Eine kettenförmige η5-Cp*Bi-Verbindung mit 11fach koordiniertem Bismut

C–F bond activation by pentamethylcyclopentadienyl-aluminium(i): a combined experimental/computational exercise

Although (AlCp*)₄ is one of the longest known stable aluminium(i) compounds, it still has surprising reactivities in store as illustrated by the ability to break strong C–F bonds.

Bis(η(5)-penta-methyl-cyclo-penta-dien-yl)aluminium tetra-bromido-aluminate

The title compound, [Al(C₁₀H₁₅)₂][AlBr₄], was formed during the reduction of a mixture of Cp*AlBr₂ and AlBr₃. The Al^III atoms of the two crystallographically independent cations each lie on an inversion center, and the [AlBr₄]⁻ anions are on general positions. At 123 K, the structure exhibits disorder in two of the Br atoms of the [AlBr₄]⁻ ion, with a ratio occupancy of 0.733 (6): 0.267 (3). In the crystal, there is possible weak hydrogen bonding between some methyl groups and Br atoms. The interactions link the moieties in a three-dimensional array.

Anisotropic NMR interaction tensors in the decamethylaluminocenium cation

Solid-state NMR experiments, analytical and numerical simulations of solid NMR powder patterns, ab initio self-consistent field and hybrid density functional theory calculations, and single-crystal X-ray diffraction are used to characterize the molecular structure and anisotropic NMR interaction tensors in the bis(pentamethylcyclopentadienyl)aluminum cation, [Cp(2)Al](+). This highly symmetric main group metallocene has a structure analogous to that of ferrocene and the cobaltocenium cation. The single-crystal X-ray diffraction structure is reported for [Cp(2)Al][AlCl(4)]. Solid-state (27)Al[(1)H] magic-angle spinning and static NMR experiments are used to study the aluminum chemical shielding and electric field gradient tensors, revealing axial symmetry in both cases with a large chemical shielding span of Omega = 83(3) ppm and a small nuclear quadrupole coupling constant, C(Q)((27)Al) = 0.86(10) MHz. Carbon-13 CPMAS NMR experiments in combination with ab initio calculations and simulations of the effects of chemical exchange on (13)C static powder patterns reveal dynamic rotation of rings and suggest a low internal rotational barrier for this process. Theoretical computations of interaction tensors using the Gaussian 98 and Amsterdam Density Functional software packages are in good agreement with experiment and lend insight into the molecular origin of these NMR interactions. Orientations of the NMR tensors determined from theory, the large chemical shielding span, and the very small value of C(Q)((27)Al) can all be rationalized in terms of the high molecular symmetry.