Reactions of 9-Carbene-9-Borafluorene Monoanion and Selenium: Synthesis of Boryl-Substituted Selenides and Diselenides

Abstract

Reactions of 9-carbene-9-borafluorene monoanion (1) with elemental selenium and selenium-containing reagents are reported. When compound 1 is reacted with grey selenium in THF, various boryl-substituted selenides and diselenides are produced (2−6), including molecules resulting from migration of the carbene ligand Dipp group (Dipp = 2,6-diisopropylphenyl). However, when a similar reaction between 1 and grey selenium is performed in toluene in the presence of 18-crown-6, boryl-substituted selenide 7 is obtained as the sole boron-containing product. As compound 7 is the monomeric variant of organoselenide 3, 18-crown-6 promotes both product selectivity and solubility in a nonpolar solvent. Diselenide 5, which features a trans-bent B−Se−Se−B core, was directly isolated via reaction of 1 with Se 2 Cl 2 in THF. Computational modeling suggests that the formation of 5 proceeds via a radical mechanism. This was supported by an experiment demonstrating that the CAAC-borafluorene radical also reacts with SeCl 2 to yield 5 [CAAC = (2,6-diisopropylphenyl)-4,4-diethyl-2,2-dimethyl-pyrrolidin-5-ylidene]. Energy decomposition analysis of 5 indicates a covalent borafluorene−diselenide bond (ΔE int , −168.9 kcal mol −1 ). All of the new compounds were fully characterized via single-crystal X-ray diffraction and multinuclear nuclear magnetic resonance ( 1 H, 13 C, 11 B, and 77 Se).

Homoleptic Ni(ii) dithiocarbamate complexes as pre-catalysts for the electrocatalytic oxygen evolution reaction

“…cobalt, 6 copper, [7][8][9][10] iron, 11,12 and manganese, 13 have attracted tremendous attention due to their economic viability and high abundance. 14 The Earth abundant and biologically important nickel metal in the development of electrocatalysts for water oxidation has also been investigated. These nickel catalysts exhibited promising OER activity at lower overpotentials with good catalytic stability.…”

Systematic Electronic and Structural Studies of 9-Carbene-9-Borafluorene Monoanions and Transformations into Luminescent Boron Spirocycles

“…56 Recently, we demonstrated that 1 may serve as a single-electron reducing agent with diselenides to undergo subsequent radical coupling. 39 Single-electron transfer (SET) can occur spontaneously, provided the energies of the donor HOMO and acceptor LUMO are close. Quinones are especially susceptible to SET reactions as the carbonyl π* orbital is easily reduced to generate an electronically stabilized ketyl radical anion.…”

“…Theoretical modeling identifies that these low-field signals are due to a large paramagnetic contribution at boron as a result of reduced HOMO–LUMO gaps in charge-separated borafluorenes. The ability to easily tune the HOMO of 9-carbene-9-borafluorene monoanions not only allows for the modification of the anion’s electronic structure but may also prove useful as a means to control reactivity. , Moreover, when reacting 3 with 9,10-phenanthrenequione and 1,10-phenanthroline-5,6-dione, novel charge-separated boron spirocycles ( 5 and 6 ) are synthesized via carbene elimination, with computational mechanistic studies suggesting this reactivity proceeds via an electron-transfer mechanism. Compounds 5 and 6 display bright green and orange luminescence under UV light and are air-stable in the solid state.…”

Recent Advances in the Domain of Cyclic (Alkyl)(Amino) Carbenes

“…When 9-carbene-9borafluorene monoanion (142) was treated with selenium grey powder, a mixture of boryl-substituted selenides and diselenides including Dipp group transferred products were obtained. [206] However, when the same reaction was performed in toluene with 18-crown-6, boron substituted monoselenide product (143) was obtained only (Scheme 52).…”

“…This monomeric species 205 can be regarded as a heavier ketenimine (R 2 C=C=NÀ R) analog with Si and P atoms in place of C and N atoms, respectively. It is surprising to note that dark red color crystals of a dimer [(cAAC)Si(P-Tip)] 2 (206) were isolated instead of monomer 205 (Scheme 63).…”