Heterobimetallic complexes stabilized by the PN macrocyclic ligand system: synthesis and reactivity of a rhodium-copper system that activates molecular hydrogen.

The synthesis and reactivity of the bimetallic rhodium-copper complex, Rh(COE)[PN]Cu, which is stabilized by the PN macrocycle, is reported. In the solid state, the rhodium and copper centers are on opposite sides of the macrocyclic ring with the Cu(I) in a linear environment and the Rh(I) in a square planar array. However, in solution a very symmetrical structure is suggested on the basis of the H NMR data, which is consistent with at least two separate fluxional processes, rotation of the cyclooctene unit and movement of the Rh(I) unit between the two amido donors. Addition of H to Rh(COE)[PN]Cu results in the formation of ([PNH]RhH(μ-H)Cu) hydrogenation of the coordinated cyclooctene unit, oxidative addition of H to the rhodium center and hydrogenolysis of the copper amido unit. Monitoring the reaction of H by NMR spectroscopy indicated the formation of a number of intermediates which suggests hydrogenolysis of the copper amido linkage occurs to generate CuH in some form, along with Rh(COE)[PNH], which is converted to Rh(H)[PNH] by hydrogenation of the cyclooctene, which then recombines with the CuH present to generate the final product. Deuteration studies indicate that there is considerable H/D scrambling in the cyclooctane produced that we attribute to reversible beta-elimination, migratory insertion steps.