This PhD thesis addresses two main topics. The synthetic chapter reports on the isomerization and oligomerisation of Lewis acid/base-stabilized phosphanylalanes. NMR investigations - together with theoretical computations performed by Prof. Alexey Y. Timoshkin (University of St. Petersburg) - gave insight into the amine exchange in four-membered aluminium-phosphorus hetero-ring systems. The combination of analytical and computational methods also allowed the detailed clarification of the successive oligomerization at, for example, the tungsten pentacarbonyl- and trimethylamine-stabilized derivative. Furthermore, ethyldimethylamine was introduced as a new Lewis base and an unprecedented structural motif for aluminium phosphorus compounds was described. Finally, the reactivity of Lewis acid free derivatives of phosphanylalanes was explored and the scope was widened to stiba- and bismaboranes. In addition to the synthetic results, 132 crystal structures were determined. Crucial problems in crystallography are reported using selected examples, including: disorder, twinning, space group problems, solvent treatment and a modulated structure.