Le probleme de la conjugaison a travers un atome de silicium π-lie dans les systemes sila-2 butadieniques

Synthesis, Structure, Photoluminescence and Photoreactivity of 2,3‐Diphenyl‐4‐neopentyl‐1‐silacyclobut‐2‐enes

“…[14]) unquestionably confirms the identity of the secondary photoproducts 2-R/3-R. Although we could not observe the intermediate species directly, the close analogy of the trapped secondary products to that for (Ph-)DMSCB [15][16][17][18][19][20][21][22][23] strongly suggests the presence of the intermediate silabutadiene 5-R (Scheme 2c). Moreover, the fact that only the initial starting compound was isolated in the absence of trapping agents indicates that 5-R is metastable and can return to 1-R though thermal ring-closure.…”

“…In the second part of this paper we present a study of the photoreactivity of 1-R in solution and doped-polymer thin films. In terms of related photochemical compounds, the derivatives 1-R possess similar structural characteristics to: i) the previously reported compounds (Ph-)DMSCB which exhibit an efficient electrocyclic ring-opening reaction due to excited-state cleavage of the strained 1,4-SiÀC bond to yield a short-lived silabutadiene (SBD) intermediate; [15][16][17][18][19][20][21][22][23] and ii) stilbenoids [28,36] (including DPCs [29] ) where electrocyclic ring closure between the Ph groups forms the corresponding dihydrophenanthrene (DHP) analogue. We show that both these photoreactions are observed for 1-R in solution, by characterization of the isolated secondary products yielded www.chemeurj.org from subsequent trapping reactions.…”

“…Silacyclobutene ring-opening photoreaction: It is well established that a electrocyclic ring opening reaction occurs in the silacyclobutenes DMSCB and Ph-DMSCB (Figure 1b) when excited in their lowest-energy absorption band (below ~230 nm), [15][16][17][18][19][20][21][22][23] analogous to the case of cyclobutene. [42] The resultant photoproduct is a short-lived silabutadiene (silene) which in the absence of trapping agents undergoes thermal ring-closure to form the starting compound (e.g., with t ~1.5 ms for DMSCB in hexane [21] ).…”

“…Here we present the synthesis, crystal structures, and photophysical/photochemical behavior of a set of organosilicon compounds, 1,1-R 2 -2,3-diphenyl-4-neopentyl-1-silacyclobut-2-enes (1-R, see Figure 1 for structures). [12][13][14] The relatively small number of previous reports on 1-silacyclobut-2-enes (SCBs) [15][16][17][18][19][20][21][22][23] have been chiefly devoted to the 1,1-dimethyl and 1,1-dimethyl-2-phenyl derivatives (DMSCB, Ph-DMSCB) and the ring-opening photoreaction that occurs upon excitation of the lowest-energy (p-p*) absorption band. This band lies at relatively short wavelengths (i.e., below 230 nm), [22] and the photophysical and photochemical properties are similar to those of (alkyl-substituted) cyclobutene derivatives (such as the 3,4-dimethyl derivative, DMCB).…”

Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes

“…These compounds have proven to be tremendously useful as photochemical precursors for transient silenes, in experiments aimed at detecting the silenes directly and studying the kinetics and mechanisms of their reactions with alcohols and other "silenophiles" (9)(10)(11)(12)(13)(14)(15)(16)(17). Photochemical silene formation proceeds with useful efficiencies from silacyclobutanes that bear alkyl, vinyl, ethynyl, silyl, and phenyl substituents at silicon, and possess UV absorption maxima between 190 and 250 nm (2,4,12,13,(17)(18)(19)(20). In contrast, alkoxy substitution either directly at silicon or on the aromatic rings of phenylated derivatives renders the silacyclobutane moiety inert to photocycloreversion (13,17).…”