Syntheses, Structures, and Surface Aromaticity of the New Carbaalane [(AlH)₆(AlNMe₃)₂(CCH₂R)₆] (R = Ph, CH₂SiMe₃) and a Stepwise Functionalization of the Inner and Outer Sphere of the Cluster

Abstract

The reaction of the acetylene RC triple bond CH (R = Ph, CH(2)SiMe(3)) with an excess of AlH(3).NMe(3) in boiling toluene leads to the carbaalane [(AlH)(6)(AlNMe(3))(2)(CCH(2)R)(6)] (R = Ph 1, CH(2)SiMe(3) 2) in good yield. Treatment of 2 with BCl(3) under varying conditions gives the chlorinated products [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] 3 and [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(2)Cl)(6)] 4, respectively. The latter clearly demonstrates that the cluster can be stepwise functionalized within the inner and outer sphere. The X-ray single-crystal structures of 1, 2, and 4 have been determined. All compounds have in common that the central core consists of a cluster having eight aluminum and six carbon atoms. The bonding properties in this cluster are described as a new manifestation of three-dimensional surface aromaticity. Each Al(4)C fragment of the cube is formed by four bonds with three electron pairs, thus leading to a strong delocalization of the electrons. A phenomenological modeling using a three-dimensional Hückel scheme with fitted parameters to reproduce the energies from ab initio calculations revealed that the orbital scheme localized at one Al(4)C fragment possesses an orbital sextet with a large HOMO-LUMO gap. This is in line with the criteria of aromaticity. The idea of aromaticity was sustained also by qualitative valence bond reasons enumerating the different resonance structures by means of graph theoretical methods.

Synthesis, characterization and reactivity of an imidazolin-2-iminato aluminium dihydride

“…To the best of our knowledge, the only related examples refer to the halogenation of Al-H moieties in carbaalane clusters employing the higher haloboranes. 65,66 Obviously, the direct conversion of an aluminium hydride complex with X 2 offers an alternative methodology for halogenation at the metal centre. For this procedure we found few reports in the literature merely reporting on respective iodinations.…”

A Threefold AlH2‐Coordinated Carbon Atom as Part of the First Carbaalanate

“…[5] No reactive intermediates such as RCH 2 C(AlH 2 ·NMe 3 ) 3 were detected in the reaction mixture.…”

“…[4] By the reaction of a terminal alkyne with 3 equivalents of AlH 3 ·NMe 3 in boiling toluene we obtained the carbaalane [(AlH) 6 -(AlNMe 3 ) 2 (CCH 2 R) 6 ] (R = Ph, CH 2 SiMe 3 ) in good yields. [5] However, the reaction of tBuC CH with AlH 3 ·NMe 3 under the same conditions resulted in traces of [(AlH) 6 -(AlNMe 3 ) 2 (CCH 2 tBu) 6 ], which could not be characterized unambiguously. As a result of the low boiling point of tBuC CH (37-38 8C), the compound evaporates from the mixture before any reaction takes place.…”

“…[5] Two lithium cations are each coordinated through hydride bridges to the neutral [tBuCH 2 C(AlH 2 ·NMe 3 ) 3 ] moiety in which three AlH 2 ·NMe 3 groups are bound covalently to one carbon atom. The three Al atoms are disordered with two different positions (~68 % for Al(A) and~32 % for Al(B)) for each Al atom (Figure 2).…”

Synthesis and electrochemical behavior of the ferrocenyl units assembled on imidoalane and carbaalane clusters

“…Solvents were purified according to conventional procedures and were freshly distilled prior to use. Compounds 4 [14,15], 5 [16,17], 8 [13,18], ferrocenylnitrile [19], ferrocenylacetylene [20,21] and AIH 3 ' NMe3 [22] were prepared as described in the literature. IR spectra were recorded on a Bio-Rad Digilab FTS7 spectrometer.…”