CARBON-DIOXIDE COORDINATION CHEMISTRY .3. VIBRATIONAL, NMR, AND THEORETICAL-STUDIES OF NI(CO2)(PCY3)2

Complete assignments of FTIR and Raman spectra are proposed for Ni(CO2)(PCy3)2 and its (CO2)-C-13- and (CO2)-O-18-labeled derivatives. Normal coordinate analysis gives a relevant force-field for side-on complexation at the solid state and shows that the complex can also exist with an 'end-on'' coordination mode. FTIR study in various solvents at different temperatures allows us to conclude that similar coordination modes are found in solution. Results are compared to that obtained by C-13 and P-31 NMR (including CPMAS studies) concerning the fluxionality of Ni-(CO2)(PCy3)2. The paper also deals with CAS-SCF calculations of Ni(CO2)L2 isomers and shows that the end-on coordination might account for the fluxional behavior of such systems.