PHOTO-CHEMICAL GENERATION OF ARYL PHOSPHONIUM YLIDES

A series of diaryl-and arylalkyl ketones have been shown to form phosphonium ylides upon irradiation (45-80%) with long wavelength ultraviolet light in the presence of triphenylphosphine. Although the quantum yield for the process is low (ca. 0.025), the photoreaction appears to be fairly general (in the cases examined) for aryl ketones with n,σ* lowest triplet states. The reaction fails or proceeds very much less efficiently with σ,σ* ketones, aldehydes, and aliphatic ketones. A mechanism for ylide formation is suggested. Quenching studies point to the existence of an intermediate formed by the interaction of the excited triplet with phosphine. The relevance of such reactions to the study of exciplex and charge-transfer complexes of ketones and tervalent phosphorus compounds is discussed. © 1979, American Chemical Society. All rights reserved.