David R. Tyler

Photochemical disproportionation of metalmetal bonded carbonyl dimers

Mecanismes de reactions radicalaires dans la majorite des reactions de dismutation relatives a Mn 2 (CO) 10 , Re 2 (CO) 10 , Co 2 (CO) 8 , Cp 2 Mo 2 (CO) 6 , Cp 2 Fe 2 (CO) 4 , Cp 2 Ni 2 (CO) 2

Photochemical studies of M(CO)6 (M = Cr, Mo, W) at low temperature in solution. Infrared spectra of M(CO)5 (solvent) (solvent = methylcyclohexane, methylene chloride) and W(CO)5L (L = aromatic hydrocarbon)

Abstract The infrared spectra of M(CO) 5 (MCH) (MCH = methylcyclohexane; M = Cr, Mo, W), formed by 366 nm irradiation of M(CO) 6 at −78°C in rigorously purified methylcyclohexane, are reported. The previously reported spectrum of “W(CO) 5 ” at low temperature in methylcyclohexane/isopentane solution is attributed to W(CO) 5 (impurity), where the impurity is probably an aromatic or olefinic hydrocarbon. Spectra in methylene chloride solution are also discussed. The photochemical reactions of W(CO) 6 with aromatic hydrocarbon ligands in methylcyclohexane solution were also studied at −78°C in a low temperature infrared cell. Irradiation (366 nm) of W(CO) 6 at −78°C in rigorously purified methylcyclohexane solution containing approximately 5% (v/v) toluene, benzene, mesitylene, biphenyl, or p -xylene initially produces the complex W(CO) 5− (MCH). In the presence of the aromatic hydrocarbon, this complex is unstable and it decomposes in a dark reaction to give a complex which has an infrared spectrum typical for a C 4 v M(CO) 5 X molecule. It is proposed that the product of the dark reaction is W(CO) 5 (aromatic), formed by reaction of W(CO) 5 (MCH) with the aromatic ligand in solution. The infrared spectra of the W(CO) 5− (aromatic) complexes are different from the spectra previously reported for these complexes. It is shown that the spectra previously reported for W(CO) 5− (aromatic) are actually attributable to W(CO) 5 (hexane) (hexane was the solvent used in the previous study); these spectra were probably obtained before W(CO) 5 (hexane) had time to react with the aromatic hydrocarbon.

Product distribution of a photochemical reaction as a function of light intensity

Abstract Disproportionation and substitution occur as parallel reactions when (MeCp) 2 Mo 2 (CO) 6 (MeCp ue5fc η 5 -CH 3 C 5 H 4 ) is irradiated in the presence of P(OCH 3 ) 3 . The products of the disproportionation reaction are (MeCp)Mo-(CO) 3 − and (MeCp)Mo(CO) 2 (P(OCH 3 ) 3 ) 2 + while the product of the substitution reaction is (MeCp) 2 Mo 2 (CO) 4 (P(OCH 3 ) 3 ) 2 . The ratio of the quantum yield for disproportionation to that of substitution is dependent on the intensity of the exciting light. This result is in agreement with mechanisms proposed for the disproportionation and substitution reactions.

Photochemically initiated electron transfer catalyzed substitution reactions of metal carbonyl complexes

On etudie les complexes de ruthenium, dosmium et de fer substitues par la dimethylphenylphosphine. Mecanisme de reaction

Self-consistent-field-Xα-scattered-wave molecular orbital calculation of [CpMoS(μ-S)]2, a molecule that undergoes a photochemically induced isomerization

Abstract A self-consistent-field-Xα-scattered-wave molecular orbital calculation was carried out on the [CpMoS(μ-S)] 2 (Cp = η 5 -C 5 H 5 ) complex. The calculated results were used to rationalize the observed photochemical isomerization of the title complex to [CpMo(μ-S)][μ-S 2 ]. It is proposed that a terminal sulfur (S t ) → Mo charge-transfer excitation is responsible for the isomerization, which is an intramolecular redox; i.e. Mo(V) is reduced to Mo(IV) and S 2− is oxidized to S 2 2− , a result consistent with the charge-transfer character of the excitation. Specifically, the transition responsible for the isomerization is proposed to be 16 b u → 18 a g ( 1 A g → 1 B u ). The 18 a g orbital is primarily Mo in character but it is also Moue5f8S t π-antibonding; cleavage of the Moue5f8S t π-bond facilitates the isomerization.

An analysis of the dependence of the quantum yields of photochemical coupling reactions on the light intensity

Abstract If a product is formed by the coupling of two photochemically generated intermediates then the quantum yield for the appearance of the product may be intensity dependent. The quantum yields of a generalized photochemical coupling reaction were examined with the goal of elucidating the limitations and restrictions that apply in the use of this rule. For the general reaction pathway it was found that the quantum yield Φ of product formation will be directly proportional to I when k12/k2 is much greater than φI and Φ will be constant (with a value of φ 2 ) when k12/k2 is much less than φI. Other values of k12/k2 lead to quantum yields that are intensity dependent but not directly proportional to I. If Φ is to be experimentally determinable then k12/k2 must be no greater than 104φ2I.

Reduction of water-soluble substrates in micellar solutions using photochemically generated nineteen-electron organometallic complexes

Nineteen-electron organometallic complexes were generated photochemically in the benzene phase of micellar and reverse micellar solutionsl methylviologen and ferricyanide were reduced in order to demonstrate that these powerful reducing agents can be used to reduce water-soluble substrates contained in the aqueous phase.

Photochemically generated organometallic radicals as reducing agents

Irradiation of metal–metal bonded carbonyl dimers in the presence of appropriate ligands generates a class of intermediates which are powerful reducing agents; Ru3(CO)12, CpMo(CO)3Cl (Cp = cyclopentadienyl), and the ferricyanide ion were reduced in order to demonstrate the utility of these photogenerated reducing agents.

Computer analysis of consecutive photochemical reactions

Abstract A computer program was written to analyze consecutive photochemical reactions of the type If the experimental values for the concentrations of A, B and C versus time are known, then the program can calculate he quantum yields of the partial reactions. Conversely, if the quantum yields of the partial reactions are known, then the program will calculate the concentrations of A, B and C after a given irradiation time. The program will also calculate the time required to obtain the maximum amount of B. To test the computational validity of the program the photosubstitution of W(CO) 6 by pyridine was studied: W(CO) 6 → W(CO) 5 py → cis -W(CO) 4 (py) 2 . The concentrations of the tungsten carbonyl species were monitored by IR spectroscopy and compared with the calculated concentrations; good agreement was obtained. Applications of the program to synthetic and mechanistic studies are discussed.