Hydrogen-bonding network in new scorpionate-type ligand composed of pyridine/pyrrole hybrid and anion-binding behavior of the corresponding rhodium complexes in alkyne cyclotrimerization reaction

New heteroscorpionate ligands (1 and 2) having a di(pyridin-2-yl)(1H-pyrrol-2-yl)methane substructure are synthesized. X-ray crystallographic analysis on 1 and 2 reveals that they form unique hydrogen bonding networks depending on the size of neighboring groups in solid states. 1 and 2 can form cationic rhodium(I) complexes, wherein the counter anions form hydrogen bondings with the pyrrolic NH moiety. In alkyne cyclotrimerization reactions using those complexes as catalyst, the catalytic activity is significantly enhanced when electron-donating counter anions is placed near the metal center.

Graphical abstractIn the alkyne cyclotrimerization reactions catalyzed by the rhodium(I) complexes of new heteroscorpionate ligands composed of pyrrole and pyridine, electron donating counter anions placed near the metal center considerably enhanced the reactivity through anion recognition with the pyrrolic NH moiety.Figure optionsDownload full-size imageDownload as PowerPoint slide