Coordinative versatility of $C_2B_9H_11^{2-}$(dicarbollide) ligand has known to be stemmed from its divers hapticity. Especially, in the transition metal and main group element homoleptic sandwich type dicarbollyl complexes, the extent of the dicarbollyl cage slipping from the metal center increases as the electron density in d-orbital and the number of nuclear charge increases respectively. In these regards, the dicarbollyl sandwich complexes of group 12 elements would be interesting because they consist of boundary between transition metals and main group elements. But examples of this kind are not well established.
To pursue this subject in detail, a set of sandwich type examples [$M(C_2B_9H_11)_2$]$(PPN)_2$ㆍS(1: M=Zn, S=$0.5CH_3CN$; 2: M=Cd, S=DMF; 3: M=Hg, S=no solvate, PPN = bis(triphenylphosphoranylidene)ammonium) have been synthesized in high yield(1; 41.6%, 2; 54.3%, 3; 56.6%) by reacting $MCl_2$ with two fold amount of $Tl_2C_2B_9H_11$ and PPNCl in THF or THF/DMF. The isolated complexes were fully characterized by measure of various spectroscopy and a single crystal X-ray diffraction study.
In all these cases, the tendency of the dicarbollyl cage slipping in all three compounds is consistent with that found in earlier reported complexes. The unusual structural feature found is the asymmetric intermediate hapticity between $η^1$ and $η^2$.
