*2.3.1 Palladium on clay composite carrying phosphinite-functionalized ionic liquid moieties (CCPIL)*

A clay composite comprising of phosphinite-functionalized ionic liquid moieties was synthesized, in which palladium nanoparticles were uniformly ligated, and this system is called as clay carrying phosphinite-functionalized ionic liquid (CCPIL) moieties or systems. The preparation involves the synthesis of an epoxy functionalized clay, which is reacted with 1-methyl imidazole and chlorodiphenyl phosphine yielding the required CCPIL. The CCPIL material thus obtained was separated by simple filtration to which later palladium was complexed. This novel catalytic material combines the advantages of homogeneous IL phase, phosphorylated ligands, and a new heterogeneous clay support for Pd catalyzed C-C bond formation in green media. The catalytic material is pictorially represented as **Figure 1**.

The heterogeneous catalyst was successfully exploited for the Suzuki coupling of aryl iodides in aqueous media to give biaryls in high yields. Bromide and chloride substrates too gave the biaryls but required longer reaction times. Recycling was repeated for five runs with little leaching observed where each run required the same reaction times. These catalysts were also used for solvent-free MH reaction. Further, copper-free Sonogashira-Hagihara reaction of aryl iodides, bromides, and chlorides with phenylacetylene was also catalyzed by these Pd on CCPIL. Recycling was also possible with little depletion, and the added advantage is that the catalyst was air and moisture stable [15].

*Solvents, Ionic Liquids and Solvent Effects*

**2.1 SILP in macrocellular silica**

and TOF reached 68,400 and 8000 h<sup>−</sup><sup>1</sup>

**2. Supported ionic liquid phase (SILP)**

In view of recycling and reusing the transition metal catalytic materials, the technology of immobilization or heterogenization was exploited, and the notable methodologies include polymer supports, macrocellular silica-based foams, magnetic Fe3O4, carbon nanotubes (CNT), multiwalled carbon nanotubes (MWCNT), mesoporous solids, functionalized magnetic Fe3O4, metal organic framework (MOF), monolithic ionogels, and SILP. Among them, the SILP technology is the most recent one; there are debates that the use of ILs is not cost-effective; however, the whole SILP system is reusable and recyclable and hence the cost can be abruptly reduced; the technology ranks to be green in nature since there is no escape of volatile organic compounds (VOCs). Metal in the form of oxides, ions, metal complexes coordinated to the cation or anion, or as nanoparticles was supported in an IL matrix through a thin film. In the SILP system, IL is a part of the support material; accordingly, the bulk properties of IL such as solvation strength, conductivity, viscosity and density are altered. ILs with hydrophobic in nature can offer excellent surface support. ILs can also act as nanoparticles stabilizers. Even though the stabilization mechanism has not been proved, ILs seem to create an electrostatic and steric barrier between nanoparticles; a stabilization type Derjaguin-Landau-Verwey-Overbeek (DLVO) has been proposed due to their polymeric structure.

The preparation of macrocellular silica is quite simple; the transition metal compounds of interest is suspended in a solution employing an ionic liquid in an volatile organic solvent. Upon stripping the volatile organic compound, the free-flowing immobilized catalytic material can be obtained where the transition metals are trapped within the SILP system. The materials thus trapped within the SILPs were found to be useful in promoting the organic functional group transformations catalyzed by transition and/or noble metals. Mainly the aryl-X activation (Mizoroki-Heck reaction) was carried out using palladium containing SILPs (in imidazolium ILs). With low palladium loading, the Heck-type coupling reaction was performed, and the reaction of iodobenzene with cylohexyl acrylate yielded the corresponding cinnamates with high turnover numbers (TON) and turnover frequency (TOF) [8]. Palladium acetate Pd(OAc)2 supported on amorphous silica immobilized in [bmim] PF6 (1-butyl-3-methylimidazolium hexafluorophosphate) was reported to be highly efficient towards the promotion of the Heck-type coupling reaction without any additional ligands, gave the trans-cinnamates in preparative yields [9], and the TON

, respectively.

A variation for the synthesis of heterogeneous IL-based palladium-containing catalytic system was developed by Shi et al. [10], through a one pot synthesis of heterogeneous ionic liquid encapsulated on silica involving sol-gel method. These catalysts provided excellent activity for the carbonylation of aniline and nitrobenzene to synthesize diphenyl urea in (Pd or Rh)-EMImBF4/silica gel (1-ethyl-3-methylimidazolium tetrafluoroborate) or (Pd or Rh)-DMImBF4/silica gel (0.1 g, 50–60 mesh), (1-decyl-3-methylimidazolium tetrafluoroborate), or DMImBF4 ionic liquid (2.5 g) containing Rh complex (1 mg) or 0.11 wt%Rh 35 wt% DMImBF4/SiO2 (0.1 g, for the purpose of comparison). The selectivity, yield, and turnover number (TON) were excellent. In the same publication, the identical catalytic system was

**2.2 Heterogeneous ionic liquid (HIL)-encapsulated IL on silica**

**128**
