For as long as I can remember, I have been told that silicone grease on glass joints is a bad idea. I remember taking this advice to heart because the alternative was to see an IR-like mess in the aliphatic region of my proton NMRs. The benefits of cleaner spectra outweighed an occasional frozen glass joint, although now that I think about it, Teflon tape on the inside had similar lubricating effect (and turned into my preferred way of avoiding frozen joints during grad school). Later on, I would tell this same story about grease to several generations of my doctoral students. The silicone nightmare is part of our synthetic folklore and efforts to avoid it represent a broadly accepted laboratory practice. However, we have a bit of a dilemma here, especially if we look at the review article quoted below. The title has “grease” and “serendipity” in it, so you can see where the paper is headed. We are conditioned not to use grease in reaction setup because we do not want to see garbage in NMR spectra. But it is possible to make things a bit too sterile, isn’t it? Otherwise certain serendipitous findings, such as the nickel example on display, will never be made. I am not saying that this particular carbene complex is noteworthy as a catalyst precursor, but who knows? There may very well be a niche for “OSiOSiO” bridges out there. They are interesting and largely underexplored. Unless generated unintentionally, that is… The “OSiOSiO”-based ligand was observed during an attempt to run what many would consider a fairly standard inorganic prep to make nickel-carbene complexes. I do think that the wording “greased Schlenk” might be a bit much, but I am here to faithfully reproduce what I see, ladies and gentlemen. I note that this review by Saito is not his first paper on the subject (this is more of a “Grease 2.0”). I salute you, Professor Saito, and I am glad that grease is developing a faithful following.
This is totally new to me and I have to say I haven’t read the paper yet. Are these reactions really reproducible? How much grease can cause the formation of these species? Are they just single crystals isolated from reaction mixtures or do they really isolate them in good yield? So many questions. I will definitely read the paper. Thanks for the highlight.
While these cases are interesting, it is indeed tough to see how they are of preparative value. The described processes do suggest what is possible and, if there is interest, the corresponding reactions can be optimized.
it would be interesting to try to make the corresponding cyclic boronate ester with a 6-membered siloxane containing ring, to see if there is any advantage over the pinacolato boronates
Why not? An interesting idea!