Synthesis, Reactions, and Stereochemical Studies of New Bicyclic Organosilicons, 3-silabicyclo[3.2.1]octanes and 2-silabicyclo[2.2.1]heptanes

Author

Craig Blankenship, Marquette University

Date of Award

2-1982

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Sheldon E. Cremer

Second Advisor

Daniel Haworth

Third Advisor

Charles A. Wilkie

Abstract

Several members of two new classes of bicyclic organosilicons, 3-silabicyclo[3.2.1]octanes (3-SBO) and 2-silabicyclo[2.2.t]heptanes (2-SBH), were prepared by five- and seven-step synthetic sequences, respectively. Reaction of the bis-organomagnesium reagent of cis-1,3-bis(bromomethyl)cyclopentane with trichloromethylsilane, trichlorophenylsilane, or silicon tetrachloride was used to prepare derivatives of the 3-SBO system. Platinumcatalyzed intramolecular hydrosilation of 4-dichloro­silyl)methyl]cyclopentene or 4-[(chloromethylsilyl)methyl]cyclopentene gave access to the 2-SBH series. New compounds were characterized by elemental analysis, ¹H and ¹³C NMR, IR, and/or mass spectrometry, ²⁹Si NMR spectra were obtained for 3-SBO, endo- and exo-3-methyl­ 3-SBO, 2-SBH, and endo- and exo-2-methyl-2-SBH. A unique mode of fragmentation was observed in the mass spectra of the isomers of 3-methyl-3-SBO involving loss of H₂; this fragmentation gave the base peak in the spectrum of exo-3-methyl-J-SBO, whereas a corresponding peak of low intensity was observed for endo-3-methyl-3-SBO. Electron diffraction analyses were obtained for 3-SBO and endo-3-methyl-3-SBO; the latter analysis provided an unambiguous isomer assignment which was extended to six other isomer pairs in the 3-methyl-3-SBO series through correlation of several physical properties. Isomers of 2-methyl-2-SBH derivatives were assigned from the NMR spectral properties.

The stereochemistry of several reactions of 3-methyl­ 3-SBO derivatives was studied; the results paralleled those observed for acyclic organosilicons. Studies of the stereochemistry of reactions of 2-methyl-2-SBH derivatives were initiated. LAH reduction of 3-chloro-3-methyl-3-SBO occurred with inversion of configuration, but the stereo­ chemistry of reduction of 2-chloro-2-methy-l2-SBH was more- complex.

The isomers of 3-methyl-3-SBO, 3-methoxy-3-methyl­ 3-SBO, 3-methyl-3-phenyl-3-SBO, and 2-methyl-2-SBH were equilibrated by treatment with CsF in polar, aprotic solvents; (+)-α-naphthylphenylmethylsilane (1) was also readily racemized. The order of reactivity toward isomerization was I>2-methyl-2-SBH~3-methoxy-3-methyl­ 3-SBO > 3-methyl-3-SBO > 3-methyl-)-phneyl-3-SBO. Isomerization of 3-methyl-3-SBO was examined with respect to the nature of the fluoride salt, solvent, and added crown ether. The proposed mechanism involves reversible formation of a pentacoordinate intermediate which can undergo pseudorotation.

Two new types of reactions were observed for the bicyclic silyl hydrides in the presence of fluoride ion. A facile conversion of Si-H to Si-F was found. Some unique reactions with carboxylic amides were observed in which the silyl hydride was converted to a disiloxane.