Spectroscopic detection and theoretical confirmation of the role of Cr 2(CO)5(C5R5)2 and ·Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by ·Cr(CO)3(C5R5) (R = H, CH3)

George C. Fortman; Tamás Kégl; Qian Shu Li; Xiuhui Zhang; Henry F. Schaefer; Yaoming Xie; R. Bruce King; Joshua Telser; Carl D. Hoff

doi:10.1021/ja075008o

Spectroscopic detection and theoretical confirmation of the role of Cr ₂(CO)₅(C₅R₅)₂ and ·Cr(CO)₂(ketene)(C₅R₅) as intermediates in carbonylation of N=N=CHSiMe₃ to O=C=CHSiMe₃ by ·Cr(CO)₃(C₅R₅) (R = H, CH₃)

George C. Fortman, Tamás Kégl^*, Qian Shu Li, Xiuhui Zhang, Henry F. Schaefer, Yaoming Xie, R. Bruce King, Joshua Telser, Carl D. Hoff

^*Corresponding author for this work

School of Chemistry and Chemical Engineering

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Abstract

Conversion of N=N=CHSiMe₃ to O=C=CHSiMe₃ by the radical complexes ·Cr(CO)₃C₅R₅ (R = H, CH₃) derived from dissociation of [Cr(CO)₃(C ₅R₅)]₂ have been investigated under CO, Ar, and N₂ atmospheres. Under an Ar or N₂ atmosphere the reaction is stoichiometric and produces the Cr≡Cr triply bonded complex [Cr(CO)₂(C₅R₅)]₂. Under a CO atmosphere regeneration of [Cr(CO)₃(C₅R₅)] ₂ (R = H, CH₃) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, ·Cr(CO)₂(ketene)(C ₅R₅) and Cr₂(CO)₅(C ₅R₅)₂ have been detected spectroscopically. The complex ·Cr(¹³CO)₂(O=¹³C=CHSiMe ₃)(C₅Me₅) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(⁵³Cr) = 125 MHz; A(¹³CO) = 22.5 MHz; A(O=¹³C=CHSiMe₃) = 12.0 MHz. The complex Cr₂(CO)₅(C₅H ₅)₂, generated in situ, does not show a signal in its ¹H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from ³Cr₂(CO)₅-(C₅H₅) ₂ producing ¹[Cr(CO)₂(C₅H ₅)]₂ and CO addition to ³Cr₂(CO) ₅(C₅H₅)₂ producing ¹[Cr(CO)₃(C₅H₅)]₂ have been measured by kinetics and show ΔH^† ≅ 23 kcal mol^-1 for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)ⁿ(C₅H₅)]₂ (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr≡Cr bond strength in [Cr(CO)₂(C₅H ₅)]₂ as 72 kcal mol^-1. The complex [Cr(CO) ₂(C₅H₅)]₂ does not readily undergo ¹³CO exchange at room temperature or 50°C implying that ³Cr₂(CO)₅(C₅H₅) ₂ is not readily accessed from the thermodynamically stable complex [Cr(CO)₂(C₅H₅)]₂. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N₂ is proposed on the basis of a combination of experimental and theoretical data.

Original language	English
Pages (from-to)	14388-14400
Number of pages	13
Journal	Journal of the American Chemical Society
Volume	129
Issue number	46
DOIs	https://doi.org/10.1021/ja075008o
Publication status	Published - 21 Nov 2007

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Fortman, G. C., Kégl, T., Li, Q. S., Zhang, X., Schaefer, H. F., Xie, Y., King, R. B., Telser, J., & Hoff, C. D. (2007). Spectroscopic detection and theoretical confirmation of the role of Cr ₂(CO)₅(C₅R₅)₂ and ·Cr(CO)₂(ketene)(C₅R₅) as intermediates in carbonylation of N=N=CHSiMe₃ to O=C=CHSiMe₃ by ·Cr(CO)₃(C₅R₅) (R = H, CH₃). Journal of the American Chemical Society, 129(46), 14388-14400. https://doi.org/10.1021/ja075008o

@article{a0276d6187da4f1c922120c2971f9092,

title = "Spectroscopic detection and theoretical confirmation of the role of Cr 2(CO)5(C5R5)2 and ·Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by ·Cr(CO)3(C5R5) (R = H, CH3)",

abstract = "Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes ·Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C 5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr≡Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)] 2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, ·Cr(CO)2(ketene)(C 5R5) and Cr2(CO)5(C 5R5)2 have been detected spectroscopically. The complex ·Cr(13CO)2(O=13C=CHSiMe 3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H 5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5-(C5H5) 2 producing 1[Cr(CO)2(C5H 5)]2 and CO addition to 3Cr2(CO) 5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show ΔH† ≅ 23 kcal mol-1 for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr≡Cr bond strength in [Cr(CO)2(C5H 5)]2 as 72 kcal mol-1. The complex [Cr(CO) 2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50°C implying that 3Cr2(CO)5(C5H5) 2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.",

author = "Fortman, {George C.} and Tam{\'a}s K{\'e}gl and Li, {Qian Shu} and Xiuhui Zhang and Schaefer, {Henry F.} and Yaoming Xie and King, {R. Bruce} and Joshua Telser and Hoff, {Carl D.}",

year = "2007",

month = nov,

day = "21",

doi = "10.1021/ja075008o",

language = "English",

volume = "129",

pages = "14388--14400",

journal = "Journal of the American Chemical Society",

issn = "0002-7863",

publisher = "American Chemical Society",

number = "46",

}

Fortman, GC, Kégl, T, Li, QS, Zhang, X, Schaefer, HF, Xie, Y, King, RB, Telser, J & Hoff, CD 2007, 'Spectroscopic detection and theoretical confirmation of the role of Cr ₂(CO)₅(C₅R₅)₂ and ·Cr(CO)₂(ketene)(C₅R₅) as intermediates in carbonylation of N=N=CHSiMe₃ to O=C=CHSiMe₃ by ·Cr(CO)₃(C₅R₅) (R = H, CH₃)', Journal of the American Chemical Society, vol. 129, no. 46, pp. 14388-14400. https://doi.org/10.1021/ja075008o

Spectroscopic detection and theoretical confirmation of the role of Cr ₂(CO)₅(C₅R₅)₂ and ·Cr(CO)₂(ketene)(C₅R₅) as intermediates in carbonylation of N=N=CHSiMe₃ to O=C=CHSiMe₃ by ·Cr(CO)₃(C₅R₅) (R = H, CH₃). / Fortman, George C.; Kégl, Tamás; Li, Qian Shu et al.
In: Journal of the American Chemical Society, Vol. 129, No. 46, 21.11.2007, p. 14388-14400.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - Spectroscopic detection and theoretical confirmation of the role of Cr 2(CO)5(C5R5)2 and ·Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by ·Cr(CO)3(C5R5) (R = H, CH3)

AU - Fortman, George C.

AU - Kégl, Tamás

AU - Li, Qian Shu

AU - Zhang, Xiuhui

AU - Schaefer, Henry F.

AU - Xie, Yaoming

AU - King, R. Bruce

AU - Telser, Joshua

AU - Hoff, Carl D.

PY - 2007/11/21

Y1 - 2007/11/21

N2 - Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes ·Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C 5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr≡Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)] 2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, ·Cr(CO)2(ketene)(C 5R5) and Cr2(CO)5(C 5R5)2 have been detected spectroscopically. The complex ·Cr(13CO)2(O=13C=CHSiMe 3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H 5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5-(C5H5) 2 producing 1[Cr(CO)2(C5H 5)]2 and CO addition to 3Cr2(CO) 5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show ΔH† ≅ 23 kcal mol-1 for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr≡Cr bond strength in [Cr(CO)2(C5H 5)]2 as 72 kcal mol-1. The complex [Cr(CO) 2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50°C implying that 3Cr2(CO)5(C5H5) 2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.

AB - Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes ·Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C 5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr≡Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)] 2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, ·Cr(CO)2(ketene)(C 5R5) and Cr2(CO)5(C 5R5)2 have been detected spectroscopically. The complex ·Cr(13CO)2(O=13C=CHSiMe 3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H 5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5-(C5H5) 2 producing 1[Cr(CO)2(C5H 5)]2 and CO addition to 3Cr2(CO) 5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show ΔH† ≅ 23 kcal mol-1 for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr≡Cr bond strength in [Cr(CO)2(C5H 5)]2 as 72 kcal mol-1. The complex [Cr(CO) 2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50°C implying that 3Cr2(CO)5(C5H5) 2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.

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