Helena Antropiusová

Preparation of μ-(η5:η5-Fulvalene)-di-μ-hydrido-bis(η5-cyclopentadienyltitanium) by the reduction of Cp2TiCl2 with LiAlH4 in aromatic solvents

Summaryμ-(η5:η5-Fulvalene)-di-μ-hydrido-bis(η5-cyclopentadienyltitanium) (1) can be prepared by the reduction of Cp2TiCl2 with LiAlH4 in methylbenzenes and in tetralin at their boiling temperatures in yields greater than 90%. The reduction proceedsvia the bis(η5-cyclopentadienyl)titanium(III) chloride dimer which is further transformed into the unstable [Cp2TiH] species. Thermal decomposition of the latter accompanied by hydrogen evolution gives rise to (1). μ-(η5:η5-Fulvalene)-μ-hydrido-μ-chloro-bis(η5-cyclopentadienyltitanium), the first fulvalene containing compound observed in the system is formed by hydrido-chloro exchange of (1) with (Cp2TiCl)2 and aluminium chlorohydrides.

[6+2]Cycloadditions catalyzed by titanium complexes

Abstract The Ziegler catalyst TiCl4-Et2AlCl and the arenetitanium(II) complex (η6-C6H6)Ti(II)(AlCl4)2 induce [6 + 2]cycloaddition reactions of cycloheptatriene with dienes and acetylenes. Addition to 1,3-butadiene affords 7 - endo - vinyl - bicyclo[4.2.1]nona - 2,4 - diene (main product) and bicyclo[4.4.1]- undeca - 2,4,8 - triene, a product of [6+4]cycloaddition. Isoprene reacts similarly, yielding mainly 7- endo - isopropenyl - bicyclo[4.2.1]nona - 2,4 - diene. 2,3 - Dimethyl - 1,3 - butadiene gives 8,9dimethylbicyclo [4.4.1]undeca - 2,4,8 - triene, a product of [6 + 4]cycloaddition, while [6 + 2]cross-adducts are minor products. The reaction of cycloheptatriene with norbornadiene gives mainly hexacyclo[6.5.1.02,7.03,12.6,10.09,13]tetradec - 4 - ene via [6+2]cycloaddition followed by intramolecular Diels-Alder reaction. As a by-product, pentacyclo[7.5.0.02,7.03,5.048]tetradeca - 10,12 - diene is formed by a [2+2+2]mechanism. Addition of cycloheptatriene to diphenylacetylene and bis - (tri- methylsilyl)acetylene furnishes sustituted bicyclo[4.2.1]nona - 2,4,7 - trienes. Alkenes, E,E-2,4 - hexadiene and 1,3 - cyclooctadiene are unreactive. The [6+2]cycloaddition is made possible by coordination of cycloheptatriene to titanium, which changes the symmetry of the frontier orbitals in the triene. The reactivity of the trienophile is also enhanced by coordination to the catalyst.

Effects of methyl substituents at the cyclopentadienyl ligand on the properties of C5H5TiCl3 and C5H5TiAl2Cl8-x(C2H5)x (x = 0–4) complexes

The methyl substituents in the series of CpTiCl3 compounds (CP = Cp, MeCp, Me3Cp, Me4Cp, Me5 Cp and EtMe4Cp) shift the position of their CT absorption band from λ = 384 nm to max. 438 nm and decrease the rate of reduction of CpTiCl3 by ethylaluminium compounds yielding the trinuclear CpTiAl2Cl8 - xEtx (x = 0–4) complexes. In the CpTiCl3/excess Et2AlCl systems the rate of reduction was controlled by pseudomonomolecular decomposition of the proposed octahedral intermediate CpTiEt(Cl2AlEt2)(Cl3AlEt). The rate constants for reduction decreased in the above series of CpTiCl3 compounds from 1.10 × 10−3 to 6.15 × 10−5 s−1. The methyl substituents in the CpTiAl2Cl8-xEtx complexes shifted the charge transfer bands to longer wavelengths, the d-d transition to shorter wavelengths and the ESR g-value away from the free electron value. The opposite shifts were induced by the replacement of the outer chlorine atoms in the chloroaluminate ligands by ethyl groups. On going from Cp to Me5Cp the thermal stability of the CpTiAl2Cl8 complexes decreased while the complexes CpTiAl2Cl4Et4 became stable even with the excess of Et3Al. The CpTiAl2Cl8-xEtx complexes were also formed in the redox reaction of non-dimerizing methylcyclopentadienes (Me3CpH/EtMe4CpH) with bis(di-μ-chloroalane)(benzene)titanium(II) complexes C6H6 · TiAl2Cl8-xEtx (x = 0–2). The reaction was found stoichiometric except for the perchloro complexes forming diamagnetic byproducts.

Direct proof of the molecular structure of dimeric titanocene; The X-ray structure of μ(η5:η5-fulvalene)-di-(μ-hydrido)-bis(η5-cyclopentadienyltitanium)· 1.5 benzene☆

Abstract The dimeric titanocene crystallizes as a benzene solvate with molar ratio 1: 1.5. The crystals are monoclinic, space group P 21 n / n with Z = 4 and lattice parameters α = 5.978(4), b = 14.541(6), c = 26.963(8) A and β = 92.11(2)°. In the series of (C 10 H 8 )(C 5 H 5 )TiX] 2 complexes, where X  H, H/Cl (1: 1), Cl or OH, the dihydrido complex has the shortest Ti-Ti distance (2.989 A) and largest dihedral angle between the planes of C 5 H 4 rings of the fulvalene ligand (17.7°).

Titanium-catalyzed Diels-Alder cycloaddition of conjugated dienes to bis(trimethylsilyl)acetylene. 1,2-bis(trimethylsilyl)cyclohexa-1,4-diene, 1,2-bis(trimethylsilyl)benzene, and their methyl derivatives

Abstract The catalytic system Et 2 AlCl/TiCl 4 induces Diels-Alder cycloaddition of bis(trimethylsilyl)acetylene to 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and ( E )-1,3-pentadiene affording 1,2-bis(trimethylsuyl)cyclohexa-1,4-dienes in high yields. The cyclohexadienes are readily converted to the corresponding 1,2-bis(trimethylsilyl)benzenes upon heating to 240°C. Mass, infrared, 1 H, 13 C and 29 Si NMR spectra of all the products obtained are reported and briefly discussed. The crowded character of aromatic compounds is reflected in their mass, 13 C and 29 Si NMR spectra.

Ethyl-substituted (π5-cyclopentadienyl)-bis(dihaloalanedi-μ-halo)titanium(III) and (η6-benzene)bis(dihaloalanedi-μ-halo)titanium(II) chloro and bromo complexes

Abstract Ethyl-substituted trinuclear complexes CpTiAl 2 Cl 8− n Et x ( x = 1-4) were prepared by by the reaction of CpTicl 3 with two equivalents of ethylaluminium compounds. The complexes were characterized by the half-width of their EPR single-line spectra, which decreased from 1.9 mT for x = 1 to 0.85 mT for x = 4, and by the position of their d-d absorption bands. From these data the composition of ethylated titanium complexes formed in the systems CpTiAl 2 Cl 8 -Et 3− x AlCl x ( x = 0, 1, 2) was determined. In the system C 6 H 6 · TiAl 2 Cl 8− Et 3− x AlCl x the formation of only the first two members of ethylated arenetitanium(II) series C 6 H 6 · TiAl 2 Cl 7 Et and C 6 H 6 · TiAl 2 Cl 6 Et 2 could be observed. The latter complexes differed from the parent complex in the position of the charge transfer band Ti II → C 6 H 6 and, after addition of an equimolar amount of cyclopentadiene, the EPR spectra of corresponding CpTi III trinuclear complexes were observed. In both, Ti III and Ti II series, the stability of the complexes decreased with increasing content of ethyl groups. The properties of CpTi III trinuclear complexes are compared with those of the binuclear complexes Cp 2 TiAlCl 4− x Et x ( x = 0, 1, 2). Results for the series of bromo complexes were mostly analogous.

Polymethylcyclopentadienyltitanocene tetrahydridoaluminates and their reaction with butadiene; a spectroscopic study

Abstract The CP ★ 2 TiAlH 4 complexes (CP ★  Cp, MeCp, Me 3 Cp, Me 4 Cp, Me 5 Cp and EtMe 4 Cp) were prepared from CP ★ 2 TiCl and LiAlH 4 in toluene. On aging, all the CP ★ 2 TiAlH 4 complexes, except for the peralkylated ones, formed paramagnetic clusters composed probably of the CP ★ 2 TiH and CP ★ 2 TiAlH 4 units. The clusters reacted with an excess of butadiene to give (1-methyl-η 3 -allyl)titanocenes and CP ★ 2 TiAlH 4 complexes. The CP ★ 2 TiAlH 4 complexes yielded the same allyltitanocene products, but in a slower subsequent reaction. Aging of the peralkylated CP ★ 2 TiAlH 4 complexes led to the thus far unknown paramagnetic products which are unreactive to butadiene. The (1-methyl-η 3 -allyl)titanocenes were also prepared from CP ★ 2 TiCl by reaction with LiAlH 4 in the toluene/butadiene mixture. The CP ★ 2 TiAlH 4 1 complexes which formed transiently in these systems were found to have ESR parameters different from those obtained in pure toluene. The effects were established of themethyl substituents in the CP ★ ligands on the ESR and electronic absorption spectra of the CP ★ 2 TiAlH 4 complexes and (1-methyl-η 3 -allyl)titanocenes.

The isomerization catalyst (C5H5)2TiCl2-LiAlH4. Influence of the nature of unsaturated hydrocarbons on the catalyst activity

Abstract The reaction pathway between the components of the catalytic system Cp 2 TiCl 2 -LiAlH 4 -unsaturated hydrocarbon, depends considerably on the nature of the reaction medium. In dienes which are able to form stable η 3 -allyltitanocene derivatives, these represents the main reaction product; they are catalytically active in the double bond shifts. In dienes not forming stable η 3 -allyltitanocene derivatives and in α-olefins, the catalytically-active η 1 -alkenyl- and alkyl-titanocenes are transiently formed, deactivating rapidly to give the [(C 5 H 5 )(C 5 H 4 )TiHAlR 2 ] 2 complexes and minor amounts of η 3 -allyltitanocene derivatives in a side reaction involving intermolecular hydrogen transfer. In all α-olefinic hydrocarbons, the formation of alkyl-, η 1 -alkenyl- or η 3 -allyl-titanocene derivatives is preceded by the hydroalumination reaction, yielding Cp 2 TiCl 2 AlR 2 complexes. In internal olefins the hydroalumination reaction does not occur and the alkyltitanocenes which are formed catalyze the transformation of (Cp 2 TiCl) 2 into μ-(η 5 : η 5 -fulvalene)-di-μ-chlorobis(η 5 -cyclopentadienyltitanium), thus inducing the self-deactivation of the system.

Ring closure in 1,2-divinylcyclohexanes and isomerization to 3-methyl-3a,4,5,6,7,7a-hexahydro-1h-indenes catalyzed by titanocene hydride derivatives

Abstract Titanocene hydride derivatives induce the cyclization of 1,2-divinylcyclohexanes to trans- and cis-1-methylene-octahydro-1H-indene and their isomerization to trans- and cis-3-methyl-3a,4,5,6,7,7a-hexahydro-1H-indene.

Redox reaction of arenetitanium(II) complexes with cyclopentadiene leading to (η5-cyclopentadienyl)titanium(III) complexes: an epr study

Abstract Bis(dichloroalanedi-μ-chloro)(η 6 -arene)titanium(II) complexes are readily oxidised by cyclopentadiene to yield (η 5 -clopentadienyl)bis(dichloroalanedi-μ-chloro)titanium(III). Upon further addition of cyclopentadiene the AlCl 4 ligand is replaced by cyclopentadienyl to give (di-η 5 -cyclopentadienyl)(dichloroalanedi-μ-chloro)titanium(III). Similar reactions were observed with bis(dibromoalanedi-μ-bromo)(gh 6 -benzene)titanium(II). The structures of both the initial and final complexes are confirmed by this redox reaction.