Intramolecular C–F and C–H bond cleavage promoted by butadienyl heavy Grignard reagents

Abstract

Organomagnesium compounds (Grignard reagents) are among the most useful organometallic reagents and have greatly accelerated the advancement of synthetic chemistry and related sciences. Nevertheless, heavy Grignard reagents based on the metals calcium, strontium or barium are not widely used, mainly due to their rather inert heavy alkaline-earth metals and extremely high reactivity of their corresponding Grignard-type reagents. Here we report the generation and reaction chemistry of butadienyl heavy Grignard reagents whose extremely high reactivity is successfully tamed. Facile synthesis of perfluoro-π-extended pentalene and naphthalene derivatives is realized by the in situ generated heavy Grignard reagents via intramolecular C-F/C-H bond cleavage. These obtained perfluorodibenzopentalene and perfluorodinaphthopentalene derivatives show low-lying LUMO levels, with one being the lowest value so far among all pentalene derivatives. Our results set an exciting example for the meaningful synthetic application of heavy Grignard reagents.

Pinning of the Fermi Level in CuFeO2 by Polaron Formation Limiting the Photovoltage for Photochemical Water Splitting

“…The anisotropic photo deposition of Pt and Ag onto anisotropic particles has been observed before for SrTiO 3 and BiVO 4 . [20,21] The anisotropic photodeposition might be caused by dissimilar band bending across the different exposed facets, as measurements on single crystals suggest. [25,26] However, highly anisotropic electrical conductivities perpendicular and parallel to the c-axis, as observed for 3R CuFeO 2 single crystals, [27] might also be the reason for the observed anisotropic photodeposition.…”

“…Li et al have shown that anisotropic SrTiO 3 and BiVO 4 heterostructured powders could be synthesized through a photodeposition process using anisotropic SrTiO 3 and BiVO 4 powders with two different kinds of exposed facets. [20][21][22] Moreover, these anisotropic heterostructures exhibited improved water splitting efficiencies with respect to heterostructures with randomly deposited cocatalysts, because of a suggested synergistic charge carrier separation-cocatalyst effect.…”

Extreme Mechanics of Probing the Ultimate Strength of Nanotwinned Diamond

“…When σ max zz = 0, this relation describes the pure shear process considered in previous studies [13][14][15][16][17][18][19][20][21]23]. In the opposite limit of σ max zz → ∞, the normal stress is always proportional to the shear stress [28,30]. Here, we examine a compressible indenter that has a large but finite peak normal stress σ max zz .…”

“…To determine the indentation strength, calculations were carried out under a biaxial stress field that contains a shear (σ zx ) and a normal compressive (σ zz ) stress component that obey the relation σ zz = σ zx tanφ, where φ is the centerline-to-face angle of the indenter [28]. Here the diamond indenter is assumed to be incompressible and, therefore, the two stress components are always proportional to each other, which is a good approximation for most materials, including those with strengths comparable to that of cubic diamond [29,30]. We will show below, however, that when the indented material is much stronger than cubic diamond, as in the case of nt-Dia, the deformation-limited finite peak strength of the diamond indenter has a major influence on the deformation modes and stress response of the indented material and must be explicitly considered.…”

Facile Access to Fluoroaromatic Molecules by Transition-Metal-Free C-F Bond Cleavage of Polyfluoroarenes: An Efficient, Green, and Sustainable Protocol

“…Recently, the Xi group found that the in situ generated highly active butadienyl heavy Grignard reagents could be used as good coupling partners for the facile synthesis of perfluoro-p-extended pentalene and naphthalene derivatives via intramolecular C-F bond cleavage (Scheme 9). [19] This reaction was carried out at 2958C in THF without the assistance of any catalyst. Through density functional theory (DFT) calculations, a definite conclusion was reached that the obtained perfluorinated compounds possessed the lowest LUMO levels among reported pentalene systems, and the introduction of multiple F atoms onto the pentalene backbones significantly lowered the orbital energy levels.…”