(Hydrotris(3,5-dimethylpyrazolyl)borato)niobium alkyne complexes: Dichloro and dialkyl derivatives and formation of a butadienyl complex with an α-agostic interaction

Michel Etienne, Fabienne Biasotto, René Mathieu, Joseph L. Templeton

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Abstract

A high-yield one-pot synthesis of Tp*NbCl2(alkyne) is described [Tp* = hydrotris(3,5-dimethylpyrazolyl)borate; alkyne = PhC≡CCH3 (1a), PhC=CCH2CH3 (1b), PhC≡CCH2CH2-CH3 (1c), CH3C=CCH3 (1d), PhC=CPh (1e)]. It involves treatment of NbCl3(DME) (DME = 1,2-dimethoxyethane) with first an alkyne and then with KTp*. The dimethyl derivatives Tp*Nb(CH3)2(alkyne) (alkyne = PhC≡CCH3 (2a), PhC≡CCH2CH3 (2b), PhC≡CCH2CH2CH3 (2c)) and the dibenzyl complex Tp*Nb(CH2Ph)2(PhC≡CCH3) (3a) have been obtained from the appropriate dichloro complex and 2 equiv of either methyllithium or benzylmagnesium chloride, respectively. These 16-electron niobium(III) d2 complexes, 1a-e, 2a-c, and 3a, have been characterized spectroscopically. In all cases the alkyne is shown to occupy the molecular mirror plane. The barrier to alkyne rotation is high and could be measured only in the case of Id (68 kJ mol-1 at 358 K). On the basis of qualitative arguments, the structure of these complexes is basically governed by steric interactions. A comparison with the isoelectronic cyclopentadienyl derivatives is provided. When 1a is treated with 2 equiv of ethylmagnesium chloride, the formal dehydrogenation of an ethyl group results in the alkyne-coupled product Tp*Nb(CH2CH3)[C(Ph)C(CH3)CHCH 2] (4a), which has been spectroscopically characterized. 1H and 13C NMR data suggest that an α-agostic interaction is present in the ethyl group in this complex.

LanguageEnglish (US)
Pages1106-1112
Number of pages7
JournalOrganometallics
Volume15
Issue number4
DOIs
StatePublished - Feb 20 1996

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Niobium
Alkynes
alkynes
niobium
methylidyne
Derivatives
interactions
Chlorides
Borates
Dehydrogenation
chlorides
Mirrors
Nuclear magnetic resonance
dehydrogenation
borates

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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(Hydrotris(3,5-dimethylpyrazolyl)borato)niobium alkyne complexes : Dichloro and dialkyl derivatives and formation of a butadienyl complex with an α-agostic interaction. / Etienne, Michel; Biasotto, Fabienne; Mathieu, René; Templeton, Joseph L.

In: Organometallics, Vol. 15, No. 4, 20.02.1996, p. 1106-1112.

Research output: Contribution to journalArticle

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title = "(Hydrotris(3,5-dimethylpyrazolyl)borato)niobium alkyne complexes: Dichloro and dialkyl derivatives and formation of a butadienyl complex with an α-agostic interaction",
abstract = "A high-yield one-pot synthesis of Tp*NbCl2(alkyne) is described [Tp* = hydrotris(3,5-dimethylpyrazolyl)borate; alkyne = PhC≡CCH3 (1a), PhC=CCH2CH3 (1b), PhC≡CCH2CH2-CH3 (1c), CH3C=CCH3 (1d), PhC=CPh (1e)]. It involves treatment of NbCl3(DME) (DME = 1,2-dimethoxyethane) with first an alkyne and then with KTp*. The dimethyl derivatives Tp*Nb(CH3)2(alkyne) (alkyne = PhC≡CCH3 (2a), PhC≡CCH2CH3 (2b), PhC≡CCH2CH2CH3 (2c)) and the dibenzyl complex Tp*Nb(CH2Ph)2(PhC≡CCH3) (3a) have been obtained from the appropriate dichloro complex and 2 equiv of either methyllithium or benzylmagnesium chloride, respectively. These 16-electron niobium(III) d2 complexes, 1a-e, 2a-c, and 3a, have been characterized spectroscopically. In all cases the alkyne is shown to occupy the molecular mirror plane. The barrier to alkyne rotation is high and could be measured only in the case of Id (68 kJ mol-1 at 358 K). On the basis of qualitative arguments, the structure of these complexes is basically governed by steric interactions. A comparison with the isoelectronic cyclopentadienyl derivatives is provided. When 1a is treated with 2 equiv of ethylmagnesium chloride, the formal dehydrogenation of an ethyl group results in the alkyne-coupled product Tp*Nb(CH2CH3)[C(Ph)C(CH3)CHCH 2] (4a), which has been spectroscopically characterized. 1H and 13C NMR data suggest that an α-agostic interaction is present in the ethyl group in this complex.",
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N2 - A high-yield one-pot synthesis of Tp*NbCl2(alkyne) is described [Tp* = hydrotris(3,5-dimethylpyrazolyl)borate; alkyne = PhC≡CCH3 (1a), PhC=CCH2CH3 (1b), PhC≡CCH2CH2-CH3 (1c), CH3C=CCH3 (1d), PhC=CPh (1e)]. It involves treatment of NbCl3(DME) (DME = 1,2-dimethoxyethane) with first an alkyne and then with KTp*. The dimethyl derivatives Tp*Nb(CH3)2(alkyne) (alkyne = PhC≡CCH3 (2a), PhC≡CCH2CH3 (2b), PhC≡CCH2CH2CH3 (2c)) and the dibenzyl complex Tp*Nb(CH2Ph)2(PhC≡CCH3) (3a) have been obtained from the appropriate dichloro complex and 2 equiv of either methyllithium or benzylmagnesium chloride, respectively. These 16-electron niobium(III) d2 complexes, 1a-e, 2a-c, and 3a, have been characterized spectroscopically. In all cases the alkyne is shown to occupy the molecular mirror plane. The barrier to alkyne rotation is high and could be measured only in the case of Id (68 kJ mol-1 at 358 K). On the basis of qualitative arguments, the structure of these complexes is basically governed by steric interactions. A comparison with the isoelectronic cyclopentadienyl derivatives is provided. When 1a is treated with 2 equiv of ethylmagnesium chloride, the formal dehydrogenation of an ethyl group results in the alkyne-coupled product Tp*Nb(CH2CH3)[C(Ph)C(CH3)CHCH 2] (4a), which has been spectroscopically characterized. 1H and 13C NMR data suggest that an α-agostic interaction is present in the ethyl group in this complex.

AB - A high-yield one-pot synthesis of Tp*NbCl2(alkyne) is described [Tp* = hydrotris(3,5-dimethylpyrazolyl)borate; alkyne = PhC≡CCH3 (1a), PhC=CCH2CH3 (1b), PhC≡CCH2CH2-CH3 (1c), CH3C=CCH3 (1d), PhC=CPh (1e)]. It involves treatment of NbCl3(DME) (DME = 1,2-dimethoxyethane) with first an alkyne and then with KTp*. The dimethyl derivatives Tp*Nb(CH3)2(alkyne) (alkyne = PhC≡CCH3 (2a), PhC≡CCH2CH3 (2b), PhC≡CCH2CH2CH3 (2c)) and the dibenzyl complex Tp*Nb(CH2Ph)2(PhC≡CCH3) (3a) have been obtained from the appropriate dichloro complex and 2 equiv of either methyllithium or benzylmagnesium chloride, respectively. These 16-electron niobium(III) d2 complexes, 1a-e, 2a-c, and 3a, have been characterized spectroscopically. In all cases the alkyne is shown to occupy the molecular mirror plane. The barrier to alkyne rotation is high and could be measured only in the case of Id (68 kJ mol-1 at 358 K). On the basis of qualitative arguments, the structure of these complexes is basically governed by steric interactions. A comparison with the isoelectronic cyclopentadienyl derivatives is provided. When 1a is treated with 2 equiv of ethylmagnesium chloride, the formal dehydrogenation of an ethyl group results in the alkyne-coupled product Tp*Nb(CH2CH3)[C(Ph)C(CH3)CHCH 2] (4a), which has been spectroscopically characterized. 1H and 13C NMR data suggest that an α-agostic interaction is present in the ethyl group in this complex.

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