A tetrameric allyl complex of sodium, and computational modeling of the Na-23-allyl chemical shift

作者：McMillen C Heather; Gren Cameron K; Hanusa Timothy P^*; Rheingold Arnold L

来源：Inorganica Chimica Acta, 2010, 364(1): 61-68.

DOI：10.1016/j.ica.2010.07.079

• Allyl ligands
• X-ray crystal structure
• Sodium
• Density functional theory calculations
• Nuclear magnetic resonance

Transmetallation of Li[A'] (A' = [1,3-(SiMe3)(2)C3H3]) with sodium tert-butoxide produces the corresponding sodium salt, which crystallizes from THF/toluene in the form of a cyclic tetramer, {Na[A'](thf)}(4). The Na atoms are in a square planar arrangement, bridged with pi-bound allyl ligands; the Na-C distances range from 2.591(3)-2.896(3) angstrom, with an average of 2.70 angstrom. The geometries of several model organosodium complexes containing cyclopentadienyl and allyl ligands were optimized with density functional theory methods. The optimized structures were used with the gauge-including atomic orbital (GIAO) method to calculate their Na-23 NMR magnetic shielding values. Unlike the case with NaCp, the chemical shift of unsubstituted Na(C3H5) is very sensitive to the presence of coordinated THF (causing a 20 ppm upfield shift); silyl substitution has an even larger effect (30 ppm upfield shift). The observed Na-23 shift of delta - 3.3 ppm for Na[A'] in THF-d(8), however, cannot be reliably distinguished from that calculated for the [Na(thf)(4)](+) cation alone.

• 出版日期2010-12-15