Synthesis and Calorimetric, Spectroscopic, and Structural Characterization of Isocyanide Complexes of Trialkylaluminum and Tri-tert-butylgallium

Abstract

Addition of tert-butylisocyanide or 2,6-dimethylphenylisocyanide to a solution of trialkylaluminum or trialkylgallium results in formation of complexes R(3)M·C≡N(t)Bu (M = Al, R = Me (1), Et (2), (i)Bu (3), (t)Bu (4); M = Ga, R = (t)Bu (9)) or R(3)M·C≡N(2,6-Me(2)C(6)H(3)) (M = Al, R = Me (5), Et (6), (i)Bu (7), (t)Bu (8); M = Ga, R = (t)Bu (10)), respectively. Complexes 1, 4, 5, and 8-10 are isolated as solids, whereas the triethylaluminum and triisobutylaluminum adducts 2, 3, 6, and 7 are viscous oils. Complexes 1-10 were characterized by NMR ((1)H, (13)C) and IR spectroscopies, and the molecular structures of 4, 5, and 8-10 were also determined by X-ray crystallography. The frequency of the C≡N stretch of the isocyanide increased by 58-91 cm(-1) upon complexation, consistent with coordination of the isocyanide as a σ donor. Enthalpies of complex formation for 1-10 were determined by isothermal titration calorimetry. Enthalpy data suggest the following order of decreasing Lewis acidity: (t)Bu(3)Al ≫ (i)Bu(3)Al ≥ Me(3)Al ≈ Et(3)Al ≫ (t)Bu(3)Ga. In the absence of oxygen and protic reagents, the reported complexes do not undergo insertion or elimination reactions upon heating their benzene-d(6) solutions to 80 °C.

Aluminium-mediated carbon–carbon coupling of an isonitrile

“…organolithiums). With simple alanes, coordination of isonitriles to the aluminium centre is reported, 15,16 though adducts do not transfer alkyl or aryl substituents to the isonitrile carbon. Cp 3 Al has also been observed to form stable adducts with isonitrile ligands.…”

Lewis acid–base adducts of Al(N(C6F5)2)3 and Ga(N(C6F5)2)3 – structural features and dissociation enthalpies

“…2), an Al–C distance of 2.047(2) Å and a longer Ga–C distance of 2.074(2) Å are observed. The corresponding literature known CN t Bu adducts Al(C 5 H 5 ) 3 ·CN t Bu, 32 Al( t Bu) 3 ·CN t Bu 33 and Ga( t Bu) 3 ·CN t Bu 33 exhibit longer metal carbon bond lengths. In contrast to the metal carbon distance, the C–N bond length in Ga(N(C 6 F 5 ) 2 ) 3 ·CN t Bu (1.137(3) Å) is slightly shorter than in the corresponding aluminum species (1.146(3) Å).…”

“…These C–N distances in the tert -butyl isocyanide adducts are similar to or slightly longer than in the three literature examples. 32,33…”

“…Dalton Transactions distances in the tert-butyl isocyanide adducts are similar to or slightly longer than in the three literature examples. 32,33 Despite its lower FIA value, the THF adduct of the Lewis acid GaCl 3 (FIA = 434 kJ mol −1 , 3 Ga-O: 1.919(3) Å) 34 shows a considerably shorter Ga-O distance than Ga(N(C 6 F 5 ) 2 ) 3 •THF (FIA = 472 kJ mol −1 , 10 Ga-O: 1.978(1) Å). Higher values were found for the THF adducts of the also less Lewis acidic Ga(C 6 F 5 ) 3 (FIA = 453 kJ mol −1 ), 3,35 Ga(CH 2 Ph) 3 36 and the sterically crowded GaPh 2 (Si(SiMe 3 ) 3 ).…”

Boron, aluminium, gallium, indium and thallium

“…Al(OC(CF 3 ) 3 ) 3 was used as a halide abstracting agent to form trityl salts and when coordinated to fluorinated alcohols formed Brønsted acids of sufficient acidity to protonate mesitylene and Et 2 O. 284 Isocyanide adducts of trialkylaluminium complexes were synthesised with no insertion reactivity observed; enthalpy data suggested the following order of Lewis acidity: tBu 3 Al c iBu 3 Al Z Me 3 Al E Et 3 Al c tBu 3 Ga. 285 AlCl 3 was shown to readily insert into Sn-C bonds of [{m-1,3-C 6 H 4 (PhPQS) 2 C}Sn] 2 . 286 The structures of AlX 3 Lewis acids (X = Cl, Br or I) were investigated in pyridine and H 2 O solution by NMR spectroscopy, X-ray diffraction and, for H 2 O and chloride, by molecular dynamic calculations.…”