Thermodynamic studies of transition-metal intermediates are crucial for understanding of metal-catalyzed transformations. Herein, a series of arylpalladium cyanomethanides were synthesized and characterized. Their palladium-carbon bond heterolysis energies (Δ(Pd-C)) were determined in DMSO for the first time by equilibrium methods. Δ(Pd-C) values of 7.9-19.1 kcal/mol, located between the Δ(Pd-O) and Δ(Pd-N) scales previously established, are much smaller than the corresponding Δ(C-H)s of phenylacetonitrile (30.0 kcal/mol). Linear free energy relationship (LEFR) analysis reveals insights into the structure-property relationship and the factor dictating the thermodynamics of metalation. These Δ(Pd-X)s in combination with Δ(X-H)s are successfully used to diagnose the reaction feasibility and selectivity of X-H bond activation.
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