## Magnetically Separable Base Catalysts: Heterogeneous Catalysis _vs. Quasi_-Homogeneous Catalysis  
**[PERSON] 1** and [PERSON] 2,*  
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binding of catalysts to organic polymer solids or inorganic solids, could facilitate the separation and the recycling of the heterogenized catalysts. However, the reactivity and the selectivity of these catalysts were significantly lower than with their homogeneous analogues. A Sol-gel process, which is based on the hydrolysis and polycondensation of metal alkoxides, has been also utilized extensively for the preparation of heterogenized catalysts [2, 3, 4, 5, 6]. According to this method, the heterogenization process can be achieved via physical encapsulation of homogeneous catalyst or by covalent binding of catalysts functionalized with trialkoxysilane groups. Recently, _quasi_-homogeneous catalysis has emerged as a new stream in catalysis that is considered as a promising way for bridging homogeneous and heterogeneous catalysis [7, 8]. This method is based on immobilization of homogeneous catalysts on supports of nanometric dimensions such as gold nanoparticles. Because these nano-supports have a large surface area, they can preserve the reactivity and selectivity of the immobilized catalysts. In spite of that, the separation and the recycling of such catalytic systems usually require a cumbersome procedure. Magnetic nanoparticles (MNP) have been investigated due to their potential biomedical applications in various fields such as drug delivery [9, 10], magnetic resonance imaging [11], biomolecular sensors [12, 13], bioseparations [14, 15], and magneto-thermal therapy [16, 17]. In addition, recent studies show that magnetic nanoparticles are excellent supports for various catalysts [18, 19, 20, 21]. The supported catalysts proved to be effective and easily separated from the reaction media by applying an external magnetic field. Moreover, the ability of magnetic nanoparticles to serve efficiently as nano-support for organocatalytic systems has been recently reported [22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32]. We have described the highly selective hydroformylation reaction using rhodium catalysts supported on dendronized magnetic nanoparticles [33]. We have also developed a catalytic system for the chemoselective hydrogenation of \(a\), \(\beta\)-unsaturated aldehydes and alkynes, based on platinum nanoparticles supported on nano-magnetic, Fe\({}_{3}\)O\({}_{4}\), modified with ionic liquid groups [34]. Furthermore, in our recent work we showed a method based on magnetic nanoparticles and sol-gel process that facilitates the separation of two solid catalysts after catalyzing one-pot reactions in a single vessel and enables their reuse in other catalytic reactions [35]. The condensations of activated methylene groups with aldehydes, in particular Knoevenagel [36] and nitroaldol [37] condensations, are efficient carbon-carbon bond forming reactions. These reactions are utilized widely in the synthesis of valuable organic compounds that are of importance to different biological and pharmaceutical applications. Usually, these condensations are catalyzed under homogeneous conditions by bases such as primary, secondary and tertiary amines.