Tellurenyl halides

Association of Sulfenyl, Selenenyl and Tellurenyl Halides with Chelating Substituents... 

Organotellurium(II) compounds can also contain a three-center, four-electron bond as shown for 39 to 42 in Fig. 19. Typically, these molecules contain an odd number ligands around the central atom and an electronegative atom helps to stabilize a tellurenyl halide or selenenyl halide bond through chelation to form a four, five, or six membered ring. " Such molecules are described as lO-Te-3 and lO-Se-3... 

Halogenated derivatives of tellurium in the oxidation state +2, namely tellurenyl halides, are unfamiliar compounds compared to the well-known selenium analogues. 

Tellurophosphoranes, obtained through a transylidation reaction between tellurenyl halides and phosphoranes, react with aldehydes to give the expected vinylic tellurides as an E Z isomeric mixture (method a). One other methodology involves the treatment of equimolar amounts of phenyl tellurenyl bromide and phosphonium salts with t-BuOK followed by an aldehyde (method b). Under these lithium-salt-free conditions, (Z)-vinylic tellurides are the main products. ... 

The alkyne hydrozirconation protocol was also applied to acetylenic tellurides furnishing the zirconated vinyl tellnrides in cis fashion and high regioselectivity. Subsequent treatment with tellurenyl halides affords telluro ketene acetals with total retention of configuration. ... 

From alkynyl Grignard and lithium compounds and organyl tellurenyl halides... 

When such groups are not present, the organotellurium halide cannot be isolated. In these cases, aryl, alkenyl, and alkyl tellurenyl halides, usually bromides and iodides, are prepared and used in situ. ... 

Organo tellurium halides, also named organo tellurenyl halides, are in principle easily accessible through controlled halogenolysis of diorgano ditellurium compounds. However, 2-naphthyl tellurium iodide, prepared in 19592 from bis[2-naphthyl] ditellurium and iodine, remained the only compound of this type until 1971/72, when a series of ortho-carbonyl substituted phenyl tellurium halides were synthesized3-4. Aryl tellurium halides without substituents in the ortho-position to tellurium were isolated and characterized in 1975s. 

The cyclic structure of tellurenyl halides 2 stabilized by an intramolecular coordination 0->Te bond provides for their peculiar reactivity unusual for tellurenyl halides without such a bond. Whereas reduction of the latter gives diaryl ditellurides (99ZOK981), 2 under the same condititions are transformed into /u. v(2-aroylvi-nyl)tellurides 21 (in more than 80% yield), ditellurides 22 being formed as a minor product (86JOC1692) (Scheme 11). 

Reactions of aromatic aldehydes and ketones containing a tellurenyl halide group in an o-position with organometallic compounds provide an approach to less accessible o-alkyltellurocarbonyl compounds (72BSF3559, 78T655, 81JOM(208)11) (Scheme 14). 

If the diaryl ditelluride is previously converted in situ into the corresponding tellurenyl halide, both the electrophilic tellurium moieties are used. (The stable crystaUine 2-naph-thylteUurenyl iodide (see Section 3.7) reacts similarly.) The reaction is of general application, giving high yields of the expected tellurides with aromatic, aliphatic, cycloaliphatic, vinylid and acetylenic Grignard reagents, under mild conditions. 

This reaction is an apphcation of the general method for the preparation of unsymmet-rical tellurides (see Section 3.1.3.5). The tellurenyl halide is prepared in situ by halogeno-lysis of the corresponding ditelluride. ... 

---