Photochemical studies of rhenium .eta.-cyclopentadienyl complexes in matrixes and in solution: detection of rhenocene and mechanisms of hydrogen transfer

Chetwynd-Talbot, Jennifer; Grebenik, Peter D.; Perutz, Robin N.; POWELL, M. H. A.

doi:10.1021/ic00153a024

Cited by 28 publications

(6 citation statements)

References 2 publications

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“…The new (CO) bands observed in this study are not attributable to this dimeric species. The two bands at 1,902 and 1,963 cm Ϫ1 can be assigned to the solvated dicarbonyl species Re(Cp)(CO) 2 (CH 4 ) (7) by comparison to previous lowtemperature IR and room temperature TRIR experiments (38,44). The bathochromic shift in the (CO) bands compared with the parent species is consistent with loss of the -acceptor ligand.…”

supporting

confidence: 57%

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Cowan

Portius

Kawanami

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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We have used fast time-resolved infrared spectroscopy to characterize a series of organometallic methane and ethane complexes in solution at room temperature: W(CO)5(CH4) and M( 5 OC5R5)(CO)2(L) [where M ‫؍‬ Mn or Re, R ‫؍‬ H or CH3 (Re only); and L ‫؍‬ CH4 or C 2 H 6 ]. In all cases, the methane complexes are found to be short-lived and significantly more reactive than the analogous nheptane complexes. Re(Cp)(CO)2(CH4) and Re(Cp*)(CO)2(L) [Cp* ‫؍‬ 5 OC5(CH3)5 and L ‫؍‬ CH4, C2H6] were found to be in rapid equilibrium with the alkyl hydride complexes. In the presence of CO, both alkane and alkyl hydride complexes decay at the same rate. We have used picosecond time-resolved infrared spectroscopy to directly monitor the photolysis of Re(Cp*)(CO)3 in scCH4 and demonstrated that the initially generated Re(Cp*)(CO)2(CH4) forms an equilibrium mixture of Re(Cp*) ( T here is considerable interest in sigma-bonded organometallic alkane complexes, particularly since they have been identified as key intermediates in the transition metal-mediated COH activation process (1-3). Although such complexes generally are very short-lived intermediates (4), they have been known for over 30 years. Early experiments involved the photolysis of complexes such as Cr(CO) 6 and Fe(CO) 5 to generate the unstable intermediates Cr(CO) 5 or Fe(CO) 4 in low-temperature matrices, where coordination to cocondensed CH 4 results in the formation of Cr(CO) 5 (CH 4 ) and Fe(CO) 5 (CH 4 ) (5, 6).Flash photolysis experiments have demonstrated that the photolysis of Cr(CO) 6 in cyclohexane solution at room temperature forms Cr(CO) 5 (cyclohexane) (7). Subsequently, several examples of alkane complexes in solution have been reported, and studies on the mechanism of the COH activation process have clearly demonstrated the role of these complexes in oxidative addition reactions (1,8,9). Time-resolved infrared (TRIR) spectroscopy has proved to be a powerful tool for the study of metal carbonyl alkane complexes. Their reactivity decreases on going both across and down groups 5, 6, and 7 (10-12), and these observations led to the identification of a very long-lived alkane complex, Re(Cp)(CO) 2 (nheptane) (Cp ϭ 5 OC 5 H 5 ), which has a lifetime of Ϸ25 ms at room temperature (13). The relative stability of Re(Cp)(CO) 2 (alkane) complexes allowed Re(Cp)(CO) 2 (C 5 H 10 ) to be observed at 180 K by NMR spectroscopy (14), and subsequent NMR studies have been carried out to determine the binding modes of a series of related alkanes to the Re(CpЈ)(CO) 2 moiety (15, 16).The activation of methane is of particular interest because of the potential of using this abundant hydrocarbon as both an energy source and chemical feedstock (17). Organometallic methane complexes have been characterized in low-temperature matrix isolation experiments (5,6,18). In solution, the existence of methane complexes has been inferred by examining product ratios and from the rates of COH activation and reductive elimination reactions in isotopic labeling experiments (19).The lifetime of the...

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supporting

confidence: 57%

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Cowan

Portius

Kawanami

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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“…~~ In this search for compounds which would add to the C-H bonds of alkanes we have used tungstenocene as a model. Tungstenocene has been characterised under matrix isolation conditions as having a triplet, d 4 electronic configuration 20, 21 and photoelectron studies on tungstenocene derivatives [W(q-(C,H,),X2] (X = H, Me, or CI) or [W(q-C5H5),L] (L = CO or q-ClH4) show them to have low first ionisation energies which conform to the classification that the tungstenocene centre is high-energy (ele~tron-rich).~~ An advantage of highenergy d" electrons on a metal centre is that oxidation of the metal centre will be favoured and hence the oxidative-addition of C-H enhanced. In other words we see a high-energy highest occupied molecular orbital (h.o.m.0.)…”

Section: Discussionmentioning

confidence: 99%

Synthesis of [Mo(η-C₅H₄Prⁱ)(PR₃)₂H₃][R₃= Me₃or Me₂Ph), [Mo(η-C₅H₄Prⁱ)(Prⁱ₂PCH₂CH₂PPrⁱ₂)H₃], and analogues and their ability to catalyse the photoinduced hydrogen–deuterium exchange of carbon–hydrogen bonds; crystal structure of [{Mo(η-C₅H₄Prⁱ)(µ-Cl)₂}_2<

Grebenik¹,

Green²,

Izquierdo³

et al. 1987

J. Chem. Soc., Dalton Trans.

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H, ] in deuteriobenzene together with the substrates (CH,),O, CH,CO,CH,, toluene, mesitylene, ferrocene, bis(q -toluene)tungsten, and other organometallic compounds causes hydrogen-deuterium exchange between the C, D, and some or all of the substrate hydrogens. The [ Mo(q-C,H,Prl) (PR,),H,] derivatives are less active catalysts towards photoinduced H-D exchange reactions. * Tetra-~-chloro-bis[(~-isopropylcyclo~ntadienyl)molybdenum(~~~)].

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“…Cp 2 ReH produced the rhenocene fragment, HCO, and a monocarbonyl species; deuteration experiments confirmed that the Re–H bond was cleaved homolytically . Later results identified a competing photochemical pathway that involved partial ring decoordination plus concomitant ligand addition to yield CpReH(η 3 -C 5 H 5 )(L) (L = CO, N 2 ) . Rhenocene was generated photochemically in Ar matrices, allowing magnetic circular dichroism and laser-induced fluorescence investigations to be undertaken (see section ).…”

Section: Metal Hydride Photochemistry By Transition Metal Groupmentioning

confidence: 99%

Photochemistry of Transition Metal Hydrides

2016

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Photochemical reactivity associated with metal-hydrogen bonds is widespread among metal hydride complexes and has played a critical part in opening up C-H bond activation. It has been exploited to design different types of photocatalytic reactions and to obtain NMR spectra of dilute solutions with a single pulse of an NMR spectrometer. Because photolysis can be performed on fast time scales and at low temperature, metal-hydride photochemistry has enabled determination of the molecular structure and rates of reaction of highly reactive intermediates. We identify five characteristic photoprocesses of metal monohydride complexes associated with the M-H bond, of which the most widespread are M-H homolysis and R-H reductive elimination. For metal dihydride complexes, the dominant photoprocess is reductive elimination of H2. Dihydrogen complexes typically lose H2 photochemically. The majority of photochemical reactions are likely to be dissociative, but hydride complexes may be designed with equilibrated excited states that undergo different photochemical reactions, including proton transfer or hydride transfer. The photochemical mechanisms of a few reactions have been analyzed by computational methods, including quantum dynamics. A section on specialist methods (time-resolved spectroscopy, matrix isolation, NMR, and computational methods) and a survey of transition metal hydride photochemistry organized by transition metal group complete the Review.

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Photochemical studies of rhenium .eta.-cyclopentadienyl complexes in matrixes and in solution: detection of rhenocene and mechanisms of hydrogen transfer

Cited by 28 publications

References 2 publications

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Photochemistry of Transition Metal Hydrides

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Photochemical studies of rhenium .eta.-cyclopentadienyl complexes in matrixes and in solution: detection of rhenocene and mechanisms of hydrogen transfer

Cited by 28 publications

References 2 publications

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Synthesis of [Mo(η-C5H4Pri)(PR3)2H3][R3= Me3or Me2Ph), [Mo(η-C5H4Pri)(Pri2PCH2CH2PPri2)H3], and analogues and their ability to catalyse the photoinduced hydrogen–deuterium exchange of carbon–hydrogen bonds; crystal structure of [{Mo(η-C5H4Pri)(µ-Cl)2}2<

Photochemistry of Transition Metal Hydrides

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