An efficient metal-free, photomediated
iodo perfluoroalkylation
under mild conditions was developed. Using catalytic amounts (10 mol
%) of phosphines and blue light irradiation, various olefins are transformed
into the corresponding addition products within short reaction times.
For this purpose, a modular and convenient 3D printed photoreactor
was constructed, which is presented as an open source model. The reaction
presumably proceeds upon generation of perfluoroalkyl radicals, which
are formed by catalyst-induced absorption enhancement.
The frustrated Lewis pair‐catalyzed iodoperfluoroalkylation of olefins, its substrate activation mode, and catalyst degradation pathways are mechanistically investigated by kinetic measurements. The transformation most likely proceeds via coordination of the phosphane to the perfluoroalkyl iodide and involves radical intermediates.
In an effort to explain the experimentally observed variation of the photocatalytic activity of t Bu 3 P, n Bu 3 P and (MeO) 3 P in the blue-light regime [Helmecke et al., Org. Lett. 21 (2019) 7823], we have explored the absorption characteristics of several phosphine– and phosphite–IC 4 F 9 adducts by means of relativistic density functional theory and multireference configuration interaction methods. Based on the results of these computational and complementary experimental studies, we offer an explanation for the broad tailing of the absorption of t Bu 3 P-IC 4 F 9 and (MeO) 3 P-IC 4 F 9 into the visible-light region. Larger coordinate displacements of the ground and excited singlet potential energy wells in n Bu 3 P-IC 4 F 9 , in particular with regard to the P–I–C bending angle, reduce the Franck–Condon factors and thus the absorption probability compared to t Bu 3 P-IC 4 F 9 . Spectroscopic and computational evaluation of conformationally flexible and locked phosphites suggests that the reactivity of (MeO) 3 P may be the result of oxygen lone-pair participation and concomitant broadening of absorption. The proposed mechanism for the phosphine-catalyzed homolytic C–I cleavage of perfluorobutane iodide involves S1 ← S0 absorption of the adduct followed by intersystem crossing to the photochemically active T 1 state.
A comparison of two catalytic, metal-free iodoperfluoroalkylation protocols is presented. Frustrated Lewis pairs [
t
Bu3P/B(C6F5)3] or phosphines/phosphites under visible light irradiation efficiently mediate the functionalization of non-activated alkenes and alkynes. A comprehensive account of the corresponding substrate scopes as well as insights into the mechanistic details of both reaction pathways are provided.
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