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.
Dong et al. (Fri,) studied this question.