Disiladioxetane

Disilenes have much lower oxidation potentials than olefins , and consequently they are much more reactive toward 02. Typically, disilenes 93 react in solution with triplet oxygen to give 1,2-disiladioxetanes 94 as the major product, accompanied at room temperature by a smaller amount of disilaoxirane 95 (equation 93) °. ... 

The mechanism of the oxidation process depicted in Scheme 10.19 has been investigated in detail for 1,2-dimesityl-1,2-di-tert-butyldisilene by using iso-topically labelled The intermediate 1,2-disiladioxetane 10.45 was iso-... 

The general profile of the dioxygen oxidation of tetraaryldisilenes is shown in Eq. (63).7 Both in the solid state and in solution, the initial oxidation product of a tetraaryldisilene is the corresponding 1,2-disiladioxetane 145, whose intramolecular isomerization gives the thermodynamically more stable 1,3-disiladioxetane 146. All the steps of the oxidation occur intramolecularly and with the retention of stereochemistry around the Si-Si bond. While a small amount of disilaoxirane 147 is produced in the oxidation in low-temperature solution, 147 is converted to 146 smoothly in the presence of excess oxygen. 

The reaction of stable disilenes with oxygen in solution is much faster. It eventually yields the same 1,3-cyclodisiloxane, but it clearly is not the initial product. Two intermediates have been isolated, a 1,2-disiladioxetane and a disiloxirane. At least one more is probably present. In spite of this progress, the mechanism of the oxidation reaction has not yet been elucidated918,92. 

At — 78°C, some of the disiloxirane 35 is still formed, but the major product is a thermally unstable isomer of the 1,3-disiloxane, apparently either a 1,2-disiladioxetane, 36, or a disilene perepoxide, 37. At 0°C, this isomer rearranges to the 1,3-cyclodisiloxane 34. The 1,2-disiladioxetane structure 36 was considered more likely, and equation 31 appears probable for the reaction. Perhaps the perepoxide 37 is the primary product, undergoing two competing secondary reactions reduction to 35 with a second molecule of the disilene and rearrangement to 3691a. 

Compounds 27 (1,3,2,4-disiladioxetanes) are well known from the work of West et al 1 Due to drastic reaction conditions, it is understandable that 28 (S = 293.7) partially isomerizes into 28 (8 = 281.9). However, such an isomerization process was previously unknown for phosphaalkenes. 

C. Disiladioxetanes Oxidation of Disilenes with Molecular Oxygen. 819... 

Diethoxy-1,3 -disiladioxetane, 1758b f 1,2-Diethoxy ethane, 2541 f Diethoxymethane, 2010 f 3,3-Diethoxypropene, 2854 f Diethyl acetal, see 1,1-Diethoxyethane, 2540 Diethyl acetylenedicarboxylate, 2982 Diethylaluminium bromide, 1664 Diethylaluminium chloride, 1665 Diethylaluminium hydride, 1713 Diethylaluminium 2,2,2-trifluoroethoxide, 2460 f Diethylamine, 1720... 

At lower temperature in solution, the aerial oxidation of disilenes initially furnishes the 3,4-disiladioxetanes 119 together with small amounts of the disilaoxiranes 120, both of which react further in the solid state and in solution to give the cyclodisiloxanes 121 (Scheme 4). 

Oxidation of the disilene 13 follows a somewhat different course although a 3, 4-disiladioxetane is formed in a first step, the subsequent products are the cyclodisiloxane... 

The Si=Si jr-bond is cleaved in practically all reactions of disilenes while the cr-bond remains intact. Even the action of the very reactive oxygen on the Si=Si bond initially results in the formation of the 3,4-disiladioxetanes 119 which, however, rapidly rearrange to give the cyclodisiloxanes 121. The reactions of the disilenes 9, 10 and 14 [R = Mes, 2, 6-Me2C6H3, 4-f-Bu-2,6-Me2CgH2 (Dmt)] with white phosphorus follow a different course and proceed with cleavage of both Si=Si bonds to furnish the bicyclo[1.1.0]butane derivatives 127-129 (equation 30)126 127. 

On the other hand, treatment of 6 with weto-chloroperbenzoic acid (otCPBA) afforded the product 15 consisting of two disiladioxetane rings with retention of the Si-Si single bondJ ... 

Since the isolation of the first molecular compound with an Si-Si double bond in 1981 [1] the chemistry of the disilenes has experienced an almost explosive development, as is reflected in numerous review articles [2]. Addition or cycloaddition reactions to this double bond provide an entry to a series of three- and four-membered ring compounds that are hardly accessible by other routes. Of particular interest among these systems are the disilaoxiranes and disiladioxetanes, both of which open up new questions about the bonding situation in small rings made up of main group elements. 

Scheme 2. The reaction of disilene with atmospheric O2 yields 3,4-disiladioxetane, which rearranges to 2,4-disiladioxetane (2) [4].

Scheme 4. Reaction of the disilene 4 with atmospheric oxygen or with m-chloroperbenzoic acid (m-CPBA) yields the 2,4-disiladioxetane 7 or the disilaoxirane 8, respectively.

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