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[摘要]：Triplet carbenes t-butylpentadiynylidene (t-BuC5H, 1a) and dimethylpentadiynylidene (MeC5Me, 1b) have been produced photochemically from their corresponding diazo compound precursors and studied spectroscopically in cryogenic matrices (N-2 or Ar) at 10 K. The infrared, electronic absorption, and electron paramagnetic resonance spectra of these species exhibit numerous similarities to the spectra of penta-diynylidene (HC5H) and methylpentadiynylidene (MeC5H) recorded previously. EPR spectra yield zero-field splitting parameters that are typical for triplet carbenes with axial symmetry (t-BuC5H, 1a: D/hc = 0.61 cm(-1), E/hc similar to 0 cm(-1); MeC5Me, 1b: vertical bar D/hc vertical bar = 0.62 cm(-1), similar to 0 cm(-1)). Electronic spectra are characterized by weak absorptions (T-1 <- T-0) in the near-UV and visible region (350-430 nm) with extended vibronic progessions. The electronic transitions of several -C-5- carbenes are compared, and an apparent dependence of the transition wavelength on the level of alkyl substitution of the carbon chain is found. Chemical trapping of triplet la in an O-2-doped matrix affords carbonyl oxides derived predominantly from attack at C-3. Both t-BuC5H (1a) and MeC5Me (1b) undergo photochemical rearrangement upon UV irradiation. |
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