Robert A. Benkeser

Trichlorosilane-imine complexes. A new method for the reduction of imines to amines

Abstract It has been found that trichlorosilane adds regio-specifically to the carbon—nitrogen double bond of imines under mild conditions to yield hydrolytically unstable N -trichlorosilyl intermediates. The latter can be hydrolyzed in situ by alcoholic base to give the corresponding amines in moderate to good yields. Variously substituted aldo and keto imines, both alkyl and aryl, were tested to demonstrate the scope of the reaction. The facility of trichlorosilane addition appears to depend on the nature of the groups directly attached to the carbon—nitrogen double bond. Hydride trapping experiments suggest an intramolecular rather than intermolecular hydride transfer during the course of the reaction.

Silane addition reactions - their synthetic utility and mechanism

The addition of silanes ( compounds containing the _ SiH group) to unsaturated organic compounds ( olefins and acetylenes) is a reaction of tremendous irnportance in the field of organosilicon chernistry. The reaction can be effected therrnallyl, by peroxides or u.v. light2, or by a variety of catalytic3 agents. It is rny purpose to review our research efforts in this area ofChernistry. Some ofthe material I will present has already been published, but a considerable portion of the work remains tobe published. For purposes of clarity my talk will be divided into three parts: ( 1) Stereochemistry of silane additions, (2) Synthetic utility of silane additions as derived frorn a knowledge of their stereochemistry, and (3) Mechanisms of silane additions catalyzed by tertiary amines and chloroplatinic acid.

The preparation and properties of cyclic silicon olefins and diene systems

Abstract A synthesis of 1-1-dichloro-1-sila-2-cyclohexene has been achieved. This olefin has been phenylated by means of phenyllithium nad 1,1-diphenyl-1-sila-2-cyclohexene thus prepared. Bromination of 1,1-dichloro-1-sila-2-cyclohexene with N-bromosuccinimide produced several products, one of which was identified as 1,1-dichloro-4-bromo-1-sila-2-cyclohexene. Pyrolysis of the latter produced principally 1,1-dichloro-1-sila-2,4-cyclohexadiene. This cyclic diene reacted with phenyllithium to produce 1,1-diphenyl-1-sila-2,4-cyclohexadiene, a compound which reacted further with maleic anhydride to form a Diels-Alder adduct.

The reduction of amides and silyl esters with trichlorosilane-t-amines

Abstract It is demonstrated that the trichlorosilane-t-amine combination is capable of reducing aromatic tertiary amides. As is customary in such reductions, the carbonyl moiety of the amide grouping is replaced by the elements of H⋯SiCl 2 . The intermediates in these reductions have been identified and characterized. A one-pot, two step synthesis has been developed for reducing aromatic tertiary amides to the corresponding benzylamines. Unexpectedly, aromatic esters proved resistants to reduction by tichlorosilane-t-amine, despite the fact that aromatic acids are readily reduced. On the other hand, silicon esters reduce with remarkable ease. The reason for the dramatic differences in rate of reduction of these carbonyl derivatives is not understood.

Chloroplatinic acid catalyzed additions of silanes to isoprene

Abstract The chloroplatinic acid catalyzed hydrosilylation of isoprene with trichlorodichloromethyl-, and trimethylsilane has been reinvestigated with the purpose of establishing the mode of addition to the substrate. This was accomplished by identifying the structures of the 1 1 adducts, their methylated derivatives and the saturated analogs of the latter. Trichlorosilane added 1,4 to the less hindered side of isoprene; dichloromethylsilane added both 1,2 and 1,4 to the less hindered side and trimethylsilane added 1,2 and 1,4 to both sides of isoprene. These results are contrary to those previously reported in the literature.

A safe and convenient new procedure for reducing aromatic compounds to birch-type products

Abstract Aromatic compounds can be reduced by a calcium-amine- t -butyl alcohol system to products which are identical to those obtained by a Birch reduction of the same substrates.

The composition of Speier's catalyst

Abstract It is proposed that the very important and useful “Speier catalyst” contains the complex H[(C3H6)PtCl3] in a solution of isopropyl alcohol. It is this platinum complex which is the active catalyst ingredient in hydrosilylation reactions. When solvent was removed from an “aged” solution of chloroplatinic acid in isopropyl alcohol, the Zeise type dimer, (C3H6)2Pt2Cl4, was deposited as an orange solid. This dimer underwent solvolysis and dissociated into a monomeric species when it dissolved in isopropyl alcohol. Spectroscopic methods involving 195Pt NMR, 1H NMR (360 MHz), far infrared, IR and ESCA were employed in reaching these conclusions.

The electrochemical reduction of organosilicon compounds

Abstract The electrochemical reduction of phenyltrimethylsilane was studied in both a divided and an undivided cell. In the undivided cell, phenyltrimethylsilane was reduced cleanly to (1,4-dihydrophenyl)trimethylsilane, but, in the divided cell, considerable cleavage of the carbon—silicon bond occured. A similar cleavage was observed for (phenylethynyl)trimethylsilane even in the undivided cell. The presence of isopropanol influenced the nature of the products in the latter case.

Selective redistribution reactions of organosilanes in the presence of chloroplatinic acid

Abstract Tetrasubstituted silanes of the general formula R 2 SiR′ 2 undergo redistribution reactions quite selectively in the presence of SiHCl 3 and chloroplatinic acid. It is the smallest and seemingly the least hindered of the R groups on the tetrasubstituted silane which exchange most readily with a chloro group on trichlorosilane.

The addition rates of dichloro- and trichlorosilane to 2-pentene and 1-octene

Abstract When mixtures of dichloro- and trichlorosilane were added to 2-pentene and 1-octene in the presence of a solution of chloroplatinic acid, dichlorosilane added much more rapidly than trichlorosilane. But when each silane was added separately under identical conditions, trichlorosilane added much more rapidly than dichlorosilane to the same olefins.