An N-heterocyclic germylene with a versatile metal-binding pocket: insights into heterodinuclear bonding and...

We report the synthesis, isolation, and characterisation of an N-heterocyclic germylene (NHGe) derived from a two-electron reduced Mg-synthon of the redox-active ^dippNBA ligand. This NHGe features a vacant binding pocket capable of coordinating various metals, which enables the formation of heterobimetallic Ge-Zn and Ge-Mg complexes. Electronic structure calculations reveal that the Ge-Zn interactions are weak, whilst the interactions between the metals found for the heterodinuclear Ge-Mg complex are stronger. These findings highlight how the nature of the Ge-M interactions adapts to the electron density requirements of the metal occupying the redox-active binding pocket flanking the Ge(ii) centre. Notably, the Ge-Mg complex undergoes a 'Metallo-Diels-Alder' reaction with unsaturated C-C bonds, activating these bonds over the Ge centre and the ligand backbone - a transformation that does not proceed without Mg. This provides a compelling example of indirect cooperativity, where the Mg centre electronically stabilises a quadruply reduced ligand, upon which Ge engages in metal-ligand cooperative activation of C-C unsaturated bonds.