Triazolylidene Iron(II) Piano-Stool Complexes: Synthesis and Catalytic Hydrosilylation of Carbonyl Compounds

A new series of iron(II) piano stool complexes was synthesized that contain monodentate triazolylidene ligands with different aryl and alkyl substituents as well as an example of a C,N-chelating pyridine-substituted triazolylidene iron complex. The electronic and steric effect of wingtip modification was assessed by electrochemical, infrared spectroscopic, and X-ray diffraction analysis. All complexes were active in the catalytic hydrosilylation of aldehydes and ketones. The monodentate systems outperform the chelating triazolylidene analogue by far, reaching turnover frequencies TOFmax as high as 14400 h(-1) at 0.1 mol % catalyst loading. Mechanistic investigations indicate a radical mechanism for the catalytic H-Si bond activation.