Assigning Hapticity to Cyclopentadienyl Derivatives of Antimony and Bismuth

The chelating diamide [Me2Si{NAr}(2)](2-) (Ar = 2,6-i-Pr2C6H3) has been used as an ancillary ligand in antimony and bismuth chemistry. In contrast to the monomeric antimony chloride compound Sb(Me2Si{NAr}(2)) Cl (1a), the bismuth derivative (1b) exists as a trimer in the solid state, linked by Bi center dot center dot center dot(arene) pi-bonding and Bi center dot center dot center dot Cl interactions. Compounds 1a,b are used as an entry point into rare antimony and bismuth compounds incorporating Cp and Cp* ligands. Reactions of the chlorides with LiCp and KCp* afford the organometallic species E(Me2Si{NAr}(2))-(C5R5) (2a, R = H, E = Sb; 2b, R = H, E = Bi; 3a, R = Me, E = Sb; 3b, R = Me, E = Bi). Variable-temperature NMR experiments indicate different fluxional processes occur in solution involving facile haptotropic shifts of the [C5R5](-) ring. Structural characterization of 2b and 3a,b reveals monomeric compounds in which the cyclopentadienyl-derived ligand adopts a low hapticity in the solid state.