Synthesis and dynamic behaviour of rhodium(I) complexes containing the di-2-pyridyl sulphide ligand

Abstract

The complexes [Rh(cod)(dps)]X 1(cod = cycloocta-1,5-diene; dps = di-2-pyridyl sulphide; X = BF₄, PF₆ or ClO₄) has been prepared by reaction of dps and AgX with [{Rh(µ-Cl)(cod)}₂]; [Rh(CO)₂(dps)]X 2 can be prepared by a similar route but higher yields are obtained by bubbling CO through a CH₂Cl₂ solution of 1. Triphenyl-phosphine or -arsine easily replaces a molecule of CO in 2 to give [Rh(CO)(PPh₃)(dps)]X 3 or [Rh(CO)(AsPh₃)(dps)]X 4. These compounds have been characterized by usual spectroscopic techniques which indicate a N, N-inside conformation for the chelate dps ligand. The reaction of [{Rh(µ-Cl)(cod)}₂] with dps gives rise to stoichiometry-, concentration-, solvent- and temperature-dependent equilibria in which the starting materials, the binuclear complex [{Rh(cod)Cl}₂(µ-dps)]5a, [Rh(cod)(dps)]⁺, [Rh(cod)Cl₂]^– and Cl^– are involved. Complex 5a and [Rh(cod)(dps)][Rh(cod)Cl₂]5b can be isolated as solids whereas [Rh(cod)(dps)]Cl is present only in solution. Conductivity measurements and electronic spectra indicate that the ionic species are stabilized in methanol, whereas in CH₂Cl₂ the starting materials and binuclear species dominate at low and higher concentration respectively. Proton and ¹³C NMR spectra, in CD₂Cl₂ indicate that exchange of the Rh(cod) unit between the starting materials, binuclear and ionic species occurs rapidly in the NMR time-scale at room temperature. When dps is added to 5a or 5b(molar ratio 1:1) the concentration of the binuclear species decreases and an equilibrium occurs between [Rh(cod)(dps)]Cl and [Rh(cod)Cl(dps)] where the dps ligand is monodentate.