Silylation of peripherally lithiated porphyrins with silyl electrophiles has realized the first synthesis of a series of directly silyl-substituted porphyrins. The meso-silyl group underwent facile protodesilylation, whereas the β-silyl group was entirely compatible with standard work-up and purification on silica gel. The meso-silyl group caused larger substituent effects to the porphyrin compared with the β-silyl group. Silylation of β-lithiated porphyrins with 1,2-dichlorodisilane furnished β-to-β disilane-bridged porphyrin dimers. A doubly β-to-β disilane-bridged Ni(II)-porphyrin dimer was also synthesized from a β,β-dilithiated Ni(II)-porphyrin and characterized by X-ray crystallographic analysis to take a steplike structure favorable for interporphyrinic interaction. Denickelation of β-silylporphyrins was achieved upon treatment with a 4-tolylmagnesium bromide to yield the corresponding freebase porphyrins.
Keywords: lithiation; porphyrin; porphyrin dimer; silylation; substituent effects.
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