Reaction of N-Isopropyl-N-phenyl-2,2′-bipyridin-6-amine with K2PtCl4: Selective C-H Bond Activation, C-N Bond Cleavage, and Selective Acylation

The selective C H bond activation of N-isopropyl-N-phenyl-2,2'-bipyridin-6-amine promoted by Pt(II) was complicated by the low selectivity of sp(2) C-H bond activation in acetonitrile and low yield of sp(3) C-H activation in acetic acid. The use of a base was found to effectively suppress the competing sp(3) C-H bond activation in acetonitrile, improving the selectivity of sp(2) C-H bond activation from 70% to 99%. In the reaction in acetic acid, the low yield was due to the competing C-N bond cleavage. The use of a base reduced the C-N bond cleavage, but not completely. The reaction of N-tert-butyl-N-phenyl-2,2'-bipyridin-6-amine with K2PtCl4 in acetic acid produced the cyclometalated complex with complete C-N bond cleavage and its acylated derivative. These results indicated that the C-N bond cleavage might proceed via heterolytic C-N bond dissociation. The acylation following the C-N cleavage in the reaction in acetic acid is regioselective. Further experiments showed that the reaction of N-phenyl-2,2'-bipyridin-6-amine with K2PtCl4 in acetic acid produced the cyclometalated complex, while the reaction in a mixture of acetic anhydride and acetic acid produced the acylated cyclometalated complex. An X-ray crystal structure study revealed strong intramolecular H bonding in the acylated complexes. The regioselectivity was explained in terms of H bonding and the electron distribution predicted by the DFT calculations.