Pd(II) complexes with N-ligands containing functional groups were synthesized and tested for Suzuki coupling reaction. The ligands were N-[3-(trimethoxysilyl)propyl]-ethylenediamine (1), 2-(2'-pyridyl)-ethyltrimethoxysilane (2), and 3-aminopropyltrimethoxysilane (3). The complexes were then heterogenized on solids support, i.e., silica. In the first step, the ligands were immobilized on the silica surface in toluene. Then, the immobilized ligands were metalated with [PdCl2(PhCN)2]. Immobilization of Pd(II) was confirmed by IR studies of the samples. Tests of the catalysts for Suzuki couplings, i.e., PhB(OH)2 + BrC6H4CH2COOH → PhC6H4CH2COOH, showed that the complexes with monodentate ligands (2 and 3) have a higher activity, while the complexes with bidentate ligand (1) appeared less active. Interestingly, the activity of the supported catalysts with the ligand 1 was found to be higher, which may be caused by the effect of site-isolation (absence of interaction between catalyst molecules leading to a formation of less active Pd nanoclusters). In addition, a filtration test did not show a notable leaching of Pd from this catalyst. Next, the effect of the reaction conditions on the conversion of the starting compounds was studied. The highest conversion is found for a DMA/water mixture with Na2CO3 as a base. The reactivity of the substituted phenylboronic acids in this reaction depends on the nature and the position of the substituent. However, non-aromatic boronic acids appear less reactive. In summary, the immobilized complex dichloro[N-(3'-trimethoxysilyl)propyl-1,2-ethanediamine-N,N']-palladium showed a high activity for Suzuki couplings, which makes it useful for biaryl compound synthesis.
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