Abstract
The formation of a stable triacylgermenolate 2 as a decisive intermediate was achieved by using three pathways. The first two methods involve the reaction of KOtBu or alternatively potassium with tetraacylgermane 1 yielding 2 via one electron transfer. The mechanism involves the formation of radical anions (shown by EPR). This reaction is highly efficient and selective. The third method is a classical salt metathesis reaction toward 2 in nearly quantitative yield. The formation of 2 was confirmed by NMR spectroscopy, UV–vis measurements, and X-ray crystallography. Germenolate 2 serves as a starting point for a wide variety of organo-germanium compounds. We demonstrate the potential of this intermediate by introducing new types of Ge-based photoinitiators 4b–4f. The UV–vis absorption spectra of 4b–4f show considerably increased band intensities due to the presence of eight or more chromophores. Moreover, compounds 4d–4f show absorption tailing up to 525 nm. The performance of these photoinitiators is demonstrated by spectroscopy (time-resolved EPR, laser flash photolysis (LFP), photobleaching (UV–vis)) and photopolymerization experiments (photo-DSC measurements).
Highlights
In organic as well as in inorganic chemistry, alkoxides of alkali metals are widely used as powerful bases
On the basis of the accessibility of acylgermanium based radical anions and taking into account the seminal work of Murphy and co-workers, merging the chemistry of strong bases and electron transfer, we explore whether the reduction of acylgermanes provides synthetically attractive reaction pathways
Analytical and spectroscopic data that strongly support the structural assignment are given in the Experimental Section, together with experimental details
Summary
In organic as well as in inorganic chemistry, alkoxides of alkali metals are widely used as powerful bases These alkoxides were found to be involved in a wide variety of reactions where single electron transfer reactions take place.[1−50] In his landmark work, Murphy et al.[51] explained the controversial electron transfer from KOtBu to benzophenone (compare Scheme 1). They showed that KOtBu and Scheme 1. The keto-derivatives of main group IV organometalloids (mainly germanium-based) have attracted considerable attention as visible light induced photoinitiators.[53−58] To date, di- and tetraacylgermanes are well established (see Chart 1), both compound classes have significant drawbacks
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