Photolysis Of 1b Research Articles

Photochemistry of 1- and 2-Methyl-5-aminotetrazoles: Structural Effects on Reaction Pathways.

The influence of the position of the methyl substituent in 1- and 2-methyl-substituted 5-aminotetrazoles on the photochemistry of these molecules is evaluated. The two compounds were isolated in an argon matrix (15 K) and the matrix was subjected to in situ narrowband UV excitation at different wavelengths, which induce selectively photochemical transformations of different species (reactants and initially formed photoproducts). The progress of the reactions was followed by infrared spectroscopy, supported by quantum chemical calculations. It is shown that the photochemistries of the two isomers, 1-methyl-(1H)-tetrazole-5-amine (1a) and 2-methyl-(2H)-tetrazole-5-amine (1b), although resulting in a common intermediate diazirine 3, which undergoes subsequent photoconversion into 1-amino-3-methylcarbodiimide (H2N-N═C═N-CH3), show marked differences: formation of the amino cyanamide 4 (H2N-N(CH3)-C≡N) is only observed from the photocleavage of the isomer 1a, whereas formation of the nitrile imine 2 (H2N-C-═N+═N-CH3) is only obtained from photolysis of 1b. The exclusive formation of nitrile imine from the isomer 1b points to the possibility that only the 2H-tetrazoles forms can give a direct access to nitrile imines, while observation of the amino cyanamide 4 represents a novel reaction pathway in the photochemistry of tetrazoles and seems to be characteristic of 1H-tetrazoles. The structural and vibrational characterization of both reactants and photoproducts has been undertaken.

Photolysis of arene chromium tricarbonyl complexes in presence of amine–boranes: Observation of σ-borane complexes in solution

Activation of the B–H σ-bond of amine–boranes on the chromium(0) center of arene chromium tricarbonyl complexes ( η 6-arene)Cr(CO) 3 (arene = fluorobenzene, 1a; benzene, 1b and mesitylene, 1c) has been studied. Photolysis of 1b in presence of ammonia–borane (H 3N·BH 3, AB) and tert-butylamine–borane ( t BuH 2N·BH 3, TBAB) resulted in H 2 evolution and precipitation of a BNH x polymer. On the other hand, photolysis in the presence of trimethylamine–borane (Me 3N·BH 3, TMAB) resulted in the formation of a σ-borane complex ( 2) along with Cr(CO) 5( η 1-HBH 2·NMe 3) ( 3). The σ-borane complexes ( η 6-arene)Cr(CO) 2( η 1-HBH 2·NMe 3) (arene = fluorobenzene, 2a; benzene, 2b and mesitylene, 2c) were characterized in solution by 1H, 11B, and 13C NMR spectroscopy. Electron withdrawing substituents on the arene ring provide the more stable σ-borane moiety in this series of complexes.

Silicon−Carbon Unsaturated Compounds. 67. Photolysis of cis- and trans-1,2-Dimethyl-1,2-diphenyl-1,2-disilacyclopentane

The photolysis of cis- and trans-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclopentane (la,b) was carried out in the presence of isobutene, acetone, and tert-butyl alcohol. Irradiation of la with a low-pressure mercury lamp inthe presence of isobutene in hexane proceeded stereospecifically to give a cis ene-type adduct (2a) and a cis [2 + 2] cycloadduct (3a) in 34% and 8% yields, respectively. Similar irradiation of la with acetone afforded a cis-ene-type adduct (4a) with high stereospecificity and 1-[hydroxymethylphenylsilyl]-3-(methylphenylsilyl)propane (5) in 28% and 15% yields. The photolysis of 1b with isobutene gave a trans [2 + 2] cycloadduct (3b) and the cis ene-type adduct 2a in 20% and 6% yields, respectively. With acetone, 1b afforded compound 5 as the major product. The photolysis of la in the presence of tert-butyl alcohol produced a mixture of cis- and trans-2,3-benzo-1-tert-butoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclohept-2-ene (6a,b) in a 4:1 ratio in 30% combined yield, in addition to a 14% yield of 1-[tert-butoxymethylphenylsilyl]-3-(methylphenylsilyl)propane (7). Similar photolysis of 1b with tert-butyl alcohol gave again a mixture of 6a and 6b in 22% yield, in a 1:4 ratio, along with 7 in 15% yield. The thermolysis of 3a and 3b proceeded stereospecifically to give the respective ene-type products 2a and 2b in quantitative yields. Computational analyses for the formation of the rearranged silenes have also been reported.

Photoinduced heterolysis of the carbon-oxygen bond in bichromophoric 1-arylmethyloxy-2-pyridones

Irradiation of the title compound having a 9-anthryl ( 1a) or a 1-pyrenyl group ( 1b) in methanol was found to give the heterolytic CO bond cleavage products: 1-hydroxy-2-pyridone and arylmethyl methyl ether, (which predominate for the reaction of 1a), along with 2-pyridone, aryl-substituted methanol and aryl aldehyde derived from the homolysis of the NO bond (that mainly occurs in the photolysis of 1b). Spectroscopic analysis of the ground-state and excited singlet-state behavior of 1 revealed that a non-emissive intramolecular exciplex (whose formation rate is much faster in 1a than in 1b) plays a key role in inducing the CO bond heterolysis.

Preparation and structure of the first ansa-molybdenocene and tungstenocene derivatives. Reaction of [O(SiMe 2C 5H 4) 2]MoH 2 with methyl methacrylate to probe the olefin attacking site

Bridged-bis(cyclopentadienyl) molybdenum and tungsten dihydrides and their derivatives have been synthesized for the first time. [(1,1,3,3-Tetramethyldisiloxane-1,3-diyl)bis(η 5-cyclopentadienyl)lmolybdenum dihydride ( 1a) and tungsten dihydride ( 1b) were prepared by sodium borohydride reduction of [O(SiMe 2C 5H 4) 2]MCl 2 ( 2a: M  Mo, 2b: M  W) which was obtained by the reaction of disodium 1,1,3,3-tetramethyl-1,3-bis(cyclopentadienyl)disiloxane with MCl 4(thf) 2 (M  Mo, W). The dichlorides 2 reacted with ZnMe 2 and NaSEt to afford [O(SiMe 2C 5H 4) 2]MMe 2 ( 3a: M  Mo, 3b: M  W) and [O(SiMe 2C 5H 4) 2]M(SEt) 2 ( 4a: M  Mo, 4b: M  W), respectively. Photolysis of 1b in benzene gave [O(SiMe 2C 5H 4) 2]WH(C 6H 5) ( 5b). An X-ray crystal analysis of 3a has proved that the bridging chain blocks one of the side positions of the complex, the siloxy unit being present at one side of the MeMoMe bisector. Consistent with side position attack by olefins, the reaction rate of 1a with methyl methacrylate was found to be nearly one half that of the parent Cp 2MoH 2 ( 6a).

Photooxidation of 1,4-Dihyropyridines

Abstract 1,4-Dihydropyridines were successfully photooxidized to corresponding pyridines under suitable conditions. The substituents of the dihydropyridines, reaction mediums, and atmospheres affect the course of the reactions. When diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (1a), diethyl 1,4-dihydropyridine-3,5-dicar-boxylate (1b), 2,6-dimethyl-3,5-diacetyl-1,4-dihydropyridine (1c), and 3,5-diacetyl-1,4-dihydropyridine (1d) were irradiated by a super high pressure mercury lamp with filter in ethanol under air or oxygen, corresponding pyridines, diethyl 2,6-dimethylpyridine-3,5-dicarboxylate (2a), diethyl pyridine-3,5-dicarboxylate (2b), 2,6-dimethyl-3,5-diacethylpyridine (2c), and 3,5-diacetylpyridine (2d) were formed in good yields. Irradiation of 1a, 1c, and 1d in acetonitrile afforded 2a, 2c, and 2d irrespective of their atomosphere, oxygen or nitrogen. On the other hand, photolysis of 1b by the same lamp and filter in ethanol or acetonitrile in an atmosphere of nitrogen resulted in the formation of photodimer (3) which on irradiation by low pressure mercury lamp in acetonitrile dissociated to 1b followed by photooxidation giving 2b. Diethyl l-acetyl-1,4-dihydropyridine-3,5-dicarbolxyate (4e) and 1,3,5-triacetyl-1,4-dihydropyridine (4f) afforded 2b and 2d in fairly good yields when the photolyses were carried out in an atmosphere of air in ethanol or acetonitrile.