Paul Ronald Jones

Unimolecular and collision induced decompositions of gas-phase group IV a enium ions (CH3)3M+

Abstract The fragmentation characteristics of the trimethyl-Group IV cations have been studied using mass analyzed ion kinetic energy (MIKE), V 1 2 / E (linked) metastable and consecutive reaction monitoring techniques. Both unimolecular (low energy) and collision induced (high energy) decompositions were studied. These methods give information on the ion of interest without interfering contributions from the precursor ion of the trimethyl cation. The results have been interpreted in terms of the decreasing metal—carbon bond strength and the increasing preference for the +2 oxidation state going down Group IV from carbon to lead.

Hyperconjugative vs. d orbital effects in unsaturated silanes : I. The energy levels in para-group IV-substituted anilines

Abstract The energy levels of a series of para substituted N,N -dimethylanilines p -MH n Me 3− n C 6 H 4 NMe 2 ( n = 0−3, M = C or Si) for the ground and lower lying excited states have been determined in acetonitrile solution. The levels for the carbon compounds are all slightly destailized relative to N,N -dimethylaniline and the effects are rather insensitive to n . The stabilizations produced by silicon substituents on all levels are markedly affected by silicons substituents, showing increasing perturbations with increasing n . It is concluded that variations in the interaction of the σ * system of the silyl substituent with the aniline π system, and not d orbital interactions, account for the trends observed.

The synthesis and stereochemical characterization of the five isomeric 1,3-diphenyl-1,3-dimethyl-2,4-dineopentyl-1,3-disilacyclobutanes

Summary The reaction of t-butyllithium with phenylmethylvinylchlorosilane at low temperature in hexane solvent gave a 48% yield of a mixture of the five isomers of the 1,3-diphenyl-1,3-dimethyl-2,4-dineopentyl-1,3-disilacyclobutanes, along with an acyclic isomer. The separation and determination of the stereochemistry of the diasteromeric 1,3-disilacyclobutanes by means of carbon-13 NMR is described.

Regioselective hydroborations of methylvinylchlorosilanes

Abstract The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl n Me3− n SiCH CH2 ( n = 0 − 3), has been investigated using BH3←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols for n = 0 and 1. For n = 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol- 0 - d provides a more effective means of derivatization. Addition of the alkenes, n = 2 or 3, to excess BH3←THF gives ca . 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes give ca . 80% of the β-boron adducts.

The methoxide promoted protonolysis of organosilylboranes

Abstract The destructive distillation or pyrolysis of borane 9-borabicyclo[3.3.1]nonane, or dicyclohexylborane adducts to vinylsilanes which have been treated with sodium methoxide in methanol gives significant yields of products resulting from protonolysis of the Cue5f8B bond. Both α- and β-boro adducts undergo the reaction, which is favored when silicon has methoxy substituents. Quantitative incorporation of deuterium in the saturated products when methanol-O-d is used as the solvent shows that the hydroxyl group of methanol is the proton source. The absence of isomerization of the alkyl groups attached to silicon in the protonolysis of the adducts to propenyltrichlorosilane or isopropenyltrichlorosilane indicates that cyclic intermediates or free carbanions are not involved in the reaction.

The vacuum ultraviolet spectra of methylvinylsilane and propylene

Abstract The VUV spectra of methylvinylsilane and propylene are reported and corresponding transitions are assigned. The small red shift of the π→π* transition and the large blue shift of the σ→σ* excitation of the methyl group in methylvinylsilane may be attributed to the +I inductive effect of silicon without involving interaction between d orbitals and the π system. No evidence for a second allowed π→π transition is found in methylvinylsilane.

Organometallic Radical Anions

Publisher Summary This chapter discusses electron transfer processes, properties of anion radicals, and alkenyl and alkynyl derivatives. Phenyllithium, n -butyllithium, or benzyllithium reacts with sterically hindered olefins––such as 1,2,3,4-tetraphenyl-butadiene or tetraphenylethylene––to form olefin radical anions. Some interesting electron-transfer reactions of sodium naphthalide have recently been reported. The trimethylsilyl radical produced either rapidly dimerizes or reacts with solvent so that very clean electron spin resonance (ESR) spectra of the radical anion––with minimum interactions with the counterion––can be obtained. Alkenyl and alkynyl derivatives of the Group IV elements react readily with alkali metals at low temperatures in donor-type solvents to give radical anions. Triphenyl silane and triphenyl-(1-propenyl)silane undergo coupling at the carbons β to silicon, whereas trimethyl(trans-β-styryl)silane couples at the carbons α to silicon, consistent with the anticipated relative stabilization of the intermediate radical anions. Aryl group IV derivatives are readily reduced in donor solvents, using either alkali metals or electrochemical reduction. The electron-exchange phenomenon is not limited to organometallic radical anions. As methyl groups on silicon are replaced by hydrogen, the electron-withdrawing effect of the silyl substituent increases to the extent that the spin distribution in the p -silyl- N , N -dimethylaniline radical anion approaches that for the p-nitro- N , N -dimethylaniline radical anion.

Hyperconjugative vs. d orbital effects in unsaturated silanes : II. The radical anions of para-silyl-substituted anilines

Abstract The radical anions of a series of para -silyl substituted N,N -dimethylanilines; p 0SiH n Me 3− n C 6 H 4 NMe 2 ( n = 0−3) have been studied by electron spin resonance spectroscopy. When n = 0 or 1 the primary radicals may be generated by either electrolytic or metal reduction. For n = 2 or 3 reduction with potassium immediately gives secondary paramagnetic species resulting from loss of hydride from silicon. Primary radicals for the n = 2 or 3 compounds may be obtained electrolytically. The ESR spectra show increasing spin delocalization into the silyl group as n increases, to the point that the spin distribution in the p -SiH 3 compound approaches that of p -nitro- N,N -dimethylaniline radical anion. A tentative analysis of the secondary and tertiary spectra is given. The results, coupled with CNDO/2 calculations for the radical anions, indicate that the primary interaction between silicon and the aromatic system involves the σ * levels of the silyl substituents and the π * orbitals of N,N -dimethylaniline.

Bonding studies in group IV substituted anilines : IV. Excited state interactions in the trimethyl derivatives

Abstract The solution ultraviolet spectra for N,N-dimethylaniline, p-t-butyl-, and p-trimethylsilyl-, p-trimethylgermyl-, and m-trimethylsilyl-N,N-dimethylaniline in acetonitrile and pentane are reported. The Group IV substituents perturb the excited states to a much larger extent than the ground states. Both the symmetric and antisymmetric π* levels are affected by π interaction with the trimethylsilyl and trimethylgermyl substituents. The magnitude of the effects are proportional to the π density at the point of substitution. Simple Huckel calculations correlate well with experimental transition energies. The model appears to exaggerate π interactions between silicon or germanium and the π* molecular orbitals.

Silene stereochemistry. IV: The configurational stability of 1-phenyl-1-methyl-2-neopentylsilene under flash vacuum thermolysis conditions

Abstract When E - or Z -1-phenyl-1-methyl-2-neopentylsilene is generated by retro Diels-Alder flash vacuum thermolysis of their corresponding cyclopentadiene or anthracene adducts at temperatures between 400 and 650°C and trapped with 2,3-dimethyl-1,3-butadiene, the stereochemical distribution of the products is independent of the stereochemistry of the silene precursor indicating that the silene is not configurationally stable towards cis-trans isomerization at these temperatures. Evidence that intermolecular “ene” reaction and the [4 + 2] cycloaddition which occur between silenes and the diene are both concerted reactions is presented.