Interaction of H2 and Prototypical Solvent Molecules with Cr(CO)5 in the Gas Phase

Wells, J. R.; House, Paul G.; Weitz, Eric

doi:10.1021/j100085a014

Cited by 56 publications

(67 citation statements)

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“…The ⌬H ‡ value (30 Ϯ 2 kJ⅐mol Ϫ1 ) for the reaction of 2 with CO can be used as a lower limit for the WOCH 4 binding enthalpy in scCH 4 . It is interesting to compare this result with previous calculations (30), which predict a WOCH 4 interaction of 18 kJ⅐mol Ϫ1 , and with gas-phase TRIR experiments, which estimate a CrOCH 4 bond-dissociation energy of 33 Ϯ 8 kJ⅐mol Ϫ1 (26). Clearly, there is a significant WOCH 4 interaction in solution at room temperature.…”

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confidence: 56%

“…TRIR measurements on Cr(CO) 6 in the gas phase demonstrated that photolysis produces Cr(CO) 5 . In the presence of CH 4 (600 torr; 1 torr ϭ 133 Pa), a 2-fold decrease in the rate of regeneration of Cr(CO) 6 was interpreted to indicate a weak interaction between the Cr(CO) 5 fragment and CH 4 , with an estimated binding enthalpy for CrOCH 4 of 33 Ϯ 8 kJ⅐mol Ϫ1 (26). We recently have used a combination of supercritical fluids and TRIR spectroscopy to characterize a series of organometallic noble gas complexes at room temperature (11), leading to the characterization of Re( i PrCp)(CO)(PF 3 )Xe by NMR (27).…”

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confidence: 99%

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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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confidence: 56%

mentioning

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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“…Table 1 lists the dissociation energies D e and D 0 of the H 2 ligand. The D 0 value for 1 a of 15.9 kcal/mol calculated at the CCSD(T) level is in very good agreement with the experimental value obtained by Weitz and coworkers (15.0 ± 1.3 kcal/mol) [43]. An estimation of the H 2 bond energy in 1 c (W(CO) 5 (H 2 )) gave D 0 > 16 kcal/mol [44], again in good agreement with our calculated CCSD(T) value of 16.3 kcal/mol.…”

Section: Resultssupporting

confidence: 90%

Transition Metal Complexes with more than one Dihydrogen Ligand: Structure and Bonding of M(CO)6-x(H2)x (M = Cr, Mo, W; x = 1, 2, 3) [1]

Dapprich

Frenking

1998

Z. anorg. allg. Chem.

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“…Other TRIR experiments monitoring the photolysis of Cr(CO) 6 in the gas phase detected a transient species, assigned to be Cr(CO) 5 (CH 4 ) [72]. Another TRIR study did not directly detect the presence of Cr(CO) 5 (CH 4 ), following the photolysis of Cr(CO) 6 in the presence of a low pressure (11.4 psi) of CH 4 and this work reported an estimation of the binding energy of the Cr(CO) 5 (CH 4 ) bond (33 (±8) kJ mol −1 ) [74].…”

Section: Organometallic Complexes Of the Lighter Alkanesmentioning

confidence: 61%

Formation and reactivity of organometallic alkane complexes

Cowan

George

2008

Coordination Chemistry Reviews

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Interaction of H2 and Prototypical Solvent Molecules with Cr(CO)5 in the Gas Phase

Cited by 56 publications

References 10 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

Transition Metal Complexes with more than one Dihydrogen Ligand: Structure and Bonding of M(CO)6-x(H2)x (M = Cr, Mo, W; x = 1, 2, 3) [1]

Formation and reactivity of organometallic alkane complexes

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