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Single and double tucked-in titanocenes react with excess CO2 by insertion into their Ti–CH2 bonds to form carboxylate-tethered species and subsequently new dimeric carbodiolates.

Cationic group 4 metallocene complexes with pendant imine and pyridine donor groups were prepared as stable crystalline [B(C6F5)4]- salts either by protonation of the intramolecularly bound ketimide moiety in neutral complexes [(η5-C5Me5){η5-C5H4CMe2CMe2C(R)═N-κN}MCl] (M = Ti, Zr, Hf; R = t-Bu, Ph) by PhNMe2H+[B(C6F5)4]- to give [(η5-C5Me5){η5-C5H4CMe2CMe2C(R)═NH-κN}MCl]+[B(C6F5)4]- or by chloride ligand abstraction from the complexes [(η5-C5Me5)(η5-C5H4CMe2CH2C5H4N)MCl2] (M = Ti, Zr) by Li[B(C6F5)4]·2.5Et2O to give [(η5-C5Me5)(η5-C5H4CMe2CH2C5H4N-κN)MCl]+[B(C6F5)4]-. Solid state structures of the new compounds were established by X-ray diffraction analysis, and their electrochemical behavior was studied by cyclic voltammetry. The cationic complexes of Zr and Hf, compared to the corresponding neutral species, exhibited significantly enhanced luminescence predominantly from triplet ligand-to-metal (3LMCT) excited states with lifetimes up to 62 μs and quantum yields up to 58% in the solid state. DFT calculations were performed to explain the structural features and optical and electrochemical properties of the complexes.

Catalytic hydrodehalogenation (HDH) of aliphatic organohalides such as trifluorotoluenes by Et3SiH proceeds in the presence of readily available group 4 metal compounds: Cp'2MX2 (Cp' = η5-C5H5 or η5-C5Me5; X = F, Cl, or Me; M = Ti, Zr, or Hf), CpTiCl3 and TiCl4 with a catalytic amount of B(C6F5)3. The use of metallocenes in combination with the borane activator leads to a better selectivity of the reaction, i.e., suppression of Friedel-Crafts alkylations of arenes.

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.

Catalytic hydrodehalogenation (HDH) of aliphatic organohalides such as trifluorotoluenes by Et3SiH proceeds in the presence of readily available group 4 metal compounds: Cp'2MX2 (Cp' = η5-C5H5 or η5-C5Me5; X = F, Cl, or Me; M = Ti, Zr, or Hf), CpTiCl3 and TiCl4 with a catalytic amount of B(C6F5)3. The use of metallocenes in combination with the borane activator leads to a better selectivity of the reaction, i.e., suppression of Friedel-Crafts alkylations of arenes.

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.

Reactions following the addition of dihydrogen under maximum atmospheric pressure to bis(trimethylsilyl)acetylene (BTMSA) complexes of titanocenes, [(η5-C5H5-nMen)2Ti(η2-BTMSA)] (n = 0, 1, 3, and 4) (1A-1D), and zirconocenes, [(η5-C5H5-nMen)2Zr(η2-BTMSA)] (n = 2-5) (4A-4D), proceeded in diverse ways and, depending on the metal, afforded different products. The former complexes lost, in all cases, their BTMSA ligand via its hydrogenation to bis-1,2-(trimethylsilyl)ethane when reacted at 80 °C for a prolonged reaction time. For n = 0, 1, and 3, the titanocene species formed in situ dimerised via the formation of fulvalene ligands and two bridging hydride ligands, giving known green dimeric titanocenes (2A-2C). For n = 4, a titanocene hydride [(η5-C5HMe4)2TiH] (2D) was formed, similarly to the known [(η5-C5Me5)2TiH] (2E) for n = 5; however, in contrast to this example, 2D in the absence of dihydrogen spontaneously dehydrogenated to the known Ti(iii)-Ti(iii) dehydro-dimer [{Ti(η5-C5HMe4)(μ-η1:η5-C5Me4)}2] (3B). This complex has now been fully characterised via spectroscopic methods, and was shown through EPR spectroscopy to attain an intramolecular electronic triplet state. The zirconocene-BTMSA complexes 4A-4D reacted uniformly with one hydrogen molecule to give Zr(iv) zirconocene hydride alkenyls, [(η5-C5H5-nMen)2ZrH{C(SiMe3)[double bond, length as m-dash]CH(SiMe3)}] (n = 2-5) (5A-5D). These were identified through their 1H and 13C NMR spectra, which show features typical of an agostically bonded proton, [double bond, length as m-dash]CH(SiMe3). Compounds 5A-5D formed equilibria with the BTMSA complexes 4A-4D depending on hydrogen pressure and temperature.

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.

The role of the ketimide ligand geometry in Ti half-sandwich complexes and the consequent effects in olefin polymerization catalysis (ethylene, styrene, 1-hexene polymerization, and ethylene/1-hexene copolymerization) were investigated under various conditions. [CpTiCl2(N=CtBu2)] (1; Cp=η5-cyclopentadienyl) was used as a reference compound for comparison with the recently described complex [{η5-C5H4CMe2CMe2C(tBu)=N-κN}TiCl2] (2 a) and a new derivative that has a longer linker between Cp and the ketimide, [{η5-C5H4CH2CH2CMe2C(tBu)=N-κN}TiCl2] (9). The presence of a distorted intramolecularly tethered ketimide moiety reduces the polymerization activity significantly in systems that contain Al-based cocatalysts (methylaluminoxane, triisobutylaluminum). However, in Al-free systems both types of compounds provided active polymerization catalysts. Notably, the recently reported activation system Et3SiH/B(C6F5)3 was for the first time demonstrated to activate Ti complexes for ethylene and 1-hexene (co)polymerization catalysis by hydride transfer.

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.

1H NMR studies of reactions of titanocene [Cp*2Ti] (Cp* = η5-C5Me5) and its derivatives [Cp*(η5:η1-C5Me4CH2)TiMe] and [Cp*2Ti(η2-CH2CH2)] with excess dihydrogen at room temperature and pressures lower than 1 bar revealed the formation of dihydride [Cp*2TiH2] (1) and the concurrent liberation of either methane or ethane, depending on the organometallic reactant. The subsequent slow decay of 1 yielding [Cp*2TiH] (2) was mediated by titanocene formed in situ and controlled by hydrogen pressure. The crystalline products obtained by evaporating a hexane solution of fresh [Cp*2Ti] in the presence of hydrogen contained crystals having either two independent molecules of 1 in the asymmetric part of the unit cell or cocrystals consisting of 1 and [Cp*2Ti] in a 2 : 1 ratio. Hydrogenation of alkyne complexes [Cp*2Ti(η2-R1CCR2)] (R1 = R2 = Me or Et) performed at room temperature afforded alkanes R1CH2CH2R2, and after removing hydrogen, 2 was formed in quantitative yields. For alkyne complexes containing bulkier substituent(s) R1 = Me or Ph, R2 = SiMe3, and R1 = R2 = Ph or SiMe3, successful hydrogenation required the application of increased temperatures (70–80 °C) and prolonged reaction times, in particular for bis(trimethylsilyl)acetylene. Under these conditions, no transient 1 was detected during the formation of 2. The bulkier auxiliary ligands η5-C5Me4tBu and η5-C5Me4SiMe3 did not hinder the addition of dihydrogen to the corresponding titanocenes [(η5-C5Me4tBu)2Ti] and [(η5-C5Me4SiMe3)2Ti] yielding [(η5-C5Me4tBu)2TiH2] (3) and [(η5-C5Me4SiMe3)2TiH2] (4), respectively. In contrast to 1, the dihydride 4 did not decay with the formation of titanocene monohydride, but dissociated to titanocene upon dihydrogen removal. The monohydrides [(η5-C5Me4tBu)2TiH] (5) and [(η5-C5Me4SiMe3)2TiH] (6) were obtained by insertion of dihydrogen into the intramolecular titanium-methylene σ-bond in compounds [(η5-C5Me4tBu)(η5:η1-C5Me4CMe2CH2)Ti] and [(η5-C5Me4SiMe3)(η5:η1-C5Me4SiMe2CH2)Ti], respectively. The steric influence of the auxiliary ligands became clear from the nature of the products obtained by reacting 5 and 6 with butadiene. They appeared to be the exclusively σ-bonded η1-but-2-enyl titanocenes (7) and (8), instead of the common π-bonded derivatives formed for the sterically less congested titanocenes, including [Cp*2Ti(η3-(1-methylallyl))] (9). The molecular structure optimized by DFT for compound 1 acquired a distinctly lower total energy than the analogously optimized complex with a coordinated dihydrogen [Cp*2Ti(η2-H2)]. The stabilization energies of binding the hydride ligands to the bent titanocenes were estimated from counterpoise computations; they showed a decrease in the order 1 (−132.70 kJ mol−1), 3 (−121.11 kJ mol−1), and 4 (−112.35 kJ mol−1), in accordance with the more facile dihydrogen dissociation.

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.

A thermally robust triple-decker complex [bis(η5-pentamethylcyclopentadienyltitanium)-μ-(η4:η4-1,2,4,5-tetrakis(trimethylsilyl)cyclohexa-1-4-diene-3,6-diyl)] (3) was obtained in 4% yield by thermolysing Cp*TiMe3 in the presence bis(trimethylsilyl)acetylene (BTMSA). The solid-state structure of centrosymmetric 3 features rather long all C–C bonds in the nearly planar bridging ligand (1.4720(14)–1.4896(15) A) and a short distance of its least-square plane to the titanium atoms (1.7381(5) A). Computational results revealed the bonding of the central ligand to be accomplished through back-bonding of its two CC bonds and through the simultaneous generation of two σ-Ti–C(H) bonds. Based on CASSCF and CASPT2 results, the molecule acquires several electronic configurations simultaneously, which hinders its representation by one single Lewis structure. Apart from being coordinated to the central ligand, the metal atoms are involved in a direct Ti–Ti bonding by the formation of one σ- and two δ-bonds between them. The bond order of this Ti–Ti overlap shows only a slight decrease upon electronic excitation. The presence of ionic contribution to the bonding of the central ligand is manifested by the charge −1.4e summed on the carbon atoms of the bridging ring. Based on computational results, the spin multiplicity of the ground state is singlet, while the first low lying excitation state is triplet. This is in agreement with the absence of EPR signal in either toluene solution and glass, and with slight downfield shifts of broadened 1H NMR signals of SiMe3 and Cp* methyl groups observed with increasing temperature.

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.

Bis{(diphenylvinylsilyl)tetramethylcyclopentadienyl}titanium dichloride [TiCl2{η5-C5Me4(SiPh2CH=CH2)}2] (1) is reduced with a half molar equivalent of magnesium to the monochloride ([TiCl{η5-C5Me4(SiPh2CH=CH2)}2] (2), whereas one molar equivalent of magnesium affords the titanocene [Ti{η5-C5Me4(SiPh2CH=CH2)}{η5:η2-C5Me4(SiPh2CH=CH2)}] (3) stabilized by η2-coordination of one of the two vinyl groups to titanium(II). In the presence of excess magnesium, the vinyl moieties of 3 undergo intramolecular coupling to afford the ansa-titanocene [Ti(η5:η5:η2-C5Me4SiPh2CH=CHCH2CH2SiPh2C5Me4)] (4) possessing the η2-coordinated double bond in lateral position of its ansa-chain. The symmetrical ansa-titanocene [Ti(η5:η5:η2-C5Me4SiPh2CH2CH=CHCH2SiPh2C5Me4)] (5) was not obtained although its DFT-calculated energy is only slightly higher than that of 4. It is considered that transient 5 gives rise to non-identified tar-like by-products which inherently accompany the formation of 4.

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 reactivity of substituted half-sandwich complexes of Ti, Zr, and Hf towards 2,6-diisopropylaniline NH2C6H3-2,6-iPr2 (LNH) and 2-[(dimethylamino)methyl]aniline NH2C6H4-2-(CH2NMe2) (LNNH) was investigated. Two series of mononuclear complexes (η5-C5Me5)LNMCl2 (M = Ti (3), Zr (4), Hf (5)) and (η5-C5Me5)LNNMCl2 (M = Ti (7), Zr (8), Hf (9)) were prepared from corresponding (pentamethylcyclopentadienyl)metal trichlorides and the lithium precursors LNLi and LNNLi. Besides the desired products a dimeric hafnium compound [(η5-C5Me5){µ-NC6H4-2-(CH2NMe2)}HfCl]2 (10) was also isolated and structurally characterized. The formation of dimeric complexes of this type was also achieved by reacting a series of (η5-C5Me4R)LCNMCl2 (M = Zr, Hf; R = Me, H; LCN = C6H4-2-(CH2NMe2)-µ2C,N) complexes with lithium precursors LNLi and LNNLi generating [(η5-C5Me4H){µ-NC6H3-2,6-iPr2}MCl]2 (M = Zr (11), Hf (13)), [(η5-C5Me5){µ-NC6H3-2,6-iPr2}MCl]2 (M = Zr (12), Hf (14)), [(η5-C5Me4H){µ-NC6H4-2-(CH2NMe2)-µ2N,N}ZrCl]2 (15), and [(η5-C5Me5){µ-NC6H4-2-(CH2NMe2)}ZrCl]2 (16), respectively. The formation of 10 by this reaction procedure was not detected; instead monomeric complexes (η5-C5Me4R)LNNLCNHfCl (R = H (17), Me (18)) were observed as major products. NMR and IR spectroscopy techniques and elemental analysis were used for characterization of the prepared complexes, whereas the structures in most cases were determined by X-ray crystallography.

M. S. thanks the Czech Science Foundation for support through the project 14-30898P. M. O. acknowledges the Czech Science Foundation for the project 13-17593P. R. E. M. thanks the EPSRC for funding (EP/K025112/1 and EP/L014475/1). Post-synthesis alumination of germanosilicate medium-pore ITH zeolites was shown to be an effective procedure for tuning their acidity. Treatment of ITH zeolites synthesized with different chemical compositions (i.e. Si/Ge = 2.5, 4.4 and 5.8) with aqueous Al(NO3)3 solution led to the formation of strong Brønsted and Lewis acid sites and an increasing fraction of ultramicro- and meso-pores in Ge-rich ITH samples (Si/Ge = 2.5 and 4.4). The concentration of Al incorporated into the framework increases with decreasing Si/Ge ratio of the parent ITH. The increasing temperature of alumination from 80 to 175 °C (HT conditions) resulted in (1) a 1.5-2-fold increase in the concentration of Brønsted acid sites formed and (2) a decreasing fraction of framework Al atoms detectable with base probe molecules (i.e. pyridine, 2,6-di-tert-butylpyridine), i.e. an increased concentration of the "inner" acid sites. The activity of prepared Al-substituted ITH zeolites in tetrahydropyranylation of alcohols is enhanced with increasing amount of accessible acid sites in bulky crystals (e.g. alumination at lower temperature) or with increasing total concentration of acid centres within tiny ITH crystals (e.g. alumination under HT conditions). This trend became more prominent with increasing kinetic diameter of the substrate molecules under investigation (methanol

This paper introduces an initial effort at a systematic approach to the typology of elevated water tanks for the purpose of solving the research project Elevated water tanks – identification, documentation, presentation, new use. It builds on the previous definition of the terminology of the problem and the definition of the object of interest. From a typological point of view, elevated water tanks are seen as an integral part of larger technological units – water supply systems. In the framework of the basic division, the typology of elevated water tanks is based on the selection of parameters – the building situation of the tower reservoirs in relation to other objects, the function of elevated water tanks, the supporting structure, the shape and material of the accumulation tank, the number of tanks and the purpose of the object.

The catalytic behavior of isomorphously substituted MIL-100(M) (M=Al, Cr, Fe, In, Sc, V) was investigated in the synthesis of nopol in the Prins condensation of β-pinene with paraformaldehyde. Large mesoporous cages of metal-organic frameworks provide a sustainable confinement for the formation of the target product (100 % selectivity to nopol over all materials studied). MIL-100(Sc) and MIL-100(V) exhibited the highest yield (up to 90 %) of nopol after just 20 min from the beginning of the reaction due to their highest amount of accessible Lewis sites possessing intermediate acidity. The high catalytic activity (reaching almost 90 % of β-pinene conversion) even after decreasing the amount of catalyst from 100 to 25 mg (0.025 and 0.0063 gcatalyst/mmolsubstrate, respectively) the stability of its structure and the possibility to use it several times make MIL-100(V) a promising material for application in acid-catalyzed reactions under mild reaction conditions.

Hydrosilane-B(C6F5)3 adducts were found to activate zirconocene dihalides and generate ternary catalytic systems possessing moderate to high activity in ethylene polymerization to high density polyethylene (HDPE). The activation efficacy of the adducts increased with increasing hydride donor ability and decreased with steric crowding of the particular hydrosilane used. NMR investigation of the HSiEt3/B(C6F5)3/Cp*2ZrF2 system (Cp* = η(5)-C5Me5) revealed the formation of a stable intermediate [Cp*2ZrF(FSiEt3-κF)](+)[HB(C6F5)3](-), whereas a crucial role of the [HB(C6F5)3](-) anion as a hydride donor for generation of an active cationic zirconium hydride center was elucidated.

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.

The paper presents a summary of input information about the research project Water towers – identification, documentation, presentation, new use. It deals with the development of tower water reservoirs in the present territory of the Czech Republic from the beginning of their creation to the present.

The titanocene-ethene complex [Ti(II)(η(2)-C2H4)(η(5)-C5Me5)2] (1) with simple internal alkynes R(1)C≡CR(2) gives complexes [Ti(II)(η(2)-R(1)C≡CR(2))(η(5)-C5Me5)2] {R(1), R(2): Ph, Ph (3), Ph, Me (4), Me, SiMe3 (5), Ph, SiMe3 (6), t-Bu, SiMe3 (7), and SiMe3, SiMe3 (8). In contrast, alkynes with R(1) = Me and R(2) = t-Bu or i-Pr afford allene complexes [Ti(II)(η(2)-CH2=C=CHR(2))(η(5)-C5Me5)2] (11) and (12), whereas for R(2) = Et a mixture of alkyne complex (13A) and minor allene (13) is obtained. Crystal structures of 4, 6, 7 and 11 have been determined; the latter structure proved the back-bonding interaction of the allene terminal double bond. Only the synthesis of 8 from 1 was inefficient because the equilibrium constant for the reaction [1] + [Me3SiC≡CSiMe3] ⇌ [8] + [C2H4] approached 1. Compound 9 (R(1), R(2): Me), not obtainable from 1, together with compounds 3–6 and 10 (R(1), R(2): Et) were also prepared by alkyne exchange with 8, however this reaction did not take place in attempts to obtain 7. Compounds 1 and 3–9 display the longest-wavelength electronic absorption band in the range 670-940 nm due to the HOMO → LUMO transition. The assignment of the first excitation to be of predominantly a b2 → a1 transition was confirmed by DFT calculations. The calculated first excitation energies for 3–9 followed the order of hypsochromic shifts of the absorption band relative to 8 that were induced by acetylene substituents: MePh ≫ SiMe3. Computational results have also affirmed the back-bonding nature in the alkyne-to-metal coordination.

Seven tin(IV) amidinates were prepared and isolated from the reactions of tin(II) bisamidinate [Cy–NC(nBu)N–Cy]2Sn with a series of various 1,2-diones ((4 + 1) oxidative cycloaddition mechanism) and chlorine/oxygen molecules, respectively. The ligand substitution effect of (non)symmetric 1,3-diones to starting stannylene as well as intermolecular CO2 activation via prepared dimeric stannoxane is also reported. All the prepared tin containing compounds as well as ligand substitution reactions were investigated by the multinuclear NMR (1H, 13C, and 119Sn) spectroscopic techniques. Molecular structures of one tin(II) and seven tin(IV) amidinates investigated were determined by X-ray diffractions and also evaluated by DFT methods. The UV–vis absorption spectra of all desired colored tin(IV) diolates and its diketo precursors were recorded and simulated by TD-DFT methods.