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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.

Two novel half-sandwich Ti complexes, both incorporating two adamantoxy (OAd) ligands coordinated to their central atoms were synthesized. The complexes were characterized by 1 H, 13 C, 19 F NMR, EI-MS and IR spectroscopy and by single-crystal X-ray diffraction. In both complexes, the coordination environment is pseudo-tetrahedral and is assembled of two O-coordinated adamantoxy and one η 5 -coordinated permethylcyclopentadienyl ligand. The fourth ligand in complex 1 is a methyl group coordinated through a regular σ-bond, whereas in complex 2 the same coordination site is occupied by the methyl group of the balancing (C 6 F 5 ) 3 BMeˉ anion. DFT computations complemented with NBO analyses of 2 have unveiled, that in addition to the electrostatic interactions occurring between the half-sandwich titanocene moiety and the anionic ligand, delocalization of one methyl C H bond into the available acceptor orbital on the central atom takes place. AIM analyses of 2 have revealed the presence of a Bond Critical Point between the metal atom and the anionic methyl group. These results prove foundation for the description of 2 as a zwitterionic complex coupled with a concurrent Ti⋯C H agostic interaction in its molecule. The comparison of 2 with its analogous complex equipped with two O t -Bu ligands instead of both OAd has suggested only a minor change in the extent of the agostic interaction, despite significant geometric differences between the two complexes.

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.

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.

Titanocene hydride [Cp*2TiH] (Cp* = η5-C5Me5) (1) readily inserts simple internal alkynes R1C≡CR2 into its Ti–H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp*2Ti(R1C═CHR2)] (2a–e) contain a σ1-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R1 = SiMe3; R2 = SiMe3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti–H agostic bond of the σ1-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a–4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d1 electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RC≡C)2 to give η3-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a–2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) chloro-alkenyl complexes [Cp*2TiCl(R1C═CHR2)] 3a–3e and chloro-alkenynes 6a and 6b, respectively. 1H and 13C NMR spectra of 3...

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 ].

Five fossil resins from various localities in the Czech Republic were investigated. To arrive at more detailed description of the resins, pyrolysis-gas chromatography/mass spectrometry with derivatisation using tetramethylammonium hydroxide, gas chromatography-mass spectrometry, and micropetrography were applied. The content of organic macerals, composition of biomarkers in the solvent extracts and in the pyrolysates have been determined and compared to amber samples. The analyses clearly indicate that all resins belong to the Class Ib type derived from regular labdane structures that lacked succinic acid. The presence of labdane type diterpenoids and the absence of plant triterpenoids in the resin point to a conifer (gymnosperm) source which contrasts with the angiosperm source of Sarawak amber from Malaysia. According to their chemical composition, all Czech resins can be assigned to the Cupressaceae family. There was an obvious difference between a Duxite sample (Miocene) and other resins that could be attributed to deposition inside wood, which did not allow degradation of the resin.

Bis(decamethyltitanocene) oxide, [(Cp*2Ti)2O] (1; Cp* = η5-C5Me5) has been obtained as a yellow crystalline solid after reacting equimolar amounts of the hydride [Cp*2TiH] and the hydroxide [Cp*2Ti(OH)]. The solid-state structure of 1 revealed a linear Ti–O–Ti arrangement and a mutual, nearly perpendicular orientation of the bent-sandwich titanocene moieties; the length of both Ti–O bonds amounted to 1.9080(3) A. A unique structural feature was a close-to-eclipsed conformation of the cyclopentadienyl ligands, attributed to the high steric congestion of 1. The molecule in toluene glass exhibited a triplet state EPR spectrum of rhombic symmetry, having zero field splitting D = 0.02159 cm–1 and E = 0.00230 cm–1. The 1H NMR spectrum of 1 in toluene-d8 displays a paramagnetic resonance at δ 4.3 ppm (Δν1/2 ≈ 270 Hz). Compound 1 reacts with 1 molar equiv of water to give [Cp*2Ti(OH)]. In CD2Cl2, 1 is oxidized to yield the major product [(Cp*TiCl2)2O] and minor product [{Cp*Ti(Cl)O}3].

Ethene complexes of titanocenes [Ti(II)(η2-C2H4)(Cp′)2] for Cp′ = η5-C5Me5 (1), η5-C5Me4t-Bu (2), η5-C5Me4SiMe3 (3), and η5-C5HMe4 (4) were prepared by reduction of corresponding titanocene dichlorides with magnesium in THF in the presence of ethene. Thermolysis of 1–3 in toluene solution at a maximum of 100 °C resulted in elimination of ethane, affording cleanly doubly tucked-in titanocene compounds 5–7, respectively. Experiments with 2 and 3 in NMR tubes proved that symmetrical isomers 6a and 7a were formed first, and these thermally isomerized to thermodynamically more stable asymmetrical isomers 6b and 7b. The energy difference between 7a and 7b calculated by DFT methods was 15.3 kJ/mol. Thermolysis of 4 in m-xylene required a temperature of 135 °C, affording a mixture of 8b > 8a and “dimeric dehydro-titanocene” 9 as a concurrent product of hydrogen abstraction. In contrast to thermolysis in solvents, heating of 1 and 2 in high vacuum to 135 °C resulted in sublimation of known titanocenes [Ti(C5Me5)2]...

Thermolysis of [TiMe2{η5-C5Me4(CH2CH2CH═CH2)}2] (1) in toluene at 120 °C for 4 h resulted in the formation of the cyclopentadiene ring-tethered titanacyclobutane [TiIV{η5-C5Me4CH2CH2CH(κ-CH)}2CH2] (2) in virtually quantitative yields. Thermolysis in an NMR tube at 100 °C revealed that initial elimination of methane is followed by addition of one 3-butenyl double bond to a titanocene−methylidene moiety. The formed titanacyclobutane intermediate [Ti{η5-C5Me4(CH2CH2CH═CH2)}{η5-C5Me4CH2CH2CH(κ-CH)CH2CH2(κ-CH2)}] (4) then underwent a metathesis reaction with the pendant 3-butenyl to give 2 and free ethene. Cleavage of Ti−C bonds of 2 with HCl afforded stable ansa-[TiCl2{η5-C5Me4(CH2)7η5-C5Me4}] (3). Sunlight photolysis of 1 gave rise to the cyclopentadiene ring-tethered titanacyclopentane [TiIV{η5-C5Me4(CH2CH2CH(κ-CH)CH2}2] (5), the known product of cycloaddition reactions following the removal of chlorine atoms from [TiCl2{η5-C5Me4(CH2CH2CH═CH2)}2] with magnesium (as found by Horacek, M.Chem. Eur. J. 2000, 6,...

Hydrogen sulfide reacts with tucked-in titanocene complexes [Ti(III){η5:η1-C5Me4(CH2)}Cp*] (Cp* = η5-C5Me5) (2) and [Ti{η4:η3-C5Me3(CH2)2}Cp*] (3) and their precursors [Cp*2TiMe] (2a) and [Cp*2Ti(η2-Me3SiC≡CSiMe3)] (3a), respectively, to give the corresponding titanocene hydrosulfides [Cp*2Ti(SH)] (4) and [Cp*2Ti(SH)2] (1), respectively. Hydrogen sulfide also cleaves intramolecular σ- or π-Ti−C bonds in ansa-[TiIII(η1:η5:η5-C5Me4SiMe2CHCH2SiMe2C5Me4)] (5) and ansa-[TiII(η2:η5:η5-C5Me4SiMe2CH═CHSiMe2C5Me4)] (6), affording hydrosulfides ansa-[(η5-CH2Me2SiC5Me4)2Ti(SH)] (7) and ansa-[(η5-CH2Me2SiC5Me4)2Ti(SH)2] (8). The S−H bonds of hydrosulfides 4 and 7 were able to react with the Ti−C bonds in 2 and 5, affording titanocene sulfides [(Cp*2TiIII)2S] (11) and ansa-[{(η5-CH2Me2SiC5Me4)2TiIII}2S] (12), respectively. Combination of 7 with 2a gave rise to the mixed titanocene sulfide [ansa-{(η5-CH2SiMe2C5Me4)2Ti}S(TiCp*2)] (13). The titanium(III) d1 electrons in 11−13 form an electronic triplet state well observa...

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 constrained geometry alkoxide [Ti(III)(η5-C5Me5){η5-C5Me4CH2CMe2O-κO}] (2) and titanocene alcoholates [Cp*2TiOR] for R = 1-adamantyl (3) and pentafluorophenyl (4) were prepared by reacting acetone and the respective alcohols with the singly tucked-in titanocene [Ti(III)(η5-C5Me5)(η5:η1-C5Me4CH2)] (1) in order to add the simplest member to constrained geometry alkoxides 5 and 6 and to extend the series of [Cp*2TiOR] (R = Me (8), tBu (7), Ph (9), and H (10)) compounds for one of the most bulky and the most electron attracting substituent. The titanocene alkoxides with the alkoxy carbon atom tethered to one of the cyclopentadienyl ligands showing the crystallographic Ti−O−C angle close to 133° are a suitable group of compounds to be compared with the [Cp*2TiOR] compounds, where the Ti−O−C angle is about 174° for 3 and 7 and 180° for 4. In spite of these Ti−O−C angle differences, the wavelength of the first electronic transition λexp(1a1 → b2), supposed to indicate the extent of the oxygen π-electron dona...

The ansa-1,2-bis(dimethylsilylene)ethane chain is exclusively activated when the parent ansa-permethyltitanocene compounds are reduced to titanium(II) either by thermolysis of titanium−methyl bonds...

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.

Reaction of [(η5-C5Me5)TiMe3] with [(c-C5H9)7Si8O12(OH)] (SIPOSS) or [(c-C5H9)7Si7O9(OSiMe3)(OH)2)] (DIPOSS′) affords stoichiometrically the half-sandwich titanium-disiloxy-methyl complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2TiMe] (1) and [(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}TiMe] (2), respectively. Compound 2 consists of the two stereoisomers possessing the (η5-C5Me5) ligand and OSiMe3 group in syn- (2a) and anti-position (2b). The more abundant 2a (2a/2b ≈ 2:1) was isolated by fractional crystallization. Compounds 1 and 2a reacted rapidly with B(C6F5)3 to give zwitterionic complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2Ti](+)[(μ-Me)B(C6F5)3](−) (3) and syn-[(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}Ti](+)[(μ-Me)B(C6F5)3](−) (4a), respectively. Infrared spectra proved that 3 and 4a were thermally stable in the solid state, and the structure of 4a was determined by X-ray single-crystal analysis. In contrast, 1H, 13C, and 19F NMR spectra of 3 in toluene C7D8 revealed that it was completely dissociated into initial component...

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.

A series of compounds [Cp*2Ti(III)OR′] where R′ is iPr3Si (2), Ph3Si (3), (tBuO)3Si (4), (c-C5H9)7Si8O12 (5), and tBu (6) were prepared by protolysis of the titanium−methylene bond in singly tucked...

The singly tucked-in permethyltitanocene 1 reacts with an excess of internal alkynes to give the 1:1 adducts 3a−c,f−i, arising from insertion of the alkyne triple bond into the titanium−methylene bond. Only the simplest species, 2-butyne, inserted two molecules to give the known compound 2; however, at a 1:1 stoichiometric ratio the 1:1 adduct 3j was also smoothly formed. 1,4-Disubstituted conjugated diynes with CMe3 or SiMe3 substituents reacted in the same way by only one triple bond to give 3d,e, respectively. The dimethylsilylene-bridged dialkynes Me2Si(C≡CR)2 (R = SiMe3, CMe3) afforded compounds 3k,l with both triple bonds reacting. After insertion of the first triple bond, the second one underwent a rearrangement which resulted in substituent shift and formation of a silacyclobutene ring linked to the titanium atom. Alkynes bearing the bulky substituents CMe3 and SiMe3 were unreactive. Among a number of olefins and 1,3-butadiene, only ethene reacted to give cleanly the 1:1 adduct 3m. The structures ...

The complex [TiCl2{η5-C5Me4(SiMe2H)}2] (3) was prepared by reacting the lithium salt of 2,3,4,5-tetramethyl-1-(dimethylsilyl)cyclopenta-2,4-diene (1) with [TiCl3(THF)3] followed by chlorination of the formed [TiCl{η5-C5Me4(SiMe2H)}2] (2) with PbCl2. The reduction of 3 with excess magnesium in THF in the presence of excess bis(trimethylsilyl)ethyne (btmse) afforded the bivalent metal ansa disilylene complex with π-coordinated btmse [Ti{η5-C5Me4(SiMe2)}2(η2-btmse)] (4). The dehydrocoupling of the SiMe2H groups was accompanied by hydrogen transfer to the free btmse. Analogous reduction of 3 with magnesium in the presence of ethene gave a mixture of titanocene [Ti{η5-C5Me4(SiMe2Et)}2] (5) and its ethene complex [Ti{η5-C5Me4(SiMe2Et)}2(η2-C2H4)] (6). The latter complex is however unstable in this mixture and rearranges with evolution of ethane to [Ti{η5-C5Me4(SiMe2Et)}{η5:η2-C5Me4(SiMe2CH═CH2)}] (7), which has its vinyl group attached by π-coordination to Ti(II). The chlorination of 4 by PbCl2 yields ansa-[TiC...

Reactions of double tucked-in permethyltitanocene [Ti{η3:η4-C5Me3(CH2)2}(η5-C5Me5)] (1) with tert-butanol or propargyl alcohol in toluene proceeded sluggishly even with excess of the alcohol and at elevated temperature. The alcoholysis of 1 with tert-butanol afforded [Ti(η5-C5Me5)(Ot-Bu)3] (3) as the major product and Ti(Ot-Bu)4 as the minor one. The other product of the alcoholysis was pentamethylcyclopentadiene. The only isolated crystalline product was the very minor hydrolytic byproduct [{TiIII(η5-C5Me5)2}(μ-O){TiIV(Ot-Bu)3}] (2). The alcoholysis of 1 containing traces of LiI with HOCH2C≡CH, containing apparently more water than t-BuOH, gave an inseparable mixture of oily products from which several crystals of an unintended hydrolytic byproduct [{Ti(η5-C5Me5)(OCH2C≡CH)(μ-O)}3LiI] (4) were isolated. X-ray crystal structures of 2 and 4 were determined.

The presence of a trimethylsilyl substituent in place of one of the methyl groups of each of the cyclopentadienyl ligands of decamethyltitanocene enhances the thermal stability of the resulting complex, [TiII{η5-C5Me4(SiMe3)}2] (1), and controls the products formed in thermolysis of its methyl derivatives. Titanocene 1 was found to be stable in toluene solution up to 90 °C, while under vacuum at 140 °C it liberated hydrogen to give the asymmetrical doubly tucked-in titanocene [TiII{η3:η4-C5Me2(SiMe3)(CH2)2}{η5-C5Me4(SiMe3)}] (3). The mono- and dimethyl derivatives of 1, the complexes [TiIIIMe{η5-C5Me4(SiMe3)}2] (5) and [TiIVMe2{η5-C5Me4(SiMe3)}2] (6), undergo thermolysis at lower temperature than do the corresponding permethyltitanocene derivatives and eliminate hydrogen from their trimethylsilyl group. Thus, the known [TiIII{η5:η1-C5Me4(SiMe2CH2)}{η5-C5Me4(SiMe3)}] (4) was obtained from 5, and compound 6 afforded [TiII{η6:η1-C5Me3(CH2)(SiMe2CH2)}{η5-C5Me4(SiMe3)}] (7) at only 90 °C, both with liberation ...

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.

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.

Reactions at elevated temperatures (150 °C) of titanocene−η2-bis(trimethylsilyl)ethyne (btmse) complexes [(η5-C5H5-nMen)2Ti(η2-btmse)] (n = 3−5; 1b−d) with bis((trimethylsilyl)ethynyl)dimethylsilane (2a) afford the unusual 1,1-bis(η5-cyclopentadienyl)-4,4-dimethyl-3,5-bis(trimethylsilyl)-1-titana-4-silacyclohexa-2,5-diene complexes [(η5-C5H5-nMen)2Ti{CC(SiMe3)}2SiMe2] (4b−d), whereas the nonmethylated precursor [(η5-C5H5)2Ti(η2-btmse)] (1a) gives under similar conditions the known dinuclear, acetylide-bridged complex [{(η5-C5H5)2Ti(μ-η1:η2-C⋮CSiMe3)}2] (3a). In contrast, analogous reactions with bis((trimethylsilyl)ethynyl)diphenylsilane (2b) give the product of simple ligand exchange [(η5-C5Me5)2Ti(η2-Me3SiC⋮CSiPh2C⋮CSiMe3)] (6d) from 1d and mixtures containing the similar complex [(η5-C5HMe4)2Ti(η2-Me3SiC⋮CSiPh2C⋮CSiMe3)] (6c) and the titanasilacyclohexadiene [Ti(η5-C5HMe4)2Ti{CC(SiMe3)}2SiPh2] (5c) from 1c. Hydrogenolysis of 5c (1 bar/3 h) affords 1,4-bis(trimethylsilyl)-5,5-diphenyl-5-silacyclopenta-1...

The five new silanes C5Me3RSiMenCl3 − n (n = 3, R = i-Pr (5); n = 2, R = i-Pr (6); n = 2, R = s-Bu (7); n = 2, R = cyclohexyl (8); and n = 3, R = t-Bu (9)) were synthesized by reaction of 1-alkyl-2,3,4-trimethylcyclopentadienyl lithium salts with appropriate chlorosilane and characterized by NMR, MS, and IR spectra. At elevated temperatures (250–360 K), all the silanes undergo a non-degenerate sigmatropic silyl rearrangement, which generates non-equivalent structures a and b. The presence of minor structure c was observed in compounds 5 and 7 only. The Diels–Alder cycloaddition of 5 with strong dienophiles tetracyanoethylene (TCNE), and dimethylacetylenedicarboxylate (DMAD) provides compounds 10 and 11, which confirmed isomers a and b, respectively. The free energy of activation of b → a isomerization for compounds 5–8 evaluated from variable temperature NMR spectra show only marginal influence of group R on the 1,2-silyl shift rate. Moreover, in compounds 5 and 7, the process b → a was found significantly faster than b → c process in the above-mentioned temperature range.

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].

The complexes [Zr(η 2 -Me 3 SiC≡CSiMe 3 )(η 5 -C 5 Me 4 R) 2 ] (R = Me (5), H (6), SiMe 3 (7)) reacted smoothly with terminal alkynes HC≡CR'(R' = CMe 3 , SiMe 3 , ferrocenyl (Fc), Ph) to give the agostic alkenyl-alkynyl complexes [Zr(η 1 -C≡CR'){η 3 -C(SiMe 3 )=CH(SiMe 3 )}(η 5 -C 5 Me 4 R) 2 ] (R/ R' = Me/CMe 3 (5a), Me/SiMe 3 (5b), H/CMe 3 (6a), H/SiMe 3 (6b), H/Fc (6c), H/Ph (6d), SiMe 3 / CMe 3 (7a), SiMe 3 /Fc (7c)). Complex 7a, formed in situ from 7 and HC≡CCMe 3 , dimerized tert-butylethyne exclusively to give the head-to-tail dimer Me 3 CC≡CC(CMe 3 )=CH 2 , and when all the terminal alkyne was consumed, 7 was restored. Complex 7 reacted similarly with 1-hexyne, phenylethyne, and (trimethylsilyl)ethyne, affording the respective alkenyl-alkynyl complexes, which also changed back to 7 on evaporation of the reaction solutions; none of these terminal alkynes was dimerized with 5-7. Heating of complex 6 with LiC≡CSiMe 3 in toluene or THF yielded the diamagnetic zirconate complex Li[Zr(η 1 -C≡CSiMe 3 )(η 2 -Me 3 SiC≡ CSiMe 3 )(η 5 -C 5 HMe 4 ) 2 ] (6e) and its solvatomorph Li[Zr(η 1 -C≡CSiMe 3 )(η 2 -Me 3 SiC≡CSiMe 3 )(η 5 -C 5 HMe 4 ) 2 ].C 4 H 8 O (6f), respectively. The lithium cation in 6e and 6f is placed in a position at the side of the alkynyl triple bond and close to C β of the η 2 -Me 3 SiC≡CSiMe 3 ligand, apparently interacting with both moieties. All presented complexes were characterized by the standard spectral methods, and the structures of 5a, 6a, 6c, 6d, and 6e were 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.

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.

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 [ZrCl2{η5-C5Me4(SiMe3)}2] (1) with excess magnesium in tetrahydrofuran affords a mixture of the monomeric zirconocene hydride [ZrH{η1:η5-C5Me4(SiMe2CH2)}{η5-C5Me4(SiMe3)}] (2) and the dimeric, tetranuclear Zr(III)− and Zr(IV)−magnesium hydride complexes 3 and 4, respectively. In the presence of bis(trimethylsilyl)ethyne (btmse), a similar reduction yields the η2-alkyne complex [Zr{η5-C5Me4(SiMe3)}2(η2-btmse)] (5) as the major product and compounds 2−4 as minor impurities. Upon thermolysis under vacuum, 5 undergoes a 2-fold hydrogen transfer from trimethylsilyl groups in the zirconocene intermediate to leaving btmse to afford [Zr{η5:η1-C5Me4(SiMe2CH2)}2] (6) and a mixture of alkenes (E)- and (Z)-Me3SiCHCHSiMe3 (E ≫ Z). Crystal structures of compounds 2 and 4−6 were 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.

Reduction of titanocene dichlorides bearing (ω-alkenyl)dimethylsilyl substituents [TiCl2{η5-C5Me5(SiMe2R)}2], where R = CHCH2 (3) and CH2CHCH2 (4), affords highly reactive Ti(II) intermediates, which immediately undergo intramolecular reactions with the pendant double bonds in a way dependent on the length of the alkenyl chain. The reduction of 4 with magnesium at 60 °C affords cleanly the cyclopentadienyl-ring-tethered titanacyclopentane, [Ti(η1:η1:η:5η5-C5Me4SiMe2CH(Ti)CH(Me)CH(Me)CH(Ti)SiMe2C5Me4] (5), which can be opened by HCl to an ansa-titanocene dichloride with a six-membered saturated bridging chain, [TiCl2{η:5η5-C5Me4SiMe2CH2CH(Me)CH(Me)CH2SiMe2C5Me4)2}] (6). An analogous reaction of 3 can be accomplished at low temperatures and only to some extent, providing a mixture of titanacyclopentane complex [Ti(η1:η1:η:5η5-C5Me4SiMe2CH(Ti)CH2CH2CH(Ti)SiMe2C5Me4] (10) and the fluxional η2-alkene complex [Ti(η5-C5Me4SiMe2CHCH2)(η2:η5-C5Me4SiMe2CHCH2)] (9). At 60 °C, the reduction of 3 yields a mixture of a...

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.

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 reduction of symmetric, fully-substituted titanocene dichlorides bearing two pendant ω-alkenyl groups, [TiCl2(η5-C5Me4R)2], RCH(Me)CH=CH2 (1 a), (CH2)2CH=CH2 (1 b) and (CH2)3CH=CH2 (1 c), by magnesium in tetrahydrofuran affords bis(cyclopentadienyl)titanacyclopentanes [TiIV{η1:η1:tlsb&endash;3%>η5:η5-C5Me4CH(Me)CH(Ti)CH2CH(CH2(Ti))CH(Me)C5Me4}] (2 a), [TiIV{η1:η1:η5:η5-C5Me4(CH2)2CH(Ti)(CH2)2CH(Ti)(CH2)2C5Me4}] (2 b) and [TiIV{η1:η1:η5:η5-C5Me4(CH2)2CH(Ti)CH(Me)CH(Me)CH(Ti)(CH2)2C5Me4}] (2 c), respectively, as the products of oxidative coupling of the double bonds across a titanocene intermediate. For the case of complex 1 c, a product of a double bond isomerisation is obtained owing to a preferred formation of five-membered titanacycles. The reaction of the titanacyclopentanes with PbCl2 recovers starting materials 1 a from 2 a and 1 b from 2 b, but complex 2 c affords, under the same conditions, an isomer of 1 c with a shifted carbon-carbon double bond, [TiCl2{η5-C5Me4(CH2CH2CH=CHMe)}2] (1 c′). The titanacycles 2 a-c can be opened by HCl to give ansa-titanocene dichlorides ansa-[{η5:η5-C5Me4CH(Me)CH2CH2CH(Me)CH(Me)C5Me4}TiCl2] (3 a), ansa-[{η5:η5-C5Me4(CH2)8C5Me4}TiCl2] (3 b), along with a minor product ansa-[{η5:η5-C5Me4CH2CH=CH(CH2)5C5Me4}TiCl2] (3 b′), and ansa-[{η5:η5-C5Me4(CH2)3CH(Me)CH(Me)CH=CHCH2C5Me4}TiCl2] (3 c), respectively, with the bridging aliphatic chain consisting of five (3 a) and eight (3 b, 3 b′ and 3 c) carbon atoms. The course of the acidolysis changes with the nature of the pendant group; while the cyclopentadienyl ring-linking carbon chains in 3 a and 3 b are fully saturated, compounds 3 c and 3 b′ contain one asymetrically placed carbon-carbon double bond, which evidently arises from the β-hydrogen elimination that follows the HCl addition.

The new class of compounds arising from unconventinal additions of 1,4-disubstituted 1,3-butadiynes to activated permethylmetallocene species of Ti and Zr can be used in facile functionalizations. For example, the chiral product 5, obtained from the addition of tBuC⋮CC⋮CtBu to activated permethyltitanocene, has been derivatized by simple means, e.g., hydrogen chloride, bromine, or dihydrogen, affording practically useful functionalized titanocene compounds containing a chiral auxiliary ligand with an intramolecularly coordinated (compound 7) or a free double bond (compounds 8a,b). The new complexes have been characterized spectroscopically. Additionally, X-ray crystal structure analyses were performed for 7 and 8a,b.

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.

Thermally induced elimination of bis(trimethylsilyl)acetylene from its titanocene complex [{η5-C5Me4(SiMe3)}2Ti(η2-Me3SiC⋮CSiMe3)] (1) afforded the stable titanocene [{η5-C5Me4(SiMe3)}2TiII] (2) in...

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.

Addition of excess ferrocenylacetylene (FcCCH) to [η 5 -(C 5 H 5 )Ti][μ:η 2 :η 2 -C 2 (SiMe 3 ) 2 ] 2 [η 5 -(C 5 H 5 )Mg] ( 1 ) affords the novel ferrocene–pseudotitanocene complex [η 5 -1,2,5,6-tetrakis(trimethylsilyl)-4-ferrocenylcyclohexa-1,4-dienyl](η 5 -cyclopentadienyl)titanium(II), [η 5 -(Me 3 Si) 4 FcC 6 H 2 ]Ti(η 5 -C 5 H 5 ) ( 2 ), as the sole isolated titanium-containing product. Its structure was established by EI MS, NMR and UV–vis spectroscopy. The formation of 2 follows the general reaction route of terminal acetylenes with 1 .

The reduction of (η5-C5H5-nMen)2TiCl2 (n = 0, 4, and 5) complexes by magnesium metal in tetrahydrofuran and in the presence of [(trimethylsilyl)ethynyl]ferrocene (2) or [(phenyl)ethynyl]ferrocene (...