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

## TL;DR

This study reports the synthesis and properties of new α-germyl ferrocenyl ketones, showing their potential for visible-light-driven chemical reactions.

## Contribution

The first synthesis of α-germyl ferrocenyl ketones and their unique visible-light reactivity up to 550 nm.

## Key findings

- All-ferrocenoyl derivatives are photoinert, while mixed acyl species show visible-light-induced α-cleavage.
- The reactivity extends to 550 nm, the longest wavelength reported for α-cleavage in acylgermanes.
- Distinct multiferrocenyl redox behavior was observed in the compounds.

## Abstract

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 KnGe(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).

We report the first synthesis of α-germyl ferrocenyl ketones, revealing photoinert all-ferrocenoyl derivatives and visible-light-induced α-cleavage (up to 550 nm) for mixed acyl species, alongside distinct multiferrocenyl redox behavior.