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The research work of the laboratory of Professor Sekiguchi is directed to the synthesis, structural, mechanistical, and reactivity studies of the new compounds, containing heavier Group elements, with unusual structures and potential applications. There are three major research topics: 1) silyl substituted pai-electron systems, 2) unsaturated small ring compounds of heavier Group 14 elements, 3) dendrimer chemistry.

1. Silyl Substituted pai-electron System
The first topic consists of the two parts. The first one is based on the dilithium salt of tetrakis(trimethylsilyl)cyclobutadiene 1, which was successfully oxidized with 1,2-dibromoethane to produce the neutral tetrakis(trimethylsilyl)cyclobutadiene 2, representing the first per-silyl substituted cyclobutadiene. The last compound was in turn converted to isomeric tetrakis(trimethylsilyl)tetrahedrane 3 under the photolysis at low temperature. This is a new tetrahedrane molecule stabilized by the four silyl substituents.

J. Am. Chem. Soc. 2001, 123, 5356-5357.
J. Am. Chem. Soc. 2000, 122, 5652-5653.
Angew. Chem., Int. Ed. 2001, 40, 1675-1677.


The second part concerns with the chemistry of silyl substituted 1,1-dilithiosilane derivatives 5, which were prepared for the first time by the reduction of the corresponding silacyclopropene derivatives 4 with metallic lithium in THF. The reactivity of 1,1-dilithiosilanes has been widely studied to synthesize new disilenes and germasilenes, which can not be prepared by other methods.

2.GIF
J. Am. Chem. Soc. 1999, 121, 10231-10232.
Organometallics, in press.

2. Heavier Group 14 Element Unsatureated Small Ring compounds
The second topic deals with the rather important field of small ring systems in the Group 14 elements chemistry, it also consists of the two parts. The first part concerns with the chemistry of neutral compounds. The cyclotrisilene 6 and 1-disilagermirene 7a have been synthesized by the reductive coupling reaction of the corresponding halo-silyl and halo-germyl precursors with metallic sodium. Isomerization of 1-disilagermirene 7a under photolysis or thermolysis produced 2-disilagermirene 7b - first stable germasilene. The metalladiene 8, for which the Si=Ge double bond length was determined for the first time, was synthesized by the reaction of 2-disilagermirene 7b with phenylacetylene.  

Angew. Chem., Int. Ed. 1999, 38, 2194-2196.
J. Am. Chem. Soc. 2000, 122, 9034-9035.
Chem. Commun. 2001, 183-184.
J. Am. Chem. Soc. 2000, 122, 12604-12605.


The last part is the synthesis of cationic species from the cyclotrimetallenes precursors. The aromatic 2pai-electron trigermacyclopropenylium cation 10+ was prepared by the oxidation of cyclotrigermene with trityl cation, whereas homoaromatic tetrasilacyclobutenylium cation 9+ was synthesized by the oxidation of cyclotrisilene 6 with triethylsilyl cation. Both 9+ and 10+ are free cations in the solid state and in the solution, which was evidenced by X-ray and NMR data.

J. Am. Chem. Soc. 2000, 122, 11250-11251.
Science 1997, 275, 60-61.
Eur. J. Inorg. Chem. 2000, 1155-1159.


The third topic is the synthesis of polysilane dendrimers and their applications to the spherical organometallic polymers. The polysilane dendrimers, up to 2nd generation with 31 silicon atoms, have been synthesized by the divergent growth method using lithiooligosilanes. The hybrid dendrimer with alternating Si and Ge atoms in the chain was also prepared using Me(PhMe2Ge)2SiLi as a branching reagent. Dynamics of the excited state of polysilane dendrimers have shown the origin of the broad visible emission in the polysilane dendrimers.
Coor. Chem. Rev. 2001, 210, 11-45.

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