cis/trans Isomers of Dimeric Dialkylaluminum and Dialkylgallium Hydrazides

Abstract

The reaction of diethylaluminum hydride with the hydrazine derivatives 1-aminopyrrole and 1- aminopiperidine afforded the corresponding dialkylaluminum hydrazides (1 and 2) by the release of elemental hydrogen. Both products are dimeric in the solid state. While 1 adopts a cis arrangement of the pyrrole groups, a trans configuration was determined for the piperidine compound 2. Only 1 gives an equilibrium mixture of cis and trans isomers in solution. Similar compounds (3 and 4) were obtained by the treatment of the same hydrazines with di(tert-butyl)gallium hydride. Both products exhibit the trans configuration in the solid state, but interestingly only the piperidine derivative 4 shows a cis/trans equilibrium in solution.

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

“…The cis arrangement of substituents at E 2 X 2 heterocycles (E = Al, Ga, In) has been observed before in rare cases, in which bulky substituents forced this unusual configuration by a minimization of the steric stress in the respective molecules. [15] The cis configuration usually results in a relatively strong folding of the inner rings, which is 21°on average across the Al1···Al2 axis in 1. In contrast planar heterocycles were usually observed for the trans forms, and the strongest deviation was detected for compound 2 (fold angle 6.4°).…”

Aluminum, Gallium, and Indium Hydrazides and the Generation of Oligonuclear Element-Nitrogen Cages: Molecular Intermediates on the Way to Element Nitrides

“…The latter isomer was found to be present in the solid-state structure of the aluminum compound featuring a planar Al 2 N 2 ring . The cis form with a puckered central ring has so far only been verified in the compounds [Me 2 InN(H)N(H)CMe 3 ] 2 and [Et 2 AlN(H)NC 4 H 4 ] 2 . , The high prevalence of the trans form may be a result of the better packing of the planar molecules in the solid state. Probably because of the small energy differences, many of the hydrazides exist in solution as an equilibrium mixture of the two isomers ,,,,,,, and, in some cases, a five-membered ring. , This has complicated the characterization of these compounds by NMR spectroscopy.…”

“…17,35 The high prevalence of the trans form may be a result of the better packing of the planar molecules in the solid state. Probably because of the small energy differences, many of the hydrazides exist in solution as an equilibrium mixture of the two isomers 13,17,18,23,26,28,29,35 and, in some cases, a five-membered ring. 13,29 This has complicated the characterization of these compounds by NMR spectroscopy.…”

“…The products are monoanionic hydrazides, [N(H)N(H)R′] − (eq ), which in solution and the solid state have dimeric structures with bridging metal atoms. − ,,,− Dissociation to the monomeric formula unit required the addition of ether or tetrahydrofuran . Alternative methods for the synthesis of these hydrazides comprise the reaction of dialkylelement halides with lithium hydrazides, ,, the treatment of adducts, R 2 ClE←NH 2 N(H)R′, with butyllithium, ,, the reaction of dialkylelement hydrides with hydrazines, ,− an amine–hydrazide exchange reaction, and the reduction of diazene with a gallium(I) compound . The reactions of trialkylelement derivatives with hydrazines are clearly superior to other methods because the synthesis of the starting organoelement compounds requires additional steps, the reactions are less selective, the products form complexes with lithium, , and, in some cases, inorganic salts are formed as side products.…”

On the reactions of the tetraindium cluster In4[C(SiMe3)3]4: Insertion of the monomeric fragments InC(SiMe3)3 into chalcogen–chalcogen bonds

“…Molecular symmetry causes a planar heterocycle in 2, while the inner rings are strongly folded in 3 and 5 with angles between the normals of the respective InSe 2 planes of 41.06(3)°and 45.97(2)°, respectively. By this folding the steric repulsion between the bulky alkyl groups is considerably diminished, following the example of dimeric hydrazides which behave similarly [33,34]. However, the indium atoms approach to relatively short distances of 3.96 and 4.06 Å.…”