Complex 1 reacts with 1,3,5,7-cyclo-octatetraene in a 2 :1 ratio in THF to form 5 and (C 9 H 7 )Sm(C 8 H 8 )(THF) x , 7, which has been fully characterized as the 2,2'-bipyridine adduct (C 9 H 7 )Sm(C 8 H 8 )(C 10 H 8 N 2 ), 7a. The reaction of 1 with azobenzene in a 2 :1 ratio forms [(C 9 H 7 )Sm(N 2 Ph 2 )(THF)] x , 8, and 5. Complexes 4-6 and 7a have been definitively identified by X-ray crystallography. Complex 4 crystallizes from THF in space group P1 [C i 1 ; No. 2] with unit cell parameters at 163 K of a = 8.072(2) A, b = 9.502(2) A, c = 12.250(3) A, α=101.42(2)°, β=90.71(2)°, γ=102.50(2)°, V= 897.7(4) A 3 and Z = 1 for D calcd = 1.704 Mg m -3 . Least-squares refinement of the model based on 3924 reflections (|F 0 | >3.0 σ (|F 0 |)) converged to a final R F = 2.4%. The geometry around each Sm atom is a distorted tetrahedron and the Sm-O-Sm angle is 180°. Complex 5 crystallizes from THF/hexanes at -35 °C in space group P6 3 [C 6 6 ; No. 173] with unit cell parameters at 163 K of a=11.7370(14) A, c= 10.1994(12) A, V=1216.8(3) A 3 and Z=2 for D calcd = 1.550 Mg m -3 . Least-squares refinement of the model based on 976 reflections (|F 0 | > 3.0σ (|F 0 |) converged to a final R F =2.3%. The three ring centroids and the THF oxygen atom define a distorted tetrahedron around samarium with a (ring centroid)-Sm-(ring centroid) angle of 116.0°. Complex 6 crystallizes from THF/hexanes as the trisolvate (C 9 H 7 )SmI 2 (THF) 3 , 6a, in space group P2 1 /n [C 5 2h ; No. 14] with unit cell parameters at 163K of a = 8.3969(12) A. b = 17.165(5) A, c= 33.592(7) A, β=96.468(15)°, V=4811(2) A 3 and Z=8 for D calcd =2.031 Mg m -3 . Least-squares refinement of the model based on 5664 reflections (|F 0 | > 2.0 σ (|F 0 |)) converged to a final R F = 3.3%. The six ligands around Sm in 6a describe a distorted octahedron. The iodide ligands are trans to each other with a 153.8(1)° I-Sm-I angle. Adduct 7a crystallizes from hot THF/toluene in space group P1 [C i 1 ; No. 2] with a unit cell parameters at 163 K of a = 7.886(7) A, b = 16.72(2) A, c = 17.48(2) A, α = 62.96(7)°, β=85.17(7)°, γ= 85.23(9)°, V=2042(3)A 3 and Z=4. The cyclooctatetraenyl and indenyl ligands generate a bent metallocene structure for 7a which contains a chelating bipyridyl group in the plane bisecting the two rings

Synthesis of the mixed-ring sandwich compound [Mo(η6-NC5H3Me2-2,6)(η6-C6H5Me)] is reported. Photoelectron spectroscopic studies of [M(η6-NC5H3Me2-2,6)2], where M = Ti, V, Cr or Mo and [Mo(η6-NC5H3Me2-2,6)(η6-C6H5Me)] established that these sandwich compounds are electronically very similar to the bis(arene) analogues, and that 2,6-dimethylpyridine is a better δ acceptor than benzene.