A nuclear magnetic resonance study of hydrogen bonding in tris(2-N-methylaminoethyl) borate and similar compounds

Devon W. Meek, Charles Jr Springer

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Tris(2-aminoethyl) borate, B(OCH2CH2NH2)3, and the analogous N-methylamino and N,N-dimethylamino compounds have been prepared by the transesterification of methyl borate with the appropriate 2-aminoethanol. The nuclear magnetic resonance spectra show that extensive association of the terminal amino groups occurs in pure tris(N-methylaminoethyl) borate and that this association can be broken apart by heating to 160° or by dissolution in polar organic solvents such as triethylamine or acetonitrile. In order to determine whether the association results from hydrogen bonding or internal B-N coordination, several model systems have been investigated. The spectra of NH2C2H5·BF3, piperidine·BF3, and (C6H5)2BO-CH2CH2NH 2 in acetonitrile contain very complicated NCH2 peaks and broad NH peaks which appear at low applied magnetic field (τ 5.26-5.56). The broadening of the NH peak in the boron-nitrogen adducts is attributed to the effect of the N14 quadrupole, whereas the complex splitting of the NCH2 multiplet is attributed to coupling with B11 in the dative bond with nitrogen and possibly with the nitrogen protons. The spectra of B(OCH2CH2NH2)3 and B(OCH2CH2NHCH3)3, on the other hand, show sharp NH peaks at somewhat higher applied magnetic fields (τ 7.84, 6.78) and contain two sharp triplets attributed to the two sets of methylene protons in the -O-CH2-CH2-N<units (τOCH2 6.26-6.55; τNCH2 7.23-7.57). The N-H peak of B(OCH2CH2NHCH3)3 appears as a sharp singlet in acetonitrile solutions owing to rapid exchange of the amine proton. Evidence is presented that the exchange is catalyzed by a trace (2CH2NHCH3)3.

Original languageEnglish (US)
Pages (from-to)445-450
Number of pages6
JournalInorganic Chemistry
Volume5
Issue number3
StatePublished - 1966
Externally publishedYes

Fingerprint

Borates
borates
Protons
Hydrogen bonds
Nitrogen
Nuclear magnetic resonance
Association reactions
nuclear magnetic resonance
acetonitrile
hydrogen
Magnetic fields
Ethanolamine
Boron
nitrogen
Transesterification
protons
Organic solvents
Amines
Ion exchange
Dissolution

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

A nuclear magnetic resonance study of hydrogen bonding in tris(2-N-methylaminoethyl) borate and similar compounds. / Meek, Devon W.; Springer, Charles Jr.

In: Inorganic Chemistry, Vol. 5, No. 3, 1966, p. 445-450.

Research output: Contribution to journalArticle

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abstract = "Tris(2-aminoethyl) borate, B(OCH2CH2NH2)3, and the analogous N-methylamino and N,N-dimethylamino compounds have been prepared by the transesterification of methyl borate with the appropriate 2-aminoethanol. The nuclear magnetic resonance spectra show that extensive association of the terminal amino groups occurs in pure tris(N-methylaminoethyl) borate and that this association can be broken apart by heating to 160° or by dissolution in polar organic solvents such as triethylamine or acetonitrile. In order to determine whether the association results from hydrogen bonding or internal B-N coordination, several model systems have been investigated. The spectra of NH2C2H5·BF3, piperidine·BF3, and (C6H5)2BO-CH2CH2NH 2 in acetonitrile contain very complicated NCH2 peaks and broad NH peaks which appear at low applied magnetic field (τ 5.26-5.56). The broadening of the NH peak in the boron-nitrogen adducts is attributed to the effect of the N14 quadrupole, whereas the complex splitting of the NCH2 multiplet is attributed to coupling with B11 in the dative bond with nitrogen and possibly with the nitrogen protons. The spectra of B(OCH2CH2NH2)3 and B(OCH2CH2NHCH3)3, on the other hand, show sharp NH peaks at somewhat higher applied magnetic fields (τ 7.84, 6.78) and contain two sharp triplets attributed to the two sets of methylene protons in the -O-CH2-CH2-N2 6.26-6.55; τNCH2 7.23-7.57). The N-H peak of B(OCH2CH2NHCH3)3 appears as a sharp singlet in acetonitrile solutions owing to rapid exchange of the amine proton. Evidence is presented that the exchange is catalyzed by a trace (2CH2NHCH3)3.",
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T1 - A nuclear magnetic resonance study of hydrogen bonding in tris(2-N-methylaminoethyl) borate and similar compounds

AU - Meek, Devon W.

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N2 - Tris(2-aminoethyl) borate, B(OCH2CH2NH2)3, and the analogous N-methylamino and N,N-dimethylamino compounds have been prepared by the transesterification of methyl borate with the appropriate 2-aminoethanol. The nuclear magnetic resonance spectra show that extensive association of the terminal amino groups occurs in pure tris(N-methylaminoethyl) borate and that this association can be broken apart by heating to 160° or by dissolution in polar organic solvents such as triethylamine or acetonitrile. In order to determine whether the association results from hydrogen bonding or internal B-N coordination, several model systems have been investigated. The spectra of NH2C2H5·BF3, piperidine·BF3, and (C6H5)2BO-CH2CH2NH 2 in acetonitrile contain very complicated NCH2 peaks and broad NH peaks which appear at low applied magnetic field (τ 5.26-5.56). The broadening of the NH peak in the boron-nitrogen adducts is attributed to the effect of the N14 quadrupole, whereas the complex splitting of the NCH2 multiplet is attributed to coupling with B11 in the dative bond with nitrogen and possibly with the nitrogen protons. The spectra of B(OCH2CH2NH2)3 and B(OCH2CH2NHCH3)3, on the other hand, show sharp NH peaks at somewhat higher applied magnetic fields (τ 7.84, 6.78) and contain two sharp triplets attributed to the two sets of methylene protons in the -O-CH2-CH2-N2 6.26-6.55; τNCH2 7.23-7.57). The N-H peak of B(OCH2CH2NHCH3)3 appears as a sharp singlet in acetonitrile solutions owing to rapid exchange of the amine proton. Evidence is presented that the exchange is catalyzed by a trace (2CH2NHCH3)3.

AB - Tris(2-aminoethyl) borate, B(OCH2CH2NH2)3, and the analogous N-methylamino and N,N-dimethylamino compounds have been prepared by the transesterification of methyl borate with the appropriate 2-aminoethanol. The nuclear magnetic resonance spectra show that extensive association of the terminal amino groups occurs in pure tris(N-methylaminoethyl) borate and that this association can be broken apart by heating to 160° or by dissolution in polar organic solvents such as triethylamine or acetonitrile. In order to determine whether the association results from hydrogen bonding or internal B-N coordination, several model systems have been investigated. The spectra of NH2C2H5·BF3, piperidine·BF3, and (C6H5)2BO-CH2CH2NH 2 in acetonitrile contain very complicated NCH2 peaks and broad NH peaks which appear at low applied magnetic field (τ 5.26-5.56). The broadening of the NH peak in the boron-nitrogen adducts is attributed to the effect of the N14 quadrupole, whereas the complex splitting of the NCH2 multiplet is attributed to coupling with B11 in the dative bond with nitrogen and possibly with the nitrogen protons. The spectra of B(OCH2CH2NH2)3 and B(OCH2CH2NHCH3)3, on the other hand, show sharp NH peaks at somewhat higher applied magnetic fields (τ 7.84, 6.78) and contain two sharp triplets attributed to the two sets of methylene protons in the -O-CH2-CH2-N2 6.26-6.55; τNCH2 7.23-7.57). The N-H peak of B(OCH2CH2NHCH3)3 appears as a sharp singlet in acetonitrile solutions owing to rapid exchange of the amine proton. Evidence is presented that the exchange is catalyzed by a trace (2CH2NHCH3)3.

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