Organotitanium compounds are compounds in which a titanium atom is connected directly to a carbon atom of organic functional groups.
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Organo-titanium compounds include homo- and hetero-ligand complexes in which the titanium atom has a formal oxidation state of +2 to +4. The structure of such compounds depends on the oxidation state of titanium. So, if the organic compounds Ti (IV) are monomeric, then the compounds Ti (III) are most often connected by bridging groups, for example, Ti (μ-R) n Ti. Little is known of organic compounds Ti (II).
As a rule, molecules of organotitanium compounds have a tetrahedral or octahedral structure; compounds with a different molecular structure are rare.
The most studied organotitanium compounds include:
- cyclopentadienyl titanium complexes in which the bond of the titanium atom with the ligand (Cp) is of the π type, for example, [Ti (L) n (π-Cp) 2 ] (n = 1, 2), [Ti (L) n ( π-Cp)] (n = 3,4), where L is an alkene, organophosphorus, acyl or carbonyl group
- titanium complexes in which the ligand is bound to the central atom by the σ-bond ([Ti (σ-R) 4-n (σ-R) n L]), n = 1, 2, where X is the acyl group, L are electron-donating ligands
- mixed complexes with π and σ bonds ([Ti (σ-R) 2 (π-R) 2 ], [Ti (σ-R) (π-R) L]).
Physical and chemical properties
A number of organotitanium compounds have a high reactivity. In particular, some of them are capable of reacting with inert organic solvents. It is possible to increase the stability of organotitanium compounds by introducing chelating ligands or ligands, due to the considerable size of their molecules, which completely shield the central atom of titanium. Many complexes are easily oxidized in air.
Ligands in the molecules of titanium complexes can easily be replaced by acyl groups. σ-R ligands are replaced even at room temperature; substitution of π-R ligands requires heating of the reagents. In this case, the substitution reaction occurs in the presence of halogens, water or alcohols according to the heterolytic mechanism. Organotitanium compounds also enter ligand modification reactions, for example, the incorporation of molecules of certain substances (CO, CO 2 , SO 2 , NO, N 2 ) via the Ti-C bond.
Receiving and applying
The most common method for the synthesis of organotitanium compounds is the interaction of anhydrous titanium salts with lithium -, sodium -, magnesium -, zinc - or organoaluminum compounds in an anhydrous medium.
The heteroligand complexes of titanium, which contain methyl, aryl or cyclopentadienyl ligands together with halogen atoms and alkoxyl groups, are widely used. They are used as an integral part of the Ziegler-Natta catalyst system in the polymerization of vinyl monomers, as combustion regulators, for the production of metal and metal oxide coatings.
Literature
- Chemical Encyclopedia / Editorial Board: Knunyants I.L. et al. - M .: Soviet Encyclopedia, 1995. - T. 4. - 639 p. - ISBN 5-82270-092-4 .