6975-92-4Relevant academic research and scientific papers
Photochemistry of 1,1-Diazenes. Direct and Sensitized Photolyses of N-(2,2,5,5-Tetramethylpyrrolidyl)nitrene, dl-N-(2,5-Diethyl-2,5-dimethylpyrrolidyl)nitrene, and N-(2,2,6,6-Tetramethylpiperidyl)nitrene
Schultz, Peter G.,Dervan, Peter B.
, p. 6660 - 6668 (2007/10/02)
The photochemistry of the 1,1-diazenes N-(2,2,5,5-tetramethylpyrrolidyl)nitrene (1), dl-N-(2,5-diethyl-2,5-dimethylpyrrolidyl)nitrene (2), and N-(2,2,6,6-tetramethylpiperidyl)nitrene (3) is reported.The fluorescence spectrum of 1,1-diazene 1 has a O-O band at 607 nm, which is the maximum.The spacing between the peaks at 607 and 672 nm corresponds to the N=N stretch of S0 consistent with the 1638 cm-1 stretch obtained from the infrared spectrum of 1.The fluorescence quantum yields are ΦF = 2 x 10-3 (MTHF, -78 deg C), 7 x 10-3 (MTHF, -196 deg C), and 1 x 10-3 (EPA, -196 deg C).The fluorescence lifetime of 1 is τF = 2.3 x 10-8 s (CFCl3, -196 deg C).Direct irradiation of 1 (466-610 nm, -78 deg C) affords four hydrocarbon products, 54percent 4, 44percent 5, 2percent 6 + 7 and tetrazene 8.Triplet-sensitized photodecomposition afforded 74percent 4, 24percent 5, 2percent 6 + 7 and tetrazene 8.An approximate quantum yield for decomposition on direct irradiation is ΦD = 1.1 x 10-2.From S1, kN2 is > 3.4 x 105 s-1, and reaction of S0 with S1, kDIM, is > 4.2 x 107 L mol-1 s-1 (at -78 deg C).The spectrum of 1,1-diazene 2 reveals a structured absorption with λmax 507 nm and a O-O band at 568 nm ( ε = 20).The vibrational spacing is 1270 cm-1.The fluorescence spectrum of 1,1-diazene 2 has a O-O band at 620 nm, which is the maximum.The spacing between the maxima at 620 and 690 nm corresponds to the N=N stretch of S0 consistent with the 1630 cm-1 stretch obtained for the infrared spectrum of 2.The fluorescence quantum yield ΦF = 9 x 10-3 (MTHF, -196 deg C).The direct and sensitized irradiation of 2 in the visible affords hydrocarbon products 14-19 and tetrazene 20 in different ratios.The retention of stereochemistry in the cyclobutane products in the direct and sensitized photodecomposition was 98 and 68percent, respectively, similar to the spin correlation effect seen in corresponding 1,2-diazene isomer.This indicates that for 2 (and by extension 1) kisc N2, consistent with a large S1-T1 gap in 1,1-diazenes.For 1,1-diazene 3 the fluorescence spectrum has a single maximum at 684 nm.The fluorescence quantum yield ΦF = 4 x 10-4 (MTHF, -196 deg C).The estimated fluorescence lifetime is τ = 4 x 10-9 s.Direct irradiation of 3 in the visible at -78 deg C afforded three hydrocarbon products, 29percent 21, 68percent 23 and tetrazene 25.
Direct Studies of 1,1-Diazenes. Syntheses, Infrared and Electronic Spectra, and Kinetics of the Thermal Decomposition of N-(2,2,6,6-Tetramethylpiperidyl)nitrene and N-(2,2,5,5-Tetramethylpyrrolidyl)nitrene
Hinsberg, William D.,Schultz, Peter G.,Dervan, Peter B.
, p. 766 - 773 (2007/10/02)
The syntheses, direct spectroscopic observation, and kinetics of thermal decomposition of the persistent 1,1-diazenes, N-(2,2,6,6-tetramethylpiperidyl)nitrene (4) and N-(2,2,5,5-tetramethylpyrrolidyl)nitrene (5) are reported.The electronic absorption spectrum of 4 at -78 deg C reveals a structured absorption for the n,?* transition: λmax = 543 nm, λ0,0 = 620 nm, and εmax = 18 +/- 3 in Et2O; λmax = 541 nm and λ0,0 = 610 in CH2Cl2; λmax = 526 nm and λ0,0 = 592 nm in i-PrOH.The electronic absorption spectrum of 1,1-diazene 5 at -78 deg C reveals a structured absorption band for the n,?* transition: λmax = 497 nm and λ0,0 = 572 nm and εmax = 20 +/- 3 in CH2Cl2; λmax = 487 nm and λ0,0 = 552 nm in i-PrOH.The infrared spectrum of 4 shows a strong absorption at 1595 cm-1 (R214N=14N stretch) and provides evidence that 1,1-diazene 4 has considerable N=N double-bond character in the ground state.The infrared spectrum of 5 shows a strong absorption at 1638 cm-1 (R214N=14N stretch).The unimolecular rate of thermal decomposition of 4 is sensitive to solvent, the rate increasing with decreasing solvent polarity (krel = 1.0, 1.7, 4.8 in THF, Et2O, and hexane, respectively).The activation parameters for the unimolecular fragmentation of 1,1-diazene 4 are as follows: log A = 11.6 +/- 0.5 and Ea = 16.9 +/- 0.7 kcal mol-1 in hexane; log A = 13.7 +/- 0.3 and Ea = 20.0 +/- 0.4 kcal mol-1 in Et2O; log A = 13.6 +/- 0.3 and Ea = 20.1 +/- 0.4 kcal mol-1 in THF.The activation parameters for the bimolecular dimerization of 4 are log A = 3.8 +/- 0.7 and Ea = 6.4 +/- 0.9 kcal mol-1 in CDCl3.The unimolecular rate of thermal decomposition of 5 is sensitive to solvent, the rate increasing with decreasing solvent polarity, krel = 1.0, 2.4, and 5.1 for THF, Et2O, and hexane, respectively.The activation parameters for the unimolecular fragmentation of 1,1-diazene 5 are as follows: log A = 10.9 +/- 0.3 and Ea = 16.8 +/- 0.5 kcal mol -1 in hexane; log A = 12.4 +/- 0.4 and Ea = 19.0 +/- 0.6 kcal mol-1 in Et2O; log A = 12.1 +/- 0.3 and Ea = 19.1 +/- 0.4 kcal mol-1 in THF.At -41.1 deg C the bimolecular rate constant for the dimerization of 5 is 8.5 * 10-5 L/(mol s), 90 times slower than that found for 4.The change from a six-membered to five-membered ring 1,1-diazene causes a shift to higher energy for the n,?* transition and a shift to increased wavenumber (cm-1) for the N=N stretching frequency, not unlike that of the isoelectronic ketones, tetramethylcyclohexanone and tetramethylcyclopentanone.Similar Ea values for the unimolecular thermal fragmentation of 4 and 5 may indicate the strain energy difference between 4 and 5 is also small.An approximate value of 30.5 kcal mol-1 for the heat of formation of the 1,1-diazene 5 is estimated, indicating the 1,1-diazene 5 has a higher heat of formation than...
