Macromolecular-Multisite Catalysts Obtained by Grafting Diaminoaryl Palladium(ii) Complexes onto a Hyperbranched-Polytriallylsilane Support

Novel silica immobilized NCN-pincer palladium(II) and platinum(II) complexes: Application as Lewis acid catalysts

“…For this study, we have used platinum and palladium complexes of so-called 'pincer' ligands of the ECE type (where ECE = [2,6-(ECH 2 ) 2 C 6 H 3 ] − , and E = NR 2 , PR 2 or SR) [34] which can act as Lewis acid catalysts in aldol condensation reactions [35][36][37][38][39][40] and double Michael addition reactions [41][42][43][44]. The metal ion in these ECE-pincer metal complexes is strongly bound through a covalent M-C bond which is complemented by ortho-chelation of the two hetero atom containing substituents.…”

“…This mer-ECE terdentate coordination provides considerable stability against metal leaching during catalysis [45,46]. In earlier efforts from our group, complexes of this type have been anchored to a variety of soluble supports like dendritic systems [35,42,47], hyperbranched polysilanes [38], methanofullerenes [43], etc., and were demonstrated to give stable, recyclable catalysts that show no leaching of metal, enabling the use of these systems in a membrane reactor for continuous operation [48]. Therefore, the metallo-pincer catalysts seem ideally suited for the grafting protocol to an insoluble support like silica as envisaged above.…”

“…In all previous works, pre-catalyst NCN-pincer palladium halide complexes are activated by removal of the halide ligand in order to generate cationic Pd-aquo complexes, which are believed to be the active catalytic species [35][36][37][38][39][40]. In this study, we prepared various types of combinations of possible immobilized catalyst systems, each time starting from hybrid material 5 (Scheme 2).…”

NCN–pincer palladium complexes with multiple anchoring points for functional groups

“…Because of the reversible binding properties of the NCN-pincer platinum complexes with SO 2 and I 2 [1,16], and the concomitant reversible color change from colorless to orange and purple, respectively, these conjugates are interesting candidates as biomarkers and biosensors. We have extensively investigated the immobilization of NCN-pincer complexes onto soluble and molecular supports for catalyst recycling, for which supports as structurally diverse as benzene rings [17][18][19], dendrons [20], dendrimers [21][22][23][24][25][26][27], hyperbranched polymers [28][29][30][31], and dendronized polymers [32] were used to covalently, as well as non-covalently immobilize these complexes. One of the major applications for which the resulting hybrid materials are tested is their use in nano-filtration set-ups for the continuous as well as batch-wise operation and separation of homogeneous catalysts [33].…”

“…This trimethylsilyl group is used as a mimic for carbosilane dendritic support systems. Earlier results indicated that once attachment to trimethylsilyl chloride is feasible, the method also holds for attachment to dimethylchlorosilyl functionalized carbosilane dendrons [23,24,26,28]. …”