•Molecular complex between ozone and n-butylferrocene isolated.•Long wavelength (λ > 600 nm) photodissociation of ozone carried out, leading to O(3P) reaction with n-butylferrocene•Multiple intermediate oxidation products observed and supported computationally.•Overall reaction mechanism proposed and calculated theoretically.The photochemical reaction of ozone and n-butylferrocene has been studied using a combination of argon-matrix isolation, infrared spectroscopy, and theoretical calculations. The dark deposition produced a vivid green matrix that, when irradiated with red light, turned a brownish-red color. This green matrix as well as slightly red-shifted O3 infrared absorptions are indicative of the formation an initial charge transfer complex between ozone and n-butylferrocene. The spectral results support the photodissociation of the complexed ozone with red light (λ ≥ 600 nm) producing an oxygen atom, O(3P), and a dioxygen molecule, O2(3Σ). The O(3P) then reacts with n-butylferrocene to form products consisting of an iron atom with a coordinated n-butylcyclopentadienyl or cyclopentadienyl ring and either: (1) a pyran, (2) an aldehyde, or (3) a bidentate cyclic aldehyde with a seven-membered ring including the iron atom. The photochemical products were characterized with FT-IR spectroscopy, 18O-labeled O3 experiments, and DFT calculations using the B3LYP functional with the 6–311++G(d, 2p) basis set. A possible mechanism for the photochemical reaction is discussed.

The reactions of ozone with ferrocene (cp2Fe) and with n-butylferrocene (n-butyl cp2Fe) were studied using matrix isolation, UV–vis spectroscopy, and theoretical calculations. The codeposition of cp2Fe with O3 and of n-butyl cp2Fe with O3 into an argon matrix led to the production of 1:1 charge-transfer complexes with absorptions at 765 and 815 nm, respectively. These absorptions contribute to the green matrix color observed upon initial deposition. The charge-transfer complexes underwent photochemical reactions upon irradiation with red light (λ ≥ 600 nm). Theoretical UV–vis spectra of the charge-transfer complexes and photochemical products were calculated using TD-DFT at the B3LYP/6-311G++(d,2p) level of theory. The calculated UV–vis spectra were in good agreement with the experimental results. MO analysis of these long-wavelength transitions showed them to be n→ π* on the ozone subunit in the complex and indicated that the formation of the charge-transfer complex between ozone and cp2Fe or n-butyl cp2Fe affects how readily the π* orbital on O3 is populated when red light (λ ≥ 600 nm) is absorbed. 1:1 complexes of cp2Fe and n-butyl cp2Fe with O2 were also observed experimentally and calculated theoretically. These results support and enhance previous infrared studies of the mechanism of photooxidation of ferrocene by ozone, a reaction that has considerable significance for the formation of iron oxide thin films for a range of applications.

The reactions between ferrocene (Cp2Fe) (2a) and ozone (O3) were studied using low-temperature matrix-isolation techniques coupled with theoretical density functional theory (DFT) calculations. Co-deposition of Ar/Cp2Fe and Ar/O3 gas mixtures onto a cryogenically cooled CsI window produced a dark-green charge-transfer complex, Cp2Fe–O3, that photodecomposed upon red (λ ≥ 600 nm) and infrared (λ ≥ 1000 nm) irradiation but was stable to green or blue irradiation. Products of photodecomposition were characterized by FT-IR, oxygen-18 labeling, and DFT calculations using the B3LYP functionals and the 6-311G++(d,2p) basis set. Likely, photochemical products included four structures having the molecular formula C10H10FeO, identified by DFT calculations based on their calculated infrared spectra and 18O isotope shifts. Each of these calculated molecules had one intact and fully coordinated η5-C5H5 cyclopentadienyl (Cp) ring and (1) an η5-C5H5O cyclic ether (pyran ring) (2b), (2) an η4-C5H5O linear aldehyde (2c), (3) a bidentate cyclic aldehyde with a seven-membered ring including the iron atom (2d), or (4) an Fe–O bond and an η2-C5H5 (Cp) ring (2e). No conclusive evidence for a gas-phase thermal reaction between ferrocene and ozone was observed under the conditions of these experiments. However, strong evidence for a surface-catalyzed thermal reaction was observed in merged-jet experiments wherein the gases were premixed before deposition. Surface-catalyzed ferrocene–ozone reaction products included a thin film of Fe2O3 observed on the walls of the merged tube as well as cyclopentadiene (C5H6), cyclopentadienone (C5H4O), and further oxidation products observed in the matrix. Possible mechanisms for both the photochemical and the thermal reactions are discussed.

The thermal and photochemical reactions of (CH3)3Ga and O3 have been explored using a combination of matrix isolation, infrared spectroscopy, and theoretical calculations. Experimental data using twin jet deposition and theoretical calculations demonstrate the formation of multiple product species after deposition, annealing to 35 K, and UV irradiation of the matrices. The products were identified as (CH3)2GaOCH3, (CH3)2GaCH2OH, (CH3)(CH3O)Ga(OCH3), (CH3)2GaCHO, and (CH3)Ga(OCH3)(CH2OH). Product identifications were confirmed by annealing and irradiation behavior, 18O substitution experiments, and high level theoretical calculations. Merged jet deposition led to a number of stable late reaction products, including C2H6, CH3OH, and H2CO. A white solid film was also noted on the walls of the merged (flow reactor) region of the deposition system, likely due to the formation of Ga2O3.

The reactions of ozone with three bicyclic alkenes, α-pinene, norbornene, and norbornadiene, were studied by low-temperature (14 K), argon matrix isolation infrared spectroscopy including 18O isotope-labeling studies. Theoretical calculations of some of the proposed reaction intermediates and products were carried out using the Gaussian 09 suite of programs, applying density functional theory (DFT), the B3LYP functional, and the 6-311G++(d,2p) basis set. In the α-pinene/ozone system, the thermal reaction between α-pinene and ozone was too slow to observe under the twin-jet or merged-jet deposition conditions of these experiments. However, red light (λ ≥ 600 nm) irradiation of the argon matrixes containing α-pinene and ozone caused new infrared peaks to appear that could be readily assigned to reaction products of α-pinene with O(3P) resulting from ozone photolysis: α-pinene oxide (with an epoxide ring) and two isomeric ketones. Norbornene and norbornadiene were both found to react with ozone in the gas phase during twin-jet or merged-jet deposition of these mixtures with argon. New peaks observed in the infrared spectra were assigned to the primary ozonides, Criegee intermediates, and secondary ozonides of norbornene and norbornadiene, indicating that the bulk of these reactions proceeded via the “classic” Criegee mechanism for ozonolysis of alkenes. Calculated infrared frequencies and molecular energies support these conclusions. Ultraviolet irradiation of these mixtures resulted in complete decomposition of the early intermediates and the formation of acids, aldehydes, alcohols, carbon dioxide, and carbon monoxide. In any case, no evidence for “unusual” chemistry, prompted by the bicyclic nature of the reactants, was observed.

The matrix isolation technique, combined with infrared spectroscopy and twin jet codeposition, has been used to characterize intermediates and stable “late” products formed during the ozonolysis of (Z)-3-methyl-2-pentene (MP). While twin jet deposition led to minimal product formation, annealing to 35 K produced a number of product bands. Based on isotopic labeling and theoretical calculations, product bands have been assigned to the primary ozonide and also tentatively to the secondary ozonide of MP. Indirect evidence for formation of one or both possible Criegee intermediates in this system is presented. While neither possible Criegee intermediate for this system was observed, the evidence overall clearly supports the mechanism first proposed by Criegee for the ozonolysis of alkenes. UV irradiation led to product arising from O atom addition to MP, while merged jet codeposition led to a number of stable products for this system.Highlights► Criegee mechanism of ozonolysis of (Z)-3-methyl-2-pentene verified by spectroscopy. ► Eight fundamental vibrations of the cis-isomer of the primary ozonide of this alkene observed for the first time. ► Photochemical oxidation of this alkene by O atom addition observed. ► “Late” reaction products observed in flow reactor deposition.

The matrix isolation technique, combined with infrared spectroscopy and merged jet deposition of ozone with propene led to the observation of “later”, more stable products of this ozonolysis reaction. The observed products, specifically formaldehyde and acetaldehyde, are precisely the products predicted by the Criegee mechanism, formed by the two fragmentation pathways from the initial primary ozonide. Hence, the merged jet results strongly support the Criegee mechanism. In contrast, twin jet codeposition experiments followed by annealing led to no visible changes in the spectra. Subsequent irradiation of these twin jet matrices involving ozone with light of λ ⩾ 220 nm led to O atom production and subsequent reaction with propene. Multiple products were observed in these photochemical experiments. Extensive 18O isotopic labeling experiments, comparisons with literature spectra, and detailed theoretical calculations at the B3LYP/6-311++G(d,2p) level provided important supporting data.

Matrix isolation studies combined with infrared spectroscopy of the twin jet codeposition of ozone and cis-2-butene into argon matrices have led to the first observation of several early intermediates in this ozonolysis reaction. Specifically, evidence is presented for the formation and identification of the long sought-after Criegee intermediate, as well as confirming evidence for earlier reports of the primary and secondary ozonides. These species were observed after initial twin jet deposition, and grew upon annealing to 35 K. Extensive isotopic labeling (18O and 16,18O mixtures) experiments provided important supporting data. Detailed theoretical calculations at the B3LYP/6-311++G(d,2p) level were carried out as well to augment the experimental work. Merged jet (flow reactor) experiments followed by cryogenic trapping in solid argon led to the formation of “late”, stable oxidation products. Photochemical reactions of ozone with cis-2-butene was studied as well, as was the photochemical behavior of the primary and secondary ozonides.

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of cyclohexane, cyclohexene, and cyclopropane with ozone. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of λ > 200 nm. Irradiation of matrices containing ozone and cyclohexane led to O atom reactions with insertion into a CH bond and a CC bond to form cyclohexanol and oxacycloheptane, respectively. Irradiation of matrices containing ozone and cyclohexene led to a mixture of products formed through oxidation of the double bond, including cyclohexanone and cyclohexene oxide. Cyclopropane and ozone were codeposited into argon matrices followed by irradiation, leading to the formation of both cyclopropanal through insertion into a CH bond and aldehydes through ring-opening and oxidation. These conclusions were supported by isotopic labeling (18O), by comparison to authentic infrared spectra, and by B3LYP/6-311G++(d,2p) density functional calculations.

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of cyclohexane and cyclohexene with CrCl2O2. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of λ > 300 nm. The irradiation was shown to lead to oxygen atom transfer, forming complexes between cyclic alcohol derivatives and CrCl2O, although complexes between ring expansion products and CrCl2O could not be ruled out. This latter result could arise from C–C bond activation and oxygen atom insertion into a C–C bond. For the cyclohexene system, the cyclohexanone–CrCl2O complex was also observed. The identification of the complexes was further supported by isotopic labeling (2H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level.

B2H6 was copyrolyzed at 335°C in separate experiments with C2H2 and C2H4 in a flow reactor followed by trapping into an argon matrix at 14 K. Small but distinct and reproducible yields of C2H4 and C2H6, respectively, were observed in these experiments indicating that some hydrogenation is occurring, while no evidence for alkylboranes was obtained. Extensive experiments with C2D2 and C2D4 yielded B2H5D, C2HD and several additional species indicative of extensive hydrogen isotope exchange. Possible reaction mechanisms are discussed.