**4. Conclusions**

In summary, we have described the catalytic applications of palladium catalysts deposited over silica gel bearing composite amide-donor functional moieties at the surface in the Sonogashira-type cross-coupling of acyl chlorides with terminal alkynes producing synthetically useful 1,3-disubstituted prop-2-yn-1-ones. The collected data suggest a generally good catalytic performance of these heterogeneous catalysts alone (i.e., without a co-catalyst) in the reactions of aromatic acyl chlorides with aryl alkynes under relatively mild reaction conditions. Nevertheless, a careful optimization is required for achieving good catalytic results, as the catalytic properties are significantly affected by the reaction conditions (solvent and base) and depend on the nature of the functional pendant at the support's surface. Of the tested catalysts, the poorest performance surprisingly exerted catalyst **7** bearing the phosphine moieties, which contrasts with the general notion that phosphine ligands give rise to active cross-coupling catalysts. When recycled, however, the studied catalysts lost their catalytic activity and, therefore, could not be efficiently reused. Very likely, the catalysts serve as a source of catalytically active Pd species that efficiently mediate the cross-coupling reaction but are not redeposited without deactivation.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4344/10/10/1186/s1, Table S1: Yields of the coupling product **11ad** and the amount of leached-out Pd in the recycling experiments.

**Author Contributions:** P.Š. conceived the study and, in collaboration with M.S. and F.H., interpreted the collected data and wrote this article; M.S. and F.H. performed all syntheses and catalytic tests; all authors contributed to the characterization of the coupling products. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work has been supported by Charles University Research Centre program No. UNCE/SCI/014.

**Acknowledgments:** The authors thank I. Císaˇrová from the Department of Inorganic Chemistry, Faculty of Science, Charles University for collecting the diffraction data and J. Rohovec from Institute of Geology, Academy of Sciences of the Czech Republic for ICP OES-MS analyses.

**Conflicts of Interest:** The authors declare no conflict of interest.
