Hexamethyl disilane

As discussed insection3.9.1.,more recent work1316 gives [(CH3)3Si-Si(CH3)3] = 67.3 kcal.mole.-1 

The thermal decomposition is first-order and the rate coefficient is given by k = 1.7 x 1014 exp(—51,000/i T) sec-1. The mean metal-carbon bond dissociation energy in this alkyl is 58.0 kcal.mole-1. In view of the normal frequency factor, it might seem reasonable to relate the observed activation energy to 

Z [(C2H5)3Ge-C2H5]. However, the product distribution indicates complexities in the mechanism that make this unlikely. 

---

Whereas ethylene oxide gives with 17 at ambient temperature a quantitative yield of l-trimethylsilyloxy-2-iodoethane [5, 31], substituted epoxides such as 846b react with 17 to give 848 as the main product [32]. Excess 17, however, leads to the bis-iodo compounds 849 and HMDSO 7 [4, 5]. In the presence of DBU the epoxides 850 are converted by 17, which is generated in situ from hexamethyl-disilane 857 and I2, into the allyl alcohols 851 [4, 32] (Scheme 6.14). Cycloctene epoxide 852 is opened by SiCl4 at -78 °C in the presence of catalytic amounts of the asymmetric catalyst 853 to give 61% of the chlorohydrin 854 in 98% ee [33]. 

A unique bis-silylation system, in which a bis(silyl)palladium intermediate is generated via recombination of two Si-Si bonds, has been developed.8,97 A bis(disilanyl)dithiane reacts with alkynes in the presence of a palladium/ isocyanide catalyst, giving five-membered ring bis-silylation products in high yield with elimination of hexamethyl-disilane (Scheme 14). The recombination, that is, bond metathesis, is so efficient that no product derived from direct insertion of acetylene into the Si-Si bonds of the bis(silyl)dithiane is formed at all. 

Aromatic aldehydes undergo a pinacol reaction when treated with hexamethyl-disilane and tetra-n-butylammonium fluoride [55] using procedure 3.1.14.D. 

Hexamethylethane suffers a twist of 5° from symmetry around its central C—C bond. This twist was reproduced, albeit in somewhat exaggerated form, by MM calculations (56) and ascribed to nonbonded H-H interactions across the central bond (56). In contrast, the global minimum energy conformation of hexamethyl-disilane (1) is predicted to haveDad symmetry, since the Si—Si bond is longer (2.34 A) (61). 

Am Beispiel des Hexamethyl-disilans konnte ein solcher Mechanismus eindeutig nachgewiesen werden (173) ... 

Another convenient in situ preparation involves the reaction of hexamethyl-disilane with iodine at 50° (equation I). ... 

Addition Reactions.- The irradiation through Pyrex of the electron-acceptor alkenes (20) in acetonitrile solution with phenanthrene and hexamethyl disilane brings about a regio-... 

A number of other reagents have been used for the reductive conversion of nitroalkanes to carbonyl compounds or oximes,3,4 including hexamethyl disilane,13 Bu3P/PhSSPh,14 and catalytic Cu(acac).15... 

Arylsilanes. The conversion of ArBr into ArSiMe3 on reaction with hexamethyl-disilane is catalyzed by the Pd-complex in the presence of (2-hydroxyphenyl)diphenyl-phosphine. This ligand activates both Pd and Si by providing both a soft and a hard donor. 

---