No abstract

Geometries, relative stabilities and singlet–triplet gaps of pyrazyl-, pyridazyl-, and pyrimidylcarbenes as well as their heavier analogues are investigated at B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level of theory. Relative stability of these divalent species is mainly determined by both the position of nitrogen atoms related to divalent centers and the position of nitrogen atoms related to each other as well as the stability of the heteroaryl substituents. While all species benefit from the common π–p interaction of the heteroaryls, singlet silylenes and germylenes with an ortho nitrogen atom have a stable nonplanar structure. The electron deficient centers of these structures prefer another mode of stabilization, n–p, through the interaction of vacant p orbital of the divalent center with the ortho nitrogen lone pair. Results including NBO atomic charges, philicity indices (N and ω), calculated UV–vis spectra, and isodesmic reactions support this finding.