Support-controlled chemoselective olefin-imine addition photocatalyzed by cadmium sulfide on a zinc sulfide carrier.
The semiconductor catalyzed photoaddition of cyclopentene or cyclohexene to various novel electron-poor imines of type p-XC(6)H(4)(CN)C[double bond, length as m-dash]N(COPh) (X = H, F, Cl, Br, Me, MeO) was investigated as a function of the nature of the cadmium sulfide photocatalyst. Irradiation (lambda>/= 350 nm) of silica supported cadmium sulfide surprisingly did not afford the expected olefin-imine adducts but an imine hydrocyanation product via an unprecedented dark reaction. However, when silica was replaced by zinc sulfide as the support for cadmium sulfide, the expected homoallylic N-benzoyl-alpha-amino cyanides were isolated in yields of 65-84%. Thus, chemoselectivity is introduced through replacing an insulating by a semiconducting support, a hitherto unknown effect in semiconductor photocatalysis. From the sign of the time resolved photovoltage it is found that the mixed metal sulfide interface CdS/ZnS increases the lifetime of photogenerated electron-hole pairs by about one order of magnitude as compared to the SiO(2)/CdS system. The reaction rate increases with increasing imine sigma-Hammett constants and decreasing stability of intermediate benzyl radicals.
Gärtner
Marc
M
Universität Erlangen-Nürnberg, Institut für Anorganische Chemie, Egerlandstr. 1, D-91058, Erlangen, Germany.
Ballmann
Joachim
J
Damm
Cornelia
C
Heinemann
Frank W
FW
Kisch
Horst
H
D019187:Cadmium Compounds / Q000737:chemistry* / Q000528:radiation effects; D002384:Catalysis; D018360:Crystallography, X-Ray; D053138:Cyclohexenes / Q000737:chemistry* / Q000528:radiation effects; D003517:Cyclopentanes / Q000737:chemistry* / Q000528:radiation effects; D007097:Imines / Q000737:chemistry* / Q000528:radiation effects; D008958:Models, Molecular; D015394:Molecular Structure; D010777:Photochemistry; D012666:Semiconductors; D012822:Silicon Dioxide / Q000737:chemistry / Q000528:radiation effects; D013440:Sulfides / Q000737:chemistry* / Q000528:radiation effects; D013997:Time Factors; D014466:Ultraviolet Rays; D017967:Zinc Compounds / Q000737:chemistry* / Q000528:radiation effects
D019187:Cadmium Compounds; D053138:Cyclohexenes; D003517:Cyclopentanes; D007097:Imines; D013440:Sulfides; D017967:Zinc Compounds; C034939:cadmium sulfide; C052568:cyclohexene; D012822:Silicon Dioxide; C031238:zinc sulfide