Hydrogallierungsreaktionen mit den Monoalkinen H5C6‐C≡C‐SiMe3 und H5C6‐C≡C‐CMe3 – cis/trans‐Isomerie und Substituentenaustausch

Hepp

et al. 2009

Eur J Inorg Chem

Self Cite

Dialkylaluminum hydrides R2Al–H (R = Me, Et, iBu, CH2tBu, tBu), reacted with tert‐butylethyne, H–C≡C–CMe3, by hydroalumination and formation of the corresponding vinylic compounds, R2Al–C(H)=C(H)–CMe3. The products are dimeric in the solid state with the negatively charged vinylic carbon atoms in the bridging positions and adopt usually a centrosymmetric structure with the C=C double bonds on different sides of the central Al2C2 heterocycle. Only with R = Me the C2v structure with the cis arrangement of the alkenyl groups was found. Complicated mixtures of isomeric substances were detected in solution. Quantum‐chemical calculations revealed a considerable charge separation in the C=C double bonds of the dimeric formula units. The α‐carbon atoms coordinated by both aluminum atoms show high negative NBO charges of about –1.0, while the β‐carbon atoms are almost uncharged (0.0 to –0.1). The rotational barriers decreased upon dimerization. Hence, the formation of such dimers may be the key step in the well‐known cis/trans isomerization process of hydroalumination and hydrogallation products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Section: Introductionmentioning

confidence: 99%

Treatment of Terminal Alkynes R–C≡C–H with Dialkylaluminum Hydrides: Hydroalumination versus Deprotonation

Hepp

et al. 2009

Eur J Inorg Chem

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“…The respective 3 JA C H T U N G T R E N N U N G (Si,H) coupling constants of the corresponding cis isomers were typically found to be around 20 Hz. [15][16][17] Solid-state structure determinations of 2 a and 2 c revealed the presence of dimeric molecules with four-coordinate gallium atoms and one terminal and two bridging chlorine atoms and confirmed the trans configuration of the vinyl substituent. [12] The alkylation of the Ga À Cl functionalities of 2 a and 2 b with two equivalents of tert-butyl lithium proceeded smoothly at À78 8C to give the alkyl derivatives 3 a and 3 b in moderate yields of 52 and 61 % (Scheme 1).…”

Section: Resultsmentioning

confidence: 80%

“…[16] The solution NMR spectra of 3 a-c are again indicative of the trans isomer as evident from the small 3 JA C H T U N G T R E N N U N G (Si,H) coupling constants ( % 11 Hz). The solid-state structure of 3 a (Figure 1) is similar to previously described compounds of that type.…”

Section: Resultsmentioning

confidence: 92%

“…The solid-state structure of 3 a (Figure 1) is similar to previously described compounds of that type. [15][16][17] The atom Ga1 is essentially planar and only 0.3 pm above the plane of the three adjacent carbon atoms (C1, C2, C3). There are additional long-range contacts to the ipso-and one ortho-C atom of two phenyl substituents (Ga1 À C101 337.1 pm, Ga1 À C106 307.0 pm, Ga1 À C121 341.3 pm, Ga1 À C122 356.0 pm), thereby resulting in a very distorted pentagonal bipyramidal arrangement around gallium.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Vinylgallium and Alkyllithium Compounds: Transmetalation and Generation of Oligolithium Cages

Kovert

Layh

et al. 2011

Chemistry A European J

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Vinylgallium compounds [C(6)H(6-n){(H)C=C(SiR(2) R')-GaR''(2)}(n ] (3, R=Ph, Me; R'=Ph, Me; R''=tBu, Et; n=1, 2) are easily accessible by hydrogallation of the corresponding alkynylbenzene derivatives with H-GaCl(2) and subsequent reaction with alkyllithium derivatives. Treatment of 3 with an excess amount of tert-butyl- or ethyllithium yielded by transmetalation and ortho-deprotonation of the aromatic rings the unprecedented solvent-free oligolithium cluster compounds [{(C(6)H(4)Li)HC=C(SiPh(3))Li}(2)(tBuLi)(2)] (4), [{(C(6)H(4)Li)HC=C(SiPh(2)Me)Li}(4)] (5) and [{(C(6)H(3)Li){HC=C(SiMe(3))Li}(2)}(3)] (6) in moderate yields. Their solid-state structures revealed the presence of unique molecular lithium clusters with 6, 8, or 9 lithium atoms that may be derived from two edge-sharing Li(4) tetrahedra (4), three Li(4) tetrahedra in a chain joined by two common edges (5) or a tricapped trigonal prism of lithium atoms (6).

“…Compounds 5 follow the expected trend with E-C(sp 2 ) bond lengths being shorter than the corresponding E-C(sp 3 ) distances. Surprisingly this trend is reversed in case of compound 6 probably caused by the increased steric bulk in these compound (c. f. [31,32]). Other bond lengths and an- Table 3.…”

Section: Resultsmentioning

confidence: 93%

Hydroalumination versus Deprotonation of Alkynes with Sterically Demanding Substituents

Zeitschrift Für Naturforschung B

Layh

Rhotert

et al. 2013

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Treatment of sterically highly shielded terminal alkynes, H-C≡C-aryl, with dialkylaluminium and dialkylgallium hydrides, R 2 E-H, afforded by hydrogen release dimeric dialkylelement alkynides with a four-membered E 2 C 2 heterocycle independent of the bulk of the aryl groups. A rare example of a monomeric alkynylaluminium compound was only obtained with very bulky CH(SiMe 3 ) 2 groups attached to the metal atoms and by salt elimination reaction. The steric shielding by the bulky aryl groups did not prevent condensation reactions. Hydroalumination of 1-(trimethylsilyl)-2-(2,6-dimethylphenyl)ethyne using Me 2 Al-H resulted in a divinyl compound by elimination of trimethylaluminium.