Dialkynyl Carbene Derivatives: Generation and Characterization of Triplet tert-Butylpentadiynylidene (t-Bu−C≡C−C̈−C≡C−H) and Dimethylpentadiynylidene (Me−C≡C−C̈−C≡C−Me)

Abstract

Triplet carbenes t-butylpentadiynylidene (t-BuC(5)H, 1a) and dimethylpentadiynylidene (MeC(5)Me, 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 pentadiynylidene (HC(5)H) and methylpentadiynylidene (MeC(5)H) recorded previously. EPR spectra yield zero-field splitting parameters that are typical for triplet carbenes with axial symmetry (t-BuC(5)H, 1a: |D/hc| = 0.61 cm(-1), |E/hc| ∼ 0 cm(-1); MeC(5)Me, 1b: |D/hc| = 0.62 cm(-1), |E/hc| ∼ 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 progressions. 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 1a in an O(2)-doped matrix affords carbonyl oxides derived predominantly from attack at C-3. Both t-BuC(5)H (1a) and MeC(5)Me (1b) undergo photochemical rearrangement upon UV irradiation.

Pentadiynylidene and Its Methyl-Substituted Derivates: Threshold Photoelectron Spectroscopy of R1-C5-R2 Triplet Carbon Chains

“…In contrast, n = 5 carbon chains have so far been investigated predominately in low temperature matrices. Infrared, UV/vis and EPR spectra in Ar or N 2 matrix are available for 1 , 2 , and in part for 3 . − While propargylene favors a slightly bent geometry with C 2 symmetry, a linear geometry with D ∞ h symmetry was found for 1 , as confirmed by coupled cluster calculations . In a valence bond picture, pentadiynylidene can be described by two resonance structures (see Figure ), one corresponding to a 1,5-biradical and a second dominating one to a diethynylcarbene.…”

“…In the pyrolysis of 6 a small peak appears at m/z = 91. It originates from the 13 C isotope of m/z = 90 as evident from the relative peak intensities in the mass spectrum and not from a H-atom addition product. b. Photoionization of precursors 4, 5 and 6.…”

Bond length and electric current oscillation of long linear carbon chains: Density functional theory, MpB model, and quantum spin transport studies

“…28 From our studies, we suspect that the bond length behavior could be related the a π bond resonance between carbon atoms. One example of the resonance effect in linear chains is the case of tert-butylpentadiynylidene and dimethylpentadiynylidene, 29 where computational and experimental studies indicated this behavior. In agreement with other works, 28 our results suggest that the bonds present a resonance effect.…”

Electron spin resonance

“…When an O 2 -doped matrix was used, carbonyl oxides derived predominantly from attack at C 3 were formed, while both t-BuC5H and MeC5Me rearrange photochemically upon UV irradiation. 139 By photolysis of the diazidopyridines, 4-amino-2,6-diazido-3,5-dichloropyridine and 6-amino2,4-diazido-1,3,5-triazine, triplet-triplet nitrene pairs were produced, yielding ESR spectra characteristic of the quintet spin state. The high-spin state (S = 2) results from the exchange interaction between two triplet molecules with the zero-field splitting parameters |D| = 1.0280 cm À1 and |E| = 0.0038 cm À1 and the angle between two C-N nitrene bonds y = 1331.…”