Linear Dimerization of Terminal Alkynes by Bis(tetramethylphenylcyclopentadienyl)titanium-Magnesium Hydride and Acetylide Complexes

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Title:Linear Dimerization of Terminal Alkynes by Bis(tetramethylphenylcyclopentadienyl)titanium-Magnesium Hydride and Acetylide Complexes
Creators:
Mach, Karel
Gyepes, Róbert
Horáček, Michal
Petrusová, Lidmila
Kubišta, Jiří
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 68, 10, pp. 1877-1896
Uncontrolled Keywords:Titanium, Dimerization, Hydrides, Homogeneous catalysis, Magnesium, Metallocenes, Alkynes, Crystal structure, ESR spectroscopy, Titanocene acetylide

Abstract

New tetramethylphenylcyclopentadienyl trinuclear titanocene hydride-magnesium hydride complexes [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>R)<sub>2</sub>(μ-H)<sub>2</sub>}<sub>2</sub>Mg], where R = Ph (<strong>1</strong>) or 4-fluorophenyl (FPh; <strong>2</strong>), the dinuclear [Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>Ph)[η<sup>5</sup>:η<sup>1</sup>{Ti:Mg}-C<sub>5</sub>Me<sub>4</sub>(<i>o</i>-C<sub>6</sub>H<sub>4</sub>)](μ-H)<sub>2</sub>Mg(THF)<sub>2</sub>] (<strong>3</strong>) and [Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>Ph)<sub>2</sub>(μ-H)<sub>2</sub>MgC(Me)=CHMe] (<strong>4</strong>) complexes, and the [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>Ph)<sub>2</sub>(η<sup>1</sup>-C≡CSiMe<sub>3</sub>)<sub>2</sub>}<sup>-</sup>{MgCl(THF)}<sup>+</sup>] (<strong>5</strong>) tweezer complex initiated the dimerization of (trimethylsilyl)ethyne (TMSE) or 1-hexyne (HXYN) to exclusively head-to-tail (HTT) dimers at 60 °C with the turnover number ranging from 300 to 500 mol alkyne per mol of the Ti complex. In contrast, all of them were inactive in the dimerization of <i>tert</i>-butylethyne (TBUE). Monitoring of reactions of the <strong>1</strong>-<strong>5</strong> complexes with the alkynes by electron spin resonance (ESR) method revealed a decay of the initial complexes <strong>1</strong>-<strong>5</strong> in the dimerizing systems with TMSE and HXYN or a conversion of complexes <strong>3</strong>, <strong>4</strong>, and <strong>5</strong> into the Ti(III) acetylide [Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>Ph)<sub>2</sub>(η<sup>1</sup>-C≡CCMe<sub>3</sub>)] (<strong>6</strong>) in systems with TBUE. The acetylide <strong>6</strong> also initiated the dimerization of TMSE and HXYN to HTT dimers only. This fact together with the absence of ESR signals of tweezer complexes and acetylides in the reacting hydride systems allow us to assume that the rate of conversion of complexes <strong>1</strong>-<strong>4</strong> to tweezer complexes is slower than the rate of dissociation of the tweezer complexes to give the acetylides which are apparently the ultimate catalytic species. Most of the evidence on the catalytic complexes has been obtained from ESR spectra which are reliably characteristic of each type of the complexes. Crystal structures of <strong>4</strong> and <strong>6</strong> were determined. <p>

Title:Linear Dimerization of Terminal Alkynes by Bis(tetramethylphenylcyclopentadienyl)titanium-Magnesium Hydride and Acetylide Complexes
Creators:
Mach, Karel
Gyepes, Róbert
Horáček, Michal
Petrusová, Lidmila
Kubišta, Jiří
Uncontrolled Keywords:Titanium, Dimerization, Hydrides, Homogeneous catalysis, Magnesium, Metallocenes, Alkynes, Crystal structure, ESR spectroscopy, Titanocene acetylide
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:68
Number:10
Page Range:pp. 1877-1896
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20031877UNSPECIFIED
ID Code:2158
Item Type:Article
Deposited On:06 Feb 2009 17:16
Last Modified:06 Feb 2009 16:16

Citation

Mach, Karel; Gyepes, Róbert; Horáček, Michal; Petrusová, Lidmila; Kubišta, Jiří (2003) Linear Dimerization of Terminal Alkynes by Bis(tetramethylphenylcyclopentadienyl)titanium-Magnesium Hydride and Acetylide Complexes. Collection of Czechoslovak Chemical Communications, 68 (10). pp. 1877-1896. ISSN 0010-0765

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