Abstract:The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of sub-valent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. While carbon is too electronegative to affect the reduction of elements of lower relative electronegativity, the highly reducing nature of the B=B double bond enables reactions with Se 0 and Te 0 . The capacity of multiple bonds between boron to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions.The energy stored in small, highly strained cyclic molecules has made them an integral part of modern synthetic chemistry. Since this "strain energy" increases with decreasing ring size, it is greatest for three-membered rings, and when these rings are heterocyclic the charge-asymmetry induced in the molecule provides sites ready for reaction. Accordingly, an enormous amount of research has gone into both the synthetic paths to, and reactions of, members of this class of compounds, most prominently oxiranes (C2O rings) and aziridines (C2N rings). The most common route to these materials is the oxidation of olefins using, in the case of oxirane formation, subvalent oxygen species such as O2, peroxides, peroxyacids, and ozone, or with reagents that impart a degree of electron deficiency to an oxygen atom, such as chlorite or iodosylbenzene. [1] Aziridination of olefins is most frequently accomplished through the in situ generation of nitrenes from azides or other electron deficient nitrogen sources such as iodinanes, hydroxylamines, and hydrazines. [1a,2] These alkene-oxidations are made possible by the relatively high electronegativity of oxygen and nitrogen, (χPauling = 3.44 and 3.04, respectively), relative to carbon (χPauling = 2.55).Thiiranes (C2S rings) are comparatively less common, and though examples of the direct addition of elemental sulfur to alkenyl double bonds are not unknown, [3] their syntheses are more likely than their first row neighbors to involve non-redox routes. [4] The similar electronegativities of carbon and sulfur (χPauling = 2.58) decreases the thermodynamic driving force for alkene oxidation, further exemplified by the noted willingness of thiiranes to thermally extrude atomic sulfur [5] and by their utility as sulfur atom transfer reagents. [6] Three-membered heterocycles featuring heavier chalcogens (Se and Te) are even less prevalent. Though seleniranes have been proposed as reactive intermediates in a handful of transformations, [7] the isolated examples of these compounds are few and none have been crystallographically verified. [8] To date, there are no known examples of telluriranes. The heavy chalcogens have roughly equal (χSe = 2.55) or smaller (χTe = 2.10...

Cationization of Bi(NPh 2 ) 3 has recently been reported to allow access to single-and double-CH activation reactions, followed by selective transformation of Bi−C into C−X functional groups (X = electrophile). Here we show that this approach can successfully be transferred to a range of bismuth amides with two aryl groups at the nitrogen, Bi(NR aryl 2 ) 3 . Exchange of one nitrogen-bound aryl group for an alkyl substituent gave the first example of a homoleptic bismuth amide with a mixed aryl/ alkyl substitution pattern at the nitrogen, Bi(NPhiPr) 3 . This compound is susceptible to selective N−N radical coupling in its neutral form and also undergoes selective CH activation when transformed into a cationic species. The second CH activation is blocked due to the absence of a second aryl moiety at nitrogen. The Lewis acidity of neutral bismuth amides is compared with that of cationic species "[Bi(aryl)(amide)(L) n ] + " and "[Bi(aryl) 2 (L) n ] + " based on the (modified) Gutmann−Beckett method (L = tetrahydrofuran or pyridine). The heteroaromatic character of [Bi(C 6 H 3 R) 2 NH(triflate)] compounds, which are iso-valence-electronic with anthracene, is investigated by theoretical methods. Analytical methods used in this work include nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction, mass spectrometry, and density functional theory calculations.

Reduction of (CAAC)BBr2(NCS) (CAAC=cyclic alkyl(amino)carbene) in the presence of a Lewis base L yields tricoordinate (CAAC)LB(NCS) borylenes which undergo reversible E/Z‐isomerization. The same reduction in the absence of L yields deep blue, bis(CAAC)‐stabilized, boron‐doped, aromatic thiazolothiazoles resulting from the dimerization of dicoordinate (CAAC)B(NCS) borylene intermediates.

The one-electron reduction of a cyclic (alkyl)(amino)carbene (CAAC)-stabilized arylborylene carbonyl complex yields a dimeric borylketyl radical anion, resulting from an intramolecular aryl migration to the CO carbon atom. Computational analyses support the existence of a [(CAAC)B(CO)Ar] •radical anion intermediate. Further reduction leads to a highly nucleophilic dianionic (boraneylidene)methanolate.

Boron tribromide and aryldihaloboranesw ere found to undergo 1,3-haloboration across one WÀNN moiety of ag roup 6e nd-on dinitrogen complex (i.e. trans-[W(N 2) 2 (dppe) 2 ]). The N-borylated products consist of ar educed diazenido unit sandwiched between aW II center and at rivalent boron substituent (WÀN=NÀBXAr), and have all been fully characterized by NMR andI Rs pectroscopy,e lementala nalysis, and single-crystal X-ray diffraction. Both the terminal Na tom and boronc enteri nt he WÀN=NÀBXAr unit can be further derivatizedu sing electrophiles and nucleophiles/Lewis bases, respectively.T his mild reduction and functionalization of aw eakly activated N 2 ligand with boron halides is unprecedented, and hints at the possibility of generatingv alue-added nitrogen compounds directly from molecular dinitrogen.