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.