Use of high-pressure/variable-temperature infrared flow cell to examine the reaction kinetics of the migratory insertion intermediate ({eta}{sup 5}-C{sub 5}H{sub 5})Fe(CO)C(O)CH{sub 3} by time-resolved spectroscopy
The reactive intermediate CpFe(CO)C(O)CH{sub 3} (1; Cp = {eta}{sup 5}-C{sub 5}H{sub 5}) was prepared by flash photolysis of CpFe(CO){sub 2}C(O)CH{sub 3} (A) in cyclohexane solutions and its reaction kinetics interrogated by time-resolved infrared spectroscopy in a flow system designed to allow equilibration of photolysis solutions at elevated temperatures and high carbon monoxide pressures. The high CO pressures (P{sub CO} {le} 28 atm) allowed for the measurement of the previously undetermined second-order rate constant (k{sub CO}) of CO trapping of 1 to regenerate A, which under these conditions occurs in competition with migration of the methyl group from the carbonyl carbon to the iron (K{sub M}). These rates were also measured over the temperature range 25--45 C, which allowed the determination of the activation parameters for methyl migration ({Delta}H{double{underscore}dagger}) = 44 {+-} 2 kJ mol{sup {minus}1}, {Delta}S{double{underscore}dagger} = {minus}5 {+-} 8 J K{sup {minus}1} mol{sup {minus}1} and for reaction with CO ({Delta} H{double{underscore}dagger} = 34 {+-} 2 kJ mol{sup {minus}1}, {Delta}S{double{underscore}dagger} = {minus}28 {+-} 6 J K{sup {minus}1}mol{sup {minus}1}). The mechanistic implications of these results are discussed. Details regarding the design of the high-pressure/variable-temperature TRIR flow cell are also discussed.
- Research Organization:
- Univ. of California, Santa Barbara, CA (US)
- Sponsoring Organization:
- USDOE; National Science Foundation (NSF)
- DOE Contract Number:
- FG03-85ER13317; FG05-91ER79039
- OSTI ID:
- 20013604
- Journal Information:
- Organometallics, Vol. 18, Issue 21; Other Information: PBD: 11 Oct 1999; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
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