Photolysis Of 1a Research Articles

Stereochemistry of Disilanylene-Containing Cyclic Compounds. Thermal Reactions of cis- and trans-3,4-Benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene

The thermal reaction of cis-3,4-benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene (1a) with tert-butyl alcohol at 300 °C for 24 h proceeded with high stereospecificity to give erythro-1-(...

Comparisons of Photoinduced Oxidative Addition of B−H, B−B, and Si−H Bonds at Rhodium(η5-cyclopentadienyl)phosphine Centers

Ultraviolet irradiation of [Rh(η5-C5H5)(PMe3)(C2H4)] (1a), [Rh(η5-C5H5)(PPh3)(C2H4)] (1b), and [Rh(η5-C5H4CF3)(PMe3)(C2H4)] (1c) (collectively abbreviated as [Rh(Cp‘)(PR3)(C2H4)]) in the presence of HBpin (pinacolate = pin = 1,2-O2C2Me4) results in elimination of C2H4 and B−H oxidative addition, leading to the formation of boryl hydride complexes [Rh(Cp‘)(Bpin)(H)(PR3)]. Complete conversion is achieved in liquid HBpin or by photolysis in hexane at −10 °C. Similarly, photolysis of 1a−c in the presence of B2pin2 in hexane at −10 °C leads to B−B oxidative addition products, [Rh(Cp‘)(Bpin)2(PR3)]. Irradiation at room temperature leads to formation of [Rh(Cp‘)(PR3)2] in addition to the desired products. The rhodium boryl products were characterized by multinuclear NMR spectroscopy and, in the case of [Rh(η5-C5H5)(Bpin)(H)(PPh3)], by X-ray crystallography. The structure reveals a Rh−B distance of 2.0196(15) Å. The H···B separation of 2.09(2) Å together with the bond angles at the metal suggest some residual H···B interaction. Photolysis of 1a−c in the presence of tertiary and secondary silanes (HSiEt3, HSiiPr3, HSi(OMe)3, HSiMe2Et, HSiMeEt2, and H2SiEt2) results in rhodium silyl hydride complexes [Rh(Cp‘)(SiR‘2R‘ ‘)(H)(PR3)]. The structure of [Rh(η5-C5H5)(SiiPr3)(H)(PMe3)] was determined by single-crystal X-ray diffraction, yielding a Rh−Si bond length of 2.3617(3) Å and a Rh−H bond length of 1.508(17) Å. The H···Si distance of 2.278(17) Å and the very unequal H−Rh−P and H−Rh−Si angles suggest some residual H···Si interaction. Competition reactions were performed with 1b dissolved in hexane in the presence of HBpin and B2pin2 simultaneously. 31P NMR measurements, made after brief irradiation, showed a slight preference for B−B oxidative addition over B−H oxidative addition. Similar experiments with three-way competition among HBpin, HSiMe2Et, and HC6F5, analyzed by 1H NMR spectroscopy, showed negligible selectivity among H−B, H−C, and H−Si oxidative addition. Molecular structures were also determined by single-crystal X-ray diffraction for 1b, 1c, [Rh(η5-C5H5)(PPh3)2], and [Rh(η5-C5H5)Cl2(PPh3)].

Synthesis, Structure, and Photochemistry of Disilyl Derivatives of the Fp (Fp = (η5-C5H5)Fe(CO)2) System: FpMeSi(CH2)4SiMeFp and FpPhMeSiSiMePhFp

The synthesis of (1a) is reported (Fp = [(η5-C5H5)Fe(CO)2), along with small amounts of (2). Photolysis of 1a with a medium-pressure Hg lamp for 8 h resulted in the formation of two different types of intermediate silylene-bridged complexes, [(η5-C5H5)Fe(CO)]2(μ-CO)(μ-SiMeSi(CH2)4) (4) and (5), each existing as a mixture of three equilibrating geometrical isomers, respectively; 4 slowly photoisomerized to the isomers 5 prior to expulsion of the second CO group. Prolonged irradiation of 5 gave a mixture of the cis and trans isomers of the bis(silylene)-bridged complex [(η5-C5H5)Fe(CO)]2(μ-SiMe2)(μ-Si(CH2)4) (6). Similar photolysis of FpMePhSiSiPhMeFp (3) resulted in the sequential formation of the mono(silylene)diiron complex [(η5-C5H5)Fe(CO)]2(μ-CO)(μ-SiMeSiMePh2) (7) and the bis(silylene)diiron complex [(η5-C5H5)Fe(CO)]2(μ-SiPh2)(μ-SiMe2) (8). The molecular structures of 1a, 5a, and 6a have been determined by X-ray diffraction analysis.

Silicon–carbon unsaturated compounds. 68. Reactions of silenes produced thermally and photochemically from acylpolysilanes with diketones

The reactions of the silenes produced thermally from (Me 3Si) 3SiCOR ( 1a– 1d; R= t-Bu, Ad, Ph, and Mes) with benzil in a sealed glass tube at 140 °C gave the respective five-membered cyclic compounds, 2,5-dioxa-1-silacyclopent-3-enes ( 2a– 2d) in high yields. The silenes from 1a– d also reacted with 4,4′-dimethylbenzil to give the 2,5-dioxa-1-silacyclopent-3-ene derivatives. The photolysis of 1a and 1b in the presence of benzil in a benzene solution gave the respective products, 3,6-dioxa-1-silacyclohex-4-enes ( 3a and 3b) arising from [2+4] cycloaddition in high yields. The thermolysis of 3a and 3b in a sealed tube at 140 °C afforded 2a and 2b, respectively, in quantitative yields.

Synthesis of Self-Stabilized and Donor-Free Silyl(silylene)tungsten Complexes

Photolysis of Cp‘W(CO)3Me (1a, Cp‘ = η-C5Me5; 1b, Cp‘ = η-C5Me4Et) in the presence of excess HSiMe2SiMe3 afforded a self-stabilized silyl(silylene)tungsten complex with a dimeric structure, [Cp‘W(CO)2(SiMe2)(SiMe3)]2 (2a, Cp‘ = η-C5Me5; 2b, Cp‘ = η-C5Me4Et), respectively. In contrast, photolysis of 1a in the presence of HSiMe2SiMeMes2 (Mes = 2,4,6-Me3C6H2) resulted in the formation of the first donor-free silyl(silylene) complex with only alkyl and aryl substituents on the silicon atoms, Cp‘W(CO)2(SiMes2)(SiMe3) (3).

Photoinduced diradical formation and decay in uncomplexed and metal-bound benzotriazine systems: mechanistic implications to chemically and biologically relevant photochemistry

The photochemical reactivities of 3-hydroxy-1,2,3-benzotriazine-4(3H)-one (1a) and tris[3-hydroxy-1,2,3-benzotriazine-4(3H)-one]iron(III) (1b) have been studied in solution and low temperature (5–77 K) glasses. Photoexcitation (λ345 nm) of 1a and 1b ultimately results in population of a ligand-centered excited state that releases N2. Electron paramagnetic resonance reveals the presence of S = 1 and S = 0 diradical intermediates upon photolysis of 1a and 1b, respectively, at 4 K. These species convert to an S = 1/2, nitrogen-centered monoradical species (aN = 23 G) upon warming to 77 K ia H-atom abstraction from the matrix. In solution, the first intermediates observed upon photolyses (λ = 355 nm) of 1a and 1b are oxime ketenes (5: λ = 385, 440 nm; 9: λ = 390, 430, 740 nm) that are formed from collapse of the diradical to generate a 4-membered β-lactam ring. The decay kinetics for the oxime ketene 5 decay can be fitted to a biexponential expression representing a parallel reaction mechanism with an element of reversibility. Thus, the data proposes the existence of an equilibrium between the oxime ketene and the spectroscopically silent β-lactam intermediate, as well as a first or pseudo first-order solvent-dependent pathway for the oxime ketene. The kinetics for formation and decay of the ketene are strongly influenced by the presence of the Fe(III) center, which leads to an increase in the lifetime of the diradical in solution, and a retarded rate of formation for the oxime ketene 9. The solution lifetimes suggest that the diradical intermediates only persist sufficiently long to react with bound solution substrates, whereas the ketene intermediates have suitable kinetic viabilities to react bimolecularly in solution.

Solvent-Dependent Photochemical Rearrangements of Ethers of Styrylheterocycles

Direct photolysis of p-RO(R = alkyl or aryl)-2-styrylfurans (1a−f), 2-styrylthiophenes (2a−f), and 2-styryl-N-methylpyrrole (3) in hydrated dichloromethane gives 5-(3-oxo-1-butenyl)benzo[b]furan (4), -thiophene (5), and N-methylpyrrole (6), respectively, in good isolated yields. However, photolysis of 1a,b,e and 2a,b,e in dehydrated benzene gives 5-(3-RO-1,3-butadienyl)benzo[b]furans (7a,b,e) and -thiophenes (8a,b,e) in good yields. Photolysis of 7 and 8 in hydrated dichloromethane produces 4 and 5, respectively.

Photolysis ofcis- andtrans-[FeIII(cyclam)(N3)2]+Complexes: Spectroscopic Characterization of a Nitridoiron(V) Species

Reaction of cis-[FeIII(cyclam)Cl2]Cl in acidic H2O/CH3OH or CH3CN/H2O mixtures with NaN3 at 50 °C produced upon addition of NaClO4 or NaPF6 the complex trans-[FeIII(cyclam)(N3)2]ClO4 (1a) or the hexafluorophosphate salt 1b, whereas at −18 °C the same reaction produced cis-[FeIII(cyclam)(N3)2](ClO4) (2) (cyclam = 1,4,8,11-tetraazacyclotetradecane). The crystal structures of 1b and 2 were determined by single-crystal X-ray crystallography. Complexes 1a, b, contain a low-spin (S = 1/2) and 2, a high-spin ferric ion (S = 5/2) as was established by variable-temperature magnetic susceptibility measurements and Mossbauer and X-band EPR spectroscopy. The low-spin trans-[(cyclam)FeII(N3)2] and high-spin cis-[(cyclam)FeII(N3)2] species were generated electrochemically in CH3CN solution and were characterized by Mossbauer spectroscopy. Photolysis of 1a in CH3CN at −35 °C and 20 °C with a Hg immersion lamp generated within 15 min a yellow solution. EPR and Mossbauer spectra show that a single high-valent species with...

The Photochemistry of M3(CO)12 (M = Ru, Os) with Pyrazole and Its Substituted Derivatives

The photochemistry of M3(CO)12 [M = Ru (1a), Os (1b)] with pyrazole, 3,5-dimethylpyrazole, and 3,5-diphenylpyrazole is documented. With 1a, photolysis with pyrazole leads to the substitution product HRu3(CO)10(C3H3N2) (2a). In the case of 1b, the initial product is the ortho-metallated species HOs3(CO)10(C3H3N2) (3b), heating of which yields HOs3(CO)10(C3H3N2) (2b). Photolysis of 1a and 1b with 3,5-dimethylpyrazole yields HRu3(CO)10(C3HMe2N2) (4a) and HOs3(CO)10(C3HMe2N2) (4b), respectively. The molecular structure of 4b has been determined by X-ray crystallography. There is no reaction on photolysis of 1a and 1b with 3,5-diphenylpyrazole.

The Photochemistry of M3(CO)12 (M = Ru, Os) with Pyrazole and Its Substituted Derivatives

The photochemistry of M3(CO)12 [M = Ru (1a), Os (1b)] with pyrazole, 3,5-dimethylpyrazole, and 3,5-diphenylpyrazole is documented. With 1a, photolysis with pyrazole leads to the substitution product HRu3(CO)10(C3H3N2) (2a). In the case of 1b, the initial product is the ortho-metallated species HOs3(CO)10(C3H3N2) (3b), heating of which yields HOs3(CO)10(C3H3N2) (2b). Photolysis of 1a and 1b with 3,5-dimethylpyrazole yields HRu3(CO)10(C3HMe2N2) (4a) and HOs3(CO)10(C3HMe2N2) (4b), respectively. The molecular structure of 4b has been determined by X-ray crystallography. There is no reaction on photolysis of 1a and 1b with 3,5-diphenylpyrazole.

ChemInform Abstract: δ3‐1,3,4‐Telluradiazolines, a Novel Tellurium Containing Heterocycle: One‐Pot Synthesis, Structure, and Reactivity.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Δ3-1,3,4-telluradiazolines, a novel tellurium containing heterocycle: One-pot synthesis, structure, and reactivity

Abstract The one-pot reaction of sterically hindered hydrazones with tellurium dichloride or tellurium tetrahalide in the presence of triethylamine in benzene afforded Δ3-1,3,4-telluradiazolines 1, a novel heterocycle, via 1,3-dipolar cycloaddition of telluroketones and diazo compounds, both generated in situ. The molecular structure of 1a was established by X-ray crystallographic analysis. The photolysis of 1a led to instant and quantitative formation of the corresponding azine 8a, whereas the thermolysis of 1a in the solid state afforded the corresponding retrocyclization products.

Photochemistry of [Ru3(CO)12] with nitrogen heterocycles

The photochemistry of [M 3 (CO) 12 ] (M = Ru 1a or Os 1b) with nitrogen heterocycles has been studied. In all cases photolysis leads to photosubstitution products, the heterocycles inhibiting the photofragmentation pathway. With pyridine (py) 1a formed the orthometallated complex [Ru 3 H(CO) 10 (C 5 H 4 N)] 2a. With osmium, the simple substitution product [Os 3 (CO) 11 (py)] 3b can be isolated. With 2-methylpyridine (mpy) [Ru 3 H(CO) 10 (2-MeC 5 H 3 N)] 5a and [Os 3 (CO) 11 (mpy)] 6b were formed from 1a and 1b respectively. With 2,6-dimethylpyridine no net photoreaction was observed. Photolysis of 1a and 1b with 2,2′-bipyridine led to the formation of [M 3 (CO) 10 (bipy)] (M = Ru 7a and Os 7b). The molecular structure of 7b has been obtained by single-crystal X-ray diffraction studies. Photolysis of 1a and 1b with pyridazine (pydz) led to the substituted products [M 3 (CO) 10 (pydz)] (M = Ru 8a or Os 8b).

Photochemical reactions of anthracene–naphthalene bichromophoric systems linked by a three-carbon chain

Photochemical reactions of bichromophoric compounds having 9-anthryl and 1-naphthyl groups linked by a three-carbon chain have been investigated in solution and in the solid state. Direct photolysis of 1a–c,e–g in degassed benzene gave both cyclomers 2a–c,e–g and head-to-tail anthracene dimers 3a–c,e–g through intra- and inter-molecular [4 + 4] cycloaddition, respectively, while 1-acetoxy derivative 1d gave only cyclomer 2d. The reactivity for the cyclomerisation of 1a–g was lower than that of the bisanthracene system. The conjugated carbonyl group in 1e and 1f significantly retarded the reactions. On biacetyl sensitisation neither cyclomerisation nor dimerisation occurred, but alkene 1e underwent cis–trans isomerisation. In the solid state, (E)-1e gave dimer 3e in 22% yield, while the other compounds were photostable or gave the corresponding dimer in a lower yield. X-Ray structure analysis showed that in the crystal of (E)-1e adjacent anthracene rings related by an inversion centre were stacked with 3.45 A separation, which was favourable for head-to-tail dimerisation.

Phototransformations of Bridgehead-Disubstituted Dibenzobarrelenes. Interesting Rearrangements of Dibenzosemibullvalene Intermediates Derived from 9-(Hydroxyalkyl)-10-methoxy-Substituted Dibenzobarrelenes1

The photochemistry of 11,12-dibenzoyl-9,10-dihydro-9-(hydroxymethyl)-10-methoxy-9,10-ethenoanthracene and 11,12-dibenzoyl-9,19-dihydro-9-(1-hydroxyethyl)-10-methoxy-9,10-ethenoanthracene has been studied through steady-state photolysis, product analysis, and laser flash photolysis. Irradiation of 7a in benzene, methanol, or acetone gave 69-72% yields of a dibenzopentalene ketone 11a, arising through a dibenzosemibullvalene precursor. Irradiation of 7b, which exists in equilibrium with its cyclic form 7b{prime}, gave a mixture of the dibenzopentalene ketone 11b (41%) and the dibenzopentalenopyran derivative, 16b{prime} (26%). The photochemistry of 11,12-dibenzoyl-9,10-dihydro-9,10-dimethoxy-9,10-ethenoanthracene (17) has been reinvestigated. Irradiation of 17 in benzene and methanol gives a 90% yield of an isomeric pentacyclic product 24, formed through the rearrangement of a dibenzosemibullvalene precursor. Irradiation of 17 in aqueous methanol gives a mixture of the dibenzopentalene ketone 22 (40%) and a pentacyclic methanol adduct 21 (34%). The structures of 7b{prime}, 11a,b,16b{prime},21, and 24 were confirmed through X-ray crystallographic analysis. The 308 nm laser flash photolysis of 1a,b in benzene results in the formation of their triplets ({phi}{sup T} = 0.55-0.76). These triplets possess short lifetimes (0.45-0.75 {mu}s) and are quenched by oxygen, 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO), 4-hydroxy-2,2,6,6- tetramethylpiperidinyl-1-oxy (HTEMPO), ferrocene, and {beta}-carotene at rates in the range (0.26-4.7) x 10{sup 9} M{sup -1} s{sup -1}. 21 refs., 1 fig., 1 tab.

Generation, reactions, direct observation, and kinetics of decafluorodiphenylcarbene

Bis(pentafluorophenyl)diazomethane (1a) was prepared, and reactivities of perfluorodiphenylcarbene (2a) generated by photolysis of 1a were investigated not only in terms of product analysis but also by using matrix isolation spectroscopy as well as laser flash photolysis techniques. Product ditributions observed in the reactions of 2a in benzene, cyclohexane, and trans-1,2-dichloroethylene suggested that 2a reacted with those substrates with moderate reactivities toward carbene mostly in its singlet state presumably owing to the increased electrophilicity induced by fluorine substituents while the reaction with the alkane C-H bonds in concerted fashion was retarded partly due to steric effect in the singlet state which thus decayed to the triplet states that underwent predominantly H atom abstraction forming tetraarylethane

Chemistry, kinetics, and spectroscopy of highly hindered diarylcarbenes. The case of decachlorodiphenylcarbene

Bis(pentachlorophenyl)diazomethane (1a) was prepared, and reactivities of perchlorodiphcnylcarbene (2a) generated by photolysis of 1a were investigated not only in terms of product analysis but also by using flash photolysis techniques. Although the major reaction found for 2a was dimerization forming perchlorotetraphenylethylene and was essentially similar to that observed for 2,2',4,4',6,6'-hexachlorodiphenylcarbene (2b), product distribution clearly indicated that the carbenic center in 2a is more rigidly protected than that in 2b by the four ortho chloro substituents which are buttressed by the four meta chloro groups

Organische Synthesen mit Übergangsmetall‐Komplexen, 59[1] Cyclobutanimine aus Carbenchrom‐ oder ‐wolfram‐Komplexen, Isocyaniden und Alkenen durch [2 + 2]‐Cycloadditionen intermediärer Ketenimin‐Komplexe; Liganden‐Abspaltung mit Pyridin

Organic Syntheses via Transition Metal Complexes, 59[1]. – Cyclobutanimines from Carbenechromium or ‐tungsten Complexes, Isocyanides, and Alkenes by [2 + 2]‐Cycloaddition Reactions of Ketenimine Complexes; Ligand Disengagement with Pyridine10‐Iminotricyclo[5.3.0.02,9]deca‐3,5‐diene complexes syn/anti‐4 are obtained in yields higher than 90% by the addition of isocyanides RNC 2 [R = c‐C6H11 (a), CH3 (b)] to (cycloheptatrien‐1‐ylmethyl)carbene complexes LnM=C(OEt)CH2(C7H7) 1 [LnM = Cr(CO)5 (a), W(CO)5 (b)]. The reactions involve an intermediate formation of ketenimine complexes LnM[RN=C=C(OEt)CH2C7H7] 3 by the insertion of 2 into the M=C bonds of 1. Complexes 3 isomerize to give the cyclo‐butanimines 4 by an intramolecular [2s + 2a]‐cycloaddition reaction of the ketenimine to the alkene unit. The structure of anti‐4c has been determined by a crystal structure analysis. Complexes 4 react with pyridine by the fragmentation of the four‐membered ring to yield a tetrahydroazulen‐1‐imine 6 which was hydrolyzed to the corresponding ketone 7;7 is also obtained along an independent route by the photolysis of 1a in the presence of carbon monoxide. The first isolated product of the latter reaction is the tricyclo[5.3.0.02,9]deca‐3,5‐dienone 9, which presumably is formed via an intermediate ketene complex N and the tricyclic ketone O; 9 on warming with pyridine rearranges to 7.

PHOTOCHEMISTRY OF QUINOLYLMETHYLISOTHIORONIUM SALTS. GUANINE SELECTIVE DNA PHOTOCLEAVAGE REAGENTS

Quinolylmethylisothioronium salts (1a and 4a) cleave DNA upon irradiation. The cleavage is more than 10-fold enhanced by piperidine treatment and subsequently shows a high preference for guanines. Photolysis of 1a, 2a and 4a in water at lambda greater than 300 nm resulted in photoheterolysis. Irradiation of 1a in 2-propanol gave only products from photohomolysis, irradiation of 1a in methanol and 2a and 4a in 2-propanol resulted in products from both photoheterolysis and photohomolysis. Quantum yields for the disappearance of 1a in water and 2-propanol were determined. The presence or absence of oxygen had no effect in water, whereas oxidation products were observed upon irradiation in methanol and 2-propanol in the presence of oxygen. The guanine specific DNA photoreaction is proposed to take place by alkylation at N7 via the quinolylmethyl carbocation and thus to represent a photoalkylation.

ChemInform Abstract: PHOTOCHEMICAL REACTIONS OF 4‐FLAVANOLS IN THE PRESENCE OF KETONE SENSITIZERS

AbstractBestrahlung einer O2‐freien Benzollösung des Flavanols (I) in Gegenwart von (II) liefert die Verbindungen (III)‐(VI).