Copper and Silver Complexes of <i>o</i>-Ph₂PC₆H₄C(O)N(H)C₉H₆N: Synthesis and Catalytic Applications of Cu^I Complexes

In this article, synthesis of an amide-based PNN ligand <i>o</i>-Ph₂PC₆H₄C(O)N(H)C₉H₆N(<b>1</b>), its oxide <i>o</i>-Ph₂P(O)C₆H₄C(O)N(H)C₉H₆N (<b>2</b>), and Cu^I, Cu^II, and Ag^I complexes are described. Reactions of <b>1</b> with Cu^IX resulted in both monometallic [CuX{(<i>o</i>-Ph₂P)C₆H₄C(O)N(H)C₉H₆N}₂] (<b>3</b>, X = Cl; <b>4</b>, X = Br; <b>5</b>, X = I) and bimetallic complexes [{Cu(μ₂-X)(<i>o</i>-Ph₂P)C₆H₄C(O)N(H)C₉H₆N}₂] (<b>6</b>, X = Cl; <b>7</b>, X = Br; <b>8</b>, X = I). Similar reactions of compound <b>2</b> with Cu^IX yielded the (P = O)NN coordinated complexes [{Cu(μ₂-X)(<i>o</i>-Ph₂P(O))C₆H₄C(O)NC₉H₆N}₂] (<b>9</b>, X = Cl; <b>10</b>, X = Br; <b>11</b>, X = I). Reactions of <b>1</b> with AgX (X = Br, I) afforded [{(<i>o</i>-Ph₂P)C₆H₄C(O)N(H)C₉H₆N}₂AgX] (<b>12</b>, X = Br; <b>13</b>, X = I). Monometallic complexes <b>3</b>, <b>4</b>, and <b>5</b> are insoluble in most common organic solvents. A shorter Cu1-Cu1' distance of 2.5372(5) Å in <b>8</b> indicates the presence of Cu···Cu interactions. Copper complex <b>8</b> showed good catalytic activity toward the heteroannulation reaction of 2-halophenols and terminal acetylenes to give benzofurans. Controlled experiments indicate that the reaction is homogeneous and does not follow the radical pathway.