Facile Synthesis of Aluminum‐Bridged [3,3,3]Cyclophanes by Hydroalumination

Abstract

The reaction of 1,3,5‐tris(3,3‐dimethyl‐1‐butinyl)benzene C6H3(C≡C–CMe3)3 with the dialkylaluminum hydrides HAl(CMe3)2 and HAl(CH2CMe3)2 gave the addition of one Al–H bond to each C–C triple bond (hydroalumination). Spontaneous condensation by the release of the corresponding trialkylaluminum derivatives afforded [3,3,3]cyclophane derivatives 6 and 7 in which three tricoordinate Al atoms are in the bridging positions between two functionalized benzene rings. The aluminum atoms behave as Lewis acids, and treatment with thf yielded adduct 6·3thf. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Hydroalumination and Hydrogallation Reactions with Tri(ethynyl)silanes – Generation of Compounds with up to Three Coordinatively Unsaturated Aluminium Atoms

“…Heteroadamantane cages with localised Ga–C bonds were isolated instead from the analogous reactions of gallium alkynides with dialkylgallium hydrides 7. Similar condensation reactions have been observed with oligoalkynes ( t BuC≡C) x C 6 H 6– x ( x = 2, 3) which gave compounds with a cyclophane‐type molecular structure 8,9. Steric shielding in the case of the bulky CH(SiMe 3 ) 2 substituent10 or coordinative saturation via bridging vinyl groups in the case of small substituents9 seem to prevent these reactions by stabilisation of the primary addition products.…”

The influence of halogen substituents on the course of hydrogallation and hydroalumination reactions

“…The pentafluoro compound F 5 C 6 C≡CSiMe 3 behaved similarly upon treatment with HGaCl 2 , eqn (4). A mixture of cis/trans isomers (cis-5 : trans-5) was formed with a molar ratio of 1 : 5 and the preferred formation of the trans addition product.…”

“…A different reaction course was observed when the dibromo compound 1,3-dibromo-2-trimethylsilylethynylbenzene was treated with HGaCl 2 , eqn (4). First, only the cis-addition product (cis-4) could be detected by 1 H NMR spectroscopy.…”

“…In the latter cases carbaalane clusters 2 or Ga 6 C 4 heteroadamantane cages 3 were isolated, while cyclophane type molecules with two and three Al or Ga atoms in the bridging positions resulted for tert-butylethynes. 4,5 Condensation reactions did not take place with sterically highly shielded dialkylaluminium hydrides [R = CH(SiMe 3 ) 2 ], 6 with terminal alkynes 7 and interestingly also with dialkylgallium hydrides bearing small alkyl groups (R = Et, nPr), 5 for which the substituent exchange may be prevented by strong intermolecular interactions between gallium and vinylic carbon atoms. The simple addition products have also been isolated with trimethylsilylethynes, C 6 H 6-x (C≡CSiMe 3 ) x .…”

Hydroalumination of dialkynylgermanes—synthesis of alkenyl–alkynylgermanes with intramolecular aluminium–carbon interactions

“…2 )-R 0 0 , are only transient species which give very fast secondary reactions via condensation and release of the corresponding trialkylelement derivatives. 2 Carbaalane clusters 3 or cyclophane-type molecules with up to three aluminium atoms bridging two benzene rings 4,5 are the most prominent products of these reactions. Condensation was prevented with very small alkyl groups attached to aluminium (caused by polymerization), 5 by steric shielding with very bulky substituents 6 or with trimethylsilylethyne derivatives.…”