Bis amino silylenes

The first bis(amino)silylene 1 was described in 1992, but was stable only up to 77 The transient Si(NPr 2)2 was identified by trapping reactions and by electronic spectra at low temperatures. The major breakthrough in the chemistry of stable silylenes was the report... 

The chemistry of bis(amino)silylenes, particularly of 2 and 3 and to a lesser extent 4, has been studied in some detail and has relatively recently been comprehensively reviewed " hence only an outline of these researches will be featured in Sections... 

The colourless, monomeric rac-bis(amino)silylene SiN(Bu ) C(H)Me 2NBu (25) was prepared by KCg reduction in thf/NEt3 of the roc-dibromosilane precursor. At ambient temperature, unlike its methyl-free analogue 4 (for the low temperature monomeric X-ray structure of 4, see Ref. 50), it showed no tendency to oligomerise. Attempts to make a thermally stable Et or Bu analogue of 3 failed, although presumably they were transient intermediates along the pathway to the salts 10 and 11, Equation (9.3) (a preliminary... 

Also, 2,4,6-tri+-butyl-l,3,5-triphosphabenzene 147 undergoes [1+4] cycloaddition with the stable bis(amino)silylenes 83-85 to afford the structurally characterized l,3,5-triphospha-7-silanorbornadienes 148. In the case of silylene 85 this reaction was shown to be reversible (Equation 13) <1999CC2451, 2002JCD484>. The higher reactivity of benzo[ ]-... 

Treatment of bis(amino)silylene 78 with ketones gave disiloxatene 129 (Scheme 46) <19970M4861>. However, the likely pathway for these reactions involves the formation of an oxasilacyclopropane intermediate 128, as a substrate for the insertion of the second silylene molecule. 

A Thermally Stable Silylene Reactivity of the Bis(amino)silylene Si[ N(CH2/Bu) 2C6H4-1,2 ]... 

Although transient silylenes have been known since the middle of the sixties, the first stable divalent and two-coordinate silicon compound, the bis(amino)silylene Si[N(/Bu)CHCHNfflu], was reported only in 1994, including its gas phase structure by electron diffraction [1]. 

The bis(amino)silylene 1 (abbreviated as "SiN2") reacted readily at room temperature with benzophenone to give the 1,2,3-oxadisiletane 2 (Scheme 1 X-ray structure in Figure 1). These oxadisiletanes have only previously been observed by reaction of a disilene with a ketone [9, 10]. The formation of 2 is thought to proceed via an oxasilacyclopropane intermediate. The reaction of 1 with u(Me)C=0 yielded a similar disilaoxetane. 

Thermally stable cyclic bis(amino)silylenes 01JOM(617-618)209. 

Scheme 2. Some Si chemical shifts (i5 Si) of monomeric silylenes. Note the large difference between 1 and the bis(amino)silylenes 4-7.

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