Unexpected influence of the counteranion fin the κ2 vs κ3 hapticity of polydentate N-donor ligands in [RhI(N-ligand)L2]+ complexes

A study of the complexes [Rh(N-ligand)L-2](+) in which N-ligand is bis(1-pyrazolylmethyl)ethylamine and L are cyclooctadiene or carbonyl ligands is presented. The presence of three nitrogen donor atoms opens the possibility that the N-ligand acts as a kappa(2) or a kappa(3) ligand. Experimental results show that it is coordinated in a kappa(3) coordination mode in the solid state, but both isomers coexist in solution. Theoretical calculations have been carried out to analyze the factors that determine the choice of the hapticity. The reproduction of the experimental stabilities requires the explicit consideration of the counteranion in the calculation. The transition state for the interconversion of kappa(3) and kappa(2) isomers has been located. The process takes place in one step, but involves simultaneous decoordination and inversion of the apical aminic nitrogen. A theoretical study of the hapticity of the related tris(pyrazolyl)borate complexes is also presented and compared with the results found in our system.