1,4-Bis(4-nitrosophenyl)piperazine: novel bridging ligand in dinuclear complexes of rhodium(III) and iridium(III)

The synthesis, spectroscopic characterization and crystal structures of the first 1,4-bis(4-nitrosophenyl)-piperazine (BNPP) (4) bridged dinuclear complexes of rhodium(III) and iridium(III) are presented. The reaction of the mu(2)-halogenido-bridged dimers [(eta(5)-C5Me5)IrX2](2) [X = Cl (5a), Br (5b), I (5c)] and [(eta(5)-C5Me5)RhCl2](2) (6a) with 4 yields the dinuclear complexes [(eta(5)-C5Me5)IrX2](2)-BNPP (7a-c) and [(eta(5)-C5Me5)RhCl2](2)-BNPP (8a). All new compounds were characterized by their NMR, IR and mass spectra. The X-ray structure analyses of the obtained half-sandwich complexes revealed a slightly distorted pseudo-octahedral configuration ("three-legged pianostool") for the metal(III) centers. The bridging BNPP ligand is sigma-N coordinated by both nitroso groups and shows different conformations of the piperazine ring depending on the solvent used for crystallization. Moreover the crystal structures of 1,4-bis(4-nitrosophenyl) piperazine (4) and its precursor 1,4-diphenylpiperazine (3) are reported.