{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/70260"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/70260","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Intramolecular Ligand Permutation at Tetracoordinate and Pentacoordinate Silicon (Pseudorotation, Hypervalent)","abstract":"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.","abstract_html":"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.","abstract_has_math":false,"creators":["Stevenson, William Hartin, Iii"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Chemistry","degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2014,"date_issued":"2014-12-15T23:18:13Z","date_published":"2014-12-15T23:18:13Z","updated_at":"2026-07-22T22:26:02Z","subjects":["Chemistry, Organic"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["(UMI)AAI8422162"],"render_values":[{"text":"(UMI)AAI8422162","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/70260","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Stevenson, William Hartin, Iii"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2014-12-15T23:18:13Z","10000-01-01","1984"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemistry"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Chemistry, Organic"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/70260","(UMI)AAI8422162"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["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.","The inversion of 1 at silicon observed in weakly nucleophilic media is proposed to occur by a mechanism involving pseudorotation of a 10-Si-5 intermediate, 3 (i.e. Nu + 1 (DBLARR) 3 (DBLARR) (')3 (DBLARR) (')1 + Nu, where (')1 and (')3 are enantiomers of 1 and 3). Supporting this mechanism are kinetic studies which indicate that the rate is first-order in nucleophile and has no apparent correlation with the solvent ionizing power of the nucleophile or of the nonnucleophilic solvent. An equilibrium between 1 and 3 is frozen out in the low temperature ('1)H, ('19)F, and ('29)Si NMR spectra of mixtures of 1 and nucleophiles p-dimethylaminobenzaldehyde (DMAB) or methanol. Low temperature rate studies of the inversion of intermediate 3 (Nu = DMAB) are consistent with inversion by intramolecular pseudorotation ((DELTA)G(,183K)('*) = 10.2 kcal/mol). The reaction is fast enough to explain the inversion of 1 observed at higher temperatures.","Measurement of the rate of silane 1 inversion in nonnucleophilic solvent decahydronaphthalene-d(,18) gives evidence for a unimolecular process via a planar 8-Si-4 transition state ((DELTA)G(,422K)('*) = 26.1 (+OR-) 0.3 kcal/mol). A bimolecular inversion process is also detected. This is proposed to proceed through pseudorotation of a 10-Si-5 intermediate formed by coordination of the weakly nucleophilic oxygen of 1 at the silicon of another molecule of 1.","Made available in DSpace on 2014-12-15T23:18:13Z (GMT). No. of bitstreams: 1 8422162.pdf: 4502800 bytes, checksum: 2459890c19bb6ce26f9c828bb68e3b0e (MD5) Previous issue date: 1984","Embargo set by: Seth Robbins for item 70426 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","U of I Only","157 p.","Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984."]},{"key":"dc:title","label":"Title","values":["Intramolecular Ligand Permutation at Tetracoordinate and Pentacoordinate Silicon (Pseudorotation, Hypervalent)"]}]}],"canonical_facts":{"dc:creator":["Stevenson, William Hartin, Iii"],"dc:date":["2014-12-15T23:18:13Z","10000-01-01","1984"],"dc:description":["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.","The inversion of 1 at silicon observed in weakly nucleophilic media is proposed to occur by a mechanism involving pseudorotation of a 10-Si-5 intermediate, 3 (i.e. Nu + 1 (DBLARR) 3 (DBLARR) (')3 (DBLARR) (')1 + Nu, where (')1 and (')3 are enantiomers of 1 and 3). Supporting this mechanism are kinetic studies which indicate that the rate is first-order in nucleophile and has no apparent correlation with the solvent ionizing power of the nucleophile or of the nonnucleophilic solvent. An equilibrium between 1 and 3 is frozen out in the low temperature ('1)H, ('19)F, and ('29)Si NMR spectra of mixtures of 1 and nucleophiles p-dimethylaminobenzaldehyde (DMAB) or methanol. Low temperature rate studies of the inversion of intermediate 3 (Nu = DMAB) are consistent with inversion by intramolecular pseudorotation ((DELTA)G(,183K)('*) = 10.2 kcal/mol). The reaction is fast enough to explain the inversion of 1 observed at higher temperatures.","Measurement of the rate of silane 1 inversion in nonnucleophilic solvent decahydronaphthalene-d(,18) gives evidence for a unimolecular process via a planar 8-Si-4 transition state ((DELTA)G(,422K)('*) = 26.1 (+OR-) 0.3 kcal/mol). A bimolecular inversion process is also detected. This is proposed to proceed through pseudorotation of a 10-Si-5 intermediate formed by coordination of the weakly nucleophilic oxygen of 1 at the silicon of another molecule of 1.","Made available in DSpace on 2014-12-15T23:18:13Z (GMT). No. of bitstreams: 1 8422162.pdf: 4502800 bytes, checksum: 2459890c19bb6ce26f9c828bb68e3b0e (MD5) Previous issue date: 1984","Embargo set by: Seth Robbins for item 70426 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","U of I Only","157 p.","Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984."],"dc:identifier":["http://hdl.handle.net/2142/70260","(UMI)AAI8422162"],"dc:subject":["Chemistry, Organic"],"dc:title":["Intramolecular Ligand Permutation at Tetracoordinate and Pentacoordinate Silicon (Pseudorotation, Hypervalent)"],"dc:type":["text"],"thesis:degree_discipline":["Chemistry"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:26:02Z"}