Intramolecular Ligand Permutation at Tetracoordinate and Pentacoordinate Silicon (Pseudorotation, Hypervalent)

The X-ray crystal structures of 3,3,3',3'-tetrakis(trifluoromethyl)-1,1'(3H,3'H)-spirobi{2,1-benzoxasilole}(silane 1) and tetramethylammonium bis {(alpha),(alpha)-bis(trifluoromethyl)benzene-methanolato(2-)-C('2),O} phenylsilicate (2) are described. Silane 1 is a distorted tetrahedron at silicon with a significant deviation towards the trans planar geometry; the 10-Si-5 phenylsiliconate, 2, is nearly trigonal-bipyramidal at silicon. Evidence that the bidentate ligands of 1 preferentially stabilize the trigonalbipyramidal geometry of 10-Si-5 compounds, 3, relative to 8-Si-4 and 12-Si-6 forms is presented. Rates of ligand permutation for a series of siliconates, 3, are consistent with a mechanism proceeding by nondissociative Berry-type pseudorotation. The energy barrier to inversion for phenylsiliconate 2 ((DELTA)G(,422K)('*) = 26.0 kcal/mol) is lower than that for the isostructural, isoelectronic phosphorane ((DELTA)G(,422K)('*) = 28.3 kcal/mol). The rate of monodentate Si-C bond cleavage of arylsiliconates 3 by bromine and triflic acid decreases markedly as the electron withdrawing ability of the monodentate ligand increases. Phenyl- and n-butylsilicontes 3 react with bromine at comparable rates to give selective cleavage of the monodentate Si-C bond.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Stevenson, William Hartin, Iii

• Chemistry, Organic

Identifier

(UMI)AAI8422162

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70260