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The geometries and energies of the iminopnictoranes (H3MNH; M = P, As, Sb, and Bi) and their reaction paths with formaldehyde are predicted by means of ab initio calculations. The multiplicity of MN bonds is discussed by comparing the MN and M−H bond lengths, the bond length ratios MN:M−N, the bond angles of M−N−H, and the barrier to internal rotation about the MN bond with those of the ylides, and it was concluded that the contribution of the ionic canonical form M+−N- is much more important than that of the MN form. For the two reaction routes of the iminopnictoranes with formaldehyde (aza-Wittig and Corey−Chaykovsky-type reactions), all of the stationary points and transition states were fully optimized by using an analytical gradient with the LANL1DZ and the 9s5p-d/[3s2p-d] basis set (DZ-d) at the MP2 level. For M = P and As, the aza-Wittig reaction is more favorable than the Corey−Chaykovsky-type reaction from both the thermodynamic and the kinetic viewpoint. In the case of M = Sb and Bi, the Corey−Chaykovsky-type reaction takes place predominantly. The higher level calculations, such as MP4(SDTQ)/DZ-d//MP2/DZ-d and QCISD(T)/DZ-d//MP2/DZ-d, were performed to get accurate energies of these intermediates and transition states.

The photoreactions of 2,4,6-triphenyl- (TPP), 2-t-butyl-4,6-diphenylpyrylium (2BDPP) and 2,4,6-triphenylthiopyrylium (TPTP) salts in tetrahydrofuran (THF) and/or 1,2-dimethoxyethane were investigated. Photoproducts were identified to be pyranyl radicals on the basis of photochemical behavior and ESR spectra. Quantum yields of one-electron reduction reactions of TPP, 2BDPP, and TPTP were obtained to be 0.21, 0.047, and 0.53, respectively. The hf coupling constants of protons in the radicals were determined by simulation. The photoillumination of TPP in THF at low temperatures revealed that a certain intermediate radical species was involved in this one-electron photoreduction.

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