Low-temperature equilibriums in solutions of isocyanide-phosphine complexes of palladium(II) chloride

摘要

cis-[PdCl2(CNR)(PPh3)] [R = Cy, t-Bu, C(Me)(2)CH2C(Me)(3)] have been synthesized via the interaction of [(PPh3)ClPd(mu-Cl)(2)PdCl(PPh3)] with isocyanide in CH2Cl2 at room temperature with 90-98% yield and characterized by means of mass spectrometry as well as H-1, C-13{H-1, P-31}, and P-31{H-1} NMR spectroscopy. The complexes structure in the solid phase has been elucidated by means of X-ray diffraction analysis. Dynamic processes in the solutions of the complexes in CDCl3 and CD2Cl2 at temperature of-95 to 60A degrees D have been studied by means of H-1 and P-31 NMR spectroscopy. It has been found that the studied compounds existed exclusively in the cis-[PdCl2(CNR)(PPh3)] form in the solutions. In the case of cis-[PdCl2(CNCy)(PPh3)] in CH2Cl2, the conformational transitions of the equilibrium forms (the transition of the substituent in the cyclohexyl cycle between the equatorial and axial positions) are slowed down, the equatorial conformer prevailing in the solution (2: 1 at-95A degrees D). Quantum-chemical simulation (DFT) has revealed that the standard Gibbs energy of the conformational transition from the axial form of cis-[PdCl2(CNCy)(PPh3)] into the equatorial one in the CH2Cl2 solution at 178 K equals-2.5 kJ/mol, being in agreement with the experimental data.