Synthesis, structure, photochemical and electrochemical properties of α-germyl ferrocenyl ketones

Owing to their well-defined and tunable properties, acylgermanes are attractive photoinitiators for polymerization reactions. This paper focuses on the previously unexplored acylgermanes containing the ferrocenylcarbonyl group. For example, compound FcC(O)Ge(SiMe₃)₃ (4, Fc = ferrocenyl) was synthesized from the reaction of (chlorocarbonyl)ferrocene with the germanide K[Ge(SiMe₃)₃] generated from KOtBu and tetrakis(trimethylsilyl)germane (1) in a continuous flow setup. In contrast, a complete replacement of the silyl groups in 1 in the presence of KOtBu and KF under conventional conditions produced the tetraacylgermane (FcC(O))₄Ge (5). Additionally, mixed-acyl compounds, (FcC(O))_nGe(C(O)Mes)_4-n (n = 1: 6, n = 2: 7; Mes = mesityl), were obtained by salt metathesis of the respective germenolates K_nGe(C(O)Mes)_4-n (2 and 3) with FcC(O)Cl. All compounds, along with the model silane FcC(O)Si(SiMe₃)₃ (4Si), prepared from in situ-generated KSi(SiMe₃)₃ and FcC(O)Cl, were fully characterized by elemental analysis, NMR and UV-vis spectroscopy, single-crystal X-ray diffraction analysis, and their electrochemical properties were studied using voltammetric techniques. Compounds bearing exclusively ferrocenoyl substituents were photoinert, whereas mixed ferrocenoyl/mesitoyl derivatives showed α-cleavage upon visible-light irradiation. Remarkably, this reactivity extended up to 550 nm, representing the longest wavelength reported for α-cleavage in acylgermanes and underscoring their potential for mild, visible-light-driven applications. Preliminary experiments suggested a limited reactivity of 4 and 4Si, likely due to steric effects. Only the reaction of the silane with benzil at elevated temperature produced siladioxacyclopentene FcC(SiMe₃)₂{Si(OSiMe₃)O₂C₂Ph₂} (8).