Silylcarbenes isolable

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... 

The X-ray structure of this complex was reported by Bottomley and coworkers [88]. Remarkably, the electronic structure of such a complex was predicted before its preparation [72], Reduction of trichloromethyltrimethyl-silane by iron(II) tetraarylporphyrins in the presence of a reducing agent also leads to the carbide complex [89]. This surprising result can be explained by the involvement of an unstable a-silylcarbene ferroporphyrin complex. A het-erometallic /i2-carbido complex was isolated from the reaction of a dichloro carbene iron porphyrin and pentacarbonylrhenate (Eq. 13) [90]. The X-ray structure of this trinuclear complex, [(TPP)Fe = C = Re(CO)4Re(CO)5], shows a 1,3-dimetalla-allene system. 

The matrix-isolation technique is the method of choice for the direct spectroscopic observation of carbenes . However, efforts to generate and to observe silylcarbenes in solid matrices at cryogenic temperatures met with limited success. When (trimethylsi-lyl)diazomethane, (dimethylsilyl)diazomethane or bis(trimethylsilyl)diazomethane were irradiated in an argon matrix at <10 K, no IR spectra of the corresponding carbenes 3a-c could be obtained " . However, weak ESR signals were observed which were typical for a linear carbene with a triplet ground state . These results indicate that at least small amounts of carbenes 3a-c were present in the matrix. 

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