Activation of an Unstrained C(sp2)–C(sp2) Single Bond Using Chelate-Bisphosphinite Rhodium(I) Complexes

The reaction of [Rh(coe)2Cl]2 with the ligands P(iPr)2-O-PhpX-CO-PhpX-O-P(iPr)2 (L1 X = H and L2 X = OMe) containing a benzophenone moiety resulted in the quantitative oxidative addition of the PhC–CO single bond under very mild conditions (193 K, 2a/b). For L2 the mechanism and the kinetics of the oxidative addition were investigated. Only complex 2a (X-ray crystal structure included) shows an exchange of the metal-bonded carbon moieties via migratory extrusion/insertion (3a) in solution. Thermodynamic parameters for this process were determined (for 3a → 2a ΔH° = 9.3 ± 0.5 kJ/mol, ΔS° = 53.8 ± 1.8 J/(K mol)). The further fate, in particular the reductive elimination, of 2a/b was investigated and compared to the behavior of Ir. The reaction of 2a/b with several Lewis bases such as CO, 13CO, tert-butyl isonitrile, pyridine, acetonitrile, and 15N-acetonitrile was investigated. DFT calculations for the most important steps were performed.