Two Isomers with an Al4C8 Framework

Abstract

The co-condensation, by annealing from À 196 8C to room temperature, of the high-temperature species AlCl and 3-hexyne (EtCCEt) with an excess of toluene leads to the formation of the compound (AlCl´EtCCEt) 4 . Characterisation by X-ray analysis revealed the presence of two isomers in the same crystal: a dimeric 1,4-dialumina-2,5-cyclohexadiene and a 1,4,7,10-tetralumina-2,5,8,11-cyclododecatetraene. Both isomers exhibit aluminium ± olefin p-bonding, with the Al 4 entities present in a tetrahedral arrangement. The bonding in both isomers is discussed on the basis of ab initio calculations performed for model compounds.

Dialane with a Redox‐Active Bis‐amido Ligand: Unique Reactivity towards Alkynes

“…In complex 5 , the Al(1)C(38) and Al(2)C(37) bonds are slightly different (1.955(3) and 1.983(3) Å, respectively). The Al⋅⋅⋅Al separation in complex 5 (3.363 Å) falls in the range of their corresponding values in [Et(thf)Al] 2 (μ 2 ‐η 1 :η 1 ‐PhCCPh) 2 16a (3.472 Å) and [Cl(Et 2 O)Al] 2 (μ 2 ‐η 1 :η 1 ‐MeCCMe) 2 16c (3.335 Å). It is interesting to discuss the molecular features of compounds 1 – 7 from a standpoint of the steric factors by using a model of the solid angles of the ligand 17.…”

“…Some elongation of the C(37)C(38) bond (1.356(4) Å) in compound 5 compared to those in complexes 3 , 4 , 6 , and 7 (Table 1) may be explained by repulsion between the C(37) and C(38) atoms, which are both negatively charged in complex 5 . The structure of compound 5 can be further compared with the structures of complexes [Et(thf)Al] 2 (μ 2 ‐η 1 :η 1 ‐PhCCPh) 2 16a and [Cl(Et 2 O)Al] 2 (μ 2 ‐η 1 :η 1 ‐MeCCMe) 2 ,16c which also contain of 1,4‐dialumina‐2,5‐cyclohexadiene fragments. In these last two complexes, which both contain symmetrical alken‐1,2‐diyl ligands, the AlC bonds are virtually the same (1.985(2) and 1.959(2) Å, respectively).…”

Aluminium-mediated carbon–carbon coupling of an isonitrile

“…When smaller substituents -such as chloride or alkyl groups -are present at the aluminium centre, aluminacyclopropenes, the product of a [2+1] cycloaddition with an alkyne, are proposed (but not observed) as intermediate products. 6,7 These strained 3-membered rings dimerise to produce the ultimately isolated 1,4-dialuminacyclohexadienes (e.g. A, Fig.…”

“…1). 7 The reaction of Roesky's NacNacAl(I) compound with alkynes allows the isolation of aluminacyclopropenes such a B, [8][9][10] presumably stable against dimerisation because of steric hindrance and a four-coordinate aluminium centre. In some cases, alternative dimerisation products such as D have been observed, 11 which is proposed to result from the dimerisation of the unobserved (despite its extreme steric bulk) intermediate C.…”

Ring Expansion to 1‐Bromo‐1‐alumacyclonona‐2,4,6,8‐tetraene by Insertion of Two Alkyne Molecules into the AlC Bonds

“…Meanwhile, reductive elimination of [D 10 ]‐ 5 would afford [D 10 ]‐ 3 accompanied by the extrusion of the aluminum(I) species BrAl: ( 6 ) 13. 14 Although attempts to trap transient species 6 have been unsuccessful so far, it might react with the alkyne to afford unidentified organoaluminum compounds 15…”