Coordination Complexes of Bismuth Triflates with Tetrahydrofuran and Diphosphine Ligands

The reaction of CH3OSO2CF3 (MeOTf) with BiBr3 in tetrahydrofuran
(THF) yields (THF)2BiBr2(OTf) (1), which is converted to (dmpe)­BiBr2(OTf) (2Br) upon displacement of the THF ligands with bis­(dimethylphosphino)­ethane
(dmpe). The chloride derivatives (dmpe)­BiCl2(OTf) (2Cl) and (dmpe)­BiCl­(OTf)2 (3) are
obtained from the reaction of BiCl3 and dmpe with 1 and
2 equiv of Me3SiOSO2CF3 (TMSOTf),
respectively. The complexes readily decompose in solution to give
elemental bismuth and a mixture of products. The solid-state structures
reveal dimeric units bridged by both triflate O–S–O
interactions and weak Bi–X–Bi interactions (X = Cl,
Br). Comparison of the solid-state structures illustrates that both
cis and trans configurations of halides are possible in complexes
of the form L2BiX2(OTf), depending upon the
denticity of the ligand. The experimentally observed configurations
are consistent with minima calculated at the MP2 level for the triflate-free
cations in the gas phase. Examination of the MP2-calculated electronic
structure of 3 reveals the presence of low-lying π-type
orbitals that may result in Z-type ligand activity. However, the attempted
coordination of 3 with the electron-rich metal center
in K2PdCl4, via metal-to-ligand back-donation,
leads instead to halide abstraction, giving [(dmpe)2Pd]­[(CH3CN)2Bi2Cl6(OTf)2] (8). The anion in 8 consists of two octahedral
bismuth environments bridged along one edge by two triflate anions.
The results illustrate new coordination chemistry for bismuth.