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Reduction of ansa-titanocene dichlorides [X(η5-C5H4)2TiCl2] (X = SiMe2 (1) and CMe2 (2)) in tetrahydrofuran (THF) by preactivated magnesium in the presence of bis(trimethylsilyl)acetylene (BTMSA) yielded complexes [X(η5-C5H4)2Ti(η2-BTMSA)] (X = SiMe2 (3) and CMe2 (4)). The prolonged action of excess magnesium and BTMSA resulted in the formation of ansa-titanium-magnesium complexes [μ-X{(η5-C5H4)Ti(η2-SiMe3C≡CSiMe3)2}{(η5-C5H4)Mg(THF)}] (X = SiMe2 (5) and CMe2 (6)), which had their metals bounded via the ansa-ligand and ionic bonding between magnesium and the BTMSA ligands. Compounds 5 and 6 easily isomerized to 5a and 6a through rotation of their {(C5H4)Mg(THF)} moiety around the ansa- X–C bond. This rotation canceled the interaction of magnesium with the BTMSA ligands, which resulted in a large high-field shift of acetylenic carbon resonances. The geometry of both structures optimized by Density Functional Theory (DFT) computations together with the good correlation of computed magnetic shieldings and experimental 13C NMR shifts of 5 and its isomer 5a approved the above isomerization. The simultaneous ionic bonding of Mg2+ to the cyclopentadienyl ligand, which is η5-coordinated to the {Ti(η2-BTMSA)2} moiety in 5a got also confirmed by computational results. Reduction by magnesium was used to obtain Ti(III) dimers of ansa-titanocene acetylides [{X(η5-C5H4)2Ti (μ-η1:η2-C≡CSiMe3)}2] (X = SiMe2 (7) and X = CMe2 (8)) via redox splitting of 1,4-bis(trimethylsilyl)buta-1,3-diyne (BSD) by transient Ti(II) titanocene. The thermally stable Ti(II) compounds 3 and 4 were also shown to react with BSD yielding respectively 7 and 8. The reduction of 1 and 2 with magnesium in THF afforded Ti(III) monochloride dimers [{ansa-X(η5-C5H4)2Ti(μ-Cl)}2] (X = SiMe2 (10); CMe2 (11)), which in contrast to the non-ansa dimer [(η5-C5H5)2Ti(μ-Cl)}2] were silent in toluene glass EPR spectra. No evidence of obtaining quadruply bridged dititanium complexes capped with the ansa-ligands was encountered among crystal structures of 7–11, even though the total energy of optimized molecules 7 and 10 and their capped congeners differed by more than 45 kJ/mol, favouring the capped isomers in both cases.

The singly tucked-in titanocene [(η5-C5Me5)TiIII{η5:η1-C5Me4(CH2)}] (1) reacted with one equivalent of 1-tert-butylpropyne to yield the propenyl-tethered regioisomer [(η5-C5Me5)Ti(η5:η1-C5Me4CH2C(t-Bu) = κCMe)] (3). The exclusive formation of paramagnetic 3 was proved experimentally and steric reasons were clarified by DFT calculation of transition state which involves both π-systems on the alkyne for bonding interaction with the metal and with sp2 carbon atom of exomethylene group of 1. The obtained compound 3 is by 40 kJ/mol lower in energy than its hypothetical isomer having t-Bu group on Cα of the tether.

A series of hybrid catalysts of the type, support-ligand-Pd (Sup-L-Pd), has been prepared and characterized and their activity in C-C coupling (Suzuki-Miyaura), selective oxidations and dehalogenation‑hydrogenation processes studied. The hybrid Sup-L-Pd catalysts are made up of (i) different nano-sized supports, such as halloysite nanotubes (HNTs), SiO2, Al2O3 and mesoporous silica nanoparticles (MSNs), (ii) ligands (L) with N-, S- or P-donor atoms and (iii) different quantities of Pd. Several combinations of support, ligand, and Pd quantity were used to determine the optimal composition of the nanostructured systems for the proposed catalytic reactions. The system based on HNTs functionalized with 2-(diphenylphosphino)ethyltriethoxysilane (PPETS) and 0.25% wt. Pd (HNTs-PPETS-Pd0.25) showed the most promising catalytic behaviour with multifunctional applicability in different catalytic processes and potential reusability. This catalyst gave turnover frequency (TOF) values of up to 155 h−1 in catalytic Suzuki-Miyaura C-C coupling reactions, up to 43 h−1 in selective catalytic oxidations and up to 65 h−1 in dehalogenation‑hydrogenation processes of halogenated aromatic compounds. Furthermore, the system demonstrated in the different catalytic reactions, good recyclability after consecutive cycles with low Pd leaching.

Scandium and yttrium half-sandwich chloride complexes (η5-C5Me4R)ScCl2(THF)2 R = CH2Ph (3) or SiMe2CH2CH2Ph (5) and (η5-C5Me4R)YCl2(THF)2 R = CH2Ph (4) or SiMe2CH2CH2Ph (6) were prepared by metathetic reactions of the corresponding substituted lithium or potassium cyclopentadienides with scandium or yttrium trichloride. A mutual comparison of the determined solid state structures of 4 and 5 revealed the tetranuclear character in the case of scandium complex containing C5Me4SiMe2CH2CH2Ph ligand, while a formation of the trinuclear ate-complex 4 incorporating lithium was observed for the combination of yttrium and the benzyl substituted tetramethyl cyclopentadienyl. Moreover, the steric effect of addition of another differently substituted cyclopentadienyl ring into the molecule was evaluated.

Sunlight photolysis of the triplet state (S = 1) dititanium compound 1 induced its rearrangement to diamagnetic 2, which was a molecule containing two hydrogens less. The cage structure of 2 was determined by single crystal X-ray diffraction and was corroborated fully by 1H and 13C NMR spectra that identified three simple bridging moieties — a hydrogen atom, a methine carbon and a methylene carbon. Its extremely short Ti−Ti distance 2.7537(7) A causes a strong distortion of the bridging fulvalene ligand, which becomes η5- bonded to one Ti(IV) and connected by two σ-bonds from nearest carbon atoms of its other ring to the other Ti(IV) of 2. Other photolytical byproducts in very minor amounts were also isolated, which differed from 2 by the absence of one bridging moiety: compound 4 lacked the methine group and compound 5 had no bridging hydrogen. In the latter cases, the Ti−Ti distance fell in the range 3.2077(8) – 3.5543(12) A and the fulvalene ligand was coordinated in the common µ-η5: η5-mode to both titanium atoms. The octamethylfulvalene ligands in 4 and 5 had their ring planes rotated mutually by about 40° in order to relieve the steric hindrance between their methyl groups. The thermally robust µ-oxo complex 3 obtained from reacting 2 with water showed a very similar structure.

This review is focused on the chemistry of titanocene sulfide compounds. The linking element for all compounds discussed in this review is the presence of a bent titanocene fragment consisting of two aromatic cyclopentadienyl rings and one electron deficient central titanium atom coordinated between them. Several types of sulfur ligands bonding to titanocene fragment, such as hydrosulfide, sulfide or thiolate are described, as well as the various types of sulfur ligand functions in titanocene complexes have been observed. The titanocene sulfide chemistry is more than fifty years old, but since it is still evolving, it offers a plethora of surprises and challenges.

Solutions of permethylcyclopentadienyl-tethered titanium(IV) chlorides incorporating one double bond in their tethers were exposed in glass vessels to sunlight, which triggered their photolytical reactions providing mixtures of products. Although the formation of several different products was apparent from 1H NMR spectra, only a single product could be identified in the crude reaction mixtures. This product was dicyclopentadiene [C10Me10], which arose from the recombination of the generally photodissociated C5Me5 radical. Amongst products that contained titanium, three complexes (3a, 3b and 4a) could be isolated after employing fractional crystallization and these complexes were characterized. The mechanism of 3a formation involves photodissociation of one η5-C5Me5 ligand from the parent complex, complemented by chlorine abstraction from another reactant molecule. Complexes 3b and 4a become formed via tether rearrangement, which starts with dissociating the tether Ti–C bond and is followed by rotating the tether, reattaching it subsequently through its available radical terminus.

The permethylcyclopentadienyl diphenylsilylene-bridged titanium constrained geometry complex [TiCl2{η5-C5Me4(SiPh2NCMe3-κN)}] (2) was synthesised following the common synthetic route and subsequently characterised by spectral analyses and by single-crystal X-ray diffraction. The comparison of its solid-state structure with that of the parent dimethylsilylene CGC complex [TiCl2{η5-C5Me4(SiMe2NCMe3-κN)}] (1) revealed only negligible geometry differences between their cyclopentadienyl centroid-Ti-N-Si skeletons. A significantly different positioning was however observed for the amine tBu substituent of the DFT-optimised methyl-substituted cationic catalytical species (1a, 2a), which are supposed to be generated from 1 and 2 in the presence of methylaluminoxane (MMAO). A lower ethylene polymerisation activity of 2-MMAO system compared to that of 1-MMAO is compatible with the higher steric congestion at the metallic centre due to the tBu ligand becoming rotated more into the open space in 2b. This arrangement aggravates monomer access throughout the catalytical process and decreases the coordination unsaturation of the central atom through the formation of auxiliary agostic interaction.

Several approaches to the intramolecular activation of a pendant nitrile group attached to the group 4 metallocene framework have been probed starting with the complexes [(η5-C5Me5)(η5-C5H4CMe2CH2CN)MCl2] (M = Zr, 1; M = Ti, 2). A reduction induced activation of the nitrile moiety was effected for the Zr derivative either by the treatment with Mg, or by the alkylation using t-BuMgCl followed by spontaneous reductive elimination. In both cases, the reactions finally yielded the zirconocene cyano complex with an intramolecularly tethered alkyl substituent, [(η5-C5Me5)(η5:κC1-C5H4CMe2CH2)Zr(CN-κC)] (4), which resulted from the C–C bond cleavage in the pendant arm. Furthermore, a by-product was isolated which contained two zirconocene fragments bridged through a MgCl2 moiety featuring a rare σ,π-bridging mode of the pendant nitrile group, [{(η5-C5Me5)(μ-η5:η2:κN-C5H4CMe2CH2CN)(μ-Cl)Zr}2Mg] (3). The solid-state structure of 3 was elucidated and this compound together with the product 4 and the tentative intermediate [{(η5-C5Me5)(η5:η2-C5H4CMe2CH2CN)Zr] (3′) were also investigated by DFT calculations. In another approach, 1 and 2 were treated with Li[B(C6F5)4]∙Et2O to generate cationic complexes. Accidental hydrolysis of these species afforded complexes bearing an intramolecularly tethered amide group [{(η5-C5Me5)(η5:κO-C5H4CMe2CH2CONH2)M], of which the Ti derivative (6) was isolated and structurally characterised. Finally, reaction of the zirconocene dimethyl complex [(η5-C5Me5)(η5-C5H4CMe2CH2CN)ZrMe2] (8) with (Ph3C)[B(C6F5)4] was studied.

A series of tetramethyl-(Cp′) and pentamethylcyclopentadienyl (Cp*) metal complexes (η5-C5Me4R)ZrCl2LCO (R = H(1), Me(2)) and (η5-C5Me4R)HfCl2LCO (R = H(3), Me(4)) where LCO is a bifunctional β-diketiminate ligand [2-(MeO)–C6H4)]NC(Me)CHC(Me)N[2-(MeO)–C6H4)] (LCO) were prepared from corresponding tetramethyl- and (pentamethylcyclopentadienyl)metal trichlorides and the lithium precursor LiLCO. All complexes were characterized by their melting point, elemental analysis, 1H and 13C NMR spectroscopy, IR spectroscopy. In addition their solid-state structures were determined by X-ray diffraction techniques. In all cases, a pseudo-tetragonal pyramidal coordination environment of the metal centre with cyclopentadienyl ligand on the top and nearly isobidentately bonded nitrogen atoms of the chelating LCO ligand in an open η5-fashion was observed. The oxygen atoms positioned at the diketiminate periphery remained uncoordinated to transition metal in the solid phase as well as in solution. Besides the desired compounds, two hafnium complexes bearing either 2-methoxyaniline or 2-methoxyanilide ligands were isolated and structurally characterized as minor decomposition and dismutation products of 3 and 4, respectively. Complexes containing the β-diketiminate ligand as well as its precursors were tested for catalytic activity in the polymerization of ethylene using different activators (MAO, MMAO and AliBu3/(Ph3C)+ [B(C6F5)4]−). Among the new complexes, the best activity as high as 340 kgPE (molMhbar)−1 was achieved with 1/AliBu3/(Ph3C)+ [B(C6F5)4]− system. In attempts to clarify the activation process of group 4 metal-based precatalysts, the synthesis and NMR studies of the aluminium β-diketiminate complex Al(iBu)2LCO were also carried out.

Cyclopentadienyl-arene complexes [(η 5 -C 5 H 4 CMe 2 Ph)Ti(O i Pr) 3 ] ( 2 ) and [(η 5 -C 5 H 4 CMePh(CH 2 CH 2 CH CH 2 ))Ti(O i Pr) 3 ] ( 3 ), where Me = methyl, Ph = phenyl, i Pr = isopropyl, were prepared and characterized by spectroscopic methods (NMR, IR, ESI-MS) and elemental analysis (EA). 2 was anchored on two siliceous supports SiO 2 and SBA-15 (pre-treated at 200, 700, and 800 °C) predominantly by a covalent Ti–O–Si bond. 3 was grafted onto SiMe 2 H-modified silica by hydrosilylation at 25 and 90 °C. 3 was attached by a flexible covalent tether –(CH 2 ) 4 SiMe 2 – from the ligand to the silica surface. Models for immobilized surface species [(η 5 -C 5 H 4 CMe 2 Ph)Ti(POSS-O 3 )] ( 4 ) (where POSS-O 3 = open silsesquioxane) and [(η 5 -C 5 H 4 {CMePh(CH 2 ) 4 SiMe 2 OSi(O t Bu) 3 })Ti(O i Pr) 3 ] ( 6 ) (where t Bu = tertiary butyl) were also prepared and characterized. Comparison of homogenous catalysts 1 – 4 and 6 /MAO (where 1 = [(η 5 -C 5 H 4 CMe 2 Ph)TiCl 3 ]; MAO = methylaluminoxane) for ethylene trimerization showed that activity was influenced mainly by the σ-ligand. The alkyl (R) substituent of CMePhR had a negligible effect. Activity of the heterogeneous 2 /support/MAO catalyst increased with increasing pre-treatment temperature (i.e. decreasing amounts of residual surface silanol groups). However, the leaching test showed, that a significant activity could be attributed to an active species leached from the support. We propose that an easy cleavage (methylation) of Ti–O–Si linkage by an excess of MAO would be the main origin of leaching. The inactivity of 3 /support/MAO towards ethylene trimerization was attributed to close contact between the catalytically-active species and the surface.

The Hoveyda–Grubbs type Zhan catalysts (ZC) and Grubbs second generation catalyst (GII) were immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions and phosphine linkers, respectively. Both hybrid catalysts proved to be highly active and selective in cardanol metathesis and cardanol cross-metathesis with ethene and cis -1,4-diacetoxy-2-butene (DAB). GII/SBA-15 was less active than ZC/SBA-15, however, Ru leaching was significantly lower for GII/SBA-15 (0.5%) than for ZC/SBA-15 (2.5%). In ethenolysis of cardanol, 3-(non-8-enyl)phenol was isolated as a major product. In cross-metathesis with DAB 9-(3-hydroxyphenyl)non-2-enyl acetate and non-2-enyl acetate were formed with high selectivity. Easy catalyst–product separation and low Ru leaching provide the products (applicable as detergent precursors and fragrance and flavor agents) free from the catalyst residue.

New titanocene dihydrosulfide compounds [(C 5 Me 4 CH 2 Ph) 2 Ti(SH) 2 ] ( 6 ) and [(C 5 Me 4 t -Bu) 2 Ti(SH) 2 ] ( 7 ) were obtained by addition of hydrogen sulfide to the corresponding doubly tucked-in titanocenes, and titanocene hydrosulfide compounds [(C 5 Me 4 CH 2 Ph) 2 TiSH] ( 8 ) and [(C 5 Me 4 t -Bu) 2 TiSH] ( 9 ) by H 2 S-induced protonolysis of σ-Ti–C bonds in [(η 5 -C 5 Me 4 CH 2 Ph)Ti(III)(η 5 :η 1 -C 5 Me 4 CH 2 - o -C 6 H 4 )] and [(C 5 Me 4 t -Bu)Ti(III)(η 5 :η 1 -C 5 Me 4 CMe 2 CH 2 )], respectively. The crystal structures of 6 , 8 , and 9 and electronic absorption spectra of 6 – 9 in hexane solution highly resemble those of corresponding [Cp* 2 Ti(SH) 2 ] ( 1 ) and [Cp* 2 TiSH] ( 2 ), however, compounds 6 and 7 strongly differ in their sensitivity to sunlight mutually and with respect to 1 . The sunlight photolysis of 6 in toluene proceeded similarly to the process described previously for 1 except that about three times longer exposition (300 h) was required to obtain the cyclopentadienyltitanium sulfide cage cluster [{(C 5 Me 4 CH 2 Ph)Ti} 4 S 6 ] ( 10 ) in 48% yield. In contrast, compound 7 photo-decomposed very efficiently to give compound 9 as the only isolated titanium-containing product in 87% yield. The formation of 10 can be accounted for the redox elimination of the cyclopentadiene followed by elimination of hydrogen sulfide in intramolecular condensation reaction whereas the formation of 9 requires the dissociation of SH radicals. Both the processes were recognized by Rosenthal and Beweries to concur in photodecomposition of [Cp* 2 Ti(OH) 2 ].

The previously known complexes {[}Ti\{(Me2CMe2C)(eta(5)-C5H4)(2)\}Cl-2] (1), {[}Ti\{Me2C(eta(5)-C5H4)(2)\}Cl-2] (2), {[}Ti \{Me2Si(eta(5)-C5H4)(2)\}Cl-2] (4), {[}Ti\{MePhSi(eta(5)-C5H4)(2)\}Cl-2] (5) and {[}Ti\{MePhSi(eta(5)-C5Me4)(2)\}Cl-2] (6) have been prepared following reported procedures. The novel complex {[}Ti\{MePhC(eta(5)-C5H4)(2)\}Cl-2] (3) has been prepared and characterized. The cytotoxic activity of 1-6 has been tested after 72 h on melanoma A375 and B16, prostate cancer DU145 and LNCaP and colon cancer HCT116, SW620 and CT26CL25 cell lines observing a high cytotoxic activity of complexes 1 and 6 compared to the reference compound ({[}Ti(eta(5)-C5H5)(2)\}Cl-2]). 1 and 6 have also been tested against primary normal mouse keratinocytes and lung fibroblasts. While viability of both type of primary cells was significantly less affected by 1 in comparison to the reference compound {[}Ti(eta(5)-C5H5)(2)Cl-2], compound 6 was completely nontoxic for nonmalignant cells, indicating a potential selectivity of this compound towards cancer cell lines. In addition CFSE staining, cell cycle analysis, AnnexinV-FITC/PI staining, detection of caspase activity and mitochondrial potential showed that 1 and 6 were acting through inhibition of proliferation and subsequent induction of mitochondrial dependent apoptosis in colon cancer cell lines, HCT116 and SW620, which express low sensitivity to cisplatin. Compound 6 was found to be the leading drug in this group since it shows the fastest and most selective anticancer profile. (C) 2013 Elsevier B.V. All rights reserved. Ministerio de Educacion y Ciencia, Spain {[}CTQ-2011-24346, CTQ-2012-30762]; Ministry of Science and Technological Development of the Republic of Serbia {[}173013]; Grant Agency of the Czech Republic {[}P207/12/2368]

Molecular weight (MW) and configurational stabilities of a series of high- cis poly[(2,4-difluorophenyl)acetylene]s (PdFPhA, M w from 2.2 × 10 4 to 9.7 × 10 5 ) exposed to the atmosphere and diffuse daylight are reported. Polymers dissolved in THF- d 8 undergo simultaneous cis -to- trans isomerization and degradation under formation of a bimodal MW distribution. Degradation and isomerization rates are tightly connected and decrease with decreasing MW of the parent PdFPhAs. This finding may be interesting for the functional applications of substituted polyacetylenes. The partly aged PdFPhAs contain two separable fractions: higher-MW high- cis macromolecules containing a low amount of unpaired electrons and lower-MW deeply isomerized cis / trans macromolecules enriched in the unpaired electrons content. The difference in MW of these fractions reflects the various degradation rates of isomerized and high- cis macromolecules. Only a slow degradation without changes in the configurational structure proceeds if PdFPhA is allowed to age in the solid state. The suppression of the cis -to- trans isomerization reflects the suppression of motion of the polymer chains segments in the solid state.

The series of half-sandwich metallocenes of group 4 metals containing the C,N-chelating ligand (η5-C5Me4R)MCl2(C6H4CH2NMe2-κ2C,N) (M = Ti(1), Zr(2), Hf(3); R = Me(C), H(D)) were prepared by reacting the corresponding pentamethyl- and tetramethyl-substituted cyclopentadienylmetal trichlorides (η5-C5Me4R)MCl3 (M = Ti(1), Zr(2), Hf(3); R = Me(A), H(B)) with 2-[(dimethylamino)methyl]phenyl lithium. The X-ray crystal structure analysis of 1C–3C showed that they are isostructural/isomorphous containing two pairs of enantiomers in a P21/c unit cell, whereas crystals of 2D and 3D contained only one enantiomer in a P212121 unit cell. The presence of enantiomers in solution was resolved in variable temperature 1H NMR spectra below the temperature of signal coalescence. The transition state for interconversion of the two enantiomers for 1C was identified by DFT results to be on a 2nd order saddle point. Synthesis of η5-tetramethylcyclopentadienylmetal trichlorides 2B and 3B and their tetrameric and dimeric crystal structures are also reported.

Decamethylchromocene [Cr(η5-C5Me5)2] reacted with cyclopentadienyltitanium trichlorides [Ti(η5-C5H5-nMen)Cl3] (n = 0–5) in toluene to precipitate yellow finely crystalline ion pairs [Cr(η5-C5Me5)2]+[Ti(η5-C5H5-nMen)Cl3]− (1–6). Evidence for the chromocenium cation and titanate anions was obtained by paramagnetic 1H NMR spectra of 1–6 in CD2Cl2. The resonance of the cation was invariant at δ 6.9 ppm (Δν1/2 ~ 0.4 kHz) whereas resonances of the titanate anions were shifting in response to the number of methyl groups (δ 10.5–8.4 ppm (CpMe) and δ 26.6–39.0 ppm (CpH)). The presence of toluene of crystallization in 1–6 was observed by 1H NMR spectra, and in the crystal structure of 6. Crystallization of 6 from tetrahydrofuran afforded solvent-free crystals of 6A. In crystal structures of both 6 and 6A the [Ti(η5-C5Me5)Cl3]– titanate anion possessed shorter Ti–Cg distances and longer Ti–Cl bonds than the neutral species.

The efficient catalytic dehydropolymerization of phenylsilane by homogeneous zirconocene bissilanolates ([{(c-C5H9)7Si8O12O}2Zr(η5-C5H5)2] (1a); [{(c-C5H9)7Si8O12O}2Zr(η5-C5H4Bu)2] (1b) [{(c-C5H9)7Si7O9(OSiMe3)O2}Zr(η5-C5H5)2] (4); [{(Me3CO)3SiO}2Zr(η5-C5H5)2] (5)) and chlorosilanolates ([{(c-C5H9)7Si8O12O}ZrCl(η5-C5H4Bu)2] (2); ([{(c-C5H9)7Si7O9O3}Zr2Cl(η5-C5H5)4] (3a); [{(c-C5H9)7Si7O9O3}Zr2Cl(η5-C5H4Bu)4] (3b)) has been demonstrated. The presence of at least one silanol ligand in the zirconocene moiety was found essential for high catalytic performance. Solid state structure of complex 1a was determined by single crystal X-ray diffraction analysis. A series of nine zirconocene-siliceous catalysts were prepared by grafting of zirconocene moiety onto silica using three general methods: (a) reaction of [(η5-C5H5)2ZrCl2] with silica in the presence of NEt3; (b) reaction of [(η5-C5H5)2ZrMe2] with silica; (c) reaction of solely [(η5-C5H5)2ZrCl2] with silica. Supported catalysts were characterized by ICP-MS, FT-IR, TGA and selected examples by XPS analysis. Those catalysts prepared by method (a) and (b) were found efficient in the phenylsilane polymerization although a higher Zr/monomer ratio had to be used in comparison with homogeneous analogues. The low concentration of residual silanol groups in supported catalysts was found essential for their high catalytic performance. Advantageous reusability of supported catalysts was demonstrated using SiO2(500)/Cp2ZrCl2/NEt3(5.8). The catalytic performance was retained in three consecutive cycles producing polymers with almost identical properties.

The diphenyl zirconocene [(η5-C5H5){η5-C5H4CMe2(CH2)2CH CH2}ZrPh2] (2) was readily obtained from the corresponding zirconocene dichloride 1 and two equivalents of phenyllithium. Upon thermal treatment at 80 °C, complex 2 released benzene, with concomitant activation of the pendant double bond and formation of intramolecularly α-tethered zirconaindane [(η5-C5H5){η5,η1,η1-C5H4CMe2(CH2)2CHCH2C6H4}Zr] (3). Both Zr–C σ-bonds in 3 easily undergo nucleophilic reactions with two equivalents of HCl or one equivalent of Cl2PPh giving rise to zirconocene dichlorides with pendant phenyl group [(η5-C5H5){η5-C5H4CMe2(CH2)4Ph}ZrCl2] (4) or with 1-phenylphosphindolinyl moiety [(η5-C5H5){η5-C5H4CMe2(CH2)2cyclo-CHCH2C6H4P(Ph)}ZrCl2] (5), respectively.

The preparation of a new functionalized cyclopentadienyl ligand bearing a nitrile pendant substituent, (C 5 H 4 CMe 2 CH 2 CN) − is reported. The corresponding lithium salt of this ligand ( 1 ) was prepared by the reaction of in situ lithiated acetonitrile with 6,6-dimethylfulvene. The ligand was subsequently utilized for the synthesis of group 4 metal complexes [(η 5 –C 5 H 4 CMe 2 CH 2 CN) 2 MCl 2 ] (M = Ti, 2 ; M = Zr, 3 ; M = Hf, 4 ), [(η 5 –C 5 H 5 ) (η 5 –C 5 H 4 CMe 2 CH 2 CN)MCl 2 ] (M = Ti, 7 ; M = Zr, 8 ), and [(η 5 -C 5 Me 5 ) (η 5 C 5 H 4 CMe 2 CH 2 CN) 2 ZrCl 2 ] ( 9 ). Alternative route to 2 comprised the preparation of half-sandwich complex [(η 5 –C 5 H 4 CMe 2 CH 2 CN)TiCl 3 ] ( 6 ). The prepared compounds were characterized by common spectroscopic methods and the solid state structures of complexes 2 , 3 , 4 , 7 , and 9 were determined by the single-crystal X-ray diffraction analysis. In addition, compound 7 was converted to the corresponding dimethyl derivative [(η 5 –C 5 H 5 ) (η 5 –C 5 H 4 CMe 2 CH 2 CN)TiMe 2 ] ( 10 ) and also treated with the chloride anion abstractor Li[B(C 6 F 5 ) 4 ] to generate the cationic complex with the coordinated nitrile group, as suggested by the NMR spectroscopy. A formation of yet another cationic complex was observed upon treating compound 10 with (Ph 3 C)[B(C 6 F 5 ) 4 ].

The singly tucked-in titanocene [Ti(η5-C5Me5)(η5:η1-C5Me4CH2)] (1) reacts smoothly with ethylene glycol or hydroquinone to give bis(titanoceneoxide) (TiIII) complexes [CH2OTi(η5-C5Me5)2]2 (2) and [(η5-C5Me5)2TiOC6H4OTi(η5-C5Me5)2] (3) containing dimethylene and 1,4-phenylene link, respectively. EPR spectra of 2 in 2-methyltetrahydrofuran glass and 3 in toluene glass revealed that the unpaired d1 electrons are in interaction to form triplet state molecules. The Ti–Ti distance derived from the zero-field splittings D for the two conformations of 2 (7.42 A and 7.66 A) are in good agreement with the Ti–Ti distance of 7.2430(7) A from the X-ray diffraction single-crystal analysis. For 3, however, the Ti–Ti distance derived from D (7.65 A) is by 1.47 A shorter than the crystallographic distance of 9.1230(8) A that indicates an enhancement of the through-space dipole–dipole interaction due to the presence of a conjugated quinonide link.

The new ansa -titanocene dichloride [{(SiMePh)(η 5 -C 5 H 4 ) 2 }TiCl 2 ] ( 1 ) was prepared by one pot reaction, whereas synthesis of its methylated analogue [{(SiMePh)(η 5 -C 5 Me 4 ) 2 }TiCl 2 ] ( 3 ) was performed in two steps with isolation of corresponding silane intermediate SiMePh(HC 5 Me 4 ) 2 ( 2 ). The reaction of 1 and 3 with TiCl 4 afforded the dinuclear complexes [(SiMePh){(η 5 -C 5 R 4 )TiCl 3 } 2 ] (R = H ( 4 ) and R = Me ( 5 )). The catalysts formed from 4 and 5 after their activation with excess MAO exhibited a modest activity in ethylene polymerization. The polymer products consisted of high molar mass linear polyethylenes with a broad molar mass distribution. The presence of three paramagnetic titanium species in the mixture 4 /MAO was revealed by EPR spectroscopy. All new prepared compounds 1 – 5 were characterized by multinuclear NMR, EI-MS, IR, and solid-state structures of 1 , 3 and 5 were determined by X-ray single crystal diffraction.

Elimination of methane during thermolysis of title compounds results in the formation of σ-Ti–C bond to t-butyl or benzyl group. The t-butyl-containing titanocene methyl compound [Ti(III)Me(η5-C5Me4t-Bu)2] (5) eliminates methane at 110 °C to give cleanly [Ti(III)(η5:η1-C5Me4CMe2CH2)(η5-C5Me4t-Bu)] (6). The methyl derivative of analogous benzyl-containing titanocene [Ti(III)Me(η5-C5Me4CH2Ph)2] was not isolated because it eliminated methane at ambient temperature to give [Ti(III)(η5:η1-C5Me4CH2-o-C6H4)(η5-C5Me4CH2Ph)] (7) with one phenyl ring linked to titanium atom in ortho-position. The corresponding titanocene dimethyl compound [TiMe2{η5-C5Me4t-Bu)}2] (9) eliminates two methane molecules at 110 °C to give the singly tucked-in 1,1-dimethylethane-1,2-diyl-tethered titanocene [Ti{η5:η1:η1-C5Me3(CH2)(CMe2CH2)}(η5-C5Me4t-Bu)] (11). In distinction, the analogous benzyl derivative [TiMe2(η5-C5Me4CH2Ph)2] (10) eliminates at 110 °C only one methane molecule to afford [TiMe(η5:η1-C5Me4CH2-o-C6H4)(η5-C5Me4CH2Ph)] (12) containing one phenyl group attached to titanium in o-position and one methyl group persisting on the titanium atom. This compound is stable at 150 °C for at least 3 h. The crystal structures of 5, 6, 7, and 10 were determined.

Thermolysis of [TiMe 2 (η 5 -C 5 Me 4 Ph) 2 ] ( 4 ) at 145 °C for 5 h afforded the singly tucked-in paramagnetic titanocene [Ti(III)(η 5 -C 5 Me 4 Ph){η 5 :η 1 -C 5 Me 3 Ph(CH 2 )}] ( 9 ). In distinction to the singly tucked-in permethyltitanocene [Ti(III)(η 5 -C 5 Me 5 ){η 5 :η 1 -C 5 Me 4 (CH 2 )}] ( 1 ) which was found crystallographically disordered [J.M. Fischer, W.E. Piers, V.G. Young, Jr., Organometallics 15 (1996) 2410] the single crystal X-ray diffraction analysis of 9 afforded molecular parameters with nearly by one order better precision as measured by esd-values.

New metallocene dichlorides [η 5 -(1,4-Me 2 -2,3-Ph 2 -C 5 H) 2 TiCl 2 ] ( 2 ), [η 5 -(1,4-Me 2 -2,3-Ph 2 -C 5 H) 2 ZrCl 2 ] ( 3 ) and [η 5 -(1,4-Me 2 -2,3-Ph 2 -C 5 H)η 5 -(C 5 H 5 )ZrCl 2 ] ( 4 ) were prepared from lithium salt of 1,4-dimethyl-2,3-diphenylcyclopentadiene ( 1 ) and [TiCl 3 (THF) 3 ], [ZrCl 4 ] and [η 5 -(C 5 H 5 )ZrCl 3 (DME)], respectively. Compounds 2–4 were characterized by NMR spectroscopy, EI-MS and IR spectroscopy, and the solid state structure of 3 was determined by single crystal X-ray crystallography. The catalytic systems 3 /MAO and 4 /MAO were almost inactive in polymerization of ethylene at 30–50 °C, however, they exhibited high activity at temperature 80 °C. The catalyst formed from 2 and excess of MAO was practically inactive at all temperatures.

Thermally stable zwitterionic complex [(η5-C5Me5)Ti(Ot-Bu)2](δ+)[(μ-Me)B(C6F5)3](δ−) (5) was formed by mixing equimolar quantities of [(η5-C5Me5)TiMe(Ot-Bu)2] and [B(C6F5)3]. The compound was recrystallized from hot toluene and has been stable so far for 1 year at ambient temperature in the solid state and in toluene solution. The 1H, 19F and 1D NOESY NMR spectra in C6D6 solution proved the inner sphere ion pair structure of 5. The X-ray crystal structure of 5 revealed that the bridging methyl group is σ-bonded to boron, and all its C–H bonds fulfil criteria for agostic bonding interaction with the titanium atom. In contrast to the stable solution in C6D6 compound 5 decomposed in CD2Cl2 solvent within hours at room temperature.

In the series of the methylated compounds (η5-C5H5−nMen)TiCl3 (n = 0–5) 1–6, linear correlations of λmax of the absorption band and δ 49,47Ti chemical shift with the number of Me groups were found. It is due to the dependence of both the magnitudes on the HOMO–LUMO energy gap which is influenced by electron donating methyl substituents. The catalysts made by combining 1–6 with MAO (molar ratio Al/Ti 500) showed only a gross dependence of decreasing activity with the number of methyl groups. For compounds (η5-C5Me4R)TiCl3 7–14 and (η5-C5H(1,2,3-)Me3R)TiCl3 15–20 where R = alkyl, silyl or phenyl no correlation between λmax and δ was found. Limited DFT calculations were performed to assign HOMO/LUMO orbitals involved. Crystal structures of 16 and 20 were determined and some other inspected to prove the absence of steric hindrance. The poor correlation of the spectroscopic properties with the catalytic activity is not surprising because steric effects of cyclopentadienyl ligands at cationic polymerization centers are generally anticipated.

Reduction of isopropyldimethylsilyl-substituted titanocene dichloride [TiCl2(η5-C5Me4SiMe2Pri)2] (1) by excess magnesium in the presence of excess bis(trimethylsilyl)ethyne (btmse) in tetrahydrofuran at 60 °C yielded a mixture of products amongst them only the trinuclear Ti–Mg–Ti hydrido-bridged complex Mg[Ti(μ-H)2(η5-C5Me4SiMe2Pri)]2 (3) was isolated and characterized. The precursor of titanocene, [Ti(η5-C5Me4SiMe2Pri)2(η2-btmse)] (6), was obtained from the identical system which, after initial formation of [TiCl(η5-C5Me4SiMe2Pri)2] (2), reacted at −18 °C overnight and then the solution was rapidly separated from the remaining magnesium. Titanocene [Ti(η5-C5Me4SiMe2Pri)2] (7) was obtained by thermolysis of 6 at 75 °C in vacuum. Crystal structures of 1, 2, 3, 6, and 7 were determined.

The [TiCl 2 (η 5 -C 5 Me 5 ) 2 ]/Mg excess /tetrahydrofuran system reacts with but-2-yne in excess to give paramagnetic (η 5 :η 1 -1,2,3,4-tetramethyl-5-(2,3,4,5-tetramethylpenta-2,4-dien-1,5-diyl-κC5)cyclopentadienyl)(η 5 -pentamethylcyclopentadienyl)titanium(III) ( 1 ) as the main product. The crystal structure of 1 shows a minimum steric hindrance between the methylated cyclopentadienyl ligands and non-coplanar conjugated double bonds in the C 5 tether.

Single tucked-in titanocene [Ti(η5-C5Me5)(η5:η1-C5Me4CH2)] adds to B(C6F5)3 to give the paramagnetic cationic complex [Ti(η5-C5Me5){η5-C5Me4CH2B(C6F5)3}] (1). Doubly tucked-in titanocene [Ti(η5-C5Me5){η3:η4-C5Me3(CH2)2}] reacts with B(C6F5)3 by one methylene group to give [Ti(η5-C5Me5){η5:η1-C5Me3(CH2)CH2B(C6F5)3}] (6). The crystal structure of 6 revealed that one hydrogen of the methylene group attached to boron agostically interacts with Ti(IV).

The ethene–styrene copolymerization has been investigated using the dimethylsilylene-bridged (amidocyclopentadienyl)dichlorotitanium(IV) complexes [TiCl 2 {η 5 -1-(SiMe 2 N t -Bu-κN)-2,3,4-Me 3 -5-R-C 5 }], where R = Me ( 1 ), H ( 2 ), Bu ( 3 ), Ph ( 4 ), 4-fluorophenyl ( 5 ), and but-2-en-2-yl ( 6 ) in combination with methylalumoxane (MAO) as catalysts. The nature of the substituent R strongly influenced the catalyst activity and selectivity and the copolymer microstructure and molecular weight. The catalysts derived from 1 to 3 were by about one order more active than those derived from 4 to 6 . At the optimum Al/Ti molar ratio of 900, the highly active catalysts produced a pseudo-random copolymer (95–97 wt.%) containing up to 47.8 mol% of incorporated styrene. The low-active catalysts gave mixtures of a pseudo-random copolymer (76–85 wt.%) with polyethene (10 wt.%) and polystyrene sequences (3–7 wt.%). The X-ray diffraction crystal structures of 2 and 4 were determined. Comparison of crystal structures of 1 and 2 versus 4 and 5 revealed a slightly shorter distances Ti–Cg (Cg – centroid of the cyclopentadienyl ring) and slightly larger Cl–Ti–Cl angles in 1 and 2 , indicating a higher electron density at the titanium atom. An electron attracting effect of phenyl or alkenyl substituents as well as their steric hindrance can account for a low catalytic performance of 4 – 6 /MAO catalysts.

Paramagnetic titanocene complexes containing the unsaturated carbyl group which consists of one and half molecule of 1,4-bis(trimethylsilyl)buta-1,3-diyne (BSD) are formed by the reduction of titanocene dichlorides with one molar equivalent of magnesium in the presence of 1.5 molar equivalent BSD in tetrahydrofuran (THF) for titanocene moieties Ti(η5-C5H5 − nMen)2 (n = 5 (1), 4 (2), and 3 (3)) and Ti{Me2Si(η5-C5Me4)2} (4). The non-methylated titanocene moiety affords under identical conditions known diamagnetic bis(η5-cyclopentadienyl)-2,4-bis(trimethylsilylethynyl)-3,5-bis(trimethylsilyl)titanacyclopenta-2,4-diene (5) as the major product. Crystal structures of 3 and 4 show the same bonding scheme for the 1,4,6-tris(trimethylsilyl)hex-3-ene-1,5-diyne-3-yl ligand as previously found for compound 1 [P.-M. Pellny, F.G. Kirchbauer, V.V. Burlakov, A. Spannenberg, K. Mach, U. Rosenthal, Chem. Commun. (1999) 2505]. Compound 1 is stable against weak proton donors like methanol or alk-1-ynes even at 90 °C, however, it undergoes retroreaction when oxidized by PbCl2 in THF, yielding nearly quantitatively BSD and [TiCl2(η5-C5Me5)2].

Bis{η5-(N,N-dimethylaminodimethylsilyl)tetramethylcyclopentadienyl}dichlorotitanium(IV), [TiCl2{η5-C5Me4(SiMe2NMe2)}2] (1), reacts with sulfane under cleavage of both Si–N and Ti–Cl bonds to give sulfido-tethered titanocene compound bis{η5-1,2,3,4-tetramethyl-5-(dimethylsilylsulfido-κS)cyclopentadienyl}titanium(IV), [Ti{η5-C5Me4(SiMe2S- κS)}2] (4), and dimethylamine hydrochloride as the byproduct. The crystal structure of compound 4 has been determined by single-crystal X-ray diffraction.

Reduction of methyl-substituted titanocene dichlorides bearing pendant double bonds [TiCl2{η5-C5Me4(CH2CMeCH2)}2] (1) and [TiCl2{η5-C5Me4(SiMe2(CH2)2CHCH2)}2] (2) with magnesium yielded diamagnetic Ti(IV) compound [Ti{η1:η1:η5-C5Me3(CH2)(CH2CH(Me)CH2)}{η5-C5Me4(CH2C(Me)CH2)}] (4) and paramagnetic Ti(III) compound [Ti{η5-C5Me4(SiMe2CH2CHCHMe)}(μ-η3,η1:η5,η1(Ti:Mg){C5Me3(CH2)(SiMe2CHCHCMe)})Mg(OC4H8)2] (6), respectively. The reluctance of titanocene intermediates to undergo intramolecular cyclization to cyclopentadienyl-ring-tethered titanacycles (as typically observed) can be explained by a shortness of the 2-methylallyl group and steric hindrance of its double bond in the former case and, in the latter case, by an attack of magnesium on the titanocene intermediate, faster than cyclization reactions. The crystal structures of 4 and 6 were determined by single-crystal X-ray diffraction.

Paramagnetic complexes ansa-[Ti(C CCMe3){η5:η5-C5Me4SiMe2CH CHCH2CH2SiMe2C5Me4}] (1) and ansa-[Ti(OH){η5:η5-C5Me4SiMe2CH2CH CHCH2SiMe2C5Me4}] (2) were prepared by reactions of ansa-[Ti(III){η3:η5:η5-C5Me4SiMe2CHCHCHCH2SiMe2C5Me4}] (3) with t-butylethyne or water, respectively. The X-ray single crystal diffraction analysis of 1 and 2 showed that the cis-double bond is situated asymmetrically in the ansa-bridge of 1 whereas, in 2, the double bond is trans, and lies in the bridge centre. ESR and UV-near IR spectra indicated a weaker oxygen π-electron donation into the Ti–O bond of 2 compared to analogous methoxide ansa-[Ti(III)(OMe){η5:η5-C5Me4SiMe2CH2CH CHCH2SiMe2C5Me4}] (4) or decamethyltitanocene hydroxide (5).

An easy and inexpensive three-step synthesis of new 2,3-dimethyl-1,4-diphenylcyclopentadiene (3) ligand and the titanium and zirconium homometallocene dichlorides [TiCl2(η5-C5H-2,3-Me2-1,4-Ph2)2] (4), [ZrCl2(η5-C5H-2,3-Me2-1,4-Ph2)2] (5), and the mixed ligand zirconium complex [ZrCl2(η5-C5H-2,3-Me2-1,4-Ph2)(η5-C5H5)] (6) prepared thereof are described. The polymerization of ethene using 4–6/MAO catalysts revealed that zirconocene complexes 5 and 6 displayed moderate and high activity, respectively, whereas the titanium catalyst 4/MAO was inactive. The crystal structures of 4 and 5 were determined by X-ray crystallography.

Fully methylated titanocene hydroxide [Ti(OH) (η5-C5Me5)2] (1) was obtained by the reaction of single tucked-in decamethyltitanocene [Ti(η5-C5Me5){η5:η1-C5Me4(CH2)}] (2) with one equivalent of water dissolved in toluene. The X-ray single crystal diffraction of 1 revealed the bent Ti–O–H bonds (112(4)°) where the oxygen atom is only 0.038(4) A away from the Cg(1), Ti, Cg(2) (Cg – centroid of the cyclopentadienyl ring) plane, and the hydroxyl bond is directed to the cyclopentadienyl ring C(1–5). The Ti–O bond length (1.889(2) A) and energy of 1a1→b2 transition (6770(50) cm−1) indicate that the π-donation effect of the hydroxyl group is weaker compared to alkoxy groups.

Reduction of isomeric, fully-substituted titanocene dichlorides having a pendant double bond, [TiCl2(η5-C5Me4R)(η5-C5Me5)] (R=CH2CH2CHCH2 (1); R=CH(Me)CHCH2, (2)), with magnesium in THF in the presence of bis(trimethylsilyl)ethyne (btmse) affords different products depending on the alkenyl chain length. Whereas the reduction of 1 yields a compound with intramolecularly η2-coordinated double bond, [Ti(η5-C5Me5){η2:η5-C5Me4(CH2CH2CHCH2)}] (3), compound 2 affords under identical conditions a product with two new TiC bonds, [Ti{(η1:η1:η5-C5Me3(CH2)(CH(Me)CH2CH2)}(η5-C5Me5)] (4). The formation of 3 can be rationalized as a simple intramolecular stabilization of a titanocene intermediate formed by reductive removal of the chloride ligands. The formation of 4 from the respective titanocene, however, requires formally an activation (oxidative addition) of one CH bond at the methyl group adjacent to the unsaturated chain followed by a hydrogen shift (hydrometallation). Under similar conditions, the complex with asymmetric unsaturated ansa-bridge [TiCl2{η5:η5-C5Me4CH2CHCH(CH2)5C5Me4}] (5) is reduced to a titanocene–η2-alkene complex with the double bond shifted to the central position, ansa-[Ti{η2:η5:η5-C5Me4(CH2)3CHCH(CH2)3C5Me4}] (7). In the absence of btmse, analogous complex with saturated bridge ansa-[TiCl2{η5:η5-C5Me4(CH2)8C5Me4}] (6) undergoes a hydrogen abstraction to give 7 as well albeit in a lower yield. The reduction of 6 in the presence of btmse gives η2-alkyne complex ansa-[Ti{η5:η5-C5Me4(CH2)8C5Me4}(η2-Me3SiCCSiMe3)] (8) which is converted upon thermolysis at 150 °C to a mixture of asym- and sym-isomers of the doubly tucked-in complex ansa-[Ti{(η3:η4-C5Me2(CH2)2)(CH2)8(η5-C5Me4)}] (9) in 2:1 ratio; no CH activation involving methylene groups of the ansa tether was observed. The crystal structures of 4, 7, and 8 have been determined by X-ray crystallography.

Reduction of fully substituted titanocene dichlorides [TiCl2(η5-C5Me4R)2] (R=SiMe2CH2CH2Ph, 3; SiMe2Ph, 4; and SiMePh2, 5) with magnesium in THF proceeds via the formation of titanocene monochlorides [TiCl(η5-C5Me4R)2] 6–8 to afford monomeric titanocenes, [Ti(η5-C5Me4R)2], 9–11. Titanocene monochlorides give the expected EPR spectra in toluene solution and glass. The structure of 7 was further corroborated by single-crystal X-ray diffraction. Titanocenes 9–11 are EPR silent down to −196 °C but exhibit paramagnetic broadening of the signals in solution NMR spectra. The positions of the NMR signals are temperature-dependent, obeying the Curie Law in the range investigated (0–60 °C). As revealed by X-ray crystallography, titanocenes 9 and 11 possess bent metallocene structures with the cyclopentadienyl rings tilted at an angle of 9.8(1) and 14.4(2)°, respectively. Titanocenes 9–11 are easily oxidized with PbCl2 to the parent dichloride complexes 3–5. Titanocenes 9 and 10 react with bis(trimethylsilyl)ethyne (btmse) only in large excess of the alkyne to give an equilibrium concentration of the respective [Ti(η5-C5Me4R)2(η2-Me3SiCCSiMe3)] complexes. On the other hand, titanocene 11 does not observably react with btmse.

Reduction of dichloro-{1,3-bis(η 5 -tetramethylcyclopentadienyl)-1,1,3,3-tetramethyldisiloxane}titanium(IV), [TiCl 2 {η 5 :η 5 -(C 5 Me 4 SiMe 2 ) 2 O}] ( 1 ), with magnesium in the presence of bis(trimethylsilyl)ethyne affords the ansa -[Ti{η 5 :η 5 -(C 5 Me 4 SiMe 2 ) 2 O}(η 2 -Me 3 SiCCSiMe 3 )] ( 2 ) complex in high yield. Compound 2 is thermally robust, decomposing at 170 °C in high vacuum with liberation of 1,2-bis(trimethylsilyl)ethene to give predominantly an asymmetric, allydiene complex ansa -[Ti{(η 5 -C 5 Me 4 )SiMe 2 OSiMe 2 {η 3 :η 4 -C 5 Me 2 (CH 2 ) 2 }] ( 3 ) as a result of twofold CH bond activation. Crystal structures of 2 and 3 were determined by X-ray diffraction.

The paramagnetic compounds exo,exo-bis(η5-isodicyclopentadienyl)chlorotitanium(III) (3) and its analogue with trimethylsilyl-substituted isodicyclopentadienide (isodiCp) ligand (4), and the similar pair of diamagnetic exo,exo-bis(isodicyclopentadienyl)[η2-bis(trimethylsilyl)ethyne]titanium(II) complexes 5 and 6 were obtained by common reduction procedures from exo,exo-bis(isodicyclopentadienyl)titanium(IV) dichloride (1) and exo,exo-bis[η5-2-(trimethylsilyl)isodicyclopentadienyl]titanium(IV) dichloride (2), respectively. As indicated by ESR spectroscopy compound 3 is a dimer in the solid state and in frozen toluene glass but monomeric in toluene solution. Compound 4 is monomeric in solution as well as in the solid state. As judged from the red shift of the ν(CC) vibration, compound 6 binds bis(trimethylsilyl)ethyne more strongly than compound 5. A comparison of their wavenumbers with those of the [Ti(C5H5−nMen)2(η2-Me3SiCCSiMe3)] (n=2–5) complexes shows that Lewis acidity of the central titanium atom decreases in the order of ligands 1,3-dimethylcyclopentadienyl>isodiCp∼1,2,3-trimethylcyclopentadienyl>(trimethylsilyl)isodiCp∼tetramethylcyclopentadienyl. The crystal structure of the most bulky complex 6 shows a bis-lateral (anti) conformation of the isodiCp ligands with the π-coordinated five-membered rings nearly eclipsed.

A series of three ansa-titanocene monochlorides containing η5-tetramethylcyclopentadienyl ligands bridged by five- or eight-membered aliphatic chains were prepared via reduction of the corresponding dichlorides with half molar equivalent of magnesium and characterized by spectral methods. The solid-state structures of the monochloride complexes ansa-[TiCl{η5:η5-C5Me4CH(Me)CH2CH2CH(Me)CH(Me)C5Me4}] (1a) and ansa-[TiCl{η5:η5-C5Me4(CH2)3CH(Me)CH(Me)CHCHCH2C5Me4}] (4a), and of the bridge-unsaturated titanocene dichloride complex ansa-[TiCl2{η5:η5-C5Me4CH2CHCH(CH2)5C5Me4}] (3) were determined by single-crystal X-ray diffraction. All the compounds show bent metallocene structures with the ansa-chain situated in a side position with respect to Cg, Ti, Cg (Cg=centroid of the cyclopentadienyl ligand) plane. Angles subtended by the least-squares planes of the cyclopentadienyl rings and conformation of the ansa-chains indicates the absence of steric strain in the metallocene framework.

Bis{η5-(N,N-dimethylaminodimethylsilyl)tetramethylcyclopentadienyl}dichlorotitanium(IV), [TiCl2{η5-C5Me4(SiMe2NMe2)}2] (1), easily undergoes hydrolytic cleavage of the Si–N bonds to give dimethylamine and {1,3-bis(η5-tetramethylcyclopentadienyl)-1,1,3,3-tetramethyldisiloxane}dichlorotitanium(IV), ansa-[TiCl2{(η5-C5Me4SiMe2)2O}] (2), in almost quantitative yields. The crystal structures of compounds 1 and 2 were determined by single-crystal X-ray diffraction.

Titanocene complexes [Ti(η 5 -C 5 H 5− n Me n ) 2 (η 2 -Me 3 SiCCSiMe 3 )] ( n =0, 4 and 5) react uniformly with siladiynes R 2 2 Si(CCR 1 ) 2 , where R 1 =Ph, and R 2 =Ph or Me, at elevated temperature in hydrocarbon solvents to give the corresponding silacyclobutene-annelated titanacyclobutene complexes, 3-bis(η 5 -cyclopentadienyl)titana-6-diorganylsilabicyclo[2.2.0]hexa-1(2),4(5)-dienes, [(η 5 -C 5 H 5− n Me n ) 2 Ti{R 1 2 C 4 (SiR 2 2 )}]. Products arising from [Ti(η 5 -C 5 H 5− n Me n ) 2 (η 2 -Me 3 SiCCSiMe 3 )] ( n =0, 2 (1,3-isomer), 4 and 5) and Me 2 Si(CCCMe 3 ) 2 vary with n : the non-methylated titanocene complex affords a mixture of an analogous silacyclobutene-annelated titanacyclobutene and [{Ti(η 5 -C 5 H 5 ) 2 } 2 {μ-η(3–5):η(4–6)-Me 3 CCCCCCMe 3 }], the permethylated titanocene precursor gives mainly the allyldiene complex [Ti(η 5 -C 5 Me 5 )(η 3 :η 4 -C 5 Me 3 (CH 2 ) 2 )] while no titanium-containing product could be isolated for n= 4. The reaction of [Ti(η 5 -1,3-C 5 H 3 Me 2 ) 2 (η 2 -Me 3 SiCCSiMe 3 )] with Me 2 Si(CCCMe 3 ) 2 , however, cleanly affords the expected silacyclobutene–titanacyclobutene complex. All complexes were studied by spectral methods and solid-state structure of two representatives, [(η 5 -C 5 Me 5 ) 2 Ti{Ph 2 C 4 (SiMe 2 )}] and [(η 5 -1,3-C 5 H 3 Me 2 ) 2 Ti{(Me 3 C) 2 C 4 (SiMe 2 )}] was determined by single-crystal X-ray diffraction.

The titanocene–bis(trimethylsilyl)acetylene (BTMSA) complexes Cp′2Ti[η2-C2(SiMe3)2] (Cp′C5H5−nMen; n=0–5) react with acetone azine Me2CNNCMe2 (AA) in two different ways depending on the number of Me substituents at the Cp′ ligands (n). For n=0–2, BTMSA is replaced by AA, which then undergoes an oxidative addition accompanied by a proton transfer, affording titana-2-isopropyl-4-methyl-2,3-diazacyclopent-3-ene complexes A0–A2. For n=3–5, replacement of the acetylene is followed by the splitting of AA to give either (C5Me5)2Ti(III)(NCMe2) (C5) or the Ti(IV) (Cp′A)2Ti complexes B3 and B4 for n=3 and 4, respectively. The intramolecularly bridging Cp′A ligand 1-(η5-2,3,5-trimethylcyclopentadienide)-2-(η1-amide)-2,2′-dimethylethane arises from a formal insertion of the CN bond of isopropylidene amide into a CH bond of one methyl group of the cyclopentadienyl ligands before or after splitting of AA. Crystal structures of C5 and (η5:η1-C5HMe3CH2CMe2NH)2Ti(IV) (B4) were determined.

The reduction of (C5Me4Ph)2TiCl2 by magnesium in tetrahydrofuran affords a mixture of the diamagnetic doubly tucked-in titanocene complex (C5Me4Ph)[C5Me2(CH2)2Ph]Ti (1), the paramagnetic trinuclear Ti–Mg–Ti hydride bridged complex [(C5Me4Ph)2Ti(μ-H)2]2Mg (2) and the paramagnetic binuclear titanocene hydride–magnesium hydride complex (C5Me4Ph)[C5Me4(o-C6H4)]Ti(μ-H)2Mg(THF)2 (3). The X-ray diffraction analysis of 3 revealed that the magnesium atom forms the σ-bond to the ortho-carbon atom of one of the phenyl rings and binds 2 molecules of THF.

The reduction of {[η8-1,4-(SiMe3)2C8H6]Ti(μ-Cl)}2(THF) by magnesium in the presence of bis(trimethylsilyl)acetylene in tetrahydrofuran affords diamagnetic bis[μ-η5:η5-1,4-bis(trimethylsilyl)cyclooctatetraenetitanium](Ti–Ti) (1) in low yield. The X-ray crystal analysis of 1 revealed that bridging cyclooctatetraene ligands in the centrosymmetric dimer are concave-bent. An extremely short Ti–Ti distance of 2.326(2) A is compatible with the presence of a double Ti–Ti bond.

Redox properties of the substituted zirconocene dichlorides: (C 5 H 5− n Me n ) 2 ZrCl 2 ( n =0–5), [C 5 H 5− n (SiMe 3 ) n ] 2 ZrCl 2 ( n =0–3), [C 5 Me 4 (SiMe 3 )](C 5 HMe 4 )ZrCl 2 and two ansa -analogues Me 2 Si(C 5 H 4 ) 2 ZrCl 2 and Me 2 Si[C 5 H 2 (SiMe 3 ) 2 ] 2 ZrCl 2 were investigated by cyclic voltammetry on a mercury electrode in tetrahydrofuran. In the (C 5 H 5− n Me n ) 2 ZrCl 2 ( n =0–4) compounds, standard electrode potential ( E °) of the one-electron uptake shifts to more negative values by 0.071 V per one methyl group. A deviation from this linear dependence to a less negative E ° is observed for (C 5 Me 5 ) 2 ZrCl 2 . This effect is attributed to the steric hindrance between rotating C 5 Me 5 ligands which tends to decrease the angle between the cyclopentadienyl ring planes ( φ ) and consequently, the energy difference between MO frontier orbitals. In the trimethylsilylated compounds, the net effect of SiMe 3 is negligible, giving virtually the same value of E ° for n =0–3. In μ-SiMe 2 -bridged ansa -compounds the difference in E ° of 147 mV corresponds to the negative shift of 37 mV per one SiMe 3 group. Owing to the rigid angle φ , this shift can be tentatively accounted for the electronic effect of the SiMe 3 groups. In the non- ansa -compounds, the negative shift due to the electronic effect of SiMe 3 groups is assumed to be roughly compensated by a positive shift resulting from a sterically controlled diminution of φ .

The reaction between equimolar quantities of TiCl 3 (THF) 3 and 1,4-bis(trimethylsilyl)cyclooctatetraene dianion (COT″) yields a mixture of (COT″) 2 Ti ( 1 ), [(COT″)Ti] 2 (μ-Cl) 3 ( 2 ) and [(COT″)Ti(μ-Cl)] 2 (THF) ( 3 ). Crystalline 2 and 3 were isolated on the basis of different solubility in hexane. Their X-ray diffraction analyses revealed dimeric structures linked by chlorine bridges. In 3 , only one of the Ti atoms coordinates one molecule of THF. The mixed-valency Ti(III)/Ti(IV) compound 2 shows an ESR spectrum typical of mononuclear (COT″)Ti(III) complexes. The ESR spectra of 3 in toluene or 2-methyltetrahydrofuran glasses prove the triplet state of coupled Ti(III) d 1 electrons.

Methyl-substituted titanocene dichlorides (C5H5−nMen)2TiCl2 (n=0–5), [C5Me4(SiMe3)]2TiCl2, (C5Me4Ph)2TiCl2 (Ph=phenyl), [C5Me4(FPh)]2TiCl2 (FPh=para-fluorophenyl), [C5Me4(CH2Ph)]2TiCl2 and ansa-compounds Me2Si(C5H4)2TiCl2 and Me2Si(C5Me4)2TiCl2 were investigated by means of cyclic voltammetry at a mercury electrode in tetrahydrofuran. The standard potential (E°1) of the first electron uptake shifts to more negative values proportionally to the number of methyl groups in the (C5H5−nMen)2TiCl2 (n=0–3) compounds, with an increment of 0.093 V per one methyl group. A decline from this linear dependence is observed for (C5HMe4)2TiCl2 and a positive shift for (C5Me5)2TiCl2. The [C5Me4(R)]2TiCl2 (R=SiMe3, Ph, FPh and CH2Ph) compounds show even larger positive shifts of E°1. These positive shifts can be brought about by a steric strain between the cyclopentadienyl ligands which lowers the dihedral angle between cyclopentadienyl ring planes (φ) and thus decreases energies of bent titanocene 1a1 and b2 LUMO orbitals. This opinion is corroborated by the voltammetry of ansa-compounds Me2Si(C5H4)2TiCl2 and Me2Si(C5Me4)2TiCl2, having a large and fixed angle φ. Their E°1 values are close to those of (C5H5)2TiCl2 and (C5HMe4)2TiCl2, respectively.