| Research Abstract |
The purpose of this research was to stabilize silyl ligands and make use of its strong σ-donating ability to activate transition metal complexes. We succeeded in synthesizing a number of transition metal complexes having chelate ligands with silicon as a coordinating atom. In the course of this research, we developed two new methods of preparing complexes having chelate ligands coordinated to the metal through a heteroatom and a silicon :
(1) Addition of a polarized double bond to a three-membered metallacycle
(2) Addition of an alcohol to a six-membered bis(silylene) complex followed by reductive elimination of an alkoxysilane
In both methods, the starting complexes themselves had unprecedented structures, so that we carried out the mechanistic studies on the above reactions and the related reactions, and got interesting results.
We also synthesized some (2-phosphinoethyl)silylrhodium complexes containing an extremely electron-rich metal center, and found that Rh[(κ^2-Si,P)-Me_2SiCH_2CH_2
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PPh_2](Pme_3)_2 induces the dehydrocoupling of tert-silane HSiMe_2Ph to give disilane (SiMe_2Ph)_2 in high yield.
We prepared the group 8 metal complexes having a bis(silyl) chelate ligand xantsil [(9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)], I.e., (xantsil)M(CO)_4 (M = Fe, Ru, Os), and revealed their X-ray crystal structures containing extremely long metal-silicon bonds. Among them, the ruthenium complex was converted quantitatively to the toluene complex Ru(xantsil)(CO)(η^6-toluene) on simple heating in toluene. The toluene ligand in this complex was found to dissociate readily at room temperature to give a highly coordinatively unsaturated species. Thanks to this unique reactivity, this toluene complex can be led to the complexes having various other ligands under mild conditions, and works as an excellent catalyst for the oligomerization/deoligomerization of HSiMe_2SiMe_3.
In conclusion, we found that silyl ligands have a distinctive electronic effect that is stronger than we have expected, and have enough potential to grow as a promising supporting ligand. Less
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