Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1980 Synthetic and mechanistic studies of (p-p) pi- bonded organosilicon and organogermanium reactive intermediates S. Kent Hoekman Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Organic Chemistry Commons Recommended Citation Hoekman, S. Kent, "Synthetic and mechanistic studies of (p-p) pi-bonded organosilicon and organogermanium reactive intermediates " (1980). Retrospective Theses and Dissertations. 7334. https://lib.dr.iastate.edu/rtd/7334 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 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ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WCIR 4EJ, ENGLAND 8012967 HOEKMAN, S. KENT SYNTHETIC AND MECHANISTIC STUDIES OF (P-P) PI-BONDED ORGANOSILICON AND ORGANOGERMANIUM REACTIVE INTERMEDIATES lov/a State University PH.D. 1980 University Microfilms I n te r n 9,t i O n s I 300 N. Zeeb Road, Ann Arbor, MI 48106 18 Bedford Row, London WCIR 4EJ, England Synthetic and mechanistic studies of (p-p) TT-bonded organosilicon and organogermanium reactive intermediates by S. Kent Hoekman A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Department; Chemistry Major: Organic Chemistry Approved; Signature was redacted for privacy. Signature was redacted for privacy. For the Ma,j6r Department Signature was redacted for privacy. For liege Iowa State University Ames, Iowa 1960 11 TABLE OF CONTENTS Page DEDICATION iv INTRODUCTION 1 NOMENCLATURE 3 HISTORICAL 5 Germenes 5 Silanones 11 Germanones 35 Silylperoxides 38 RESULTS AND DISCUSSION 5? a-Silylcarbenes 57 Trimethylsilyl and Trimethylgermyldiazomethane 60 Bis(trlmethylsilyl)dlazomethane 64 Trimethylsilyltrimethylgermyldiazomethane 77 Bis(trijnethylgermyl)diazomethane 80 2,3-disila-l,4-dloxanes 84 Attempted Formation of Dg 96 Pyrolysis of Silylethers 98 Silylperoxides and Bis(silyl)peroxides 121 Erroneous Report of Silanone Generation 146 CONCLUSION 156 EXPERIMENTAL 158 General Information 158 Procedures arid Results 159 Ill Page BIBLIOGRAPHY 256 ACKNOWLEDGMENTS 26? iv DEDICATION To Sheri 1 INTRODUCTION Since 1966, the silicon-carbon douliLe bond has been elevated from the position of a nonexistent species to a well-established reactive intermediate. This dissertation will describe the quantitative genera­ tion of a silicon-carbon double bond by the photolytic and thermolytic decomposition of an a-silyl diazo compound. In addition to the usual trapping experiments, several new reactions of the silicon-carbon double bond will be discussed. The analogous a-germyl diazo compound was also prepared and was found to be an excellent generator of the germanium-carbon double bond. The silicon-oxygen double bond has been much less studied than the silicon-carbon double bond. This is due, in part, to the difficulty in preparing a suitable generator of silicon-oxygen double bonds. It will be shown in this dissertation that one such precursor, the 2,3- disila-1,4-dioxane system, is not the convenient, low temperature generator that was desired. A new method of generation of silicon-oxygen double bonds will be discussed. This method involves the loss of an alkyl radical from a siloxy radical in the same way that a carbon oxy radical forms a carbonyl compound. Pyrolysis of several silyl ethers generated siloxy radicals. Two reactions of siloxy radicals occurred: hydrogen ab- 2 straction and attack. No evidence demanding the intermediacy of silicon-oxygen double bonds was obtained. The chemistry of silyl and bis(silyl)peroxides will also be dis­ cussed. Thermally, these peroxides undergo an intramolecular rearrange- 2 ment rather than homolytic cleavage of the peroxide linkage. While some bis(silyl)peroxides do homolytically cleave photochemically, strong evidence will be presented to show that other bis(silyl)peroxides under­ go an intramolecular reaction to form the 2,4-disila-l,3-dioxetane system. Finally, a recent report of the generation of a silicon-oxygen double bond from the thermolysis of a silyl peroxide will be shown to be erroneous and all reports of silicon-oxygen double bonds will be brought into question. 3 NCMENGLATURE The nomenclature used in this dissertation will, with the exceptions described below, follow the conventions set down by IUP AG. Simple organosilicon compounds will be named as derivatives of silane (SiH^), while more complicated linear and cyclic systems will be named as sila-analogs of the corresponding carbon system. Examples; Me2Sl(0Me)2 dijnethyldimethoxysilane Me^SiOGHgPb benzyloxytrimethylsilane M eg Si- 1,1,3i3-tetramethyl-l,3-disilacyclobutane •SlMeg M eg Si—0 2,2-dimethyl-2-silaoxetane Me.SI \ ^ I 2,2,3,3-tetramethyl-2,3-disila-l,4-dioxane k All compounds containing (p-p) ir-bonded silicon will be named as derivatives of silene (l^Si=GH2) and silanone (H2Si=0). Examples: Me ^^,Si=CH2 1,1-dimethylsilene Me „^Si=0 dimethylsilanone MeO^ j^g,Si=0 methoxymethylsilanone All germanium compounds will be named as their silicon analogs by substituting "germane" for "silene" and "geima" for "sila." 5 HISTORICAL Unlike silenes and silanones which have been extensively studied, the analogous (p-p) IT-bonded organogermanim Intermediates are practically unknown. Germenes and germanones will here be reviewed separately. Also reviewed will be bis(silyl)peroxides which can serve as precursors to siloxy radicals. Germenes Since the initial reports suggesting the transient existance of silenes by Nametkin and coworkers in 1966 (l), and by Gusel'nikov and Flowers in 19^7 (2), there has been a flurry of activity involving the generation and trapping of these reactive intermediates. The extent of this activity is reflected in the number of reviews which have appeared in recent years (3-7)» In sharp contrast with the frequently studied silene stands the little known germene. Several theoretical studies of silenes have been reported. Walsh (8) used the kinetic data of Gusel'nikov and Flowers (2, 9, 10) and of Davidson and Lambert (11, 12) to estimate the ir-bond energy to be in the range of 28-46 kcal/mole. Curtis conducted EHMO and CNDO calculations (13). He concluded that the silene is exceedingly polar in the direction of ^E&=C and should behave like a carbanion-siliconium zwitterion. Damrauer and Williams (l4) carried out GNDO/2 calculations on H2Si=CH2, F2Si=GH2, I^Si=GF2, and F2Si=CF2. Like Curtis, these authors also found the silene to be very polar. The introduction of fluorine sub- stituents in the place of hydrogens affected the charge densities on 6 silicon and carbon in the predicted and expected manner. initio. calculations of HgSi=CH2 have been carried out by Schlegel, Wolfe, and Mislow (15)1 Strausz and coworkers (I6), and Ahlrichs and Helnzmann (I7) 00 The latter authors report that (a) Sl-C bond distance Is I.69 A (.16 A shorter than a Sl-C single bond); (b) H2Si=GH2 has a planar TT-bonded singlet ground state about 28 kcal/mole below the lowest triplet which has perpendicular structure; (c) the strength of the Si-G TT-bond as determined by the rotational barrier is 46 kcal/mole (about 70% of the G=C bond strength); (d) the Si=C bond is very polar as indicated by the charge distribution shown below; and (e) the cycloaddition reaction of sllene is characterized by a small activation energy (l4 kcal/mole) and a large reaction energy (76 kcal/mole). 0.05 -0.1 H . .H -0.4 0. G Si H H 0.05 -0.1 H. H H -4i—p ^act ~ kcal/mole 2 H^Si == CH 4, 11 ^ ^ A H = -76 kcal/mole Gusel'nikov and Nametkin (l8) used their kinetic data from the py- rolysis of 1,1-dimethyl-l-silacyclobutane to calculate a Si-G TT-bond energy of 28 + 8 kcal/mole.