TY - JOUR
T1 - Configurationally rigid pentaorganosilicates
AU - Couzijn, E.P.A.
AU - van den Engel, D.W.F.
AU - Slootweg, J.C.
AU - de Kanter, F.J.J.
AU - Ehlers, A.W.
AU - Schakel, M.
AU - Lammertsma, K.
PY - 2009
Y1 - 2009
N2 - The intramolecular substituent interchange in recently reported pentaorganosilicates is investigated by B3LYP calculations, which show excellent agreement with the experimental thermochemical data. Two types of ligand permutation are discerned (A and B), which both lead to racemization of the helical, spirocyclic anions. IRC calculations show that stereomutation A bifurcates into two enantiomeric reaction paths, which are inhibited by ortho substitution of the bidentate ligands. The other pathway (B) proceeds through a trigonal bipyramidal transition state with one bisequatorial bidentate ligand and is disfavored by increasing the π-electron density of the ligand. A more electronegative fifth, monodentate substituent increases the barrier of pathway A and lowers that of pathway B, as in bis(biphenyl-2,2'-diyl)fluorosilicate, which is the first tetraorganofluorosilicate to be isolated and fully characterized. These concepts enabled us to design and synthesize methyl- and ethylbis([2]naphthylpyrrol-2,1'-diyl)silicate as Si-chiral pentaorganosilicates that are configurationally rigid at room temperature. © 2009 American Chemical Society.
AB - The intramolecular substituent interchange in recently reported pentaorganosilicates is investigated by B3LYP calculations, which show excellent agreement with the experimental thermochemical data. Two types of ligand permutation are discerned (A and B), which both lead to racemization of the helical, spirocyclic anions. IRC calculations show that stereomutation A bifurcates into two enantiomeric reaction paths, which are inhibited by ortho substitution of the bidentate ligands. The other pathway (B) proceeds through a trigonal bipyramidal transition state with one bisequatorial bidentate ligand and is disfavored by increasing the π-electron density of the ligand. A more electronegative fifth, monodentate substituent increases the barrier of pathway A and lowers that of pathway B, as in bis(biphenyl-2,2'-diyl)fluorosilicate, which is the first tetraorganofluorosilicate to be isolated and fully characterized. These concepts enabled us to design and synthesize methyl- and ethylbis([2]naphthylpyrrol-2,1'-diyl)silicate as Si-chiral pentaorganosilicates that are configurationally rigid at room temperature. © 2009 American Chemical Society.
U2 - 10.1021/ja809154g
DO - 10.1021/ja809154g
M3 - Article
SN - 0002-7863
VL - 131
SP - 3741
EP - 3751
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 10
ER -