Metallorganische Verbindungen, LVI<sup>1a)</sup> Kinetische Untersuchung der Isomerisierung von Tri‐tert.‐butyl‐ und Tri‐2‐propylaluminium

Lehmkuhl, Herbert; Olbrysch, Otto

doi:10.1002/jlac.197319730419

Cited by 28 publications

(13 citation statements)

References 15 publications

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“…Molecular weight measurements were made in CH 2 Cl 2 with the use of an instrument similar to that described by Clark . The synthesis of Al( t Bu) 3 was performed according to a modification of the literature method . AlMe 3 , AlEt 3 , Al( i Bu) 3 , and ( i Bu) 2 AlH were generously donated by Akzo Nobel.…”

Section: Methodsmentioning

confidence: 99%

Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Toward a Quantitative Measure of Steric Bulk

et al. 1999

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To develop an understanding of the factors that control the strength of the Lewis acidbase interactions in five-coordinate compounds of aluminum, dimeric dialkylaluminum compounds [R 2 Al{µ-O(CH 2 ) n ER′ x }] 2 (n ) 2, 3; ER′ x ) OR′, SR′, NR′ 2 ) have been prepared from AlR 3 and the appropriate substituted alcohol, thiol, or amine: [R The molecular structures of compounds 1, 2, 6, 7, 12, 13, 16, 18-22, and [Me 2 Al(µ-OCH 2 -CH 2 NMe 2 )] 2 have been determined by X-ray crystallography. The solution structures have been probed by 13 C NMR spectroscopy using the alkoxide derivatives, [R 2 Al(µ-O n Bu)] 2 , R ) t Bu (8), i Bu (9), and Et (10), as a comparison, which show that compounds 1-7 and 11-23 exist as an equilibrium mixture between the four-coordinate isomer and its five-coordinate isomer, where K eq ) [4-coord]/ [5-coord]. Factors that control the extent of this equilibrium and hence the coordination about aluminum include the steric bulk of the substituents at aluminum (R) and the Lewis base donor (R′), the basicity of the neutral donor group (ER′ x ), and the chelate ring size (as determined by n). The intramolecular bond dissociation energies (BDEs) of the Lewis base donor (ER′ x ), as determined by variable-temperature NMR spectroscopy, for compounds 1, 12, 15, 16, [Me 2 Al(µ-OCH 2 CH 2 OMe)] 2 , and [R 2 Al(µ-OCH 2 -CH 2 NMe 2 )] 2 (2.3-13.2 kJ‚mol -1 ) are significantly lower than observed for their fourcoordinate analogues, R 3 Al(ER′ x+1 ) (63.8-125.5 kJ‚mol -1 ). In addition, the relative donor ability (thioether > ether > amine) is the opposite of that expected. The similarity in BDE between compound 1 and 11 suggests that no cooperative effects are present. Ab initio calculations on the four-and five-coordinate isomers of the model compound [H 2 Al(µ-OCH 2 -CH 2 OH)] 2 indicate that the surprisingly weak fifth coordination ligation in [R 2 Al{µ-O(CH 2 ) n -ER′ x }] 2 is a consequence of significant steric hindrance between the aluminum alkyl groups (R) and the Lewis base donor group. A quantitative measure of the thermodynamic destabilization that occurs upon substitution of H with Me or t Bu is proposed on the basis of the derivation of the Lennard-Jones (12,6) potential from solution thermodynamic and X-ray structural data.

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Section: Methodsmentioning

confidence: 99%

Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Toward a Quantitative Measure of Steric Bulk

et al. 1999

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“…FESEM studies were performed on JEOL JSM-6320F field emission scanning microscope. The synthesis of Al( t Bu) 3 was performed according to the literature methods . Ethylene glycol was obtained from Aldrich and was used without further purification.…”

Section: Methodsmentioning

confidence: 99%

Reaction of Al(^tBu)₃ with Ethylene Glycol: Intermediates to Aluminum Alkoxide (Alucone) Preceramic Polymers

et al. 1999

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The reaction of Al(tBu)3 with ethylene glycol (HOCH2CH2OH) in hexane yields “alucone” polymers, [Al(tBu)2 x (OCH2CH2O)1.5 - x ] n (0.3 ≤ 2x ≤ 0.8), with the concurrent formation of [Al2(tBu)3(OCH2CH2O)(OCH2CH2OH)] (1). If the reaction is carried out in Et2O solution, then [Al3(tBu)5(OCH2CH2O)2] (2) may be isolated. The molecular structure of compound 1 consists of a dimer formed by the alkoxide termini of two ligands bridging the Al(tBu) and Al(tBu)2 units. The Al(tBu) moiety is chelated by the nonbridging oxygens of the glycolate ligands, one of which remains protonated. Compound 2 consists of two Al(tBu)2 units and two glycolate ligands forming a cryptand-like 10-membered heterocycle; the Al(tBu) unit is positioned capping the four oxygen atoms. As with the previously reported ethoxy-substituted alucone polymers, [Al(OR)2 x (OCH2CH2O)1.5 - x ] n , thermolysis of [Al(tBu)2 x (OCH2CH2O)1.5 - x ] n , results in the formation of η-alumina (η-Al2O3) as determined by XRD. This is in contrast to the formation of γ-Al2O3 from the thermolysis of alumoxanes, [Al(O)(OR) x (OH)1 - x ] n , and may be rationalized by the structural relationship of compounds 1 and 2, and hence the alucones, to Bayerite rather than the boehmite core observed for alumoxanes.

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“…Molecular weight measurements were made in CH 2 Cl 2 with the use of an instrument similar to that described by Clark . The syntheses of ( t Bu) 2 AlH and Al( t Bu) 3 were performed according to modification of the literature methods . Me 2 AlH and ( i Bu) 2 AlH were generously donated by Akzo Nobel.…”

Section: Methodsmentioning

confidence: 99%

Cleavage of Cyclodimethylsiloxanes by Dialkylaluminum Hydrides and the Nature of the Siloxyaluminum Products

et al. 1999

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The interaction of R 2 AlH with cyclic siloxanes leads to rupture of the silicon-oxygen framework and yields aluminum polysiloxides. The room-temperature reaction of R 2 AlH with (Me 2 SiO) 3 yields the asymmetrical siloxide compounds R 2 Al(µ-OSiMe 2 H)(µ-OSiMe 2 OSiMe 2 -H)AlR 2 , R ) t Bu (1), i Bu (2). In contrast, the reaction of ( t Bu) 2 AlH with (Me 2 SiO) 3 or (Me 2 -SiO) 5 in refluxing toluene yields [( t Bu) 2 Al(µ-OSiMe 2 H)] 2 (4), as does the reaction of Al( t Bu) 3 with (Me 2 SiO) 3 . Me 2 Al(µ-OSiMe 2 H)(µ-OSiMe 2 OSiMe 2 H)AlMe 2 (3) is formed from the reaction of Me 2 AlH with (Me 2 SiO) 3 in hexane when using a reagent Si:Al ratio of 0.5; higher Si:Al ratios result in the formation of the siloxide-bridged compound Me 2 Al(µ-OSiMe 2 H)AlMe 2 -(µ-OSiMe 2 O)Me 2 Al(µ-OSiMe 2 H)AlMe 2 (5). The asymmetrical polysiloxide compound ( t Bu) 2 Al-(µ-OSiMe 2 H)(µ-OSiMe 2 OSiMe 2 OSiMe 2 H)Al( t Bu) 2 (6) is formed from the reaction of ( t Bu) 2 AlH with (Me 2 SiO) 4 , while compound 5 and its isobutyl analogue (7) are formed with Me 2 AlH and ( i Bu) 2 AlH, respectively. Reaction of R 2 AlH with (Me 2 SiO) 5 yields the siloxide-bridged compounds R 2 Al(µ-OSiMe 2 H)AlR 2 (µ-OSiMe 2 OSiMe 2 O)R 2 Al(µ-OSiMe 2 H)AlR 2 , R ) t Bu (8) and i Bu (9). If the reaction of ( t Bu) 2 AlH with (Me 2 SiO) 5 is carried out in the presence of THF, then ( t Bu) 2 Al(µ-OSiMe 2 H)Al( t Bu) 2 (µ-OSiMe 2 OSiMe 2 O)Al( t Bu) 2 (THF) (10) may be isolated. The reaction of Me 2 AlH with (Me 2 SiO) 5 yields compound 5. The symmetric siloxide [( t Bu) 2 Al-(µ-OSiMe 3 )] 2 ( 11) is formed from the reaction of ( t Bu) 2 AlH with (Me 3 Si) 2 O. The reaction of the noncyclic siloxane Me 3 Si(OSiMe 2 ) 2 OSiMe 3 yields a mixture of ( t Bu) 2 Al(µ-OSiMe 2 H)(µ-OSiMe 3 )Al( t Bu) 2 ( 12) and ( t Bu) 2 Al(µ-OSiMe 2 H)(µ-OSiMe 2 OSiMe 3 )Al( t Bu) 2 (13). A combination of 1 H, 13 C, 27 Al, and 29 Si NMR allow for characterization of all compounds. In addition, the 29 Si NMR spectra of compounds 1-3 and 6 exhibit unusual 3 J(Si-H) coupling (1.0 Hz), and the Al 2 O 2 core is found to exhibit a large deshielding effect on adjacent silicon. The molecular structures of compounds 1, 4, 8, 10, 11, and 12 have been determined by X-ray crystallography. The reaction pathway for the cleavage of polysiloxanes is discussed. * To whom correspondence should be addressed (http://python. rice.edu/∼arb/Barron.html).(1) (a) Rice University. (b) University of Houston. (c) Universita ¨t Go ¨ttingen.(2) Jenkner, H.

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Metallorganische Verbindungen, LVI^1a) Kinetische Untersuchung der Isomerisierung von Tri‐tert.‐butyl‐ und Tri‐2‐propylaluminium

Cited by 28 publications

References 15 publications

Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Toward a Quantitative Measure of Steric Bulk

Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Toward a Quantitative Measure of Steric Bulk

Reaction of Al(^tBu)₃ with Ethylene Glycol: Intermediates to Aluminum Alkoxide (Alucone) Preceramic Polymers

Cleavage of Cyclodimethylsiloxanes by Dialkylaluminum Hydrides and the Nature of the Siloxyaluminum Products

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Metallorganische Verbindungen, LVI1a) Kinetische Untersuchung der Isomerisierung von Tri‐tert.‐butyl‐ und Tri‐2‐propylaluminium

Cited by 28 publications

References 15 publications

Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Toward a Quantitative Measure of Steric Bulk

Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Toward a Quantitative Measure of Steric Bulk

Reaction of Al(tBu)3 with Ethylene Glycol: Intermediates to Aluminum Alkoxide (Alucone) Preceramic Polymers

Cleavage of Cyclodimethylsiloxanes by Dialkylaluminum Hydrides and the Nature of the Siloxyaluminum Products

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Metallorganische Verbindungen, LVI^1a) Kinetische Untersuchung der Isomerisierung von Tri‐tert.‐butyl‐ und Tri‐2‐propylaluminium

Reaction of Al(^tBu)₃ with Ethylene Glycol: Intermediates to Aluminum Alkoxide (Alucone) Preceramic Polymers