Generation, Characterization, and Kinetics of Triplet Di[1,2,3,4,5,6,7,8-octahydro-1,4:5,8-di(ethano)anthryl]carbene

Abstract

The title carbene has been generated by photolysis of the corresponding diazo precursors and studied by spectroscopic means, i. e., electron paramagnetic resonance (EPR) and UV/vis spectroscopy in matrixes at low temperature and laser-flash photolysis in solution at room temperature, with the product analysis. The results are compared with triplet di(2,3,5,6-tetramethylphenyl)carbene, an open-chain counterpart, which revealed that bicycloalkyl groups are acting as a fairly good kinetic protector for the triplet carbene as opposed to the open-chain counterpart. The formation of all-hydrocarbon triplet carbenes having a half-life over a second under normal conditions was realized for the first time. Effects of para-substituents on the structure and reactivities of the carbene are also investigated and discussed in terms of polar and spin electronic effects.

Triplet diphenylcarbene protected by iodine and bromine groups

“…The decay rate ( k obs ) of 3 1a increased upon the addition of methanol. However, the plot of k obs versus methanol concentration was not linear for the concentration range of 2.47–9.22 M 44, 67. A plot of better linearity was observed when the k obs was plotted against the dimer concentration of methanol.…”

“…It has been reported that the sharp peak due to the radical species around 330 mT is found when some triplet signals in 2‐MTHF at 77 K decrease by thawing the matrix 29, 30, 44. This means that the triplet diarylcarbenes decayed by abstracting a hydrogen from 2‐MTHF to form the corresponding diarylmethyl radicals.…”

Electronically Excited States of Borylenes

“…Optical spectroscopy, which probes the manifold of electronically excited states, is another important technique for identification of reactive intermediates. Particularly transient absorption and UV/vis matrix isolation spectroscopy demonstrated their usefulness in studying reactive species like carbenes − and nitrenes. − Existing knowledge, of either experimental or computational nature, on the excited states is only available for diatomic borylenes (BH, BF, BCl, BBr, and BI). Most investigations have been performed on the excited states of parent borylene (BH), ,− including the experimental determination of the singlet–triplet energy splitting that was confirmed by sophisticated computations. ,, A number of studies concerning the electronically excited states of chloroborylene (BCl), − fluoroborylene (BF), ,− and bromoborylene (BBr) ,− are available.…”

Theoretical Designs for Fullerene Carbenes, C60–E–C60 and C70–E–C70 (E = Group 14 Elements): A Target for Experimental Studies

“…In other words, the larger the atomic number of the central carbenic atom, E, the more positive is the Δ E st for C 60 –E–C 60 . It should be noted that these M06-2X computations assume that the ground state of these fullerene carbenes C 60 –E–C 60 (E = C, Si, and Ge) should be a triplet state. − This theoretical Δ E st data also demonstrates that the difference in energy between singlet and triplet state is quite small. In fact, as seen in Table , a comparison of the calculated structures for C 60 –E–C 60 in the singlet and triplet states suggests that one geometrical parameter (i.e., the bond angle, θ) allows the Δ E st value to have an important role in the C 60 –E–C 60 species.…”