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Information to Users INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. University Microfilms International A Bell & Howell Information Company 300 North Z eeb Road. Ann Arbor. Ml 48106-1346 USA 313/761-4700 800/521-0600 Order Number 9201613 Electronic requirements and stereochemistry of nucleophilic-induced rearrangement-displacements of (halomethyl)silanes Allen, John Michael, III, Ph.D. The Ohio State University, 1991 UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106 ELECTRONIC REQUIREMENTS AND STEREOCHEMISTRY OF NUCLEOPHILIC INDUCED REARRANGEMENT- DISPLACEMENTS OF (HALOMETHYL)SILANES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University b y John Michael Allen III, B.S. The Ohio State University 1991 Dissertation Committee: Approved by Dr. Gideon Fraenkel Dr. Harold Shechter Dr. John Swenton Dr. Donald Witiak Advisor Department of Chemistry ACKNOWLEDGEMENTS I thank the members of Professor Harold Shechter's research group who I have been associated with through the years and especially Dr. Harold Shechter for his patience and advise (especially these last few months). VITA January 7, 1963 Born - North Tonawanda, New York 1985 . B. S. , Niagara University 1985 - 1987 . Graduate Teaching Associate Department of Chemistry The Ohio State University, Columbus, Ohio 1987 - Present Graduate Research Associate Department of Chemistry The Ohio State University, Columbus, Ohio FIELD OF STUDY Major Field: Chemistry Study of Organic Chemistry under the guidance of Professor Harold Shechter. TABLE OF CONTENTS ACKNOWLEDGEMENTS ii VITA iii LIST OF TABLES ‘ v LIST OF FIGURES vii CHAPTER I. Statement of Problem 1 II. Historical 4 III. Preparation and Reactions of Aryl(halomethyl)- diphenylsilanes 24 IV. Discussion of Migratory Aptitudes 53 V. Stereochemistry of Rearrangement-Displacements 59 VI. Summary 86 VII. Experimental 88 REFERENCES 145 iv LIST OF TABLES Table Page 1. Displacement Reactions of (Chloromethyl)trimethylsilane (12) with Various Nucleophiles. 2 . Products (% Yield) of Reactions of Aryl(chloromethyl)- dimethylsilanes (12) with Sodium Ethoxide in Ethanol. 10 3. Product Distributions (% Yield) for Reactions of 20 with Sodium Methoxide in Varied Solvents 12 4. Migratory Aptitudes (Ar/Ph) for Reactions of 22. with Fluoride Ion at 0 °C in Tetrahydrofuran 21 5. Statistically Corrected Relative Migratory Aptitudes and Sigma-zero Values for Reactions of para-Aryl(bromo- methyl)diphenylsilanes (4a-f) with Tetrabutylammonium Fluoride at 23 °C. 32 6 . Statistically Corrected Relative Migratory Aptitudes (p-Z-Ph/Ph) in Reactions of Aryl(bromomethyl)- diphenylsilanes (4a-f) with Fluoride Ion at 0 °C and -20 o c . 36 7. Statistically Corrected Relative Migratory Aptitudes (p-Z-Ph/Ph) in Reactions of Aryl(iodomethyl)diphenyl- silanes (5a-f) with Fluoride Ion at 23 °C. 40 8 . Statistically Corrected Relative Migratory Aptitudes (p -Z-Ph/Ph) in Reactions of Aryl(bromomethyl)- diphenylsilanes (4a-f) with Methoxide Ion at 23 °C 45 v LIST OF TABLES (cont.) Table PAGE 9. The Effects of Solvents on the Migratory Aptitudes for Rearrangement-Displacements of 4f with Fluoride and Methoxide Ions at 23 °C. 48 10. Corrected Migratory Aptitudes for Rearrangement- Displacements of 4f and 4Ji at Varied Concentrations of Fluoride Ion. 49 11. Corrected Migratory Aptitudes for Fluoride-Induced Rearrangement-Displacements under Varied Conditions of 4f. 52 12. The Stereochemistry of Substitution Reactions of Chiral Methyl(l-naphthyl)phenylsilanes (941. 61 13. Stereochemistry of Alkoxide-Induced Rearrangement- Displacements of (+)-(Bromomethyl)methyl(l-naphthyl)- phenylsilanes (8.). 76 14. Reaction of (+)-(Bromomethyl)methyl(l-naphthyl)phenyl- silane (&) with Varied Amounts of Tetrabutylammonium Fluoride. 82 LIST OF FIGURES Figure Page 1. Logarithms of the Migratory Aptitudes (Ar/Ph) Plotted Against Sigma Values for Rearrangement-displacements of 53. with Fluoride Ion 22 2. Plots of the Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) Versus Sigma-zero Substituent Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-f) with Fluoride Ion at 23 °C. 34 3. Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) Plotted against Sigma-zero Substituent Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-Q with Fluoride Ion at 0 °C. 37 4. Logarithms of the Migratory Aptitudes ip-Z -P h/P h) Plotted Against Sigma-zero Values for Reactions of Aryl(bromomethyl)diphenylsilanes (4a-f) with Fluoride Ion at -20 °C . 38 5. Plot of the Logarithms of the Migratory Aptitudes (p-Z-Ph/Ph) against Sigma-zero Values for Reactions of Aryl(iodomethyl)diphenylsilanes (5a-f) with Fluoride Ion at 23 °C. 42 6. Plot of the Logarithms of the Ratios of Corrected Migratory Aptitudes for Substituted Phenyl Groups Versus Sigma-zero Substituent Values for Methoxide-induced Rearrangement-displacements of (4a-Q. 46 vii LIST OF FIGURES (cont.) Figure Page 7. Structures of the Pentacoordinate Silyl Anionic Intermediates for Rearrangement-displacements of (4a-f1 with Methoxide and Fluoride Ions. 55 8. Transition States For Fluoride-induced Rearrangement- displacements of Aryl(halomethyl)diphenylsilanes which Express Aryl Participation Processes and Cationic Cleavages. 57 viii CHAPTER I : STATEMENT OF PROBLEM The present research involves investigation of the electrical requirements and the stereochemistry of nucleophile-induced rearrangement-displacements of (halomethyl)triorganosilanes JL in which R = alkyl or aryl (Equation 1). The reactions of interest involve attack of a nucleophile at silicon rather than carbon to give a presumed pentacoordinate silyl anion 2. Collapse of the silicanionic species (2J via migration of an organic substituent from silicon to carbon with expulsion of bromide to give products of skeletal rearrangement, 2., has been documented by previous investigators.1*2 -X ^i— CH2R (1) R 1, X = halogen 3. R = alkyl or aryl 1 2 There has been considerable concern as to the controlling features of such rearrangement-displacement reactions and therefore the purpose of this research is to investigate further the mechanistic details of these processes. The first part of this work involves determination of the migratory aptitudes of the rearrangement-displacements of a series of aryl(halomethyl)- diphenylsilane,s 4 and 5., with fluoride and alkoxide nucleophiles (Equation 2). Study was made of the effects of temperature, the halide leaving group, the nucleophile and general reaction conditions on the migratory aptitudes in the rearrangement-displacements. Ph Z Nu Ph— Si— CHgX- I Ph 4 ,5 X = Br Nu— Si— CH2Ph 4a, z = c f3 5a, z — c f3 I 4£, Z = Cl 5b, Z = Cl Ph 4a, z = H 5s, Z = H Ih 44. Z = CH3 5 4 , z = c h 3 4fi, z = o ch 3 5s, z = och3 41. Z - N(CH3)2 5f, Z = N(CH3)2 3 The results from the present migratory aptitude studies along with earlier investigations *>2 lead to interest in the stereochemistry at silicon in the rearrangement-displacement reaction. The second part of this work therefore involves determination of the stereo­ chemistry of the rearranged product 9 derived from reactions of the chiral silane, (bromomethyl)methyl(l-naphthyl)phenylsilane (8_1 with alkoxide and fluoride nucleophiles (Equation 3). Correlations of configuration using reactions of known stereochemistry for 8. and £ Nu 1 - Np— jji— CH2Br ► 1 -Np—-c; j— CH2Ph (3) Ph CH3 [a]23D +8.29 a were used to determine whether the rearrangement-displacements occur with inversion, retention or racemization at silicon. CHAPTER II: HISTORICAL Although the first organosilane, tetraethylsilane was prepared by Friedel and Crafts in 1863, 3 organosilanes did not generate much interest until the past three decades. 4 Of historical interest to the research in this dissertation is that halomethyltriorganosilanes (2., R = alkyl or aryl) react with nucleophiles to give various products two of which, 10. and 1_L, are indicated in Equation 4. R R R R— j>i— CH2X NxUC" ► R— Si— CH2Nuc + Nuc— Si— CH2R (4) R R R 2. IQ 11 Early work by Whitmore and Sommer5 illustrated that (chloromethyl)trimethylsilane (12) is more reactive to Sn 2 nucleophilic displacement (Equation 5) than its carbon analog, neopentyl chloride. The increased reactivity of J_2_ is due to less steric
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