EFFECT OF PRECURSOR STRUCTURES ON ARYLCARBENE PROCESSES IN LOW-TEMPERATURE MATRICES - IMPORTANCE OF TOPOCHEMICALLY CONTROLLED PROCESSES

C-H insertion selectivities of [PhCH:] generated from diverse sources, i.e., PhCHN2 and cis-and trans-2,3-diphenyloxiranes, in 2-propanol and 2,3-dimethylbutane matrices at -196 °C showed considerable dependence on the structure of precursors, while liquid-phase experiments showed that insertion selectivities were essentially invariant regardless of source. [Ph2C:] generated from Ph2CN2, tetraphenyloxirane, and 2,2,4,4-tetraphenyloxetan-3-one showed precursor dependences of C-H insertion selectivities as well as singlet/triplet product ratio even in the liquid phase and more dramatically in the solid phase. Possible effects of precursors on the angle and energy of nascent carbene and sensitization by photofragment (Ph2CO) were excluded based on control experiments and EPR studies. Topochemical factors, i.e., contact of carbene center with the host molecules, are considered to play an important role especially in the matrix reactions and hence it has been suggested that attempts to extrapolate singlet/triplet carbene ratios from product compositions in matrices could prove unreliable since the fate of carbenes generated in a matrix may be predestined by site preference imposed upon the precursor. © 1979, American Chemical Society. All rights reserved.