Structural Studies of Piperidino‐Alanes with Halide, Amide and Hydride as further Ligands at Aluminum

Abstract Nine different derivatives of piperidino alanes of the general formula (CH 2 ) 5 N‐AlXY [X=Y=Cl ( 1 ), Br ( 2 ), I ( 3 ); X=(CH 2 ) 5 N, Y=Cl ( 4 ), Br ( 5 ), I ( 6 ); X=H, Y=Cl ( 7 ), Br ( 8 ), I ( 9 )] have been synthesized and compared with respect to their structures. All molecules form dimers with an Al 2 N 2 central cycle and aluminum and nitrogen atoms in distorted tetrahedral environments as determined from X‐ray diffraction. The three dihalide derivatives 1 , 2 and 3 have C 2h (2/m) symmetries in solution of which they maintain the Centro symmetry in the crystal lattice. The bis(piperidino) derivatives 4 , 5 and 6 have either C 1 (1) symmetry with the bridging piperidino cycles oriented in the same direction ( 4 , 5 ) or C i (ī) point symmetry as found for 6 (in solution at least one other isomer is present). Whereas the chlorine derivative 7 has crystallographic C i (ī) symmetry, the bromine 8 has almost C 2 and the iodine 9 crystallographic C 2 (2) point symmetry. In solution all derivatives 7 , 8 , 9 show equilibria between cis (C 2 ) and trans (C i ) isomeric forms ( 27 Al NMR). The longest Al−N bond lengths within the rings are found for 5 (1.969(4) Å) and the shortest for 8 (1.940(4) Å). The ratio of Al⋅⋅⋅Al to N⋅⋅⋅N non‐bonding distances in the almost square rings vary with the bulkiness of the terminal ligands at aluminum.