Silylenes oxidation

Preparation of disilylenoxane (LSi)20 L = PhC(NtBu 2) 99 Preparation of bis(silylene) oxide nickel complex [(LSiOSILINilCOD)] 100... 

PhC(NfBu)2 namely bis(silylene) oxide or disilylenoxane is synthesized by a simple synthetic approach. This involves the synthesis of disiloxane [LSiH(Cl)—O—SiH(Cl)L] from the reaction of l,l,3>3-tetrachlorodisiloxane [Cl2SiH—O—SiHCy with 2 M equiv of LLi L = PhC(NfBu)2 and its dehydrohalogenation to give the disilylenoxane. The bis(silylene) oxide upon treatment with 1 M equiv of [Ni(COD)2] in toluene at room temperature leads to the formation of a bis(silylene) nickel complex [(LSiOSIL)Ni(COD)] (Scheme 8.3.1) (5). 

Bis(silylene) oxide nickel complex can be considered as a highly electron-rich transition metal complex, being a late transition metal complex with strong 8-donation from bis(silylene) ligand. The proposed high stability and electron-rich nature make this complex a promising candidate for nickel-catalyzed coupling reactions (6). 

In the course of this development, knowledge about low valent (in the sense of formal low oxidation states) reactive intermediates has significantly increased [26-30]. On the basis of numerous direct observations of silylenes (silanediyles), e.g., by matrix isolation techniques, the physical data and reactivities of these intermediates are now precisely known [31], The number of kinetic studies and theoretical articles on reactive intermediates of silicon is still continuously growing... 

Starting from (OC)5MnSiR2H (R = Me, Ph, Cl), the p-silylene complex 70 is accessible via the oxidative addition of the Si —H bond to Pt(C2H4.)(PPh3)2 and Pt(PPh3)4, respectively. Structure 70 can be functionalized by displacement of the phosphine ligands alcoholysis and hydrolysis of the compound 70 leads to silicon-free complexes [175]. 

The major synthetic routes to transition metal silyls fall into four main classes (1) salt elimination, (2) the mercurial route, a modification of (1), (3) elimination of a covalent molecule (Hj, HHal, or RjNH), and (4) oxidative addition or elimination. Additionally, (5) there are syntheses from Si—M precursors. Reactions (1), (2), and (4), but not (3), have precedence in C—M chemistry. Insertion reactions of Si(II) species (silylenes) have not yet been used to form Si—M bonds, although work may be stimulated by recent reports of MejSi 147) and FjSi (185). A new development has been the use of a strained silicon heterocycle as starting material (Section II,E,4). 

When a C6D6 solution of the silylene-isocyanide complex 21 was treated with an equimolar amount of mesitonitrile oxide at room temperature, the blue color of 21 immediately disappeared, and the 29Si and 13C NMR spectra of the reaction mixture exhibited characteristic strong signals (8Si = 26.9, 8C = 184.3) assignable to those of compound 22a having a novel 1,2,4-oxazasilete ring system (Scheme 5). The oxazasilete 22a was not stable at ambient temperature, and... 

The formation of silaneselone 57 was evidenced by the trapping reaction with mesitonitrile oxide leading to the corresponding cycloadduct 58 and was also supported by the observation of a remarkably downfield 29Si chemical shift (8Si = 174) indicative of the Si=Se double bond of 57. Although this direct selenation of silylene 55 with an equimolar amount of selenium was not reproducible, the use of excess amount of elemental selenium resulted in the formation of a new cyclic diselenide, diselenasilirane 59, as a stable compound (8Si = -44 and... 

The insertion of 1 into element-element bonds is a crucial step in an extensive series of remarkable transformations. From the perspective of the particular substrate, such reactions are oxidative additions to a silylene-like center. The primary insertion products all possess reactive pentamethylcy-clopentadienyl-silicon cr-bonds. In this chapter only those insertion reactions... 

The sulfoxide method has been applied to the concept [319,374] of intramolecular aglycone delivery for the formation of [1-mannosidcs by means of a silylene linker. In the original work, the acceptor and a thioglycoside donor were joined by means of a silylene group before the oxidation to the sulfoxide [141]. However, it was later found that the preformed sulfoxide was tolerated by the chemistry for the introduction of the linker [286,375]. The intramolecular aglycone delivery step was shown to function effectively for the transfer of the donor to the 2-, 3- and 6-position of glucopyr-anosides, as exemplified in Scheme 4.64. 

Other than this system, metallated polysilanes contain the metal in low-valent oxidation states. Such systems have been reported by two groups. In 1995, an alternative functionalization route starting from poly[methyl(H)silylene] or poly[methyl(H)silylene-fo-methylphenylsilylene], 37, was reported, in which the polysilane Si-H moiety was hydro-silated using 1,3,5-hexatriene, affording the diene-modified polymer 67, which was metal functionalized using triiron dodecacarbonyl to give the iron tricarbonyl-polysilane coordination complex, 68.177... 

Silylated triphosphanes and triphosphides, synthesis, 31 188-194 yields, 31 194 Silylenes, 29 2-6 addition reactions, 29 4-6 to butadiene, 29 4 to ethylene, 29 4 to hexadienes, 29 5 mechanism, 29 4 nitric oxide scavenging, 29 4 complexes, 25 37, 51, 116, 118 as catalyst intermediates, 25 118 extrusion from disilanes, 25 114, 118 halides, 3 225 from hydridosilanes, 25 14 insertion into element-hydrogen bonds, 29 3-4... 

The silylenes Si(N N ) (2) and Si(N"N") (4) were studied by cyclic voltammetry (CV) and computationally (as well as electron affinities and ionisation potentials - poor correlations). " In thf or 1,2-C6H4C12, CV measurements showed irreversible waves both for oxidation (Ep. 2 > 4) and reduction 4 > 2) furthermore the silylenes were more readily oxidised or reduced than the isoleptic geriiiylenes.° Treatment of the rac-silylene 25 with oxygen gas, MeOH or H2O in hexane at —78 °C afforded the cyclodisiloxane [Si(N(Bu ) C(H)Me 2NBu )(p-O)]2. methoxyhydrosilane [Si(N(Bu ) C(H)Me 2NBu )-... 

As shown in Scheme 9.10, the silylene 3 underwent oxidative additions with alkali metal (M) bis(trimethylsilyl)amides to give new alkali metal amides, rather than metal fais(amino)silyls M[SifN. ) N(SL Ie3)2 ](thf), which, however, were suggested to have been intermediates.Whereas M[N Si(NN)fSi. Vie ,) (Si. Vlc ) (thfwith R = Me underwent a further reaction with 3 to yield M[N Si(NN)(SiMe3) 2], for R = Ph the double addition compound was the sole product in the 3/Li[N(SiMe3)(SiMe2R)] system. ... 

---