Activation of CO2 by Palladium Complexes Bearing Tridentate PCP Ligands

The present thesis deals with the activation of CO2 by insertion reactions into palladium-carbon bonds. This has been realised for the complexes {2,6-bis[(di-t-butylphosphino)methyl]benzene}palladium(II)methyl [(PCP)PdMe] and (PCP)PdCH2CHCH2. These complexes have also been used in the catalytic carboxylation of ZnMe2 and Bu3SnCH2CHCH2. Because of trans influence the palladium-methyl bond is severely weakened as indicated by the long bond distance in the crystal structure of the complex. Several (PCP)PdMe complexes have been synthesised and tested in the insertion reaction but only the most nucleophilic metal centre gave any reaction. A kinetic analysis of this reaction revealed the insertion to be first order with respect to the metal complex as well as to CO2. According to the same analysis the transition state of the reaction would consist of a complex with coordinated CO2 with a significant bond breaking and bond making. The insertion of CO2 into the palladium-allyl bond is a much faster reaction. Therefore it is considered to proceed via a different mechanism than what is operating for the (PCP)PdMe reaction. The reaction is proposed to involve a cyclic transition state and in principle not being an insertion, but due to rearrangement the product will appear as an insertion product. CO2 insertions have also been realised for palladium hydroxide and palladium hydride giving carbonato and formato complexes respectively. Both of these reactions are completed within minutes. (PCP)PdH have also been reacted with phenylacetylene in a C-H exchange reaction giving (PCP)PdCCC6H5 as the sole product. This product suggest a s-bond metathesis. The crystal structures for a number of the synthesised complexes have been solved and revealed some interesting packing arrangements governed by the possibilities for hydrogen bonding, giving rise to dimers, chains and 3D-nets