Neuartige Aluminium-haltige Ringsysteme: ein achtkerniges Strukturanalogon eines Calix[4]pyrrols

Gallium and indium hydrazides. Molecular and electronic structure of In[N(SiMe3)NMe2]3 and related compounds

Gallium and indium hydrazides, Ga[N(SiMe(3))NMe(2)](3) (1) and In[N(SiMe(3))NMe(2)](3) (2), were synthesized from the reactions of metal chlorides and Li[N(SiMe(3))NMe(2)]. Single crystal X-ray crystallographic analysis revealed that compound 2 was monomeric with trigonal planar geometries on the indium and the indium-bonded nitrogen atoms. The average In[bond]N distance of 2.078(3) A and the N[bond]In[bond]N[bond]N dihedral angles did not provide clear structural evidence of In[bond]N pi-bonding. The electronic absorption spectra of the indium hydrazido complex revealed transitions at significantly lower energies compared to those observed in the tris(amido) compounds, In[N(SiMe(3))(2)](3) (3) and In[N((t)Bu)(SiMe(3))](3) (4). The absorptions of the indium and gallium compounds were attributed to ligand-metal charge transfer transitions. Trends in the electronic transitions for compounds 2 and 3 calculated at the time-dependent density functional and configuration interaction including single excitations levels, both using a minimal basis set, were consistent with the experimental data, and Mulliken charge analyses support the assignment to ligand-to-metal charge transfer transitions. These calculations also demonstrated the presence of pi-bonding between the In and N p-orbitals, and an analogy is drawn to the frontier molecular orbitals of trimethylenemethane. The low-lying spectroscopic transition in 2, and thus its yellow color, results from mixing of the lone pair electrons on the beta-nitrogens of the hydrazido ligands with the HOMO of the InN(3) core.

Dialkylaluminum hydrazides derived from free hydrazine N2H4. Molecular Structures of [(MeC)2AlN2H3]2 and [(MeC)2Al]4(N2H2)2

The reaction of di(tert-butyl)aluminum hydride with hydrazine N2H4 afforded the hydrazide (Me3C)2AlN2H3, 1, by the release of elemental hydrogen. Compound 1 is a dimer in solution and in the solid state and possesses a six-membered Al2N4 heterocycle in a twist conformation with two intact N-N bonds. Further reaction of 1 with an excess of HAl(CMe3)2 yielded the tricyclic aluminum and nitrogen rich Al4N4 compound [(Me3C)2AlN2H2]2[Al(CMe3)2]2, 2, in which each N-N bond of a central six-membered Al2N4 ring similar to that of 1 is side-on-coordinated to an Al(CMe3)2 group. The structure of 2 may be interpreted as a dimer of the dialuminum hydrazide (Me3C)2Al-NH-NH-Al(CMe3)2.

Synthesis of aluminum hydrazides by hydroalumination of 2,3-diazabutadienes--formation of an Al4(N2)3 cage compound and an Al3(N2)3 macrocyclic ligand

Treatment of 1,1,4,4-tetramethyl-2,3-diazabutadiene with the alane adduct [AlH3(NMe2Et)] yielded the hydrazine derivative (AlH2)2-(AlH)2(N2iPr2)3 (1) by the hydroalumination of both C N double bonds. Compound 1 has a complicated cage structure formed by three hydrazido groups and four aluminium atoms. As a particularly interesting structural motif it contains a N-N group side-on-coordinated to one aluminium atom through its lone pairs of electrons. Sublimation of 1 gave a heterocubane-type compound (HAlNiPr)4 (2) by the complete cleavage of all N-N bonds, one face of which is bridged by weakly coordinated diisopropyldiazene with a N-N double bond. Repeated sublimation gave the pure, unsupported heterocubane molecule 3. Heating of the rough product of the reaction of alane and diazabutadiene to 90 degrees C in a closed vessel yielded another product Al(AlH2)3(N2iPr2)3 (4), which contains a cyclic chelating ligand formed by three hydrazido groups and three aluminium atoms. This heterocycle coordinates a fourth aluminum atom in the molecular center by close contacts to all six nitrogen atoms. A strongly flattened, distorted octahedral coordination sphere results for the inner metal atom.