β-Diketiminato Calcium and Magnesium Amides; Model Complexes for Hydroamination Catalysis

A G M Barrett, I J Casely, M R Crimmin, Michael Hill, J R Lachs, Mary F Mahon, P A Procopiou

Research output: Contribution to journalArticle

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Abstract

In a study relevant to group 2-mediated hydroamination catalysis, the reaction of the β-diketiminato magnesium alkyl complex [{ArNC(Me)CHC(Me)NAr}Mg(n/sBu)] (Ar = 2,6-iPr2C6H3) with benzylamine, 2-methoxyethylamine, pyrrolidine, and 2-methyl-4,4-diphenylpyrrolidine has been shown to yield the corresponding magnesium amide complexes [{ArNC(Me)CHC(Me)NAr}Mg(NR1R2)] (R1 = H, R2 = CH2Ph, CH2CH2OMe; R1 = R2 = -(CH2)4-, -CH(Me)CH2CPh2CH2-) within the first point of analysis (30 min) at room temperature in near quantitative yield as monitored by 1H NMR spectroscopy. Reactions proceeded non-reversibly, and the products have been characterized in both solution and the solid state. While single crystal X-ray diffraction analysis demonstrated that the magnesium amides are dimeric in the solid state, with aggregation occurring via μ2-coordinated amide ligands, NMR studies suggest that for more sterically crowded amide ligands discreet monomeric species exist in solution. In contrast, the calcium complex [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe3)2}(THF)] reacted reversibly with benzylamine at room temperature to form an equilibrium mixture of a calcium benzylamide and bis(trimethylsilyl)amide. A series of Pulsed-Gradient Spin−Echo NMR studies upon β-diketiminato calcium amides were consistent with the formation of a dimer in solution. A van’t Hoff analysis performed on this mixture allowed ΔH° = −51.3 kJ mol−1 and ΔS° = −134 J mol−1 of the protonolysis/dimerization reaction to be derived and the Gibbs’ free energy to be calculated as ΔG° (298 K) = −11.4 kJ mol−1.
LanguageEnglish
Pages4445-4453
Number of pages9
JournalInorganic Chemistry
Volume48
Issue number10
DOIs
StatusPublished - 2009

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Amides
Magnesium
amides
Catalysis
catalysis
magnesium
calcium
Calcium
nuclear magnetic resonance
Nuclear magnetic resonance
Ligands
solid state
ligands
Dimerization
room temperature
Gibbs free energy
dimerization
trucks
Dimers
X ray diffraction analysis

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Barrett, A. G. M., Casely, I. J., Crimmin, M. R., Hill, M., Lachs, J. R., Mahon, M. F., & Procopiou, P. A. (2009). β-Diketiminato Calcium and Magnesium Amides; Model Complexes for Hydroamination Catalysis. DOI: 10.1021/ic900091x

β-Diketiminato Calcium and Magnesium Amides; Model Complexes for Hydroamination Catalysis. / Barrett, A G M; Casely, I J; Crimmin, M R; Hill, Michael; Lachs, J R; Mahon, Mary F; Procopiou, P A.

In: Inorganic Chemistry, Vol. 48, No. 10, 2009, p. 4445-4453.

Research output: Contribution to journalArticle

Barrett, AGM, Casely, IJ, Crimmin, MR, Hill, M, Lachs, JR, Mahon, MF & Procopiou, PA 2009, 'β-Diketiminato Calcium and Magnesium Amides; Model Complexes for Hydroamination Catalysis' Inorganic Chemistry, vol. 48, no. 10, pp. 4445-4453. DOI: 10.1021/ic900091x
Barrett AGM, Casely IJ, Crimmin MR, Hill M, Lachs JR, Mahon MF et al. β-Diketiminato Calcium and Magnesium Amides; Model Complexes for Hydroamination Catalysis. Inorganic Chemistry. 2009;48(10):4445-4453. Available from, DOI: 10.1021/ic900091x
Barrett, A G M ; Casely, I J ; Crimmin, M R ; Hill, Michael ; Lachs, J R ; Mahon, Mary F ; Procopiou, P A. / β-Diketiminato Calcium and Magnesium Amides; Model Complexes for Hydroamination Catalysis. In: Inorganic Chemistry. 2009 ; Vol. 48, No. 10. pp. 4445-4453
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AB - In a study relevant to group 2-mediated hydroamination catalysis, the reaction of the β-diketiminato magnesium alkyl complex [{ArNC(Me)CHC(Me)NAr}Mg(n/sBu)] (Ar = 2,6-iPr2C6H3) with benzylamine, 2-methoxyethylamine, pyrrolidine, and 2-methyl-4,4-diphenylpyrrolidine has been shown to yield the corresponding magnesium amide complexes [{ArNC(Me)CHC(Me)NAr}Mg(NR1R2)] (R1 = H, R2 = CH2Ph, CH2CH2OMe; R1 = R2 = -(CH2)4-, -CH(Me)CH2CPh2CH2-) within the first point of analysis (30 min) at room temperature in near quantitative yield as monitored by 1H NMR spectroscopy. Reactions proceeded non-reversibly, and the products have been characterized in both solution and the solid state. While single crystal X-ray diffraction analysis demonstrated that the magnesium amides are dimeric in the solid state, with aggregation occurring via μ2-coordinated amide ligands, NMR studies suggest that for more sterically crowded amide ligands discreet monomeric species exist in solution. In contrast, the calcium complex [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe3)2}(THF)] reacted reversibly with benzylamine at room temperature to form an equilibrium mixture of a calcium benzylamide and bis(trimethylsilyl)amide. A series of Pulsed-Gradient Spin−Echo NMR studies upon β-diketiminato calcium amides were consistent with the formation of a dimer in solution. A van’t Hoff analysis performed on this mixture allowed ΔH° = −51.3 kJ mol−1 and ΔS° = −134 J mol−1 of the protonolysis/dimerization reaction to be derived and the Gibbs’ free energy to be calculated as ΔG° (298 K) = −11.4 kJ mol−1.

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