A sterically demanding amine, 1,2,2,6,6-pentamethylpiperidine (PMP), forms a highly reactive Lewis acid-base pair with boron trifluoride. This pair reacts with terminal acetylenes to give the products of C(sp)-H borylation, previously unknown tri- and tetraalkynylboron compounds. Trialkynylfluoroborates can serve as surrogates of alkynyltrifluoroborates for C-C coupling reactions. Using aqueous NaOH, PMP can be recovered from its tetrafluoroborate salt, which is formed as a C-H borylation byproduct. Combining the discovered borylation reactivity with the PMP recovery provides a straightforward and atom-efficient approach to synthetically useful alkynylfluoroborates.
Organoboron compounds are essential reagents in modernC ÀCc oupling reactions. Theirs ynthesis via catalytic CÀHb orylation by main group elements is emerging as ap owerful tool alternative to transition metal based catalysis. Herein, as traightforwardm etal-free synthesis of aryldifluoroboranes from BF 3 and heteroarenesisr eported. The reaction is assisted by sterically hindered amines and catalytic amountso ft hioureas. According to computational studies the reaction proceeds via frustrated Lewis pair (FLP) mechanism. The obtained aryldifluoroboranes are further stabilized againstd estructivep rotodeborylation by converting them to the corresponding air stable tetramethylammonium organotrifluoroborates.
In this study we have explored the influence of mutual position of chlorin electron donor and fullerene C60 electron acceptor on photoinduced electron transfer. Two zinc-chlorin-aza-[18]crown-6 compounds and three pyrrolidino[60]fullerenes with alkyl aminium and varying coordinative moieties were synthesized and used for self-assembling of a set of complexes via two-point binding. The aza[18]crown6 moieties were connected to chlorins via amide linker either at 13(4) or 17(4) position, hence, being attached on different sides of the chlorin plane. Furthermore, in the former case, the linker holds the crown closely spaced, whereas, in the latter, the linker gives more space and conformational freedom for the crown with respect to the chlorin macrocycle. The coordinative moieties at fullerene site, 3-pyridine, 4-pyridine, and 3-furan, were built by utilizing the Prato reaction. The two-point binding drove the molecules into specific complex formation by self-assembling; aminium ion was chelated by crown ether, while zinc moiety of chlorin was coordinated by pyridine and furan. Such pairing resulted in distinct supramolecular chlorin-fullerene dyads with defined distance and orientation. The performed computational studies at DFT level in solution, with TPSS-D3/def2-TZVP//def2-SVP, indicated different geometries and binding energies for the self-assembling complexes. Notably, the computations pointed out that for all the studied complexes, the donor-acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C60. The selective excitation of chlorin chromophore revealed efficient emission quenching in all dyads. The ultrafast spectroscopy studies suggested a fast and efficient photoinduced charge transfer in the dyads. The lifetimes of the charge separated states range from 55 to 187 ps in o-dichlorobenzene and from 14 to 60 ps in benzonitrile. Expectedly, the electron transfer rate was found to be critically dependent on the donor-acceptor distance; additionally, the mutual orientation of these entities was found to have significant contribution on the rate.
As terically demanding amine,1 ,2,2,6,6-pentamethylpiperidine (PMP), forms ahighly reactive Lewis acid-base pair with boron trifluoride.T his pair reacts with terminal acetylenes to give the products of C(sp) À Hb orylation, previously unknown tri-and tetraalkynylboron compounds. Trialkynylfluoroborates can serve as surrogates of alkynyltrifluoroborates for CÀCc oupling reactions.U sing aqueous NaOH, PMP can be recovered from its tetrafluoroborate salt, which is formed as aC ÀHb orylation byproduct. Combining the discovered borylation reactivity with the PMP recovery provides as traightforwarda nd atom-efficient approach to synthetically useful alkynylfluoroborates. Scheme 1. a) Conventionala pproach to organotrifluoroborates with organolithium or -magnesiumderivatives. b) Hypothetical atom-efficient approach to organotrifluoroborates by CÀHborylationw ith aBF 3 /organic base FLP. M = alkali metal.
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