A series of inexpensive, easily tunable, and highly reducing organic photocatalysts (PCs) that exhibit strong absorption in the visible region are described. Time-dependent density functional theory calculations were applied to corroborate the experimental observations and explain the relationship between the structure and property. The photocatalytic efficiency of these PCs was demonstrated by catalyzing
[reaction: see text]. Catalytic carbonylative alkyne-alkyne coupling proceeds using iridium-phosphine complexes under carbon monoxide at atmospheric pressure or a partial pressure of 0.2 atm. This reaction provides various cyclopentadienones in high isolated yields.
Intramolecular [2+2+1] cycloaddition of diynes with carbonmonoxide was catalyzed by Vaska's complex (IrCl(CO)(PPh3)2) or IrCl(cod)(dppp), and cyclopentadienones were obtained in good to high yields. The first catalytic synthesis of iminocyclopentadienes was achieved by portionwise additions of isocyanides to a solution of diynes and Rh catalyst ([RhCl(cod)]2).