186-04-9Relevant academic research and scientific papers
Photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene: Electronic spin determines the distribution of products
Anderson, Mark A.,Grissom, Charles B.
, p. 5041 - 5048 (1995)
The distribution of products from the photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) is determined primarily by the electronic spin state of the cyclohexane-1,4-diyl intermediate. DBO undergoes photolysis by direct irradiation of the N=N chromophore and singlet-sensitization to produce 1,5-hexadiene and bicyclo[2.2.0]hexane with a product ratio of 51:49 in n-octane. Triplet-sensitized photolysis in n-octane produces a product ratio of 70:30 1,5-hexadiene - bicyclo[2.2.0]hexane. The 14N/15N kinetic isotope effect on deazatization is 1.025 for DBO and 1.004 for the more-strained analogue, 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH). The large kinetic isotope effect on DBO photolysis is consistent with rate-limiting C - N bond scission in excited DBO. The amount of hexadiene can be increased by heavy atom solvents that contain bromine and iodine, or by an increase in photolysis intensity, to a maximum of 70:30 hexadiene:bicyclohexane. The product distribution and 15N kinetic isotope effect is insensitive to solvent viscosity, temperature, and magnetic field (up to 7.05 T). The ratio of products can be quantitatively accounted for by fast intersystem crossing (ISC) due to spin - orbit coupling as the boat conformer of the cyclohexane-1,4-diyl is forming. A statistical distribution of 25:75 singlet-triplet cyclohexane-1,4-diyl in the boat geometry is produced by direct and singlet-sensitized photolysis. The singlet cyclohexane-1,4-diyl boat collapses to form bicyclohexane with unit efficiency, whereas the triplet boat is long-lived such that relaxation to the twist-boat occurs. The triplet cyclohexane-1,4-diyl twist-boat is unreactive toward ring closure or bond scission and can only undergo further reaction after ISC to the singlet spin state. In the twist-boat, the singlet cyclohexane-1,4-diyl undergoes ring-opening to 1,5-hexadiene at a rate that is 7/3 faster than it undergoes ring closure to [2.2.0] bicyclohexane. Triplet-sensitized photolysis also produces cyclohexane-1,4-diyl in the boat geometry, but the singlet spin state is not populated because it is 22 kcal/mol higher in energy.
Increasing the heavy atom effect of xenon by adsorption to zeolites: Photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene
Anderson, Mark A.,Grissom, Charles B.
, p. 9552 - 9556 (1996)
The distribution of products in the photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) is determined by the electronic spin state of the cyclohexane-1,4-diyl intermediate. Triplet cyclohexane-1,4-diyl yields 1,5-hexadiene (HD) while singlet cyclohexane-1,4-diyl produces bicyclo[2.2.0]hexane (BCH) as the stable product. Intersystem crossing (ISC) between the two diyls is enhanced by an external heavy atom effect. Direct photolysis (366 nm) of DBO in NaY zeolite containing adsorbed xenon yields a product ratio of 75:25 in favor of the triplet product, HD. This is a 24% increase in triplet product from direct photolysis in n-octane. The dramatic enhancement of ISC may be caused by polarization of the Xe atom in the faujasite cage, thereby allowing it to reach its full potential as a heavy atom perturbant. The 3:1 product ratio derives from complete equilibration of the three triplet electron spin states and the singlet spin state either in the short-lived diazenyl diradical or on a high-energy surface of the 1,4-cyclohexanediyl in which the singlet and triplet states are degenerate. The same 75:25 product ratio is achieved (without Xe adsorbed to the zeolite) when the Na+ cation of the zeolite is exchanged with Cs+ cation. This is not surprising since Xe and Cs+ are isoelectronic and therefore should share similar spin-orbit coupling characteristics. Also reported are the product ratios when photolysis of DBO is carried out in zeolites containing other monovalent cations (Li+, Na+, K+, Rb+).
Transition-metal-promoted chemoselective photoreactions at the cucurbituril rim
Koner, Apurba L.,Marquez, Cesar,Dickman, Michael H.,Nau, Werner M.
supporting information; experimental part, p. 545 - 548 (2011/03/16)
When included in a supramolecular barrel with transition-metal ions as lids, bicyclic azoalkanes undergo phase-selective photolysis to afford new photoproducts and photoproduct distributions. In the presence of the macrocycle cucurbit[7]uril and Ag+ ions, 2,3-diazabicyclo[2.2.1]hept-2-ene forms a ternary host-guest inclusion complex in which the cations are coordinated to the carbonyl rims of the host. Direct photolysis of this ternary complex provides cyclopentene as a new photoproduct.
Homolytic Rearrangements of Bicyclohexane and Bicycloheptane
Walton, John C.
, p. 1371 - 1376 (2007/10/02)
Free radicals abstract hydrogen from both the bridge and bridgehead sites in bicyclohexane (4).The bicyclohexan-1-yl radical was observed by e.p.r. spectroscopy.The bicyclohexan-2-yl radical rearranges by stereoelectronically forbidden β-scission to give cyclohex-3-enyl radicals.Unlike other cyclobutanes, compound (4) undergoes an SH2 reaction with bromine atoms.Free radicals abstract hydrogen only from the methylene groups of the C5 ring in bicycloheptane (15a).The bicycloheptan-2-yl radicals were observed by e.p.r. spectroscopy, as was their rearrangement, by stereoelectronically allowed β-scission, to 2-(cyclopent-2-enyl)ethyl radicals.Bromine atoms abstract hydrogen from (15a) and no SH2 reaction was detected.The radicals and their rearrangements were studied by semi-empirical MINDO/3 and MNDO methods.
Photolysis of Reluctant Azoalkanes. Effect of Structure on Photochemical Loss of Nitrogen from 2,3-Diazabicyclooct-2-ene Derivatives
Engel, Paul S.,Horsey, Douglas W.,Keys, Dalen E.,Nalepa, Christopher J.,Soltero, Luis R.
, p. 7108 - 7114 (2007/10/02)
Azoalkanes containing the bicycloskeleton often prove to be remarkable stable toward loss of nitrogen.These derivatives of 2,3-diazabicyclooct-2-ene (DBO) also exhibit fluorescence whose lifetime extends to 600 ns.This paper is an attempt to understand the effect of fused rings and bridgehead substituents on the photochemical and photophysical properties of DBO.The main factor controlling quantum yields of nitrogen is a 6-11 kcal mol-1 activation barrier that differs for the singlet and triplet states and that seems to mimic the barrier to ground-state deazatization.The product distribution for DBO derivatives is rationalized on the basis of interconverting singlet 1,4-biradicaloids.
