Rh(I) complexes containing tris(pyrazolyl)amine and bis(pyrazolyl)amine ligands: synthesis and NMR studies

The tris(pyrazolyl)amine ligands: tris[2-(1-pyrazolyl)methyl]amine (tpma), tris [3,5-dimethyl-1-pyrazolyl)methyl]amine (tdma), tris[2-(1-pyrazolyl)ethyl]amine (tpea), tris[2-(3,5-dimethyl-1-pyrazolyl)ethyl]amine (tdea) and bis(pyrazolyl)amine ligands: bis[2-(1-pyrazolyl)ethyl]amine (bpea) and bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]amine (bdea) react with [RhCl(cod)]2 in presence of NaBF4 (tpma, tdma and bdea) or AgBF4 (tpea, tdea and bpea) to lead to [Rh(cod)L] (BF4) (L=tpma (1), tdma (2), bdea (3), tpea (4), tdea (5) and bpea (6)). These complexes have been characterised by elemental analyses, conductivity, IR, 1H and 13C NMR spectroscopy and liquid mass (with electrospray) spectrometry. The 1H NMR spectra of 1, 2 show the presence of two isomers in solution in a 3:1 ratio (coordination κ2 or κ3 type) in a thermodynamic equilibrium. The steric bulk of cyclo-octa-1,5-diene causes it to prefer the κ2 mode of bonding as majority. Similar to previous published results, complexes 4 and 5 exist in a sole form in solution (probably κ2 isomer). Finally, the complexes 3 and 6 are fluxional. A NMR study shows that this fluxional process is not frozen at 183 K.