Flash photolysis with infrared detection. The photochemistry and secondary thermal reactions of M(CO)6 [M = Cr, Mo, and W]

Hermann, H; Grevels, Friedrich‐Wilhelm; Henne, Andreas; Schaffner, Kurt

doi:10.1021/j100223a019

Cited by 90 publications

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“…In the presence of CO, these transient bands decay at the same rate (k obs ϭ 4.4 Ϯ 0.1 ϫ 10 5 s Ϫ1 ) as the parent band reforms. By comparison to previous matrix isolation (5) and TRIR experiments (35), these transient bands can be assigned to W(CO) 5 (CH 4 ) (2). The observed rate constant for the decay of 2 depends linearly on the CO concentration, affording the second-order rate constant for the reaction of 2 with CO in scCH 4 (k CO ϭ 7.8 Ϯ 0.8 ϫ 10 6 dm 3 ⅐mol Ϫ1 ⅐s Ϫ1 , 298 K).…”

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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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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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“…The intensities and the frequencies of these bands are consistent with the formation of W(CO) 5 -ketone adducts. 5 The carbonyl stretching region of the IR spectra of the reaction mixtures of all studied ketones displayed nearly the same features ( Fig. 1) and the measured absorption frequencies are given in Table 1.…”

Section: Methodsmentioning

confidence: 84%

“…Formation of [W(CO) 5 -ketone] complexes for all of the studied ketones was observed by FTIR spectroscopy. However, substitution at the α-position of the cyclic ketones may create steric hindrance in the [W(CO) 5 -ketone] complex to prevent the coordination of CCl 4 to complete seven coordination of tungsten as given in Scheme 3. Therefore the ketones containing substituents in the α-position (VII, VIII) could not be converted to the aldol-type products by this system.…”

Section: Methodsmentioning

confidence: 97%

“…1) and the measured absorption frequencies are given in Table 1. The IR data reveal the formation of an oxygen-bound W(CO) 5 -ketone adduct for all of the employed ketones. The CO stretching bands given in Table 1 are close in frequency to the literature values.…”

Section: Methodsmentioning

confidence: 97%

“…W(CO) 5 (C 4v ) species. 4 Addition of ketone to this solution resulted in the disappearance of these peaks, but another three peaks at ∼2075 (A 1 1 ), ∼1935 (E) and ∼1910 cm −1 (A 1 2 ) arose in the carbonyl region of the IR spectrum.…”

Section: Methodsmentioning

confidence: 99%

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A comparative study on aldol‐type condensation reactions of cyclic, acyclic and substituted cyclic ketones by the W(CO)₆/CCl₄/UV system

Altıntaş

Bozkurt

2005

Applied Organom Chemis

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Aldol-type condensation reactions of a number of cyclic, acyclic and substituted cyclic ketones were investigated using the W(CO) 6 /CCl 4 /UV system. The progress of the reactions was followed by IR and GC-MS techniques. The cyclic ketone derivatives with β-and γ -substituent gave the expected condensation products. However, the α-substituted cyclic, acyclic and unsubstituted cyclic ketones with rings larger than six did not. Formation of [W]-ketone complexes with all of the ketones used was observed by FTIR. With respect to our studies, a mechanism involving an intermediate seven-coordinate tungsten complex has been proposed.

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Fast and Ultrafast Time‐Resolved Mid‐Infrared Spectrometry Using Lasers

Grills

George

2001

Handbook of Vibrational Spectroscopy

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The sections in this article are Introduction Fast TRIR Spectroscopy Fast TRIR Spectroscopy Using IR Lasers CW CO Lasers CW CO 2 Lasers Tunable IR Diode Lasers Color Center Lasers Difference Frequency Generation Ultrafast TRIR Studies Two‐Dimensional IR Spectroscopy Conclusions

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Flash photolysis with infrared detection. The photochemistry and secondary thermal reactions of M(CO)6 [M = Cr, Mo, and W]

Cited by 90 publications

References 0 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

A comparative study on aldol‐type condensation reactions of cyclic, acyclic and substituted cyclic ketones by the W(CO)₆/CCl₄/UV system

Fast and Ultrafast Time‐Resolved Mid‐Infrared Spectrometry Using Lasers

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Flash photolysis with infrared detection. The photochemistry and secondary thermal reactions of M(CO)6 [M = Cr, Mo, and W]

Cited by 90 publications

References 0 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

A comparative study on aldol‐type condensation reactions of cyclic, acyclic and substituted cyclic ketones by the W(CO)6/CCl4/UV system

Fast and Ultrafast Time‐Resolved Mid‐Infrared Spectrometry Using Lasers

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A comparative study on aldol‐type condensation reactions of cyclic, acyclic and substituted cyclic ketones by the W(CO)₆/CCl₄/UV system