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···(arene) π-bonding and Bi···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.