# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 2 Organocatalysed Non-Asymmetric Reactions
### C-C Bond Forming Reactions  
In 2014, the solid phase synthesis of poly(propylene imine) (PPI) dendrimers was described for first time [26]. Particularly, polymer-supported PPI dendrimer **34** was prepared by synthesizing poly(propylene imine) dendrimer up to third generation on crosslinked polystyrene. An iterative method, which included a double Michael addition of acrylonitrile to the amino groups of the polymer support and subsequent LiAlH\({}_{4}\) reduction of the nitrile groups to amino groups, was followed (Scheme 14). Material **34** was employed as heterogeneous catalyst in Knoevenagel condensations. Using only 0.5 mol % of catalyst **34**, \(\alpha\),\(\beta\)-unsaturated nitriles were obtained in excellent yield (98%-100%) in ethanol at room temperature. The yields of the products obtained with this catalyst were similar to those obtained with polystyrene-supported PAMAM dendrimers [27] in the same conditions but with the catalyst **34** the reaction time was shorter. The catalyst **34** was recovered by simple filtration and reused up to eight times without loss of catalytic activity. The following year, polysilane-supported poly(propyleneimine) dendrimer **35** was used as catalyst in Knoevenagel condensations, showing the first example of PPI dendrimer grafted polysilane catalyst (Scheme 15) [28]. The material **35** was prepared by synthesizing the third-generation PPI dendrimer on the aminoethylpolysilane according to the general strategy of solid phase synthesis. The aminoethylpolysilane was previously prepared by condensation of trichoromethylsilane through Grignard coupling followed by the conversion of chloride groups in aminoethyl moieties with excess of ethylenediamine (EDA). Using 3 mol % of catalyst **35**, \(\alpha\),\(\beta\)-unsaturated nitriles were obtained in high yield carrying out the reaction at 30 \({}^{\circ}\)C and at 50 \({}^{\circ}\)C. Recycling of catalyst **35** was studied in the Knoevenagel condensation between benzaldehyde and malononitrile. Four cycles were carried out and the yields gradually decreased from 100% to 92%. A new hydrophobic mesoporous poly(ionic liquid) was used as a recyclable solid-base catalyst for solvent-free Knoevenagel condensations [29]. This material, denoted as **37**, was prepared in two synthetic steps: (a) synthesis of polymer **36** by radical copolymerization of 1-aminoethyl-3-vinylimidazolium bromide hydrobromide with divinylbenzene varying the molar ratio of two monomers; (b) ion-exchange reaction with a NaOH solution (Scheme 16). Among the various molar ratios tested in the first step, the molar ratio 1:1 was optimal. In fact, the mesoporous poly(ionic liquid) **37** with equimolar amounts of divinylbenzene and ionic liquid precursor exhibited the best catalytic activity (conversion 99%) in solvent-free Knoevenagel condensation between benzaldehyde and ethyl cyanoacetate at 70 \({}^{\circ}\)C. It was also tested in Knoevenagel condensation with various substrates, giving high conversions (93%-99%) at 70 \({}^{\circ}\)C in a short reaction time. The authors proposed a possible synergistic Lewis-Bronsted dual-base-center mechanism that justified high catalytic activity. The material **37** was used for six cycles without significant loss of activity. In 2014, [PERSON] and [PERSON] reported the first is successfully recyclable catalytic system for benzoin condensation [30]. Particularly, poly(4-vinylimidazolium) iodide [31]**39** was prepared by polymerization of 4-vinylimidazolium **38**, synthesized starting from histamine. Subsequently, the polymer was tested as an organic pre-catalyst in benzoin condensations (Scheme 17). Under optimized conditions, diverse functionalized benzoin products were obtained in 48%-96% yield with benzyl as by-product in various yields (less than 7%). In all cases, pre-catalyst **39** exhibited higher catalytic activity than the corresponding monomeric analogue **38**.