624
J . Org. Chem. 2000, 65, 624-626
without irradiation. Photolysis of some bis(organosilyl)-
P h otolysis of Bis(or ga n osilyl)im in es
imines having various silicon substituents (SiR1 ) and
3
alkyl groups (R2) is summarized in eq 1.
Akira Matsumoto† and Yoshihiko Ito*
Department of Synthetic Chemistry and Biological
Chemistry, Graduate School of Engineering,
Kyoto University, Kyoto 606-8501, J apan
Received September 14, 1999
Photolysis of acylsilanes involves two types of reac-
tions.1 One is a homolytic scission of the silicon-carbonyl
bond in carbon tetrachloride to afford a pair of radicals.2
The organosilyl radical thus generated abstracts a chlo-
rine atom from carbon tetrachloride to yield an organosi-
lyl chloride. Another reaction is a migration of the
organosilicon group to the carbonyl oxygen in methanol,
resulting in the formation of an acetal via the corre-
sponding silyloxycarbene intermediate.3
However, photolysis of bis(organosilyl)ketones is dif-
ferent from that of the acylsilanes. For instance, bis-
(triphenylsilyl)ketone, which is a red-violet solid with UV
absorption around 550 nm, is not stable in solution and
rapidly undergoes photolysis in solution to afford hexa-
phenyldisilane and carbon monoxide.4
On the other hand, N-substituted bis(organosilyl)-
imines, the preparation of which has been found by us,5
are stable not only in the solid state but also in solution.
Bis(organosilyl)imines also exhibit red-shifted UV ab-
sorption around 400 nm with relatively large extinction
coefficients (150-200), which is ascribed to n-π* absorp-
tion.6 Now, we find that bis(organosilyl)imines undergo
photolysis in a different manner from the ketone ana-
logue. Herein, we report new photochemistry of 2,6-xylyl
bis(organosilyl)imines.
A high-pressure mercury lamp was used as a light
source for all the photoreactions. UV irradiation of bis-
(organosilyl)imine (1) for 2 h in benzene-d6 containing
carbon tetrachloride led to a complete conversion, giving
a 2:1 mixture of organosilyl chloride and the correspond-
ing isocyanide together with its derivatives (eq 1). In the
reaction of 1c, the minor byproducts 4c (5.9%),7 5c
(5.6%),7 and 6c8 (6.3%)7 were separated and identified
by GC-MS analysis. The present reaction did not proceed
in refluxing benzene containing carbon tetrachloride
These results might suggest that the photolysis of
N-substituted bis(organosilyl)imines involved a stepwise
elimination of the two organosilyl radicals.9 However, this
hypothesis was ruled out by following results. No reaction
of bis(silyl)imines took place under irradiation for several
hours in benzene and acetonitrile. The photolysis of the
bis(organosilyl)imines in the presence of styrene and
methyl methacrylate in benzene-d6 did not give any
adducts. Radical trapping experiments with 2,2,6,6-
tetramethylpiperidine-1-oxyl (TEMPO) during the pho-
tolysis have also failed.
In contrast, irradiation of 1b with alkyl iodides in
benzene-d6 gave organosilyl iodide, which was readily
hydrolyzed to the corresponding siloxane, along with the
aromatic isocyanide. The photolysis of 1b with ethyl
iodide in the presence of TEMPO afforded dimethyl-
phenylsilyl-TEMPO adduct 7 together with a small
amount of dimethylphenylsilyl iodide 8 and ethyl-
TEMPO adduct 9 (eq 2). The same reaction proceeded
with isopropyl iodide and iodobenzene. No charge-
transfer complex formation in the ground state was
observed between 1b and iodobenzene.10
An exciplex intermediate may be involved prior to the
reaction with carbon tetrachloride or alkyl iodides. An
exciplex formation has also been proposed for the pho-
tolysis of acylsilanes.11 Organic halides were not decom-
posed by irradiation under the same condition, suggesting
that the reaction of 1 was not promoted by the photolysis
of organic halides.
Photoinduced electron transfer (PET) may be involved
after the exciplex formation.12 Single electron transfer
could occur from bis(organosilyl)imines to organic halide
† Additives, Ciba Specialty Chemicals K. K. J apan; 10-66, Miyuki-
cho, Takarazuka 665-8666, J apan.
(1) Brook, A. G. J . Organomet. Chem. 1986, 300, 21-37.
(2) (a) Brook, A. G.; Duff, J . M. J . Am. Chem. Soc. 1969, 91, 2118-
2119. (b) Brook, A. G.; Dillon, P. J .; Pearce, R. Can. J . Chem. 1971,
49, 133-135.
(3) (a) Brook, A. G.; Duff, J . M. J . Am. Chem. Soc. 1967, 89, 454-
455. (b) Duff, J . M.; Brook, A. G. Can. J . Chem. 1973, 51, 2869-2883.
(c) Bourque, R. A.; Davis, P. D.; Dalton, J . C. J . Am. Chem. Soc. 1981,
103, 697-699.
(4) Brook, A. G.; Peddle, G. J . D. J . Organomet. Chem. 1966, 5, 106-
107.
(5) (a) Ito, Y.; Nishimura, S.; Ishikawa, M. Tetrahedron Lett. 1987,
28, 1293-1294. (b) Ito, Y.; Matsuura, T.; Murakami, M. J . Am. Chem.
Soc. 1988, 110, 3692-3693. (c) Ito, Y.; Suginome, M.; Matsuura, T.;
Murakami, M. J . Am. Chem. Soc. 1991, 113, 8899-8908.
(6) Ramsey, B. G.; Brook, A. G.; Bassindale, A. R.; Bock, H. J .
Organomet. Chem. 1974, 74, C41-C45 and references therein.
(7) The yield is based on GC analysis. The isocyanide 3c was
produced in 82.2% yield.
(8) The formation of aromatic isocyanates by photochemical oxida-
tion with an aromatic isocyanides has been reported. Boyer, J . H.;
Ramakrishnan, V. T.; Srinivasan, K. G.; Spak, A. J . Chem. Lett. 1981,
43-46.
(9) The formation of alkyl radicals and isocyanides from imidoyl
radicals has been reported. (a) Kaba, R. A.; Griller, D.; Ingold, K. U.
J . Am. Chem. Soc. 1974, 96, 6202-6203 (b) Nanni, D.; Pareschi, P.;
Tundo, A. Tetraheadron Lett. 1996, 37, 9337-9340.
(10) UV spectra of 1b did not depend on polarity of solvent used. In
addition, no UV change was observed when iodobenzene was added to
a solution of 1b in acetonitrile and n-hexane. The mathematical sum
of UV spectra of 1b and iodobenzene measured separately was in good
agreement with UV spectra of a mixture of 1b and iodobenzene.
(11) Porter, N. A.; Iloff, P. M., J r. J . Am. Chem. Soc. 1974, 96, 6200-
6202.
10.1021/jo991443s CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/31/1999