Heats of reaction of RMo(CO)3C5H5 (R = H, CH3, C2H5) with phosphines and phosphites: Thermodynamic study of the CO-insertion reaction

Steven P. Nolan, Ramon Lopez De La Vega, Shakti L. Mukerjee, Carl Hoff

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Abstract

The heats of reaction Of HMo(CO)3C5H5 with a series of phosphines and phosphites, producing HMo(CO)2(PR3)C5H5, have been measured by solution calorimetry. The order of relative Mo-PR3 bond strengths, PMe3 ≈ P-n-Bu3 > P(OMe)3 > PMe2Ph > PMePh2, closely resembles that determined earlier for the complexes fac-(PR3)3Mo(CO)3. The heats of reaction of RMo(CO)3C5H5 (R = CH3, C2H5), producing the phosphine-substituted acyl complexes RC(O)Mo(CO)2(PR3)C5H5, were also studied thermochemically. This reaction can be viewed as involving both phosphine substitution and carbonyl insertion. With use of the enthalpy of phosphine substitution of HMo(CO)3C5H5 as a model, the enthalpy of carbonyl insertion is calculated. For both R = CH3 and R = C2H5 the carbonyl-insertion reaction is favored for more basic phosphines with a difference of about 2 kcal/mol between PMe3 (most favored) and P(OMe)3 (least favored). Carbonyl insertion into the Mo-Et bond is about 3 kcal/mol more favorable than into the Mo-CH3 bond. Attempts to prepare the unsubstituted acyls RC(O)Mo(CO)3C5H5 by carbonylation of the alkyls in THF led to facile reductive elimination of RC(O)C5H5 (35°C, 1 atm of CO), producing Mo(CO)6. Migration of the acyl group to the coordinated cyclopentadienyl ring in the presence of CO pressure and thermodynamic instability in the absence of CO pressure explain the lack of success in preparing RC(O)Mo(CO)3C5H5 for simple alkyl groups.

Original languageEnglish
Pages (from-to)1160-1165
Number of pages6
JournalInorganic Chemistry
Volume25
Issue number8
StatePublished - Dec 1 1986

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Phosphines
Phosphites
Carbon Monoxide
phosphines
insertion
Thermodynamics
phosphine
heat
thermodynamics
enthalpy
substitutes
elimination
heat measurement
Enthalpy
Hot Temperature
Substitution reactions
Carbonylation
rings
Calorimetry

ASJC Scopus subject areas

  • Inorganic Chemistry

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Heats of reaction of RMo(CO)3C5H5 (R = H, CH3, C2H5) with phosphines and phosphites : Thermodynamic study of the CO-insertion reaction. / Nolan, Steven P.; De La Vega, Ramon Lopez; Mukerjee, Shakti L.; Hoff, Carl.

In: Inorganic Chemistry, Vol. 25, No. 8, 01.12.1986, p. 1160-1165.

Research output: Contribution to journalArticle

Nolan, Steven P. ; De La Vega, Ramon Lopez ; Mukerjee, Shakti L. ; Hoff, Carl. / Heats of reaction of RMo(CO)3C5H5 (R = H, CH3, C2H5) with phosphines and phosphites : Thermodynamic study of the CO-insertion reaction. In: Inorganic Chemistry. 1986 ; Vol. 25, No. 8. pp. 1160-1165.
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abstract = "The heats of reaction Of HMo(CO)3C5H5 with a series of phosphines and phosphites, producing HMo(CO)2(PR3)C5H5, have been measured by solution calorimetry. The order of relative Mo-PR3 bond strengths, PMe3 ≈ P-n-Bu3 > P(OMe)3 > PMe2Ph > PMePh2, closely resembles that determined earlier for the complexes fac-(PR3)3Mo(CO)3. The heats of reaction of RMo(CO)3C5H5 (R = CH3, C2H5), producing the phosphine-substituted acyl complexes RC(O)Mo(CO)2(PR3)C5H5, were also studied thermochemically. This reaction can be viewed as involving both phosphine substitution and carbonyl insertion. With use of the enthalpy of phosphine substitution of HMo(CO)3C5H5 as a model, the enthalpy of carbonyl insertion is calculated. For both R = CH3 and R = C2H5 the carbonyl-insertion reaction is favored for more basic phosphines with a difference of about 2 kcal/mol between PMe3 (most favored) and P(OMe)3 (least favored). Carbonyl insertion into the Mo-Et bond is about 3 kcal/mol more favorable than into the Mo-CH3 bond. Attempts to prepare the unsubstituted acyls RC(O)Mo(CO)3C5H5 by carbonylation of the alkyls in THF led to facile reductive elimination of RC(O)C5H5 (35°C, 1 atm of CO), producing Mo(CO)6. Migration of the acyl group to the coordinated cyclopentadienyl ring in the presence of CO pressure and thermodynamic instability in the absence of CO pressure explain the lack of success in preparing RC(O)Mo(CO)3C5H5 for simple alkyl groups.",
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N2 - The heats of reaction Of HMo(CO)3C5H5 with a series of phosphines and phosphites, producing HMo(CO)2(PR3)C5H5, have been measured by solution calorimetry. The order of relative Mo-PR3 bond strengths, PMe3 ≈ P-n-Bu3 > P(OMe)3 > PMe2Ph > PMePh2, closely resembles that determined earlier for the complexes fac-(PR3)3Mo(CO)3. The heats of reaction of RMo(CO)3C5H5 (R = CH3, C2H5), producing the phosphine-substituted acyl complexes RC(O)Mo(CO)2(PR3)C5H5, were also studied thermochemically. This reaction can be viewed as involving both phosphine substitution and carbonyl insertion. With use of the enthalpy of phosphine substitution of HMo(CO)3C5H5 as a model, the enthalpy of carbonyl insertion is calculated. For both R = CH3 and R = C2H5 the carbonyl-insertion reaction is favored for more basic phosphines with a difference of about 2 kcal/mol between PMe3 (most favored) and P(OMe)3 (least favored). Carbonyl insertion into the Mo-Et bond is about 3 kcal/mol more favorable than into the Mo-CH3 bond. Attempts to prepare the unsubstituted acyls RC(O)Mo(CO)3C5H5 by carbonylation of the alkyls in THF led to facile reductive elimination of RC(O)C5H5 (35°C, 1 atm of CO), producing Mo(CO)6. Migration of the acyl group to the coordinated cyclopentadienyl ring in the presence of CO pressure and thermodynamic instability in the absence of CO pressure explain the lack of success in preparing RC(O)Mo(CO)3C5H5 for simple alkyl groups.

AB - The heats of reaction Of HMo(CO)3C5H5 with a series of phosphines and phosphites, producing HMo(CO)2(PR3)C5H5, have been measured by solution calorimetry. The order of relative Mo-PR3 bond strengths, PMe3 ≈ P-n-Bu3 > P(OMe)3 > PMe2Ph > PMePh2, closely resembles that determined earlier for the complexes fac-(PR3)3Mo(CO)3. The heats of reaction of RMo(CO)3C5H5 (R = CH3, C2H5), producing the phosphine-substituted acyl complexes RC(O)Mo(CO)2(PR3)C5H5, were also studied thermochemically. This reaction can be viewed as involving both phosphine substitution and carbonyl insertion. With use of the enthalpy of phosphine substitution of HMo(CO)3C5H5 as a model, the enthalpy of carbonyl insertion is calculated. For both R = CH3 and R = C2H5 the carbonyl-insertion reaction is favored for more basic phosphines with a difference of about 2 kcal/mol between PMe3 (most favored) and P(OMe)3 (least favored). Carbonyl insertion into the Mo-Et bond is about 3 kcal/mol more favorable than into the Mo-CH3 bond. Attempts to prepare the unsubstituted acyls RC(O)Mo(CO)3C5H5 by carbonylation of the alkyls in THF led to facile reductive elimination of RC(O)C5H5 (35°C, 1 atm of CO), producing Mo(CO)6. Migration of the acyl group to the coordinated cyclopentadienyl ring in the presence of CO pressure and thermodynamic instability in the absence of CO pressure explain the lack of success in preparing RC(O)Mo(CO)3C5H5 for simple alkyl groups.

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