Alkynes Aluminum alkyls

Cationic zirconocene species efficiently activate alkenes toward carbon—carbon bond formation via carbometalation, as has been demonstrated in studies of alkene polymerization. Today, some zirconocene catalysts are available that allow single additions of metal-alkyls (mainly aluminum-alkyls) to alkenes or alkynes, thereby forming stable alkyl- or alkenyl-metals that do not undergo any further oligomerization. On the other hand, carbozirconation with Cp2ZrRCl in the presence of stoichiometric or catalytic amounts of activators has also been realized. 

Alkenes, Cyclic Alkenes, and Dienes Alkenes, Cyclic Alkenes, and Dienes Ethylene Propylene Alkyl Halides Alkynes Aluminum Americium Amides Amides Carbofuran Dimethyl Acetamide Amines Antimony... 

It has been suggested that alkene or alkyne complexes are mechanistically important intermediates in hydroalumination and carboalumination reactions (124-126). Clear spectroscopic evidence for n interactions stems from investigations of alkenylaluminum compounds having a suitable intramolecular separation between the aluminum center and the double bond (127). IR and NMR data of these compounds show comparably lower alkene stretching frequencies and deshielded vinylic protons. Furthermore, these molecules are monomeric in solution this indicates that the tendency toward 7i-complex formation is stronger than that toward the dimeric bonding usual in aluminum alkyls. 

Reaction of Alkynes with Titanium-Aluminum-Alkyl Complexes. . . 270... 

Reductive dimerization of alkenes and alkynes can be achieved with various catalysts in the presence of dihydrogen or other hydrogen donors, such as tetrahydroborates or / -H-eliminat-ing aluminum alkyls. 

Although alkynes and alkenes do not form detectable amounts of complex with aluminum alkyls, various a,)8-unsaturated ketones and anils do form such complexes. Such systems, upon heating, do undergo 1,4-carbalumination [Eqs. (45) and (46)]. The rearrangements of com-... 

Tris(dimethylamino)sulfonium difluo-rotrimethylsilicate, 336 Xenon(II) fluoride, 345 Alkyl bromides Potassium permanganate, 258 Sodium bromide, 46 Tetraethylammonium bromide, 46 Alkyl iodides Aluminum iodide, 17 Potassium permanganate, 258 Sodium iodide, 46 Tetraethylammonium iodide, 46 Alkynes (see also Acetylenic carbonyl compounds, Diynes, Enynes, Propar-gyl alcohols)... 

An alternate route to formation of alkyl monolayers is via Lewis acid catalyzed reactions of alkenes with the hydrogen terminated surface. In this approach, a catalyst such as ethyl aluminum dichloride is used to mediate the hydrosilylation reaction of an alkene (or alkyne), resulting in the same type of product as in the case of the photochemical or thermal reactions. This type of reaction is well known based on molecular organosilane chemistry and has also been used successfully to alkylate porous silicon [31]. Although this route has been shown to work on H/Si(lll), the resulting monolayers are found to have lower coverages than those achieved using the photochemical or thermal approach [29], Another concern with this approach is the possibility of trace metal residues from the catalyst that could adversely affect the electronic properties of these surfaces (even when present at levels below the detection limit of most common surface analysis techniques). 

As a class alkynes are much more reactive in hydroalumination than are alkenes. Hence, both terminal and internal alkynes react at feasible rates with both dialkylaluminum hydrides in alkanes and lithium aluminum hydrides (LiAlRnH4-n) in ethers. Selected examples of such additions are presented in Table 2. With alkyl or aryl substituents, it should be noted that R2AIH adds in a kinetically syn manner, (5 equation 2) and (7 equation 3), and LAH yields the anti adduct (14 equation 6). 

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