Tetrarhena-heterocycle from the palladium-catalyzed dimerization of Re2(CO)8(μ-SbPh2)(μ-H) exhibits an unusual host-guest behavior.

The six-membered heavy atom heterocycles Re(2)(CO)(8)(μ-SbPh(2))(μ-H), 5, and PdRe(2)(CO)(8)(μ-SbPh(2))(μ-H), 7, have been prepared by the palladium-catalyzed ring-opening cyclo-dimerization of the three-membered heterocycle Re(2)(CO)(8)(μ-SbPh(2))(μ-H), 3. The palladium atom that lies in the center of the heterocycle 7 was removed to yield 5. The palladium removal was found to be partially reversible leading to an unusual example of host-guest behavior. A related dipalladium complex Pd(2)Re(4)(CO)(16)(μ(4)-SbPh)(μ(3)-SbPh(2))(μ-Ph)(μ-H)(2), 6, was also formed in these reactions of palladium with 3.