## 1 Introduction  
Since the discovery of periodic mesoporous organosilica (PMO) bulk materials in 1999 by three independent groups [1; 2; 3], they have been studied intensively because of their great potential in designing and fabricating new organic-inorganic hybrid materials with unique properties including high surface areas, high thermal stability, as well as facile separation and recovery as solid materials [4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. Recently, much attention has been devoted to developing nanometric-sized PMOs by utilizing organosilae monomers or mixtures of monomers [22; 23; 24]. Research on periodic mesoporous organosilica nanoparticles has covered numerous interests including biological [25; 26; 27], chemical [28; 29; 30; 31; 32; 33; 34], but mostly biomedical applications [35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48]. PMO nanomaterials with special structures and compositions have also been utilized as superior nanospupports for variable metal catalysts [49]. The homogeneous distribution of organic molecules in their frameworks and their uniform mesopores provides them with advantageous properties for hosting metal catalysts or metal nanoparticles within their voids and channels. Because of these features, catalytic transformations mediated by these PMO nanomaterials have been highly studied, developed and utilized [50; 51; 52; 53]. However, the ability to recycle these nanoreactors from the reaction medium remains one of the most challenging issues, but which has gained much less attention. The use of magnetic nanoparticles (MNPs) has offered an attractive and plausible solution for such recovery problems in many fields [54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65]. MNPs have received a great deal of attention because of their low costs, high surface areas, negligible toxicity, and their superparamagnetic properties [66; 67; 68; 69]. Owing to their unique properties, magnetic nanoparticles have become highly welcome in many biological [70; 71; 72; 73; 74; 75], chemical [76; 77; 78; 79; 80; 81; 82; 83; 84], and biomedical domains [85; 86; 87; 88; 89; 90; 91]. Lately, very few research groups have reported the preparation of magnetically recoverable PMO nanomaterials for different applications [92; 93; 94; 95; 96; 97]. Magnetic periodic mesoporous organosilacs were prepared by utilizing different synthetic routes including the well-known Stober process [98; 99], the microemulsion method [100; 101] and a hard template strategy for preparing yolk-shell nanospheres [94; 97]. All these systems were mostly prepared from a mixture of an organosilane monomer and tetraorthosilicate and were applied in different catalytic transformations. Herein, we describe the synthesis of magnetic ethylene- and phenylene-bridged PMO NPs that were prepared by a sol-gel process under mild conditions from pure organosilane precursors in the presence of a cetyltrimethylammonium bromide (CTAB) surfactant with the addition of hydrophobic magnetite nanoparticles. Both magnetic ethylene- and phenylene-bridged PMO NPs were successfully obtained; however, they displayed different morphological and textural properties. The magnetic ethylene-bridged PMO NPs (M-Ethylene-PMO NPs) exhibited highly ordered mesostructures, whereas magnetic phenylene-bridged PMO NPs (M-Phenylene-PMO NPs) exhibited smooth surface nanoparticles with no specific mesostructure ordering. M-Ethylene-PMO NPs were loaded with ruthenium oxide nanoparticles by means of sonication and evaporation under mild conditions and the resulting catalytic magnetic PMO nanoreactors, termed Ru@M-Ethylene PMO NPs, were utilized in the reduction reaction of aromatic compounds because they exhibited excellent catalytic behavior.