Tetra(hetero)arylated Cyclopentadienone Iron Tricarbonyl Complexes for Noble Metal-free Photocatalytic Hydrogen Generation

A versatile method for the straightforward synthesis of rarely known tetra(hetero)arylated cyclopentadienone iron tricarbonyl complexes 3a-3j is presented. In a [2+2+1]-cycloaddition reaction, a series of di(hetero)arylated ethynylenes 1a-1j are reacted with iron pentacarbonyl to yield the corresponding “Knölker-type” complexes, which bear substituents of different electronic nature. This type of iron complexes is active in photocatalytic hydrogen evolution reaction and the influence of the substituents on the catalytic activity was investigated.