ANNEAL-RING

ANNEAL-RING Mr. Patrick Franc NYU Industrial Liaison Office NYU Medical School New York, NY 10003, U.S.A. 

SCHEME 30.4 Effect of annealed ring size on the photochenucal Bergman cycUzation. 

The substituted five-ring OPVs have been processed into poly crystal line thin films by vacuum deposition onto a substrate from the vapor phase. Optical absorption and photolumincscence of the films are significantly different from dilute solution spectra, which indicates that intermolecular interactions play an important role in the solid-state spectra. The molecular orientation and crystal domain size can be increased by thermal annealing of the films. This control of the microstruc-ture is essential for the use of such films in photonic devices. 

Little evidence for thermal transfer of a 7T-ring in recoil studies has been published, and that only when no other ligand was present in the molecule. It is found 85, 37) that ferrocene is susceptible to thermal annealing in a ferrocene matrix, where the reaction clearly must be... 

The ring seal at A is made in the early stages and is partially annealed. This part of the assembly is then inserted into the prepared tube B which is held clamped, and, when seated well, is itself clamped at C (Figure 62, II). Using a hand torch and exerting care to warm... 

Use of CD30D or methyl tetrahydrofuran solvents to encourage electron capture, resulted in a complex set of reactions for methyl cobalamine. Initial addition occurred into the w corrin orbital, but on annealing a cobalt centred radical was obtained, the e.s.r. spectrum of which was characteristic of an electron in a d z.y orbital (involving the corrin ring) rather than the expected d2z orbital. However, the final product was the normal Co species formed by loss of methyl. Formally, this requires loss of CH3 , but this step seems highly unlikely. Some form of assisted loss, such as protonation, seems probable. 

In the presence of AIBN, tributyltin hydride is an excellent dehalogenating reagent for generating radicals. The bromoalkylcyclobutanone 206 undergoes reductive ring expansion to give, via the annealed alkoxy radical, the cis-fiised bicycle 207 stereospecifically as the major product [113], (Scheme 81)... 

Subsequent irradiation of S-14 with k > 570 nm in the presence of a nitrogen molecule in the same matrix cage results as in the case of T-10 in the recapture of nitrogen (which is also possible by annealing the matrix at 25 K). Parallel to this reaction, a photochemically induced rearrangement of S-14 to N-cyano-1 W-azirene (12) — perhaps via the ring-opened carbene 11 — and Af-cyanoketenimine occurs. 

Carbene lv is photolabile, and 400 nm irradiation produces a mixture of products.108 By comparison with calculated IR spectra the major product was identified as cyclopropene 3v. The formation of 3v is irreversible, and it cannot be thermally (by annealing the matrix) nor photochemically converted back to carbene lv. The lv -> 3v rearrangement is calculated (B3LYP/6-31G(d) + ZPE) to be endothermic by only 5.4 kcal/mol with an activation barrier of 18.2 kcal/mol. Due to the two Si-C bonds in the five-membered ring of 3v this cyclopropene is less strained than 3s, which is reflected by the smaller destabilization relative to carbene lv. The thermal energy available at temperatures below 40 K is much too low to overcome the calculated barrier of 12.8 kcal/mol for the rearrangement of 3v back to lv, and consequently 3v is stable under the conditions of matrix isolation. 

Increased ring strain in the C-4 ( = 2) and C-5 (n — 3) products may be a reason for lower yields (and longer irradiation times). The effect of strain on cyclizations is well-documented outside of cycloaromatization chemistry, as well. For example, annealing of a cyclopentene ring leads to a decrease in the cyclization rate and an inversion of the 5-exo/6-endo selectivity for all three patterns shown in Fig. 22. 

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