Cyclopentadienyltitanium compounds

Synthesis. The discovery of stable cyclopentadienyltitanium compounds, in particular Cp2TiCl2, stimulated the synthesis and study of a host of related compounds. These include both CpTiX and Cp2TiX2. 

Cyclopentadienyltitanium Compounds with Other Carbon Titanium Links. Cyclopentadienyltitanium trichloride and, particularly, CpgTiClg react with RLi or with RAl compounds to form one or more R—Ti bonds. As noted, the Cp groups stabilize the Ti—R bond considerably against thermal decomposition, although the sensitivity to air and moisture remains. Depending on the temperature, mole ratio, and stmcture of R, reduction of Ti(IV) may be a serious side reaction, which often has preparative value for Cp Ti(Ill) compounds (268,274,275). 

Organotitanium compounds are usually liable besides cyclopentadienyltitanium compounds. Therefore, titanium organic compounds are not organotitanium compounds having a Ti—C bond but titanium alkoxide having a Ti—O bond [11,35]. 

Cyclopentadienyltitanium compounds have been studied as polymerization catalysts of ethylene as Ziegler-Natta type catalysts [43—45a]. For example, as... 

Bis-cyclopentadienyltitanium(ll) species are unstable 14-electron d species, with one lone-electron pair and two vacant valence orbitals. The reactivity of Cp2Ti has been compared to carbenes. The interactions between the occupied and unoccupied orbitals can explain why Cp2Ti reacts with unsaturated compounds to give metallacycles (see Metallacycle). 

Preparations of [(>7-C5H5)TiCl2] have been described, but they are less satisfactory than the procedure given here. Relatively large quantities (> 10 g) of -cyclopentadienyltitanium dichloride can be readily obtained by this method, and from that compound a mononuclear phosphine complex, (jz-CsHs)-... 

Surprisingly, few transition organometallic compounds seem to form crown ether complexes. A complex containing a cyclopentadienyltitanium moiety attached to 18-crown-6 has been structurally characterized. There are three Ti-0 short distances (2.09, 2.14, and 2.15 A), suggesting dative bonding, and the macrocycle behaves mostly as an exo receptor [432]. 

Several more structures are described of compounds containing the di-ir-cyclopentadienyltitanium group and a variety of other ligands. In (7r-Cp)jTiPhj, the mean Ti-C(ir-Cp) distance of 2.31 A is considered to be rather short, but the Ti-C a-bond at 2.27 A is close to the sum of the relevant covalent radii. Reaction of carbon dioxide with dicyclopentadienyl-diphenyltitanium leads to carboxylation of a phenyl ring and the loss of benzene, giving product (1). In this compound, the Ti-C(w-Cp) distance. 

Substitution of the a-bonded ligands in bis-cyclopentadienyltitanium(iv) compounds is the subject of some recent kinetic and stereochemical studies. Hydrolysis of [(Cp(Cp )Ti(Cl)2] (Cp = 1J-C5H5, Cp = j-C5H4Me) proceeds according to Scheme 22." Formation of [(Cp)(Cp )TiCl]+ and of [(Cp)(Cp )Ti] + is a first-order... 

Cyclopentadienylaryl or cyclopentadienylalkyl derivatives of cyclopentadie-nyltitanium obtained by the reaction of cyclopentadienyltitanium with aryl metal compounds or alkyl metal compounds, are also stable by the stabilization action of the cyclopentadienyl ring. For example, Cp2TiCl2 reacts with phenyllithium to give the diphenyl derivatives. This compound decomposes at 105 °C to yield benzene [21]. 

Some organotin ethers of carbohydrate derivatives have been synthesised as potential pestiddes and the selected acylation of some cyclic dibutylstannylene compounds is discussed in Chapter 7. Treatment of cyclopentadienyltitanium trichloride with l,2 5,6-di-0-isopropylidene-a-D-glucofuranose affords adduct (26) which may be transformed into the chiral organometallic reagents (27)-(29). These react with aldehydes (RCHO) to give products (30)-(32), respectively, with high stereoselectivity. ... 

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