Robert Damrauer

Synthesis of 3-methylene-1,1-dichlorosilacyclobutane and 1,1-dichlorosilacyclopent-3-ene

Abstract : Silacyclobutanes have played an important role in the development of modern silicon chemistry. For example, silacyclobutanes serve as precursors to carbon-silicon double bonded intermediates silenes as well as to pentacoordinate silicon anions in the gas phase. Silacyclobutanes also undergo facile ring opening polymerization. Despite the importance of this ring system surprisingly few functionalized silacyclobutanes and silacyclobutenes have been prepared. Similarly, there is considerable interest in 1-silacyclo-pent-3-enes due to their facile conversion into other functionalized silicon heterocycles as well as due to their ability to undergo anionic ring opening polymerization. These compounds have usually been prepared by reaction of a 1,3-diene with a dihalosilane under dissolving metal reduction conditions. (jes)

A theoretical study of the silicon—carbon double bond

CNDO/2 calculations have been carried out on H2SiCH2 (I), F2SiCH2 (II), H2SiCF2 (III), and F2SiCF2 (IV). Geometries, charge densities, bond orders, and d-orbital effects have been examined. The reactivity of the silicon—carbon double bond has been discussed and calculations assuming electrostatic interactions have been performed. The stability of the silicon—carbon double bond has been discussed in terms of the above mentioned calculations.

Preparation and basicity measurements of ferrocenyl trimethylsilyl ketone

Abstract Ferrocenyl trimethylsilyl ketone, FcCOSiMe3 (I) has been prepared in good yield by a four step sequence. It exhibits an unusually low carbonyl stretching frequency of 1589 cm−1. MeOD has been used to characterize unequivocally the carbonyl stretching band as well as to estimate the basicity of I. In addition, we have measured the basicity of I in aqueous sulfuric acid solutions.

An improved cyclization procedure for 3-chloropropylchlorosilanes: Efficient syntheses of silacyclobutanes

Abstract Powdered magnesium activated by 1,2-dibromoethane has proved to be an efficient agent for cyclizing (3-chloropropyl)chlorosilanes to silacyclobutanes. 1,1-Dichlorosilacyclobutane, 1-chloro-1-methylsilacyclobutane, 1,1-dimethylsilacyclobutane, and 4-silaspiro[3,3]heptane have been prepared in yields greater than 75%. Discussion of synthetic routes to the precursors of the spiro compound are also included.

Gas phase studies of silacyclobutanes: recent developments employing triple quadrupole detection

Abstract Four silacyclobutyl anions have been prepared and studied by gas phase ion-molecule chemistry using newly modified tandem flowing afterglow instrumentation. These silacyclobutyl anions, which include a pentacoordinate adduct of 1,1-dimethylsilacyclobutane and fluoride and an α-silylcarbanion, siloxide, and mercaptide corresponding to 1,1-dimethylsilacyclobutane, have been characterized by their chemical reactivity and collision-induced loss of ethylene under a variety of conditions. The CH, OH, and SH gas phase acidities of 1,1-dimethylsilacyclobutane. 1-hydroxy-1-methylsilacyclobutane, and 1-mercapto-1-methylsilacyclobutane have been measured and show no effect of the silacyclobutyl attachment. The full capabilities of the newly modified instrumentation include the mass selection of ions, their chemical characterization, collision-induced dissociation of both mass selected ions and those prepared by chemical reactions, and triple quadrupole detection.

Nitrogen configurational stability: The effect of a neighboring ferrocene group

The diastereotopic benzyl group has been used to probe dynamic effects in systems where a ferrocene group and nitrogen are directly σ-bonded. We have studied the effect of a ferrocene group on nitrogen inversion as well as observing interesting rotational phenomena in N-ferrocenyl-benzamides and -acetamides.

SYNTHESIS AND STRUCTURE OF SILICON-CONTAINING CAGES

The synthesis and properties of two new silicon-containing cage systems are reported. These are prepared by transition metal-catalyzed cyclotrimerizations of siliconcontaining tripod triynes. Trimerizations of this type give both 1,2,4 and 1,3,5 benzene ring isomers. These isomers have been separated and characterized by a variety of means including multi-nuclear NMR and X-ray analysis. Collaborative ab initio computations have been carried out to examine the stability of in versus out isomers in related cage systems. Introduction: We recently reported the synthesis of silicon cage molecules 1 and 2 for t-Bu t-Bu 1 (1,2,4 isomer) 2 (1,3,5 isomer) n= 3. Our interest in such molecules was stimulated by studies by Pascal and coworkers who have prepared several macrocyclics including 3 and 4 . 2 6 Their work has clearly demonstrated that molecules like 3 and 4 are more stable with the hydrogen on their quaternary atom directed inside the cage. The synthetic strategy employed by Pascal and coworkers to prepare compounds like 3 and 4 begins with 1,3,5-trisubstituted benzenes and subsequently assembles the cage. Our studies were undertaken with two goals: (1) to develop other general synthetic pathways that would efficiently prepare silicon-containing macrocyles of varying structure and (2) to answer the question of whether a hydrogen on a quaternary atom would in general prefer an inside or outside orientation. In this paper, we report the synthesis of 1 and 2 for n= 2 and 9. We also will briefly summarize our collaborative studies on ab initio computations bearing on the inside-outside isomerization question. Materials and Methods: All the reported reactions were carried out under an inert gas atmosphere using handling standard techniques. Solvents were dried and all reagents were purified using standard methods. The following instruments were used for characterization purposes: GC HP5989 (FID): GC-MS HP5970 : NMR IBM-NR80, Varian VXR-300, and Bruker WM250: UV PE552A: X-ray Nicolet P3F auto diffractometer using Siemens SHELXTL. General Preparation of Silicon-Containing Cages: Tripod Synthesis (eq. 1 for n= 2, 3, and 9): The corresponding yne-1-ol (0.24 mol) in 30 ml benzene was added to a flask containing t-butyltrichlorosilane (0.08 mol), pyridine (0.23 mol), and copper powder (0.005 mol)

Carbon-13 and silicon-29 NMR spectra of some [tris(trimethylsilyl)methyl]-substituted silanes and related compounds

Fourier Transform 13C and 29Si NMR spectra are reported for series of [tris-(trimethylsilyl)methyl] dimethylsilanes, [tris(trimethylsilyl)methyl] diphenylsilanes, and for related compounds. Analysis of chemical shift values indicates that such information can be useful in determining the structure in these highly hindered, but structurally similar compounds. In particular, the carbon and silicon atoms of the trimethylsilyl groups absorb in a narrow shift range, while other carbon and silicon atoms more characteristically reflect the substitution patterns in these compounds.

Computational studies of carbodiimide rings.

Computational studies of alicyclic carbodiimides (RN═C═NR) (rings five through twelve) at the MP2/6-31G(d,p)//MP2/6-31G(d,p) level of theory were conducted to locate the transition states between carbodiimides isomers. Transition states for rings six through twelve were found. The RNCNR dihedral angle is ∼0° for even-numbered rings, but deviates from 0° for rings seven, nine, eleven, and twelve. The even- and odd-numbered ring transition states have different symmetry point groups. Cs transition states (even rings) have an imaginary frequency mode that transforms as the asymmetric irreducible representation of the group. C2 transition states (odd rings) have a corresponding mode that transforms as the totally symmetric representation. Intrinsic reaction coordinate analyses followed by energy minimization along the antisymmetric pathways led to enantiomeric pairs. The symmetric pathways give diastereomeric isomers. The five-membered ring carbodiimide is a stable structure, possibly isolable. A twelve-membered ring transition state was found only without applying symmetry constraints (C1). Molecular mechanics and molecular dynamics studies of the seven-, eight-, and nine-membered rings gave additional structures, which were then minimized using ab initio methods. No structures beyond those found from the IRC analyses described were found. The potential for optical resolution of the seven-membered ring is discussed.

The gas-phase acidity of hindered amines and some reaction chemistry of their corresponding amide ions

Abstract The gas-phase acidities of three hindered amines have been determined by equilibrium measurements using tandem flowing afterglow-selected-ion flow tube technology. These amines, tert-butylamine (ΔH°acid = 396.6 kcal mol−1), di-sec-butylamine (ΔH°acid = 386.1 kcal mol−1), and 2,2,6,6-tetramethylpiperidine (ΔH°acid = 387.5 kcal mol−1), were chosen because of their hindered nature and differing substitution patterns. The ion/molecule chemistry of the anions corresponding to these amides was studied in detail. This demonstrated quite different reactivity patterns, which are discussed in terms of steric properties and other structural features. Thus, primary and secondary substituted amides can be differentiated by reactions with N2O and ND3, and di-sec-butylamide has a strong tendency to act as a hydride donor.