We report the first catalyst based on palladium for the reaction of CO2, alkene and a base to form sodium acrylate and derivatives. A mechanism similar to a previously reported Ni(0)-catalyst is proposed based on stoichiometric in situ NMR experiments, isolated intermediates and a parent palladalactone. Our palladium catalyst was applied to the coupling of CO2 with conjugated alkenes.

A series of square planar methylnickel(II) complexes, (dppe)Ni(Me)(SAr) (dppe = 1,2-bis(diphenylphosphino)ethane); 2. Ar = phenyl; 3. Ar = pentafluorophenyl; 4. Ar = o-pivaloylaminophenyl; 5. Ar = p-pivaloylaminophenyl; (depe)Ni(Me)(SAr), (depe = 1,2-bis(diethylphosphino)ethane); 7. Ar = phenyl; 8. Ar = pentafluorophenyl; 9. Ar = o-pivaloylaminophenyl; 10. Ar = p-pivaloylaminophenyl), were synthesized via the reaction of (dppe)NiMe2(1) and (depe)NiMe2(6) with either the corresponding thiol or disulfide. These complexes were characterized by various spectroscopic methods including 31P NMR, 1H NMR, 13C NMR and infrared spectroscopies and in most cases by X-ray diffraction analyses. Solid state and solution measurements establish that 5 and 9 contain intramolecular N-H---S bonds. Carbonylation of the complexes 2-4, 7-10 leads to (dRpe)Ni(CO)2 and MeC(O)SAr via the intermediacy of the acylnickel adducts, (dRpe)Ni(C(O)Me)(SAr), detected at low temperature by 31P NMR spectroscopy. Consistent with experimental observations, density functional theory results reveal that the intramolecular hydrogen bond in 9 stabilizes the acylnickel adduct compared with its non-hydrogen-bonded adduct, 10. Oxidative addition of MeC(O)SC6F5 to (dRpe)Ni(COD) followed by spontaneous decarbonylation proceeds in modest yields generating 3 and 8.

The reactivity of a dimethyl palladium complex supported by a dicarbene chelate (MDCMes)PdMe2 towards CO2 has been investigated. In the presence of trace H2O, this reaction yields the corresponding methyl bicarbonate complex (MDCMes)PdMe(O2COH), which goes on to give the corresponding κ2-carbonato complex upon crystallization (MDCMes)Pd(CO3). This chemistry, as well as related protonolysis by acetic acid was monitored by a combination of techniques including React-IR spectroscopy.