## 3 Results and Discussion
### The Catalytic Suzuki-Miyaura Cross-Coupling Reaction
#### 3.2.3 Effect of Ionic Liquid  
With the catalytic results obtained to that point, it was significant to test the effects of the ionic liquids, including on the catalytic outputs, as well as catalyst recovery and recycling. First of all, all Pd catalysts were highly soluble in both BMImBF\({}_{4}\) and BMImPF\({}_{6}\), and the resulting mixture could be fully dispersed into the THE solvent system under vigorous magnetic stirring. These characters guaranteed the effects of \"one-phase catalysis, two-phases separation\" [48].  
Next, for the cross-coupling of halogenated and protected indazole (compound **3**) with 2-furanboronic acid (compound **4**), the introduction of two imidazolium ILs increased the yields of coupled products in the reactions catalyzed by Pd(PPh\({}_{3}\))\({}_{4}\) (entries 2-3 vs. 1, Table 1), Pd(OAc)\({}_{2}\) (entries 5-6 vs. 4, Table 1), and PdCl\({}_{2}\) (entries 8-9 vs. 7, Table 1). The use of BMImBF\({}_{4}\) in association with PdCl\({}_{2}\)(dppf) increased the yield of coupled product (entries 11 vs. 10, Table 1), but use of BMImPF\({}_{6}\) showed negative effects on the catalytic yields (entries 12 vs. 10, Table 1). On the other hand, employing either BMImBF\({}_{4}\) or BMImPF\({}_{6}\) along with PdCl\({}_{2}\)(dtbppf) did not contribute to the catalytic outputs (entries 14-15 vs. 13, Table 1).  
Therefore, it seemed that introduction of imidazolium ILs caused the coordination of N to Pd in the simple Pd salts (Pd(PPh\({}_{3}\))\({}_{4}\), Pd(OAc)\({}_{2}\), PdCl\({}_{2}\))-catalyzed reactions, probably leading to a more stable intermediate [ArPdXLn] (Pd complex) [47], further improving the catalytic yields. However, when the Pd catalysts contained sophisticated ligands, such as dppf and dtoppf, the original P-containing ferrocene-based ligands showed positive effects on stabilizing the catalytic intermediate, but the introduction of imidazolium ILs may affect this stability through coordination of N, sometimes decreasing the outputs.  
When the substrate (nucleophile) was changed to 4-methoxycarbonylphenylboronic acid (compound **7**, Scheme 1) and 3-methoxycarbonylphenylboronic acid (compound **10**), use of two imidazolium ILs generally produced enhanced yields of cross-coupled products (Tables 2 and 3), which could be ascribed to the unique structural and coordinating properties of the ILs.  
In the meantime, there was another reasonable explanation for the roles of BMImBF\({}_{4}\) and BMImPF\({}_{6}\) in the present catalysis. It was previously reported that the combination of 1-\(n\)-butyl-3-methylimidazolium bromide (BMImBr) with Pd(OAc)\({}_{2}\) in an alkaline environment produced 1-\(n\)-butyl-3-methylimidazol-2-ylidene (BMIy) complex of Pd (such as PdBr\({}_{2}\)(BMIy)\({}_{2}\) and analogues), which showed a high activity in the Heck reaction [49]. This \(N\)-heterocyclic carbene (NHC) complex (PdBr\({}_{2}\)(BMIy)\({}_{2}\)) probably has influences on both the NHC and counterion (Br\({}^{-}\)), facilitating various catalytic reactions [49]. Furthermore, no palladium metal particles (Pd\({}^{(0)}\) black) appeared in this work, probably indicating the formation of \(N\)-heterocyclic carbene (NHC) complex of Pd. On the basis of the above analysis, the possible formation of NHC complex of Pd in this work is proposed in Scheme 2.