3.2 L2 ligand Promoted Reaction
Duan et al. found that, using L2 as the ligand (entry 2 in Scheme 2), the reaction did not proceed at all and no product was obtained. To understand this interesting observation, we firstly investigated the relative stabilities of various adducts formed by the coordination of L2 ligand with Pd(OAc)2 shown in Scheme 5, and examined two sequential processes involving C(sp2)-H bond cleavage of aromatic ring through CMD process and alkyne insertion from the starting materials (L2+Pd(OAc)2 )(Figure 4).