Femtosecond IR Studies of Alkane C−H Bond Activation by Organometallic Compounds: Direct Observation of Reactive Intermediates in Room Temperature Solutions

Lian, Tianquan; Bromberg, S. E.; Yang, Han‐Kwang; Proulx, Grant; Bergman, Robert G.; Harris, Charles B.

doi:10.1021/ja9541591

Cited by 80 publications

(50 citation statements)

References 32 publications

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“…Analogous results have been obtained with a B-H bond of the borate displacing a pyrazole of a bispyrazolyl borate (38). Time-resolved IR experiments on the intermediates involved in the reaction of TpЈRh(CO) 2 with alkanes are consistent with similar conclusions (23).…”

Section: Structures Of Complexes Intermediates and Transition Statesupporting

confidence: 75%

“…In the related [TpЈRh(CO)] system, flash photolysis studies indicated that the unsaturated metal fragment first binds to the hydrocarbon to form a -alkane complex, which then undergoes C-H oxidative cleavage in a second unimolecular reaction (23)(24)(25). Density functional theory calculations have confirmed the stability of an alkane complex of TpRh(CO) (26).…”

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confidence: 99%

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Structural and dynamic properties of propane coordinated to TpRh(CNR) from a confrontation between theory and experiment

Clot

Eisenstein

Jones

2007

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

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Section: Structures Of Complexes Intermediates and Transition Statesupporting

confidence: 75%

mentioning

confidence: 99%

Structural and dynamic properties of propane coordinated to TpRh(CNR) from a confrontation between theory and experiment

Clot

Eisenstein

Jones

2007

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

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“…Previous work has shown [69,70] that after 200 ps, the monocarbonyl solvent complex changes from q3 to q2. In cyclohexane, 230 ns after initial photoexcitation the C-H bond is broken, and the final product is in an q3 state.…”

Section: Changes Inmentioning

confidence: 96%

Time resolved infrared studies of C-H bond activation by organometallics

Asplund¹

1998

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' Lhe Govermient reserves for itself and others acting on its behalf a ruyalty free, nonexclusive, irrev-le, world-wide license for governmental purpses to publish, distribute, translate, duplicate, exhibit, and perform a q such data aopyrighted by the amtractor.The U.S. Department of Energy has the right to use this document for any purpose whatsoever, including the right to reproduce all or any part thereof. Much of the study of these C-H activation reactions has focussed on the spectroscopy of the CO ligands. We have shown the spectroscopy of several non-CO modes in the system. Spectroscopy of the Rh-H stretch at 2080 cm-lhas allowed for the unambiguous assignment of the time scale of final C-H bond breaking step.

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“…We have investigated the interesting equilibrium between methane and methyl hydride complexes further by repeating these measurements using Re(Cp*)(CO) 3 (9), where there is increased electron density on the rhenium metal center. Photolysis (266 nm) of 9 was studied in solutions of both methane (4,000 psi, 298 K) and ethane (1,660 psi, 294 K), both containing CO (90 and 60 psi, respectively).…”

Section: Photolysis Of Re(cp*)(co)3 In Scch4mentioning

confidence: 99%

“…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.…”

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confidence: 99%

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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Femtosecond IR Studies of Alkane C−H Bond Activation by Organometallic Compounds: Direct Observation of Reactive Intermediates in Room Temperature Solutions

Cited by 80 publications

References 32 publications

Structural and dynamic properties of propane coordinated to TpRh(CNR) from a confrontation between theory and experiment

Structural and dynamic properties of propane coordinated to TpRh(CNR) from a confrontation between theory and experiment

Time resolved infrared studies of C-H bond activation by organometallics

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

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