A solvent-free procedure for forming amide bonds without exclusion of air and moisture is described. Using tetramethoxysilane 1, hexamethoxydisilane 2 and dodecamethoxy-neopentasilane 3 as coupling agent carboxylic acids and amines...
New methoxylated oligosilyl-substituted metallocenes
were synthesized
by the reaction of two oligosilanides with different metallocene dichlorides
(M = Ti, Zr, and Hf). The first investigated tris(trimethoxysilyl)silanide
[(MeO)
3
Si]
3
SiK (
1
) underwent a
selective monosubstitution to the respective oligosilyl-decorated
metallocenes [(MeO)
3
Si]
3
SiMClCp
2
(
2
–
4
). Surprisingly, the attempted disilylation
with this silanide was not possible. However, in the case of titanocene
dichloride, a stable radical [(MeO)
3
Si]
3
SiTiCp
2
(
5
) was formed. The unsuccessful isolation of
bisilylated metallocenes encouraged us to investigate the reactivity
of another silanide. Therefore, we synthesized a hitherto unknown
disilanide K[(MeO)
3
Si]
2
Si(SiMe
2
)
2
Si[(MeO)
3
Si]
2
K (
8
), which
was accessible in good yields. The reaction of compound
8
and different metallocene dichlorides (M = Ti, Zr, and Hf) gave
rise to the formation of heterocyclic compounds
9
–
11
in good yields.
There is an increasing interest to replace precious metal-based catalysts by earth-abundant nonprecious metals due to higher costs, toxicity, and declining availability of the former. Here, the synthesis of a well-defined supported nickel hydrogenation catalyst prepared by surface organometallic chemistry is reported. For this purpose, [LNi(μ-H)] 2 (L = HC-(CMeNC 6 H 3 ( i Pr) 2 ) 2 ) was grafted on partially dehydroxylated silica to give a homobimetallic H-and O(silica)-bridged Ni 2 complex. The structure of the latter was confirmed by infrared spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure analyses as well as hydride titration studies. The immobilized catalyst was capable of hydrogenating alkenes and alkynes at low temperatures without prior activation. As an example, ethene can be hydrogenated with an initial turnover frequency of 25.5 min −1 at room temperature.
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