Formation of the Si—Ga Bond

A scheme for bicyclic dimer formation from HMCTSN under plasma conditions has been proposed in our previous paper (J.) According to this scheme, formation of new Si-N bonds with tertiary nitrogen between trisilazane rings leads to crosslinking of the polymer, and involves the production of hydrocarbons such as methane and ethane. Indeed, gas chromatographic analysis of the gaseous residue after plasma polymerization has shown that it consists mainly of three hydrocarbons methane, ethane and ethylene in the 5 33 4 ratio. 

Recently the unprecedented example of stereoselective C—Si bond activation in cu-silyl-substituted alkane nitriles by bare CQ+ cations has been reported by Hornung and coworkers72b. Very little is known of the gas-phase reactions of anionic metal complexes with silanes. In fact there seems to be only one such study which has been carried out by McDonald and coworkers73. In this work the reaction of the metal-carbonyl anions Fe(CO) (n = 2, 3) and Mn(CO) (n = 3, 4) with trimethylsilane and SiH have been examined. The reactions of Fe(CO)3 and Mn(CO)4 anions exclusively formed the corresponding adduct ions via an oxidative insertion into the Si—H bonds of the silanes. The 13- and 14-electron ions Fc(CO)2 and Mn(CO)3 were observed to form dehydrogenation products (CO) M(jj2 — CH2 = SiMe2) besides simple adduct formation with trimethylsilane. The reaction of these metal carbonyl anions with SiFLj afforded the dehydrogenation products (CO)2Fe(H)(SiII) and (CO)3Mn(II)(SiII). ... 

Our questions regarding supersilylenes are more ambitious. Of course we would like to know what kinds of reactions they undergo, and especially if they participate in processes in which concerted formation of more than one bond occurs. While charged species like R-Si and R-C are convenient to generate and study in the gas-phase, neutral molecules such as R-B and R-Al should also be accessible and would allow study under conditions that permit larger scale reactions in solution. 

Several workers have studied the photochemistry of silacyclobutanes. In the gas phase, u.v. (185 nm < X < 210 nm) excitation of 1,1-dimethylsilacyclo-butane causes elimination of ethylene and the formation of Me2Si = CH2. This silaolefin, when formed, has an internal energy which is probably in excess of the Si—C 71-bond energy, and it may be that its reactivity is different from that of Me2Si=CH2 generated thermally or in solution. In particular it is possible that its isomerization to Me2HSiCH occurs and this might be an explanation for the substantial amounts of polymer that accompany the ethylene and 1,1,3,3-tetramethyl-l,3-disilacyclobutane as products. Mass spectrometric measurements show that the products from octamethyl-l,2-disilacyclobutane are mainly 2,3-dimethylbut-2-ene and hexamethylsilacyclopropane. The primary photoprocess is probably that shown in equation (8). 

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