Cleavage of Unstrained C(sp2)—C(sp2) Single Bonds with Ni0 Complexes Using Chelating Assistance

The reaction of Ni(COD)2 with a ligand containing a biphenyl subunit (P(iPr)2-O-Ph-Ph-O-P(iPr)2, L1) resulted in a mixture of compounds, the main product being [L1]Ni(COD), which could be quantitatively transferred to product 2 using bis(p-toluyl)acetylene. The possible activation products, cis- and trans-3 (3c and 3t, respectively), which would result from the cleavage of the bridging C—C single bond were synthesized independently. The mechanism of the cis/trans-isomerization was examined, activation parameters determined and trapping tests performed. Reaction of (PPh3)2Ni(CO)2 with L1 gave a novel complex 4 by a ligand exchange reaction. This compound, when heated to 95 °C under a 5 bar atmosphere of CO for several days, slowly incorporated CO into the bridging C—C single bond. This behavior as well as isotopic labeling experiments with 13CO indicated that, following a dissociation of CO in complex 4, an interaction between the metal center and the biphenyl moiety is induced, leading to activation. The ...