Trimethylaluminum and borane complexes of primary amines

Balázs Németh, Jean Paul Guégan, T. Veszprémi, Jean Claude Guillemin

Research output: Contribution to journalArticle

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Abstract

Trimethylaluminum (TMA) complexes of methyl-, n-propyl-, cyclopropyl-, allyl-, and propargylamine were synthesized and their experimental properties and theoretical characteristics were compared with the respective amine-borane analogues. The amine ligand of an amine-TMA Lewis acid-base complex can be easily changed by another amine through a 2:1 amine-TMA intermediate in pentane at room temperature. The exchange of the same ligands in the case of amine-boranes requires remarkably more time in line with the calculated relative energy of the respective transition state. The 1H and 13C NMR experiments examining the addition of one or more equivalent of amine to the respective Lewis acid-base complex conclude in the fast exchange of the amine ligand in the NMR time scale only in the cases of amine-TMA complexes, which could also be caused by similar 2:1 complexes. However, in gas phase, only 1:1 amine-TMA complexes are present as evidenced by ultraviolet photoelectron spectroscopy (UPS). The observed UP spectra, which are the first recorded photoelectron spectra of primary amine-TMA compounds, indicate that the stabilization effect of the lone electron pair of nitrogen atom in amines during the borane complexation is stronger than that of the TMA complexation. In line with this observation, the destabilization of the σAl-C orbitals is lower than that of σB-H orbitals during the formation of amine-TMA and amine-borane complexes, respectively. As showed by theoretical calculations, the CH4 elimination of the studied amine-TMA complexes is exothermic, indicating the possibility of using these compounds in metal organic chemical vapor deposition techniques (MOCVD). On the other hand, our experimental conditions avoid this methane elimination and constitutes the first procedure employing distillation to isolate primary amine-TMA complexes.

Original languageEnglish
Pages (from-to)346-354
Number of pages9
JournalInorganic Chemistry
Volume52
Issue number1
DOIs
Publication statusPublished - Jan 7 2013

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Boranes
boranes
Amines
amines
Lewis Acids
Ligands
Complexation
ligands
elimination
Nuclear magnetic resonance
Ultraviolet photoelectron spectroscopy
Organic Chemicals
orbitals
nuclear magnetic resonance
acids
distillation
pentanes

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Trimethylaluminum and borane complexes of primary amines. / Németh, Balázs; Guégan, Jean Paul; Veszprémi, T.; Guillemin, Jean Claude.

In: Inorganic Chemistry, Vol. 52, No. 1, 07.01.2013, p. 346-354.

Research output: Contribution to journalArticle

Németh, Balázs ; Guégan, Jean Paul ; Veszprémi, T. ; Guillemin, Jean Claude. / Trimethylaluminum and borane complexes of primary amines. In: Inorganic Chemistry. 2013 ; Vol. 52, No. 1. pp. 346-354.
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AB - Trimethylaluminum (TMA) complexes of methyl-, n-propyl-, cyclopropyl-, allyl-, and propargylamine were synthesized and their experimental properties and theoretical characteristics were compared with the respective amine-borane analogues. The amine ligand of an amine-TMA Lewis acid-base complex can be easily changed by another amine through a 2:1 amine-TMA intermediate in pentane at room temperature. The exchange of the same ligands in the case of amine-boranes requires remarkably more time in line with the calculated relative energy of the respective transition state. The 1H and 13C NMR experiments examining the addition of one or more equivalent of amine to the respective Lewis acid-base complex conclude in the fast exchange of the amine ligand in the NMR time scale only in the cases of amine-TMA complexes, which could also be caused by similar 2:1 complexes. However, in gas phase, only 1:1 amine-TMA complexes are present as evidenced by ultraviolet photoelectron spectroscopy (UPS). The observed UP spectra, which are the first recorded photoelectron spectra of primary amine-TMA compounds, indicate that the stabilization effect of the lone electron pair of nitrogen atom in amines during the borane complexation is stronger than that of the TMA complexation. In line with this observation, the destabilization of the σAl-C orbitals is lower than that of σB-H orbitals during the formation of amine-TMA and amine-borane complexes, respectively. As showed by theoretical calculations, the CH4 elimination of the studied amine-TMA complexes is exothermic, indicating the possibility of using these compounds in metal organic chemical vapor deposition techniques (MOCVD). On the other hand, our experimental conditions avoid this methane elimination and constitutes the first procedure employing distillation to isolate primary amine-TMA complexes.

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