Sterically hindered P,N-type amidophosphines {{(o-PPh2)C6H4}C(O)NH(R)}: synthesis, transition metal chemistry, and catalytic activity in stereoselective Heck coupling of aryl chlorides

Abstract

This paper reports the synthesis, coordination chemistry, and catalytic applications of two amide-based monophosphine ligands, {{(o-PPh₂)C₆H₄}C(O)N(H)(C₁₂H₁₈)} (L1) and {{(o-PPh₂)C₆H₄}C(O)NH(C₃₃H₂₈)} (L2). Ligand L1, upon reaction with [Pd(COD)Cl₂] and [Pd(OAc)₂], yielded dimeric P,N-coordinated palladium complexes [{(PdCl)₂}{(o-PPh₂)C₆H₄C(O)N(C₁₂H₁₈)}₂-κ²-P,N] (1) and [{(Pd(OAc))₂}{(o-PPh₂)C₆H₄C(O)N(C₁₂H₁₈)}₂-κ²-P,N] (2), respectively. Further treatment of L1 with CuI and AgBr afforded monodentate η¹-P coordinated copper and silver complexes, [{(CuI)₂}{(o-PPh₂)C₆H₄C(O)NH(C₁₂H₁₈)}₂-κ¹-P] (3) and [{(AgBr)₂}{(o-PPh₂)C₆H₄C(O)N(H)(C₁₂H₁₈)}₂-κ¹-P] (4). Reactions of L1 with AgBF₄ and AgClO₄ led to the formation of tridentate P,O,C-coordinated silver complexes, namely [{(AgX)₂}{(o-PPh₂)C₆H₄C(O)N(H)(C₁₂H₁₈)}₂-κ³-P,O,C], where X = BF₄ (5) and ClO₄ (6). Ligand L2 reacted with CuI to form a monodentate P-coordinated Cu^I complex, [{(CuI)₂}{(o-PPh₂)C₆H₄C(O)NH(C₃₃H₂₈)}₂-κ¹-P] (8), and with [Ru(p-cymene)Cl₂]₂ to afford a P,O-chelated Ru^II complex, [{Ru(p-cymene)Cl}{(o-PPh₂)C₆H₄C(O)NH(C₃₃H₂₈)}-κ²-P,O]PF₆ (9). Notably, the in situ-generated Pd nanoparticles derived from complex 1, stabilized by the P,N ligand, exhibited excellent catalytic performance in Heck cross-coupling reactions of aryl chlorides with styrene derivatives. These reactions proceed under mild conditions, providing trans-stilbene products in high yields (90–99%) with low catalyst loading and good functional group tolerance.