SILICON-COMPOUNDS WITH STRONG INTRAMOLECULAR STERIC INTERACTIONS .55.REACTIONS OF STERICALLY ENCUMBERED SILYLENES WITH PYRIDINE-2-CARBALDIMINES - CYCLOADDITIONS VERSUS CH INSERTIONS

N-Mesitylpyridine-2-carbaldimine reacts with photochemially generated dimesitylsilylene by insertion into the C-H bond of the acyclic > C=N- group to provide the (pyridin-2-yl)-1-silaethane derivative 3, which is isolated together with the (pyridine-2-carbaldimine-N,N')-silicon s pecies 4 as the formal [4 + 1] cycloaddition product. Treatment of N-( 2,6-diisopropylphenyl)pyridine-2-carbaldimine (5) with the sterically more encumbered bis-(2,4,6-triisopropylphenyl)silylene gives the C-H i nsertion product pylphenyl)-imino)-1,1-bis(2,4,6-triisopropylphen?? yl )-2-(pyridin-2-yl)-1-silaethane (7) almost exclusively. Upon heating, the insertion products 3 and 7 rearrange to the corresponding substitu ted (pyridine-2-carbaldimine-N,N')silicon compouunds 4 and 8. The stru ctures of the isomeric compounds 7 and 8 have been determined by X-ray crystallography. The molecular structure of 8 shows not only that the heteroaromatic ring of 5 has been converted into a system of conjugat ed double bonds but also that 8 is considerably more strained than the insertion product 7.