Synthesis and reductive splitting of tellurium-containing oligomers on the basis of 1-bromo-2-methyl-3-chloropropane

Abstract

The results of the synthesis of tellurium-containing oligomers based on 1-bromo-2-methyl-3-chloropropane are presented. By the example of the reductive splitting of tellurocol the possibility is demonstrated of the synthesis of methyltellanyl derivatives, which are valuable reagents for organic synthesis and for the design of coordination compounds.Polymers and oligomers containing tellurium atoms in the chain possess a number of practically valuable properties [1]. Generally, they are synthesized by polycondensation of organic dihalogenides with polytellurides of alkali metals M 2 Те n (M = Na, K; n = 1-3), which, in turn, are prepared from elemental tellurium in the redox systems [2]. By using such an approach, polyaryleneditellurides have been prepared [3].We prepared tellurium-containing oligomers with paramagnetic properties [4] from 1-bromo-3-chloropropane [5] and chlorex [6]. However, in the reaction of 1,2-dihaloethanes with tellurium (or selenium) under similar conditions no oligomeric products are formed, but rather dehalogenation with the evolution of ethylene and elemental chalcogens is observed [7]. A similar course of the reaction, that is, elimination of the vicinal halogen atoms (as halogenide anions) under the action of soft nucleophiles, in particular, chalcogen-containing, is a well-known reaction [8] proceeding, as many authors believe, as a halogenophilic attack of the nucleophile at the halogen atom [9]. The halogenophilic attack and the subsequent elimination of the halogen, in turn, are to a considerable extent determined by steric effects caused by the vicinal arrangement of the halogen atoms.In some cases the elimination of halogens may occur also with the derivatives of 1,3-dihalopropanes. Thus, the course of the reaction of 1,3-dibromo-and 1,3-dichloropropane with RTeLi (R = Me, Ph) depends on the temperature: at -196°С the substitution of the halogen atoms by RTe is observed, whereas at 25°С, the formation of propene and R 2 Te 2 [10]. The reaction of МеTeLi with tetrakis(bromomethyl)methane, in which the bromine atoms are in the 1,3-position to each other, the substitution of two bromine atoms by the methyltellanyl group is observed with elimination of the other two bromine atoms and the formation of the cyclopropane derivative [10].1-Bromo-2-methyl-3-chloropropane (I) has the methyl group in the vicinal position with respect to the halogen atoms. The methyl group is sterically equivalent to the bromine atom [11], so, it can create steric hindrances to conventional nucleophilic substitution and favor the halogenophilic attack and elimination of the halogen atoms.We have performed the reaction of dihalogenide I with elemental tellurium in the system hydrazine hydrate-KОН, in which tellurium suffers reductive activation with the formation of potassium telluride