Cis and trans rhenium hydride dinitrogen complexes from protonation reactions of Cp*Re(PMe(3))(2)(N-2)

The dinitrogen complex Cp*Re(PMe(3))(2)(N-2) (1) undergoes protonation at rhenium but not at the rhenium-bound dinitro(:en ligand under conditions described here. Protonation by using CF3CO2H, HBF4 . OEt(2), or CF3SO3H at 213 K afforded the respective rhenium hydride dinitrogen complexes cis-[Cp*ReH(N-2)(PMe(3))(2)][CF3CO2] (cis-2(CF3CO2)), cis-[Cp*ReH(N-2)-(PMe(3))(2)][BF4] (cis-2(BF4)), and cis-[Cp*ReH(N-2)(PMe(3))(2)][CF3SO3] (cis-2(CF3SO3). These complexes isomerized smoothly to the corresponding trans isomers as the temperature was raised to 273 K. The cis and trans isomers have been fully characterized by using a combination of IR and H-1, P-31, and N-15 NMR spectroscopy, with the dinitrogen ligand singly-labeled in either the Na or Ng positions. The trans isomers are all thermally unstable at room temperature, but trans-2(CF3CO2) is significantly more stable than its analogs, indicating that the counteranion may play a role in stabilizing these cationic rhenium hydride dinitrogen complexes.