Masahiro Asahara

Recent developments in silicon interelement linkage: the case of functionalized silyllithium, silylenoid and sila-ylide*

As one representative family of silicon interelement linkages, functionalized silyl anions and related species such as silylenoids and sila-ylides are described, focusing on the development of new synthetic methodologies and the effects of the heteroatom substituents on the bonding nature and the reactivity of these species.

Enhanced nucleophilicity of ambiphilic silylene and silylenoid bearing 8-(dimethylamino)-1-naphthyl group

Abstract Some new aspects of intramolecularly amine-coordinated silylenes, ammonium silaylide, and amine-coordinated magnesium (chloro)silylenoids are summarized. The divalent silicon species bearing the 8-(dimethylamino)-1-naphthyl group, generated by the thermal degradation of a pseudo-pentacoordinated ethoxy- or fluoro-disilane, behaves as a nucleophilic ammonium silaylide as well as the amine-coordinated silylene, whose electrophilic character is weakened in comparison with that of free silylenes in some reactions in the presence of trapping agents such as 1,3-diene, diphenyl acetylene (in the absence or presence of water), and phenylacetylene, and in the absence of any trapping agent. The amine-coordinated silylenoid also behaves as an ambiphile, but the reaction courses are different from those observed with the amine-coordinated silylene and silaylide. A novel amino-group migration from naphthyl carbon to silicon has been observed in both species.

Reaction of Hypercoordinate Dichlorosilanes Bearing 8-(Dimethylamino)-1-naphthyl Group(s) with Magnesium: Formation of the 1,2-Disilaacenaphthene Skeleton.

Migration of NMe(2) from C(naphthyl) to Si and Si-Si and Si-C bond formation to give a 1,2-disilaacenaphthene skeleton occurred in the reaction of hypercoordinate dichlorosilanes bearing the 8-(dimethylamino)-1-naphthyl group with two equivalents of magnesium [e.g., Eq. (a)]. The intermediate was isolated as the 1-isopropoxy derivative after quenching the reaction mixture with isopropyl alcohol.

The differing modes of reaction of 1-(8-dimethylamino-1-naphthyl)-1-hydrodisilane and 1-(1-naphthyl)-1-hydrodisilane in nickel-catalyzed reactions with acetylene: formation of a pseudo-pentacoordinate silole via SiSi bond cleavage vs. hydrosilation without SiSi bond cleavage

Abstract Pseudo-pentacoordinate 1-(8-dimethylamino-1-naphthyl)-1-hydrodisilanes 1 and 2 and the tetracoordinate counterpart 3 have been prepared. In the presence of an Ni(0) complex as catalyst, 1 and 2 undergo degradation to generate a silylene species and a hydrosilane. The complex with Ni of the silylene species from 1 has been trapped with an excess of diphenylacetylene to give a pseudo-pentacoordinate silole 4. The X-ray structure of 4 indicates that this silole occupies two pseudo-equatorial positions. In contrast, the tetracoordinate hydrodisilane 3 undergoes hydrosilation without SiSi bond cleavage.

Synthesis, structure, and reactivity of 1,ω-bis(pseudo-pentacoordinated) 1,ω-difluoro-oligosilanes bearing 8-(dimethylamino)-1-naphthyl groups

Abstract 1,ω-Bis[8-(dimethylamino)-1-naphthyl]-1,ω-difluorotrisilane 1 (ω=3) and tetrasilane 2 (ω=4) have been prepared. The X-ray crystallography of dl-1 and meso-1 shows unsymmetrical structures having different coordination modes at the two terminal silicons. The unsymmetrical nature of the structure of 1 can also be observed by solid state CP/MAS NMR spectroscopy. Trisilane 1 is thermochemically labile and undergoes facile degradation at 145°C, but is photochemically stable under irradiation of its benzene solution with a 6 W-low pressure mercury lamp, making a sharp contrast to the behavior of their tetracoordinate counterparts containing naphthyl groups which are thermochemically stable but photochemically active. Tetrasilane 2 undergoes a Pd(0)-catalyzed α-elimination of a fluorosilane moiety at the two pseudo-pentacoordinated silicon atoms to form the 1,2-difluorodisilane, which is trapped with diphenylacetylene as a double-silylation product.

Synthesis, structure, and reactivity of disilanes containing one neutral [4+2]-coordinate silicon center

[4+2]-Coordinate disilanes containing two 8-dimethylamino-l-naphthyl (8-Me 2 N-1-Np) groups on the same silicon atom, (8-Me 2 N-l-Np) 2 XSi-SiMe 3 , where X = F, OH, OEt, and H, are prepared. The X-ray structures of the two derivatives, X = F and OH, show that one of the coordinated dimethylamino groups is anti to the electronegative X group, while the other is anti to the trimethylsilyl group. The [4 + 2]-coordinate disilanes (X = F or OEt) are found to be thermally stable under these conditions such that the corresponding [4 + 1]-coordinate disilanes (8-Me 2 N-1-Np)XMeSi-SiMePh 2 (X = F or OEt) readily undergo degradation. In the presence of Pd(PPh 3 ) 4 as a catalyst, the [4 + 2]-coordinate disilane (X = F) undergoes degradation to generate naphthylsilane (8-Me 2 N-1-Np)-SiMe 3 , the reaction pathway being different from that of the [4 + 1]-coordinate disilane (X = F) which affords the fluorosilane, F-SiMePh 2 .