Synthesis of tricyclic 1,4-dihydro-1,4-phosphagermines - trying to establish molecular fencing of reactive centers.

Novel tricyclic 1,4-dihydro-1,4-phosphagermines (3a and 4a) were synthesised from Ge(NR)-bridged 1,3-imidazole-2-thione derivative 2a; all structures were crystallographically confirmed. In going from rather small alkyl substituents (Me, Bu) at the nitrogen centers of the 1,3-imidazole-2-thione units to sterically more demanding R = Mes and changing the employed Ge reagent from (RN)GeCl to RNGeCl we achieved access to mixed functional bis(1,3-imidazole-2-thione)-substituted germanium derivative 2c. The latter was treated with MeLi and, subsequently, with PCl to yield a pentacyclic P,Ge-heterocycle (5); its formation was rationalized using DFT theoretical calculations.