Tri silanol

The phenyl silane reacts with ozone to give a tri silanol 0Si(OH)3 which... 

The diolefin 1064 gives rise to the isoxazoline 1065, which cannot eliminate tri-methylsilanol 4 [122]. Cychzation of the co-nitroolefin 1066 with trimethylchloro-silane (TCS) 14/triethylamine at -35 °C then HCl-induced removal of trimethyl-silanol 4 leads, in 85% yield, to the dimer 1067, which is converted in two more steps into racemic pyrenophorin 1068 [112] (Scheme 7.39). Further cyclizations of co-nitroolefins [109] to monomeric or dimeric isoxazolines have been described. Conjugated dienes such as butadiene afford a mixture of the mono or bis adducts [115-117]. 

To follow the mode of grafting of an organometallic species onto Si02, the tris (neopentyl)neopentylidene tantalum complex has been used to show the reactivity of its groups with silanol groups of silica (dehydroxylated at 300 to 700 °C)... 

The tris-neopentyl Mo(VI) nitride, Mo(-CH2- Bu)3(=N) [134], reacts with surface silanols of silica to yield the tris-neopentyl derivative intermediate [(=SiO)Mo (-CH2- Bu)3(=NH)] followed by reductive elimination of neopentane, as indicated by labeling studies from labeled starting organometallic complex, to yield the final imido neopentylideneneopentyl monosiloxy complex [(=SiO)Mo(=CH- Bu)(-CH2 - Bu)(=NH)] [135]. The surface-bound neopentylidene Mo(VI) complex is an active olefin metathesis catalyst [135]. Improved synthesis of the same surface complex with higher catalytic activity by benzene impregnation rather than dichlorometh-ane on silica dehydroxylated at 700 °C has been reported [136],... 

The surface silanols are usually reacted with chloro- or alkoxy silanes, differing in substitution (mono-, di-, and tri-chloro [or alkoxy] silanes) and alkyl chain lengths (C4-C30, dominating C18 and C8). The reaction can be performed in vacuum with the total exclusion of water or in an... 

Some researchers have tried to stabilize the MCM wall by a complete hydrofobization of the surface, replacing every silanol group with a trimethy Isi ly 1 group, using e.g. trimethylchlorosilane of hexamethyldisilazane [9], Although this treatment is very effective in se, it yields a surface that is completely unreactive towards subsequent grafting of transition metals. We therefore present a silylation procedure with dimethyldichlorosilane (DMDCS), which allows - upon hydrolysis - a recreation of surface silanols. 

The reaction of (alkyl)chlorosilanes with a silica surface has been discussed and reviewed in great detail in literature [10], Although 5 different reactions are possible with di-, tri- or tetrachlorosilanes, basically two important surface species are created. The first is a monodentate silyl group, created by the monomolecular reaction of 1 silanol with 1 chlorosilane, according to reaction (A) (cfr. Figure 2). The second surface specie is a bidentate silyl group, created either by a bimolecular reaction (B) or by a consecutive reaction (C). We have reported previously [11] that the surface of MCM-48, prepared by the gemini 16-12-16 surfactant, possesses 0.9 OH/nm2. 

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