CH CHCH Research Articles

Mass Spectrometric Fragmentation of 1, 8-Bis[4-substituted-(oxazolin-2-yl)] anthracenes: Ring-contraction Rearrangement of Oxazoline Ring under Electron-Impact Ionization Conditions

The mass spectrometric fragmentation of 1, 8-bis[4-substituted(oxazolin-2-yl)] anthracenes (AnBOXes) was investigated by using mass-analyzed ion kinetic energy spectrometry under electron-impact ionization conditions. All the compounds could undergo a ring contraction by the loss of an RCH == CH 2 molecule to form 1-oxazirinyl-8-(oxazolin-2-yl) anthracene ions, which could further lose an R radical, followed by the loss of oxazoline. These ions could also eliminate an R radical and subsequently undergo ring-contraction rearrangements to lose a CHCH 2O fragment and an epoxide molecule, respectively. The ions that are formed could further lose CHCH 2O and CH 2 ==CH fragments. Several ring-contraction rearrangements of the oxazoline ring were observed under electron-impact ionization conditions.

Characterization by Theory of H-Transfers and Onium Reactions of CH 3CH 2CH 2N +H=CH 2

H-transfers by 4-, 5-, and 6-membered ring transition states to the pi-bonded methylene of CH3CH2CH2NH+=CH2 (1) are characterized by theory and compared with the corresponding transfers in cation radicals. Four-membered ring H-transfers converting 1 to CH3CH2CH=N+HCH3 (2) and CH3N+H=CH2 to CH2=NH+CH3 are high-energy processes involving rotation of the source and destination RHC= groups (R = H or C2H5) to near bisection by skeletal planes; migrating hydrogens move near these planes. The H-transfer 1 --> CH3C+HCH2NHCH3 (3) has a higher energy transition-state than 1 --> 2, in marked contrast to the corresponding relative energies of 4- and 5-membered ring H-transfers in cation-radicals. Six-membered ring H-transfer-dissociation (1 --> CH2=CH2 + CH2=N+HCH3) is a closed shell analog of the McLafferty rearrangement. It has a lower energy transition-state than either 1 --> 2 or 1 --> 3, but is still a much higher energy process than 6-membered ring H-transfers in aliphatic cation radicals. In contrast to the stepwise McLafferty rearrangement in cation radicals, H-transfer and CC bond breaking are highly synchronous in 1 --> CH3N+H=CH2 + CH2=CH2. H-transfers in propene elimination from 1 are ion-neutral complex-mediated: 1--> [CH3CH2CH2+ ---NH=CH2] --> [CH3C+HCH3 NH=CH2] --> CH3CH = CH2 + CH2=NH2+. Intrinsic reaction coordinate tracing demonstrated that a slight preference for H-transfer from the methyl containing the carbon from which CH2=NH is cleaved is due to CH2=NH passing nearer this methyl than the other on its way to abstracting H, i.e., some memory of the initial orientation of the partners accompanies this reaction.

FT-Raman spectra of n-propanol and selected partially 2H-labelled analogues

Fourier-transform Raman spectra of CH 3CH 2CH 2OH and some of its selectively deuteriated analogues have been obtained. Comparisons of the Raman spectra of the protiated and partially deuteriated species, in conjunction with polarization data, has enabled improved vibrational assignments to be made for the C–H modes. As a result, confirmation of some literature assignments of stretching and bending modes and revision of other tentative assignments for large biopolymer molecules have been proposed.

Copolymerization of carbon dioxide and cyclohexene oxide with zinc/β‐ketoiminato complexes: Investigating the influence of the electron structure of zinc/β‐ketoiminato complexes on the catalytic activity and resultant copolymer properties

AbstractA series of LZnX zinc/β‐ketoiminato complexes [L = CH3C(OH)C(CH2CHCH2)C(CH3)NAr (L1), CH3C(OH)C(CH2CH2CN)C(CH3)NAr (L2), CH3C(OH)C(CH2C6H5)C(CH3)NAr (L3), or CH3C(OH)CHC(CH3)NAr (L4); Ar = 2,6‐iPr2C6H3; and initiation group X = alcoholate or acetate (for L1) or alcoholate (for L2–L4)] were synthesized, and their activities toward the copolymerization of carbon dioxide with cyclohexene oxide were determined. The 3‐position substituents on the β‐ketoiminato ligand backbone of the zinc/β‐ketoiminato complexes played an important role not only in the catalytic activity but also in the intrinsic viscosity, chemical composition, and refined microstructure of the resultant copolymers. The order of the catalytic activity of L1ZnX with different initiation groups (X = OMe, OiPr, or OAc) was L1Zn (OiPr) > L1Zn (OMe) > L1Zn (OAc), being the opposite of the order of the leaving ability of the initiation groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6243–6251, 2006

Olefin metathesis for metal incorporation: Preparation of conjugated ruthenium-containing complexes and polymers

Olefin Metathesis for Metal Incorporation (OMMI) was used for the stoichiometric attachment of ruthenium to both small and large polyenes. The dinuclear complexes (PCy 3) 2C1 2Ru CH(CH CH) n CH Ru(PCy 3) 2Cl 2 ( n = 1, 2), were prepared by reacting 2 equiv. of the Grubbs first-generation catalyst (PCy 3) 2C1 2Ru (CHPh)) with 1 equiv. of the appropriate polyene (1,3,5-hexatriene for n = 1 and 1,3,5,7-octatetraene for n = 2). Use of excess hexatriene led to the formation of the monoruthenium complex (PCy 3) 2C1 2Ru CHCH CHCH CH 2. The mono- and di-ruthenium complexes exhibited marked differences in their spectroscopic and electrochemical properties, in addition to their Z– E isomerization rates. Nucleophilic attack of PCy 3 on the end CH 2 of the mono complex was observed, leading to both isomerization and phosphonium products. Extending the OMMI strategy to the second-generation catalyst was also done, despite the reduced initiation rate. The more reactive catalyst (H 2IMes)RuCl 2( CHPh)(3-bromopyridine) 2 allowed for ruthenium incorporation into polyacetylene, leading to the formation of polymers and oligomers with high ruthenium content.

Copolymerization of Silyl Vinyl Ethers with Olefins by (α-diimine)PdR+

This paper reports that (alpha-diimine)PdMe+ catalyzes the copolymerization of olefins and silyl vinyl ethers. The reactions of (alpha-diimine)PdMe+ (alpha-diimine = (2,6-iPr2-C6H3)N=CMe-CMe=N(2,6-iPr2-C6H3)) with excess vinyl ethers CH2=CHOR (1a-d: R = tBu (a), SiMe3 (b), SiPh3 (c), Ph (d)) in CH2Cl2 at 20 degrees C afford polymers for 1a (rapidly) and 1b (slowly) but not for 1c or 1d. The structures of poly(1a,b) indicate a cationic polymerization mechanism. The reaction of (alpha-diimine)PdMe+ with 1-2 equiv of 1a-d proceeds by sequential C=C pi-complexation to form (alpha-diimine)PdMe(CH2=CHOR)+ (2a-d), 1,2 insertion to form (alpha-diimine)Pd(CH2CHMeOR)+ (3a-d), reversible isomerization to (alpha-diimine)Pd(CMe2OR)+ (4a-d), beta-OR elimination to generate (alpha-diimine)Pd(OR)(CH2=CHMe)+ (not observed), and allylic C-H activation to yield (alpha-diimine)Pd(eta3-C3H5)+ (5) and ROH. The reaction of (alpha-diimine)PdMe+ with 1-hexene/1b and 1-hexene/1c mixtures in CH2Cl2 at 20 degrees C affords copolymers containing up to 20 mol % silyl vinyl ether. The copolymers were purified to be free of any -[CH2CHOSiR3]n- homopolymer. The copolymer structures are similar to that of homopoly(1-hexene) generated under the same conditions. The major comonomer units are CH3CH(OSiR3)CH2-, CH2(OSiR3)CH2- and -CH2CH(OSiR3)CH2-. The 1-hexene/CH2=CHOSiR3 copolymers can be desilylated to give 1-hexene/CH2=CHOH copolymers. The results of control experiments argue against cationic and radical mechanisms for the copolymerization, and an insertion/chain-walking mechanism is proposed.

Rate constants for the reaction of OH radicals with n-propyl, n-butyl, iso-butyl and tert-butyl vinyl ethers

Rate constants for the reaction of OH radicals with n-propyl vinyl ether (PVE, CH 3CH 2CH 2OCH CH 2), n-butyl vinyl ether (BVE, CH 3CH 2CH 2CH 2OCH CH 2), iso-butyl vinyl ether (IBVE, (CH 3) 2CHCH 2OCH CH 2) and tert-butyl vinyl ether (TBVE, (CH 3) 3COCH CH 2), have been measured in the temperature and pressure ranges 232–373 K and 30–300 Torr using the pulsed laser photolysis-laser-induced fluorescence method, and at 298 K and 760 Torr using the relative method. The obtained results are k 1=(9.3±0.6)×10 −12 exp[(708±20)/ T], k 2=(1.5±0.2)×10 −11 exp[(572±42)/ T], k 3=(1.6±0.1)×10 −11 exp[(567±20)/ T], k 4=(1.7±0.2)×10 −11 exp[(549±25)/ T] cm 3 molecule −1 s −1. The values at 298 K are k 1=(1.0±0.1)×10 −10, k 2=(1.0±0.1)×10 −10, k 3=(1.1±0.1)×10 −10, k 4=(1.1±0.1)×10 −10 cm 3 molecule −1 s −1. The deduced tropospheric lifetimes of these ethers for reaction with OH are of the order of 1 h and they are comparable to those for reaction with ozone.

New Family of Trisiloxane Surfactants

Abstract The interfacial properties of a series of novel aqueous trisiloxane of the general formula Me3SiOSiMeROSiMe3 [R=(CH2)3N(CH2CH(OH)CH2(OCH2CH2)nOCH3)2 n=1,2] were studied. The physicochemical parameters of these trisiloxane were discussed. These surfactants reduced the equilibrium surface tension of water to a minimum value of approximate 21∼22 mN/m at concentration levels of 10−4 mol·L−1.

Analytical pyrolysis of lignin: Products stemming from β-5 substructures

This paper addresses the behavior of β-5 substructures in analytical pyrolysis of lignin. Five phenolic 2-arylcoumarans containing a β-5 linkage, dehydrodiconiferyl alcohol ( I) and II– V, and diazomethane-methylated I ( Im), were pyrolyzed at 500 °C for 4 s. The products were analyzed by gas chromatography and gas chromatography/mass spectrometry. The major products of I– IV and Im were 4-methylguaiacol ( 4) and 1,2-dimethoxy-4-methylbenzene ( 4m), respectively, stemming from the A moiety of the 2-arylcoumarans. 2-Arylcoumarans I– IV having the ring B with a CH CHCH 2OH or CH CHCHO side chain provided 4 in a larger yield than dehydrodiisoeugenol ( V) having the ring B with a CH CHCH 3 side chain; the yields of 4 were ∼6.6, 5.7–4.6, and 0.9 mol% from I, II– IV and V, respectively. Characterization of the dimeric products of I showed the α-aryl ether opened-dimers with the hydrogenated Cα–Cβ bond being the precursors of 4. Based on these results, guaiacyl and syringyl β-5 substructures were proposed as potential pyrolytic origins for 4 and 3,5-dimethoxy-4-methylphenol in analytical pyrolysis of soft- and hardwood lignins.

The role of the functional group in double bond migration in allylic systems catalysed by ruthenium hydride complexes

The influence of functional group Q on course and rate of the reaction of 3-B, 3-C, 3-Si, 3-Sn, 3-N, 3-P, 3-O, 3-S, 3-Se, 3-Cl, 3-Br, and 3-I substituted allylic systems of type Q–CH 2CH CH 2 with hydride ruthenium complexes (primarily [RuClH(CO)(PPh 3) 3]) has been researched. It has been proved that the basic factors for the reaction course are: coordinating properties of Q group, C–Q bond strength, tendency of Q-allyl to oxidative addition to [Ru], and steric effect of Q. When Q has weak (Q = alkyl, aryl, RO, ArO, …) or medium (Q = Ph 3CS, RC(O)NR, …) complexing power, migration of the double bond in Q-allyl occurs. Most often, mixtures of ( E)- and ( Z)-1-(propenyl) derivatives are the isomerisation products. Sometimes, mainly or solely products with E configuration (e.g. Q = ArNCOMe, PhSO 2) have been formed, and in other cases—mainly or solely products with Z configuration (e.g. Q = Ph 3CS, Ph 3CO, MeCONH). Basing on mechanistic investigations and quantum calculations, it has been shown that E-selectivity of double bond migration results mainly from specific coordination effects, but also from steric effects (of Q and ligands). On the other hand, Z-selectivity of isomerisation results from steric effects. It has been also proved that when Q has strong complexing power (Q = EtS, PhS, PhS(O), Me 2N, PhCH N, allyl 2P, …), the double bond migration is not observed at all. Catalytically inert ruthenium complexes are then formed in the reaction mixture. Some of them have been isolated and their structures have been defined. The bond migration has not been observed also when allylic system has been undergoing an oxidative addition to [Ru] (e.g. Q = Cl, Br, I). A similar influence of Q on reactions between Q-allyl and [Ru]–H groups has also been observed in reactions of Q-allyl with [RuH 2(CO)(PPh 3) 3] and hydride complexes generated in situ (e.g. [RuCl 2(PPh 3) 3] + Li[AlH 4], {[RuCl 2(1,5-COD)] x } + CaH 2). Solvent effects in isomerisation reactions of allyl phenyl ether and allylbenzene or safrole have been researched as well. A very good, quantitative consistence of solvent effect (its complexing power) on the isomerisation with the observed effect of Q group has been shown. The requirements for Q–CH 2CH CH 2, enabling its isomerisation to Q–CH CHCH 3, have been defined.

Preparation and identification of functional organic monolayers on Si wafer surfaces

Monolayers of organic adsorbates formed on Si wafers are prospective materials for nanometer-scale fabrication, chemical functionalization and biochemical analysis. We have been studying the methods of preparing organic monolayers by activating hydrogen-terminated H:Si(1 1 1). In this report, the method of photo-assisted adsorption of allylamine (CH2CH–CH2–NH2) and 1-butene (CH2CH–CH2–CH3) onto H:Si(1 1 1) is described. The adsorbates were identified by high-resolution electron energy loss spectroscopy and Auger electron spectroscopy. The functional group, NH2 in allylamine, was observed reserved in the adlayer. Mixed adlayers of allylamine and 1-butene, which is practically favorable, were also prepared.

Identification of C5Hx Isomers in Fuel-Rich Flames by Photoionization Mass Spectrometry and Electronic Structure Calculations

The isomeric composition of C(5)H(x) (x = 2-6, 8) flame species is analyzed for rich flames fueled by allene, propyne, cyclopentene, or benzene. Different isomers are identified by their known ionization energies and/or by comparison of the observed photoionization efficiencies with theoretical simulations based on calculated ionization energies and Franck-Condon factors. The experiments combine flame-sampling molecular-beam mass spectrometry with photoionization by tunable vacuum-UV synchrotron radiation. The theoretical simulations employ the rovibrational properties obtained with B3LYP/6-311++G(d,p) density functional theory and electronic energies obtained from QCISD(T) electronic structure calculations extrapolated to the complete basis set limit. For C(5)H(3), the comparison reveals the presence of both the H(2)CCCCCH (i-C(5)H(3)) and the HCCCHCCH (n-C(5)H(3)) isomer. The simulations also suggest a modest amount of cyclo-CCHCHCCH-, which is consistent with a minor signal for C(5)H(2) that is apparently due to cyclo-CCHCCCH-. For C(5)H(4), contributions from the CH(2)CCCCH(2) (1,2,3,4-pentatetraene), CH(2)CCHCCH, and CH(3)CCCCH (1,3-pentadiyne) isomers are evident, as is some contribution from CHCCH(2)CCH (1,4-pentadiyne) in the cyclopentene and benzene flames. Signal at m/z = 65 originates mainly from the cyclopentadienyl radical. For C(5)H(6), contributions from cyclopentadiene, CH(3)CCCHCH(2), CH(3)CHCHCCH, and CH(2)CHCH(2)CCH are observed. No signal is observed for C(5)H(7) species. Cyclopentene, CH(2)CHCHCHCH(3) (1,3-pentadiene), CH(3)CCCH(2)CH(3) (2-pentyne), and CH(2)CHCH(2)CHCH(2) (1,4-pentadiene) contribute to the signal at m/z = 68. Newly derived ionization energies for i- and n-C(5)H(3) (8.20 +/- 0.05 and 8.31 +/- 0.05 eV, respectively), CH(2)CCHCCH (9.22 +/- 0.05 eV), and CH(2)CHCH(2)CCH (9.95 +/- 0.05 eV) are within the error bars of the QCISD(T) calculations. The combustion chemistry of the observed C(5)H(x) intermediates and the impact on flame chemistry models are discussed.

Investigation of allyl‐capped carbosilane dendrimers used as crosslinker for silicone rubber

AbstractHigh‐temperature vulcanized silicone rubber was prepared by using allyl‐capped carbosilane dendrimers, in which the core molecules were Si(CH2CHCH2)4 and Ph2Si(CH2CHCH2)2 as crosslinker and nanoscale reinforcing filler, respectively. Allyl‐capped carbosilane dendrimers improved the mechanical properties of silicone rubber. The optimum tensile strength and tear strength were 9.6 MPa and 31.0 kN/m, respectively, when using SiGn(allyl)m as the crosslinker and 10.1 MPa and 32.0 kN/m, respectively, when using Ph2SiGn(allyl)m as the crosslinker. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1772–1775, 2006

In situFourier transform infrared characterization of the plasma chemistry in varying pulsed cycles of a 1,3-butadiene discharge in an inductively coupled gaseous electronics conference cell

In situ Fourier transform infrared spectroscopy is used to characterize the plasma chemistry of pulsed 1,3-butadiene (H2CCHCHCH2) discharges subject to varying percentages of the duty cycle in a gaseous electronics conference cell. Variations in densities associated with the major observed spectral bands are closely examined as a function of duty cycle. The possible dissociation mechanisms responsible for all observed vibrations are investigated. For example, the data show that about 44% of CH2 stretching vibrations during continuous wave biasing are due to free CH2 daughter species, while only bound CH2 are observed during pulsing of the discharge. This indicates that only the π bond of the CC bond is cleaved during pulsed mode operation, with the σ being cleaved during cw biasing.

An FT-IR study of the isomerization of 1-butoxy radicals under atmospheric conditions

Relative rate-studies of the reactions of 1-butoxy radicals have been carried out using a 47 L static reactor with detection of end products by FT-IR spectroscopy. Experiments were performed at 700 torr total pressure and over the temperature range 253–295 K. The chemistry of 1-butoxy is characterized by a competition between reaction with oxygen CH 3CH 2CH 2CH 2O + O 2 → n-C 3H 7CHO + HO 2 (R2), which yields butanal and isomerization CH 3CH 2CH 2CH 2O → CH 2CH 2CH 2CH 2OH (R3), to form a hydroxylated carbonyl-product. A reference spectrum attributed to the product of 1-butoxy isomerization was obtained and used to determine the competition between 1-butoxy isomerization versus reaction with oxygen. The results indicate that isomerization is the dominant fate of 1-butoxy radicals at ambient temperature and pressure and that its importance decreases with decreasing temperature. The rate-coefficient ratio k 3/ k 2 (molecule cm −3) = 5.5 × 10 23 exp[(−25.1 ± 0.9 kJmol −1)/RT] was obtained. This agrees with other estimates based on methods without monitoring of the isomerization product.

Microwave spectrum and conformation of n-propyltrifluorosilane

The conformational properties of gaseous n-propyltrifluorosilane (CH 3CH 2CH 2SiF 3) have been investigated by microwave spectroscopy and high-level quantum chemical calculations. The microwave spectrum was investigated in the 20–62 GHz spectral range at a temperature of −78 °C. The spectra of the ground vibrational state and three vibrationally excited states of one conformer having an antiperiplanar conformation of the C–C–C–Si chain of atoms were assigned. No evidence for the existence of the synclinal ( gauche) conformer was seen in the microwave spectrum. It is concluded that the synclinal form is at least 3.5 kJ/mol less stable than the antiperiplanar conformer in the gas phase. Density functional theory calculations have been performed for the system mainly to predict the effects of centrifugal distortion. The G3 quantum chemical method has been used to test the ability of this method to predict the energy difference between the synclinal and antiperiplanar conformers.

Ferrihydrite gels derived in the Fe(NO 3) 3 · 9H 2O–C 2H 5OH–CH 3CHCH 2O ternary system

A study of gel formation in iron(III) nitrate nonahydrate (Fe(NO 3) 3 · 9H 2O)–ethanol (C 2H 5OH)–1,2-epoxypropane (propylene oxide (CH 3CHCH 2O)) ternary system has been performed. The phase boundaries for existing ferrihydrite gels were determined. It was shown that this ternary system has two different types of ferrihydrite gel phases. The dominant chemical bonds of these phases were investigated by Fourier transform infrared spectroscopy (FTIR). Both ferrihydrite phases transform to amorphous α-FeOOH phase after 6 h annealing at T = 300 °C. The temperatures of crystallization from these amorphous α-FeOOH phases to α-Fe 2O 3 phases were found.

Two new layered lead(II) diphosphonates with 1,3,5-benzenetricarboxylate ligands as an intercalated species or a multidentate metal linker

Hydrothermal reactions of lead(II) carbonate with 1,3,5-benzenetricarboxylic acid (H 3BTC) and butylimino-bis(methylenephosphonic acid) (CH 3CH 2CH 2CH 2N(CH 2PO 3H 2) 2, H 4L 1) or lead(II) acetate with H 3BTC and isobutylimino-bis(methylenephosphonic acid) (Me 2CHCH 2N(CH 2PO 3H 2) 2, H 4L 2) afforded two novel lead(II) carboxylate phosphonate hybrids, namely, Pb 5(HL 1) 2(L 1)·H 3BTC 1 and Pb 4(BTC)(L 2)(CH 3CO 2)(H 2O) 2·1.5H 2O 2. The structure of compound 1 contains a <002> lead(II) diphosphonate hybrid layer formed by Pb(II) ions interconnected by HL 1 and L 1 anions. In compound 2, the interconnection of Pb(II) ions through bridging diphosphonate L 2 anions lead to the formation of the <200> lead(II) diphosphonate 2D layer. In compound 1, the 1,3,5-benzenetricarboxylic acid acts as an intercalated species whereas in compound 2, the 1,3,5-benzenetricarboxylate anion adopts a hexadentate chelating and bridging coordination mode.

Ring opening fragmentations of ionized cyclohexylamines

Fragmentations of cyclohexylamine and dicyclohexylamine ions were studied using FTMS. Fragmentations of the molecular ions were initiated by the ring opening of cyclohexyl group to form the distonic molecular ions. The structures of fragment ions were determined by rearranging the distonic molecular ion. The major fragment ions were found to be X HC NH 2 + and c-C 6H 11 HN CH X + for cyclohexylamine and dicyclohexylamine, respectively, where X is CH CH 2 and CH 2CH CH 2. The formations of CH 2 CHCH NH 2 + and c-C 6H 11 HN CHCH CH 2 + for cyclohexylamine and dicyclohexylamine, respectively, were more favorable than the formations of the other fragment ions because of the easy rearrangement of the distonic molecular ions. Experimental and calculation results suggest that the formations of fragment ions with acyclic structures were more favorable than those with cyclic ones. It was also found that for dicyclohexylamine the formations of fragment ions with cyclohexyl group, such as c-C 6H 11 HN CH X + were more favorable than those without cyclohexyl group, such as X HC NH 2 +.

Ethylene and ethylene/1-hexene (co)polymerizations with 2,5-dimethylcyclopentadienyl ansa-titanocene and zirconocene complexes

C1-bridged 2,5-dimethylcylcopentadienyl ansa-titanocene complexes, [Me(H)C(η 5-C 5H 4)(η 5-2,5-Me 2C 5H 2)]TiCl 2 ( 4) and [(CH 3CH 2CH 2)(H)C(η 5-C 5H 4)(η 5-2,5-Me 2C 5H 2)]TiCl 2 ( 5) and a dinuclear titanium complex, Me 2Si[(η 5-2,5-Me 2C 5H 2)Ti{O(2,6- iPr 2C 6H 3)}Cl 2] ( 7) have been prepared. The solid state structure of 4 has been determined by X-ray crystallography. Ethylene polymerization reactivities of 4, 5, 7 and the structurally related ansa-zirconocene complexes, [Me(H)C(η 5-C 5H 4)(η 5-2,5-Me 2C 5H 2)]ZrCl 2 ( 1), [(Me)(H)C(η 5-2,5-Me 2C 5H 2) 2]ZrCl 2 ( 2) and [Me 2Si(η 5-2,5-Me 2C 5H 2) 2]ZrCl 2 ( 3) are investigated after activation with MAO. Interestingly, the ansa-titanocene complexes 4 and 5 show much higher activity than the ansa-zirconocene complexes 1 and 2, and the molecular weights of the polymers obtained by the titanocene complexes are significantly higher ( M w, ∼800 000) than those of polymers obtained by the zirconocene complexes ( M w, below 200 000). The Me 2Si-bridged complex 3 shows extremely high activity for ethylene polymerization and the activity (290 × 10 6 g/mol h) is 15 times higher than that of [Me 2Si(Me 4C 5)(N tBu)]TiCl 2 (CGC) under the same conditions. Ethylene/1-hexene copolymerization reactivities of 3 and 5 have been studied. The complexes are inferior to CGC in terms of comonomer incorporation ability.