%0 Journal Article %1 Kaupp.1991 %A Kaupp, Martin %A Stoll, Hermann %A Preuss, Heinzwerner %A Kaim, Wolfgang %A Stahl, Thomas %A van Koten, Gerard %A Wissing, Elmo %A Smeets, Wilberth J. J. %A Spek, Anthony L. %D 1991 %J Journal of the American Chemical Society %K adduct alkyl diazabutadiene diazabutadiene;magnesium dimethylzinc dimethylzinc;dipole diorganomagnesium diorganozinc moment organometallic;mol photochem structure thermal thermal;MO transfer zinc;crystal %N 15 %P 5606--5618 %R 10.1021/ja00015a014 %T 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 %V 113 %X Ab initio pseudopotential calcns. were used to study species formed in thermal and light-induced alkyl transfer reactions between organometallic compds. R'2M (M = Zn, Mg: R' = alkyl, aryl) and 1,4-diaza-1,3-butadienes RN:CHCH:NR (R-DAB). Geometries of the first isolable intermediates, the chelate complexes MR'2·R-DAB, have been optimized. The x-ray structure of the cryst. complex ZnMe2·tert-Bu-DAB is presented. Its main features are well-reproduced by the calcns. on systems with R = H, Me. The primary complexes exhibit a destabilized HOMO (antisym. M-C s-bond combination) and a low-lying LUMO (DAB p* orbital). The energy of the HOMO and the intense long-wavelength HOMO-LUMO transition are strongly influenced by the electronegativity of the carbanionic alkyl group and by the electronegativity of the metal. N,N'-Dimethyl substitution destabilizes the LUMO compared to R = H. Geometries of the lowest triplet-excited states and the radical anions of the primary chelate complexes can be rationalized in terms of the nodal properties of the frontier orbitals, and indicate M-C bond labilization as a prerequisite for alkyl transfer by intramol. electron transfer in the ground or electronically excited state. In agreement with expts. the M-C bond labilization is generally more pronounced for M = Mg than for the M = Zn analogs. Calcd. vertical and adiabatic electron affinities of the primary complexes are both higher for M = Mg than for M = Zn. Calcns. on the synthetically useful N- and C-alkylated products formed from the primary complexes by the alkyl transfer reaction indicate a rather small energy difference between these two possible collapse products. ESR data of several thermally or photochem. generated paramagnetic products, the anion radicals of the primary chelate complexes and the neutral radicals MR'·DAB, are in agreement with the calcd. geometrical and electronic structures. The electronic structures of all organometallic species are studied by means of localized and canonical MOs as well as Mulliken charges and calcd. dipole moments. The dependence of reactivity and product selectivity on substituent characteristics (R, R'), solvation, temp., and excitation wavelength with respect to the LLCT transition is discussed. [on SciFinder(R)]

@article{Kaupp.1991, abstract = {Ab initio pseudopotential calcns. were used to study species formed in thermal and light-induced alkyl transfer reactions between organometallic compds. R'2M (M = Zn, Mg: R' = alkyl, aryl) and 1,4-diaza-1,3-butadienes RN:CHCH:NR (R-DAB). Geometries of the first isolable intermediates, the chelate complexes MR'2·R-DAB, have been optimized. The x-ray structure of the cryst. complex ZnMe2·tert-Bu-DAB is presented. Its main features are well-reproduced by the calcns. on systems with R = H, Me. The primary complexes exhibit a destabilized HOMO (antisym. M-C \textgreek{s}-bond combination) and a low-lying LUMO (DAB \textgreek{p}* orbital). The energy of the HOMO and the intense long-wavelength HOMO-LUMO transition are strongly influenced by the electronegativity of the carbanionic alkyl group and by the electronegativity of the metal. N,N'-Dimethyl substitution destabilizes the LUMO compared to R = H. Geometries of the lowest triplet-excited states and the radical anions of the primary chelate complexes can be rationalized in terms of the nodal properties of the frontier orbitals, and indicate M-C bond labilization as a prerequisite for alkyl transfer by intramol. electron transfer in the ground or electronically excited state. In agreement with expts. the M-C bond labilization is generally more pronounced for M = Mg than for the M = Zn analogs. Calcd. vertical and adiabatic electron affinities of the primary complexes are both higher for M = Mg than for M = Zn. Calcns. on the synthetically useful N- and C-alkylated products formed from the primary complexes by the alkyl transfer reaction indicate a rather small energy difference between these two possible collapse products. ESR data of several thermally or photochem. generated paramagnetic products, the anion radicals of the primary chelate complexes and the neutral radicals MR'·DAB, are in agreement with the calcd. geometrical and electronic structures. The electronic structures of all organometallic species are studied by means of localized and canonical MOs as well as Mulliken charges and calcd. dipole moments. The dependence of reactivity and product selectivity on substituent characteristics (R, R'), solvation, temp., and excitation wavelength with respect to the LLCT transition is discussed. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Kaupp, Martin and Stoll, Hermann and Preuss, Heinzwerner and Kaim, Wolfgang and Stahl, Thomas and {van Koten}, Gerard and Wissing, Elmo and Smeets, Wilberth J. J. and Spek, Anthony L.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/229d3bf148e319f409e3c988bbab58caf/huebleriac}, doi = {10.1021/ja00015a014}, interhash = {047a8d5730c7adb630f8a0c7f93ce69e}, intrahash = {29d3bf148e319f409e3c988bbab58caf}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, keywords = {adduct alkyl diazabutadiene diazabutadiene;magnesium dimethylzinc dimethylzinc;dipole diorganomagnesium diorganozinc moment organometallic;mol photochem structure thermal thermal;MO transfer zinc;crystal}, number = 15, pages = {5606--5618}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {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}, volume = 113, year = 1991 }