Decarbonylation Products Research Articles

Liquid phase hydrogenation of dementholized peppermint oil on Pt/Al 2O 3 catalysts : Part II. A study to determine deactivation causes

In a previous work it was observed that Pt/Al 2O 3 catalysts, prepared by wet impregnation, are deactivated during liquid phase hydrogenation of dementholized peppermint oil fractions. The aim of this work is to determine the main causes for this deactivation. Fourier transform infrared (FTIR), with and without chemisorbed carbon monoxide, temperature programmed desorption (TPD), temperature programmed hydrogenation (TPH) and gas phase cyclohexane dehydrogenation were used to characterize fresh and used Pt/Al 2O 3 catalysts. It was found that metal platinum active phase is mainly deactivated by strong adsorption of surface carboxylate-like species and/or unsaturated carbon compounds. These strongly adsorbed species are generated from the interaction of catalyst surface with decarbonylation products from menthone and other carbonyl compounds present in the dementholized peppermint oil fraction. In addition, it was found that Pt/Al 2O 3 catalyst can be reactivated in hydrogen flow at temperatures between 400–450 °C. Treatments in nitrogen flow led only to a partial regeneration of the catalysts. This is because hydrogen converted surface carboxylates and unsaturated carbon compounds into methane facilitating their removal.

Liquid phase hydrogenation of dementholized peppermint oil on Pt/Al2O3 catalystsPart II. A study to determine deactivation causes

In a previous work it was observed that Pt/Al2O3 catalysts, prepared by wet impregnation, are deactivated during liquid phase hydrogenation of dementholized peppermint oil fractions. The aim of this work is to determine the main causes for this deactivation. Fourier transform infrared (FTIR), with and without chemisorbed carbon monoxide, temperature programmed desorption (TPD), temperature programmed hydrogenation (TPH) and gas phase cyclohexane dehydrogenation were used to characterize fresh and used Pt/Al2O3 catalysts. It was found that metal platinum active phase is mainly deactivated by strong adsorption of surface carboxylate-like species and/or unsaturated carbon compounds. These strongly adsorbed species are generated from the interaction of catalyst surface with decarbonylation products from menthone and other carbonyl compounds present in the dementholized peppermint oil fraction. In addition, it was found that Pt/Al2O3 catalyst can be reactivated in hydrogen flow at temperatures between 400–450 °C. Treatments in nitrogen flow led only to a partial regeneration of the catalysts. This is because hydrogen converted surface carboxylates and unsaturated carbon compounds into methane facilitating their removal.

Hydration of Propargylic Alcohols by Ruthenium Catalysts, with Dominant Anti‐Markovnikov Regioselectivity, Formation of α,β‐Unsaturated Products and Catalytic Decarbonylation to 1‐Alkenes

AbstractRuthenium catalysts — water‐soluble ruthenium sulfophthalocyanine and heterogeneous ruthenium hydroxyapatite complexes — proved to be effective for the hydration of propargylic alcohols in entirely aqueous media. 1‐Phenyl‐2‐propyn‐1‐ol underwent an unprecedented catalytic hydration‐decarbonylation‐dehydration reaction, giving rise to styrene and carbon monoxide; 2‐propyn‐1‐ol and 3‐butyn‐2‐ol gave predominantly the products of anti‐Markovnikov addition, together with products of hydration‐dehydration (α,β‐rearrangement) and, to a minor extent, the decarbonylation products, ethene or propene, respectively. Hydrations were also conducted in D2O, giving indications of the mechanism of the reactions and apparently ruling out the allenylidene route for the α,β‐rearrangement. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Photochemical reaction mechanism of cyclobutanone: CASSCF study

AbstractThe photochemical reaction channels of cyclobutanone have been studied at the CASSCF level with a 6‐31G* basis set. Starting from the n‐π* excited‐state (S1) cyclobutanone, the three reactions can take place: decarbonylation (produce CO and cyclopropane or propylene), cycloelimination (produce ketene and ethylene), and ring expansion (produce oxacarbene). Our computation indicates that decarbonylation products CO and triplet trimethylene are formed on the triplet n‐π* excited state (T1) in a stepwise way via a biradical intermediate after intersystem crossing (ISC) to T1 from S1. And, then, the triplet trimethylene undergoes a second ISC to the ground state (S0) to produce the singlet trimethylene from which cyclopropane can be produced rapidly only overcoming a 1 to 2‐kcal/mol barrier while propylene can be formed as a secondary product. The cycloelimination products ketene and ethylene are formed on the S0 in a concerted mechanism after internal conversion (IC) to S0 from S1 via a biradical conical intersection. The reaction channels corresponding to ring expansion on the S0, T1, and S1 states have also been discussed, and the likeliest reaction path is that oxacarbene is formed on the ground state following S1/S0 internal conversion. The surface topology of cyclobutanone on the S1 surface is characterized by a transition state separating the minimum from the S1/S0 conical intersection, which is consistent with the previous computations and can explain the wavelength dependence of the fluorescence emission yield. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Ab Initio Studies of Benzocyclopropenone, Benzocyclopropenone-Containing [2.2]paracyclophane, Its Benzyne Derivative, and the Bridged Benzobarrelene Formed by Intramolecular [4 + 2]Cycloaddition

Ab initio calculations were carried out on cyclopropenone, 1, benzocyclopropenone, 2, the benzocyclopropenone-containing [2.2]paracyclophane derivative tetracyclo[8.3.2.(4,7)O(11,13)]heptadeca-1(13),4,6,10,14,16-hexaen-12-one, 3, its decarbonylation product tricyclo[8.2.2.2(4,7)]hexadeca-1(12), 4,6,10,13-pentaen-15-yne, 5, a benzyne intermediate, and the bridged benzobarrelene derivative, pentacyclo[5.5.2.2.(1,4)O(4,14)O(10,13)]hexadeca-2,7,9,13,15-pentaene, 6. These calculations suggest that benzocyclopropenone-containing [2.2]paracyclophane, 3, and highly strained bridged benzobarrelene, 6, could exist as stable species. Both aryl rings of the benzocyclopropenone derivative 3 are predicted to be distorted from planarity. This distortion relieves some angle strain present in planar benzocyclopropenone due to the presence of the annulated three-membered ring. Calculations on benzobarrelene, 8, and [2.2]paracyclophane, 4, were performed for comparison to gain a better understanding of the strain borne in bridged benzobarrelene 6. The activation barrier for the intramolecular [4 + 2] cycloaddition of 5 to give 6 was estimated at 18.8 kcal/mol while that for the corresponding [2 + 2] cycloaddition, giving the less stable 9, was 54.5 kcal/mol. The [2 + 2] cycloaddition's transition state was twisted in a manner reminiscent of the conservation of orbital symmetry prediction for an unstrained system.

Regiospecificity in reactions of alkynes and phosphines with the phosphido-bridged iron–cobalt complex [(OC) 4Fe(μ-PPh 2)Co(CO) 3

The iron–cobalt phosphido-bridged complex [(OC) 4Fe(μ-PPh 2)Co(CO) 3] ( 1) can be prepared conveniently and in good yield from the reaction of [Co 2(μ-PPh 2) 2(CO) 6] with [Fe(CO) 5]. A study of the reactivity of 1 towards symmetrical and unsymmetrical alkynes, R 1CCR 2 (R 1=R 2=CO 2Me, Ph; R 1=H, R 2=Ph), has been undertaken. In all cases, five-membered ferracycle-containing products of the type [(OC) 3Fe{μ-PPh 2C(O)CR 1CR 2}Co(CO) 3] (R 1=R 2=CO 2Me ( 2a), Ph ( 2c); R 1=H, R 2=Ph ( 2b)), are initially obtained in which a molecule of CO and a molecule of R 1CCR 2 have been inserted regiospecifically into a CoP bond in 1. Decarbonylation of 2a occurs during its preparation or in low yield on its thermolysis to give the four-membered ferracyclic species [(OC) 3Fe{μ-PPh 2C(CO 2Me)C(CO 2Me)}Co(CO) 3] ( 3a). Similar thermolysis of 2b results not only in the related decarbonylation product [(OC) 3Fe(μ-PPh 2CHCPh)Co(CO) 3] ( 3b), but additionally in three other products all in low yield, namely the regioisomer of 3b, [(OC) 3Fe(μ-PPh 2CPhCH)Co(CO) 3] ( 4b), the aldehyde-substituted complex [(OC) 3Fe{μ-PPh 2C(CHO)CPh}Co(CO) 3] ( 5b) and the five-membered ferracycle-containing species [(OC) 3Fe{μ-PPh 2CHCPhC(O)}Co(CO) 3] ( 6b). Treatment of 2a and 2b with PPhMe 2 and P(OMe) 3 results in substitution of an iron-bound carbonyl group to give, respectively, [(PhMe 2P)(OC) 2Fe{μ-PPh 2C(O)C(CO 2Me)C(CO 2Me)}(μ-CO)Co(CO) 2] ( 7a) and [{(MeO) 3P}(OC) 2Fe{μ-PPh 2C(O)CHCPh}(μ-CO)Co(CO) 2] ( 7b) in high yield. In contrast, substitution of a cobalt-bound carbonyl is achieved on reaction of 3a with PPhMe 2 or PPh 2H to give [(OC) 3Fe{μ-PPh 2C(CO 2Me)C(CO 2Me)}Co(CO) 2(L)] (L=PPhMe 2 ( 8a), PPh 2H ( 9a)). Thermolysis of the secondary phosphine-substituted complex 9a results in phosphorushydrogen bond cleavage to give [(OC) 3Fe{μ-PPh 2C(CO 2Me)CH(CO 2Me)}(μ-PPh 2)Co(CO) 2] ( 10a). Single-crystal X-ray diffraction studies have been performed on complexes 7b, 8a and 10a.

Two new bimetallic phosphido carbonyl complexes of nickel(0): [Ni2(CO)2(PPh3)2(μ-CO)(μ-PPh2)]− and [Ni2(CO)4(μ-PPh2)2]2−

Toluene solutions of Ni(CO)2(PPh3)2 react with excess potassium metal to give the [Ni2(CO)4(μ-PPh2)2]2− ion (2) which contains two tetrahedral Ni centers fused along a common edge. Each Ni achieves an 18 electron configuration without the formation of a Ni–Ni bond (dNi–Ni = 3.397(1) A) in contrast to the two-electron oxidation product, Ni2(CO)4(μ-PPh2)2 (1) (dNi–Ni = 2.510(2) A). The anion 2 shows a reversible oxidation at −1.5 V and a quasi-reversible oxidation at −1.1 V vs. FeCp2/FeCp2+. The negative ion electrospray mass spectrum of 2 shows the one-electron oxidation product of 2, [Ni2(CO)4(μ-PPh2)2]−, along with three decarbonylation products [Ni2(CO)3(μ-PPh2)2]−, [Ni2(CO)2(μ-PPh2)2]−, and [Ni2(CO)(μ-PPh2)2]− where [Ni2(CO)3(μ-PPh2)2]− is the base peak. Ethylenediamine solutions of Sn94− react with Ni(CO)2(PPh3)2 in the presence of 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) to reproducibly give [Ni2(CO)2(PPh3)2(μ-CO)(μ-PPh2)]− (3), as one of three products. The anion 3 also has an edge-shared bitetrahedral geometry but, unlike 2, possesses a Ni–Ni bond (dNi–Ni = 2.4930(9) A).

Microreactor-controlled selectivity in organic photochemical reactions

Abstract Molecular-sieve zeolites, Nafion membranes, low-density polyethylene films, and mixed surfactant vesicles have been used as microreactors to carry out organic photochemical reactions. The photo-cycloadditions of diaryl compounds with long flexible chains included in NaY zeolite or low-density polyethylene films yield intramolecular photocyclomers to the exclusion of intermolecular products. The photosensitized oxidation of alkenes included in pentasil zeolites or Nafion membranes or vesicles can be directed selectively toward either the singlet oxygen-mediated or the superoxide radical anion-mediated products by controlling the status and location of the substrate and sensitizer molecules in the reaction media. The photo-Fries rearrangement of phenyl phenylacetates included within NaY and pentasil zeolites or Nafion membranes gives either ortho-hydroxyphenones or decarbonylation products depending on the size/shape of the microreactors and the substrate molecules. All these results demonstrate the utility of microreactors to control the product selectivity in organic photochemical reactions.

Dissociation chemistry of the hydrogen-bridged radical cation [CH 2O ⋯ H ⋯ OC–OCH 3] ·+: proton transport catalysis and charge transfer

Tandem mass spectrometry based experiments on the decarbonylation products of ionized methyl-β-hydroxypyruvate (MHP) and dimethyloxalate (DMO) show that the hydrogen-bridged radical cation (HBRC) CH 2O ⋯ H ⋯ OC–OCH 3 ·+ is a stable species in the gas phase. Its low energy dissociation products are protonated methylformate, HOC(H)OCH 3 +, and the formyl radical, HCO ·. The HBRC isomers HOCH 2C(O)OCH 3 ·+ (ionized methylglycolate) and (CH 3O) 2CO ·+ (ionized dimethylcarbonate) show the same dissociation characteristics. Deuterium labeling experiments dictate that loss of HCO · from the title HBRC cannot be formulated as a simple H shift from the formaldehyde moiety to the C atom of the OC ·–OCH 3 group. Ab initio molecular orbital (MO) calculations support the proposal that this dissociation proceeds via sequential transfers of a proton, electron, and another proton within ion–dipole complexes. The first step in this rearrangement process is a 1,2-proton shift catalyzed by a formaldehyde dipole. This yields an ion/dipole complex, CH 2O ⋯ H–C(O)OCH 3 ·+, that is in the correct configuration for electron transfer to occur at the energetic threshold dictated by experiment. The resulting intermediate triggers the transfer of yet another proton from the formaldehyde unit, thereby generating another stable H-bridged radical cation viz. HCO ⋯ H ⋯ OC(H)OCH 3 ·+. This final intermediate dissociates with little or no activation energy into HOC(H)OCH 3 + and HCO ·. It is further predicted by the calculations that ionized methylglycolate isomerizes into the title HBRC by a fairly high barrier that makes the communication between ionized methylglycolate and dimethylcarbonate via the title ion quite unlikely; instead an alternative route for this communication is proposed.

Identifying ylide ions and methyl migrations in the gas phase: the decarbonylation reactions of simple ionized N-heterocycles

The decarbonylation reactions of ionized 2-acetylpyridine, 2-acetylpyrazine, and 2-acetylthiazole have been investigated using the multiple collision technique of neutralization–reionization/collision-induced dissociation mass spectrometry and related techniques. The resultant heterocyclic C 6H 7N ·+, C 5H 6N 2 ·+, and C 4H 5NS ·+ ions were identified as 2-methylene-1,2-dihydropyridine, 6 ·+, 2-methylene-1,2-dihydropyrazine, 9 ·+, and 2-methylene-2,3-dihydrothiazole, 12 ·+, respectively. This result refutes proposals in the older literature that the decarbonylation would involve a methyl transfer yielding the 2-methyl species 2-methylpyridine ( 2 ·+), 2-methylpyrazine ( 8 ·+), and 2-methylthiazole ( 11 ·+). Literature proposals for a methyl transfer in the dissociation of ionized dimethyl-2,3-pyridinedicarboxylate and methyl-4-pyridinecarboxylate were also examined, but could not be substantiated either. However, the proposed gas phase synthesis of the N-methylpyridinium ylide, 1 ·+, from ionized methyl-2-pyridinethiocarboxylate did provide evidence for a genuine methyl migration. To reinforce these conclusions, the dissociation characteristics of isomers structurally related to 6 ·+ ( 3 ·+– 5 ·+ and 7 ·+), to 9 ·+ ( 10 ·+) and to 12 ·+ ( 13 ·+– 15 ·+) were also considered. Exploratory quantum chemical calculations (at the B3LYP/6-31G∗ level of theory) indicate that 6 ·+ and 12 ·+ are among the most stable isomers in the C 6H 7N ·+ and C 4H 5NS ·+ systems, lying 24 and 19 kcal/mol lower in energy than 2 ·+ and 11 ·+, respectively. Their neutral counterparts, however, are considerably less stable: 6 is calculated to be 27 kcal/mol higher in energy than 2. Nevertheless, from neutralization–reionization experiments it follows that the neutral counterparts of the ionized decarbonylation products 6, 9, and 12 are stable molecules on the microsecond time scale. Significant 1,3-hydrogen shift barriers hinder the interconversion of both the ions and the neutrals into their 2-methyl substituted counterparts, thus accounting for their stability in the dilute gas phase.

Squaric acid difluoride

Hitherto unknown squaric acid difluoride (3,4-difluoro-3-cyclobutene-1,2-dione) ( 1a) has been synthesized in 71% yield by gas phase fluorination of squaric acid dichloride ( 1c) with KF at 250°C. ( 1a) has been characterized by multinuclear NMR, mass, IR and Raman spectra. The IR spectrum is in excellent agreement with its ab initio prediction (MP2, 6-311 + G(2d, p)). The vacuum thermolysis of ( 1a) at 700°C does not yield the expected decarbonylation product FCCF ( 2a) although the precursor of the latter, F 2CCCO, and three C 3F 4 isomers (propyne, allene, cyclopropene) which are also found as decomposition products of ( 2a) have been identified.

Behavior of Biradicals Generated from a Norrish Type-I Reaction of 2,2-Diphenylcycloalkanones. Chain-Length Dependence and Magnetic Field Effects

Abstract The reaction course of acyl-diphenylmethyl biradicals (α-oxo-ω,ω-diphenyl-α,ω-alkanediyl biradicals), O=C↑–(CH2)n−2–C↑Ph2 (3BR-n), generated from the Norrish type-I reaction of 2,2-diphenylcycloalkanones (CK-n) with various ring sizes in methanol, is switched from intramolecular disproportionation (n = 6, 7), giving a diphenylalkenal, to acyl-phenyl recombination (n ≥ 9), affording a cyclophane derivative. The behavior of 3BR-9 derived from CK-9 was studied in detail; the photolysis of CK-9 afforded an open-chain and a cyclic decarbonylation product together with an unsaturated aldehyde and a 4-methylene-2,5-cyclohexadienyl ketone (a pre-cyclophane). The photolysis of this ketone gave the same products that arose from the photolysis of CK-9, presenting the possibility that the decarbonylation products and a part of the aldehyde are formed as secondary products during irradiation. The magnetic field dependence of the lifetimes of 3BR-n (n = 12 and 13) generated from CK-12 and 13, respectively, was measured in methanol by means of a pulsed-laser excitation technique. The rate constants for intersystem crossing showed a maximum at a relatively low field strength, which decreased with increasing the field strength to level off to an asymptotic value at > 1.5 kG. The results show that the role of hyperfine coupling in intersystem crossing is less important in these systems, presumably because of the presence of a carbonyl oxygen and the absence of a hydrogen atom at the radical center.

Isolation, structure and iridium-mediated decarbonylation of a sodium fluorenone dianion complex

Reaction of fluorenone with 2 equiv. of Na in THF at room temp. gave the polymeric Na–fluorenone dianion complex 1 in 79% isolated yield, which upon reaction with 0.5 equiv. of [(C5Me5)IrCl(µ-Cl)]2 afforded the decarbonylation product 2; both 1 and 2 have been structurally characterized.

Photodecarbonylation of chiral cyclobutanones

Triplet photosensitized irradiation of 2(S),3(R)-bis[(benzoyloxy)methyl]cyclobutanone gave optically pure (−)E-1(S),2(S)-bis(benzoyloxymethyl)cyclopropane as a major product in the nonpolar fraction along with its stereoisomer and cycloelimination products. The absolute stereochemistry of the chiral cyclopropane was established by independent synthesis and X-ray crystal structure determination of a synthetic precursor. The distribution of decarbonylation and cycloelimination products was inversely dependent on the concentration of the substrate. Irradiation of the same ketone in tetrahydrofuran or benzene gave mostly cycloelimination products. Addition of Michler's ketone increased the ratio of photodecarbonylation, suggesting a triplet state pathway for this process. This was corroborated by the addition of dicyanoethylene, which showed significant quenching of photodecarbonylation. Irradiation of 2(S)-[(benzoyloxy)methyl]cyclobutane in acetone gave the corresponding cyclopropane as the principal product. Keywords: photodecarbonylation, chiral cyclopropanes, cyclobutanones, triplet sensitization.

Photochemistry of phenyl phenylacetates adsorbed on pentasil and faujasite zeolites

C. Tung and Y. Ying, J. Chem. Soc., Perkin Trans. 2, 1997, 1319 DOI: 10.1039/A608300E

Synthesis of bicyclo[4.1.0]hept-2-enes (trinorcarenes) by photochemical reaction of bicyclo[2.2.2]oct-5-en-2-ones

Photochemical reaction of bicyclo[2.2.2[oct-5-en-2-ones has been investigated as a prelude to focused application to the synthesis of sesquiterpenes such as sesquicarene and sirenin. Diels–Alder reaction of cyclohexa-2,4-dienes, having different substituents (methylthiomethyl and methoxy) at the C-6 position, with a dienophile proceeds regio- and stereo-selectively to give bicyclo[2.2.2]oct-5-en-2-ones; their photolysis in benzene upon high-pressure Hg lamp irradiation affords decarbonylation products, bicyclo[4.1.0]hept-2-enes (trinorcarenes), stereoselectively. Replacement of the methylthiomethyl group with a 2-ethoxycarbonylvinyl group improves the sequential reaction.

A study of the vacuum pyrolysis of 4-diazoisothiochroman-3-one with Hel ultraviolet photoelectron spectroscopy

A newly developed ultraviolet photoelectron spectrometer apparatus that utilizes a tunable 50 W CW CO2 laser as a directed heat source is used to study the vacuum pyrolysis of 4-diazoisothiochroman-3-one (1a). Analysis of the pyrolysate with ultraviolet photoelectron spectroscopy shows that 1a undergoes a facile pyrolysis at a laser power level of less than 26 W, yielding two new compounds: thiaketene 3a, the product of a Wolff rearrangement, and benzocyclobutenthione (6a), which can be derived from thiacarbene 4a, the decarbonylation product of 3a. Activation enthalpies/energies calculated at the AM1 and ab initio levels of theory indicate that, unlike the case of 4-diazoisochroman-3-one (1b), the Wolff rearrangement of the incipient carbene may be concerted with loss of nitrogen from 1a. The activation enthalpy/energy calculated for the decarbonylation of 3a is significantly higher (AM1, 20.5 kcal/mol; RHF/6-31G(d), 11.7 kcal/mol; MP2(full)//RHF/6-31G(d), 14.3 kcal/mol) than the activation enthalpy/energy for the decarbonylation of 3b. This result is in keeping with the fact that we detect 3a, but 3b is not found in detectable amounts in the pyrolysate of 1b. Key words: vacuum pyrolysis, 4-diazoisothiochroman-3-one, HeI ultraviolet photoelectron spectroscopy, AM1 and ab initio calculations.

Synthesis and reactivity of $$(\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_9 $$ : An unusually reactive triosmium cluster

The synthesis of\((\mu - H)(\mu - \eta ^2 - H_2 )_4 )Os_3 (CO)_{10} \) (4) from piperidine and Os3(CO)10(CH3CN)2 and its solid state structure are reported. The room temperature reactions of the decarbonylation product of4,\((\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_9 \) (3), with P(C6H5)3, CNCH3, HCl and H2 are reported. Overall, the products obtained closely resemble those obtained from the analogous,\((\mu - H)(\mu _3 - \eta ^2 - H_2 )_3 )Os_3 (CO)_9 \) (1). The isomerizations of the phosphine addition products\((\mu - H)(\mu - \eta ^2 - H_2 )_n )Os_3 (CO)_9 P(C_6 H_5 )_3 \) (n = 3,6a;n = 4,5a) have been studied by1H-NMR techniques and the initial rearrangement was shown to be an intramolecular process. Slower conversion to the complex\((\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_8 P(C_6 H_5 )_3 \) (8) was observed and the solid state structure of this product is reported and compared with a related compound containing an ethyl,n-propylμ3-imidoyl ligand. Compound4 crystallizes in the triclinic space group Pl (#2) withZ= 2, and unit cell parametersa = 9.294(3) A,b = 15.758(5) A,c = 7.406(2) A,a = 81.10(2)°,β=76.47(2)°,y =74.88(2)°, andV =1013(l) A3. Least-squares refinement of 2677 reflections gave a final discrepancy factor ofR = 0.054 (R w = 0.066). Compound8 crystallizes in the space group C2/c with unit cell parametersa = 24.818(3) A,b = 16.389(3) A,c = 18.111(3) A,β= 120.94(2)°,V = 6318(4) A3, andZ = 8. Least squares refinement of 3439 reflections gave a final discrepancy factor ofR = 0.039 (R w =0.047).

Norrish Type I Reaction of Diphenyltetrahydrobenzocycloheptenones. Conformational Effects on Biradical Lifetime

Abstract Isomeric 6,6-diphenyl-6,7,8,9-tetrahydro-5H-benzocyclohepten-7-one and 7,7-diphenyl-6,7,8,9-tetrahydro-5H-benzocyclohepten-6-one (2) were photolyzed in methanol to give rise to unsaturated aldehydes as well as diphenyltetrahydronaphthalene, a decarbonylation product (for 2). Lifetimes of the intermediate triplet biradicals were dependent on their structures, indicating that cyclic conformations play an important role in the intersystem crossing of biradicals.

Synthesis of tetranuclear heterometallic cluster complexes via condensation of triosmium alkyne complexes OS 3(CO) 10(C 2R 2), R = Tol and Me, and mononuclear tungsten acetylide complexes LW(CO) 3)CCR′, L  Cp and Cp★, R′= Ph and tBu

Synthesis of tetranuclear heterometallic cluster complexes via condensation of triosmium alkyne complexes OS 3(CO) 10(C 2R 2), R = Tol and Me, and mononuclear tungsten acetylide complexes LW(CO) 3)CCR′, L  Cp and Cp★, R′= Ph and tBu