The manuscript submitted by Bantreil and co-workers presents a mechanochemical protocol for the synthesis of ruthenium-based trisbipyridyl complexes, widely utilized as photoredox catalysts in organic synthesis. While the development of a mechanochemical method for iridium-based trisbipyridyl complexes has been previously reported (ref. 19), this work is the first to achieve the highly efficient synthesis of ruthenium complexes under solvent-free mechanochemical conditions. Remarkably, this method does not require high temperature to achieve the high efficiency, showcasing the effectiveness of mechanochemical approach.

One of the standout aspects of this work is the introduction of epoxy resin milling jars, which offer superior chemical resistance, shock resilience, and transparency, allowing light irradiation during the milling process. This represents a substantial improvement over the conventional PMMA jars previously used in mechanochemical photoredox reactions. The authors highlight the practical advantage of their method by demonstrating a light-induced reductive dehalogenation reaction, combining photoredox chemistry with mechanochemistry. The marked reduction in reaction time (from 24 hours in solution to just 3.5 hours) underscores the efficiency of this approach, while similar advantages of mechano-photoredox reactions have been reported (refs. 43-46).

Overall, this manuscript presents good advancements in both mechanochemistry and photoredox catalysis. The research will likely have a broad impact and draw substantial interest from the scientific community. I recommend its publication after addressing the following points:

1. The generation of the iron complex in Scheme 2 is intriguing. Can the authors explore whether the iron complex can be selectively generated from the milling jar when the reaction is carried out without the ruthenium precursor?

2. While the results are promising, the optimized conditions require relatively large amounts of solvents (12 equivalents of EtOH and 0.25 equivalents of 1M NaOH). This can be regarded as a solution-state reaction. To demonstrate the advantages of this mechanochemical protocol over existing solution-based methods, I suggest the authors provide an environmental evaluation, such as the E-factor.

3. Given that significant amounts of solvent are still required under the mechanochemical conditions, I wonder if the reaction might proceed equally well in a test tube. Could the authors verify whether the ball milling process is truly essential for the reaction?

4. Please explain, if possible, the reason why the mechanochemical reactions for the synthesis of the ruthenium complexes proceeded successfully at significantly lower temperature under mechanochemical conditions, compared to conventional solution-based methods that typically require high temperatures. Which step requires such high temperatures?

I have thoroughly reviewed the authors' responses to the reviewers' comments and confirm that the authors have addressed the issues, resulting in substantial improvements to the manuscript. I believe the revised manuscript is now ready for publication.