PUB - Publikationen an der Universität Bielefeld

Treatment of calcium bis(tetraethylaluminate) with the bidentate N-donor ligands tetramethylmethylenediamine (L = TMMDA), tetramethylethylenediamine (L = TMEDA) and N,N'-dimethylpiperazine (L = DMP) and the tridentate N-donor ligands 1,3,5-trialkyl-1,3,5-triazacyclohexane {L = cyclo-[N(R)CH2]3, R = Me (TMTAC), Cy (TCyTAC), tBu (TtBuTAC)} resulted in the formation of complexes of the formulae [Ca(AlEt4)2L]. These compounds were characterised by NMR spectroscopy and elemental analyses. Single crystals suitable for X-ray diffraction experiments were obtained from the TMMDA, DMP, TCyTAC and TMTAC complexes. In the case of TMTAC, the complex crystallises with two TMTAC ligands bonded to the Ca atom, [Ca(AlEt4)2(TMTAC)2], but in solution only one TMTAC ligand is bonded to the Ca atom. NMR spectroscopy at various temperatures shows the tetraethylaluminate units to be dynamically bonded in these compounds (i.e., they are found to be partially dissociated). This dynamic bonding situation avoids steric overcrowding and unlike related rare-earth metal compounds this behaviour inhibits further degradation reactions. The reaction of calcium bis(tetraethylaluminate) with the NH-functional diisopropylamine leads to its deprotonation and results in the formation of a dimeric calcium amide [(?2-AlEt4)2Ca(mu-NiPr2)2Ca(?2-AlEt4)2]. This compound was characterised by single-crystal X-ray diffraction, NMR spectroscopy and elemental analyses.