Silenes generation

While infrared characterization of several silenes has been carried out, it has not always been possible to assign the observed bands unequivocally. Table II summarizes the available infrared data. The infrared spectra of reactive silenes, generated by the pyrolysis of suitable precursors, have most often been recorded in an argon matrix at 10 K, whereas the infrared... 

All silenes generated so far on the silylcarbene route are reactive intermediates themselves, which were characterized by typical subsequent reactions35 such as isomerization and dimerization or by trapping reactions (see below). However, photolysis of (silyl)diazo compounds in inert matrices at low temperature allowed the isolation and spectroscopic (IR, UV) characterization of several silenes (Scheme 2, Table 3). Irradiation of (dia-zomethyl)silanes 7 at X > 360 nm produced both diazirine 8 and silenes 10, but at shorter wavelength (X > 305 nm) the silenes were produced cleanly from both precursors the... 

Silenes are formed by rearrangement of silylcarbenes. If polysilylated diazomethanes 298-300 are employed, a selective migration of a silyl group to the carbene centre occurs and silenes 301, 92 and 302 are formed (equations 74-76)164. The outcome of trapping reactions is independent of the mode of silene generation photochemical and pyrolytic methods give the same results. 

Disilacyclobutane can be obtained by the dimerization of a transient silene generated by the salt elimination method (Scheme 18) <1996JOM181>. Other examples of head-to-head dimerization of silenes have been published C1995CB143, 1995CB1083,1996CB15>. 

But till now only methods involving an in situ formation of deprotonated 1 have been described. In this paper we present a procedure leading to pure, isolated 1-hydroxyalkyl-polysilanes 1. In presence of base fliey are easily converted into transient silenes, which were characterized by various dimerization and addition reactions. The availability of isolated 1 in the synthesis of silenes according to the Peterson concept offers the possibility of a free choice of the solvent and the base used to initiate the silanolate elimination. With respect to the significance of the reaction medium for the silene generation and its subsequent reactions, this is of particular importance. 

It was reported that trimethylsilyldiazomethane 492 thermolytically (440°C, 10 torr) (75TL2061) or under FVP conditions (750°C) (86JA7849) produces a carbene that isomerizes to 1,1,2-trimethylsilene 493, thereby furnishing the head-to-tail dimer 494 in 40% yield. Silene generated from disilanyl a-diazoacetate 495 in the presence of 7-norbornanone affords 38% of adduct 496 (82JA6830). 

Direct irradiation of [(trimethylsilyl)ethynyl]pentamethyldisilane (94) afforded a mixture of reactive intermediates, which were detected and identified by flash-photolysis techniques and trapped as methanol adducts in continuous irradiation experiments. Amongst the intermediates identified was the 1-silaallene (95), which, although a minor photoproduct, was readily observable owing to its relatively long lifetime. The stereochemistry of the addition of carbonyl compounds to silenes generated by photolysis of meso- and rac-1,2-diethyl-1,2-dimethyldiphenyldisilane has been investigated. ... 

In an early study, a series of chiral alcohols was added to prochiral silenes generated by 254 nm photolysis of silacyclobutanes and asymmetric induction in the addition reactions was observed, compatible with a planar structure of the silenes156,157. The authors pointed out the possibility that the reaction is concerted and involves the oxygen lone pair in a 4 + 2 ([Pg.1087]

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