Activation of a Nonstrained C(sp²)−C(sp²) Single Bond in a Vaska Complex Analogue Using Chelating Assistance

The reaction of Vaska’s complex with the ligand P(iPr)2−O−Ar−CO−Ar−O−P(iPr)2 (L1, p-H; L2. p-OMe) containing a benzophenone moiety, resulted in the quantitative oxidative addition of the PhC−CO bond leading to 1. For 1 three consecutive reactions can be observed: upon loss of CO trans-2 is formed, which further isomerizes first to cis-3 and finally to cis′-4. The mechanism of the oxidative addition, and the CO extrusion as well as the trans/cis/cis′ isomerization were examined, activation parameters determined, and trapping experiments performed. If 3 is placed under a 4 bar atmosphere of CO at 373 K for several days, the slow re-formation of 1 (20% after 5 days) can be observed. Labeling studies with 13CO revealed no scrambling of the 13CO into the acyl position. When the oxidative addition was examined, starting with the 13CO-labeled Vaska complex, the label remained exclusively at the metal and no carbonyl scrambling was observed during CO extrusion. Heating 3 to temperatures higher than 423 K resulted in the formation of 4. Performing this reaction under an atmosphere of 13CO revealed an incorporation of 13CO into 4. Halide abstraction from 3 failed. Using AgBF4 in chloroform resulted in the formation of the Ag-bridged dimer 6. Molecular structures of the new complexes 1a, 2−4, and 6 have been determined by single-crystal X-ray diffraction studies. DFT calculations on the major pathways have been performed.