Si─Si Bonding in an Unsupported N‐Heterocyclic Silylene Dimer Stabilized by an Iminophosphorane‐Based Scorpionate Ligand Versus Head‐to‐Tail Coordination in the Sn and Pb Tetrylenes

N,N-chelating ligands disfavor element-element bonding in heavier alkene analogs of group 13 and group 14 elements. Here, we present a series of group 14 element(II) compounds of a new sterically demanding iminophosphorane-based scorpionate ligand. The molecular structures of the Si and Ge analogs form element-element bonded interactions in the solid state in a head-to-head fashion, whereas the Sn and Pb analogs form one-dimensional coordination polymers in a head-to-tail fashion. Analysis of the Si─Si bonding by experimental, for example, X-ray diffraction, and computational methods suggests that a significant unsupported bonding interaction is present and enabled by the ligand that can be easily perturbed by the ligand sterics, including dispersion, and broken by entropic effects.