Theoretical and experimental study of diamagnetic and paramagnetic products from thermal and light-induced alkyl transfer between zinc or magnesium dialkyls and 1,4-diaza-1,3-butadiene substrates

摘要: Ab initio pseudopotential calculations were used to study species formed in thermal and light-induced alkyl transfer reactions between organometallic compounds R',M (M = Zn, Mg; R' alkyl, aryl) 1,4-diaza-1,3-butadienes RN= CHCH=NR (R-DAB). Geometries of the first isolable intermediates, chelate complexes MR',.R-DAB, have been optimized. The X-ray structure crystalline complex ZnMe,+Bu-DAB is presented. Its main features are well-reproduced by on systems with R H, Me. primary exhibit a destabilized HOMO (antisymmetric M-C a-bond combination) low-lying LUMO (DAB T* orbital). energy intense long-wavelength HOMO-LUMO transition strongly influenced electronegativity carbanionic group elec- tronegativity metal. N,N'-Dimethyl substitution destabilizes compared H. lowest triplet-excited states radical anions can be rationalized terms nodal properties frontier orbitals, indicate bond labilization as prerequisite for intramolecular electron ground or electronically excited state. In agreement experiments generally more pronounced M Mg than Zn analogues. Calculated vertical adiabatic affinities both higher Zn. Calculations synthetically useful N- C-alkylated products from reaction rather small difference these two possible collapse products. ESR data several thermally photochemically generated paramagnetic products, anion radicals neutral MR'sDAB, calculated geometrical electronic structures. structures all studied means localized canonical MOs well Mulliken charges dipole moments. dependence reactivity product selectivity substituent characteristics (R, R'), solvation, temperature. excitation wavelength respect LLCT discussed.