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, H-1 and C-13 NMR spectroscopy and liquid mass (with electrospray) spectrometry. The H-1 NMR spectra of 1, 2 show the presence of two isomers in solution in a 3:1 ratio (coordination kappa(2) or kappa(3) type) in a thermodynamic equilibrium. The steric bulk of cyclo-octa-1,5-diene causes it to prefer the kappa(2) mode of bonding as majority. Similar to previous published results, complexes 4 and 5 exist in a sole form in solution (probably kappa(2) isomer). Finally. the complexes 3 and 6 are fluxional. A NMR study shows that this fluxional process is not frozen at 183 K. (C) 2004 Elsevier B.V. All rights reserved.