Phenylsilyl radical

All the reactions may involve attack of a phenylsilyl radical formed upon irradiation on C6o to give the radical intermediate as shown in Scheme 53. There is probably a rapid equilibrium between this radical and the cyclohexadienyl radical. The product ratio depends on the relative rates of recombination with the other silicon radical produced initially. Bulky phenylalkylsilyl radicals react preferentially at the 16-position of the C6o poly cycle in the initially formed radical. In contrast, trimethylsilyl and silylsilyl radicals prefer the cyclohexadienyl ring. 

Further investigations on the photochemical bissilylation of C6o with disilanes [275c] indicate that 3C o and Qo do not play an important role in these reactions due to the fact that no absorption band for the C6o radical anion is observed in the course of the reaction and the decay of 3C 6o is not accelerated by addition of the disilanes. Another hint for the involvement of the phenylsilyl radical is that no product is formed upon irradiation at >300 nm where the cleavage of the disilane does not take place. The radical reaction pathway is further confirmed by a lower yield obtained by addition of radical scavengers. 

From the kinetic data the authors also deduced that the magnitude of the allylic stabilization in the vinyIsilyl radical is less than 7 kcal mol"1. This can be compared to the benzylic stabilization energy of about 2 kcal mol 1 which was derived for the phenylsilyl radical previously studied191. 

The most straightforward route to organodisilanes involves the coupling of atriorganosilyl halide by treatment with sodium (2,32). This method was first employed by Schlenk 32) while attempting to prepare the free tri-phenylsilyl radical and later by Kipping 32). This procedure is equally applicable to the preparation of mixed disilanes, and variations of the reaction conditions have been reported. In particular, the formation of... 

It appears that these reactions all may be explained by invoking a common intermediate phenylsilyl anion (VI) formed from the initial radical anion by reductive cleavage of a silicon-hydrogen or silicon-carbon bond ... 

Bis(acyl(methyldiphenyl)silanes) can be cyclized by a free radical procedure to the corresponding 2,6-bis(methyldi-phenylsilyl)-4,5-dihydro-6//-pyrans by treatment with tributyltin hydride and a catalytic amount of AIBN (eq 24). ... 

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