Different Oxidative Addition Mechanisms for 12- and 14-Electron Palladium(0) Explain Ligand-Controlled Divergent Site
Jacob P Norman1, Nathaniel G Larson1, Sharon R Neufeldt1
1Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.
Abstract:
In cross-coupling reactions, dihaloheteroarenes are usually most reactive at C─halide bonds adjacent to a heteroatom. This selectivity has been previously rationalized. However, no mechanistic explanation exists for anomalous reports in which specific ligands effect inverted selectivity with dihalopyridines and -pyridazines. Here we provide evidence that these ligands uniquely promote oxidative addition at 12e- Pd(0). Computations indicate that 12e- and 14e- Pd(0) can favor different mechanisms for oxidative addition due to differences in their HOMO symmetries. These mechanisms are shown to lead to different site preferences, where 12e- Pd(0) can favor oxidative addition at an atypical site distal to nitrogen.
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