Neutral and Anionic Antimony(III) Species Supported by a Bicyclic Guanidinate

Bicyclic guanidine 1,3,4,6,7,8‐hexahydro‐2 H ‐pyrimido[1,2‐ a ]pyrimidine (hppH) was investigated as a source of anionic or neutral ligand at antimony. Reaction of the in situ generated lithium guanidinate with SbCl 3 in a 1:1 or 2:1 ratio forms the expected metathesis products Sb(hpp) n Cl 3– n ( 1 , n = 1; 2 , n = 2). The molecular structures of 1 and 2 were determined by X‐ray diffraction, which shows chelating guanidinates and suggests the presence of a stereochemically active lone pair of electrons. The reaction of two equivalents of the neutral guanidine hppH with SbCl 3 proceeds via proton transfer between the hpp fragments, affording the ion pair [hppH 2 ][Sb(hpp)Cl 3 ] ( 3 ), where [Sb(hpp)Cl 3 ] – is an unusual example of a monometallic antimonate(III) anion. The molecular structure of 3 shows hydrogen bonding between two of the chlorides and the N H functionalities of the guanidinium cation.