3,4-dihydro-2H-1,2,4,3-triazaborol-3-yl-lithium 3 was synthesized and fully characterized. The (11)B NMR spectrum, X-ray diffraction analysis, and computational studies revealed the ionic nature of the B-Li bond, and indeed 3 displays nucleophilic property which allowed preparation of a series of 1,2,4,3-triazaborol-3-yl-metal complexes (Al; 5, Au; 6, Zn; 7, Mg; 8, Sb; 9, and Bi; 10). 3 reacted with CO (1 atm) and various isonitriles under ambient condition, and mechanistic study suggests that the reactions with CO and aryl isonitriles proceed via an insertion of CO and isonitrile carbon into the B-Li bond followed by isomerization to yield transient carbene species, one of which was confirmed by trapping with S8. With PhNC, compounds 5 and 7·(thf) underwent exchange of THF molecule coordinating to the metal center with isonitrile, whereas insertion of isonitrile carbon occurred at the B-Bi bond in 10 which afforded stable bismuth (boryl)iminomethane 20.

A 2,3-dihydro-1H-1,2-azaborole derivative 2 was converted to a cyclic (alkyl) (amino)carbene (cAAC) via 1,2-hydrogen migration triggered by boranes to afford cAAC-borane adducts. This procedure allowed us to develop an asymmetrical diborene cAAC·(Br)B═B(Br)·IDip 6, which was isolated and fully characterized. The B NMR spectrum, X-ray diffraction analysis and computational studies indicate that π-electrons on the central B moiety in 6 are unequivalently distributed, and thus polarized. A complete scission of the B═B double bond in 6 was achieved by the treatment with an isonitrile, which led to the formation of a base-stabilized B,N-containing methylenecyclopropane 7.

One-electron oxidation of organoboron L2PhB: 1 (L = oxazol-2-ylidene) afforded a dicationic diborane(6) species [L2PhB-BPhL2]·2X (X = OTf, BF4, AlCl4) 3, representing a new strategy to construct a B(sp(3))-B(sp(3)) covalent bond. Each boron atom in 3 is in the formal oxidation state +II, and tetracoordinate with a Ph group and two oxazol-2-ylidenes. The cyclic voltammetry of 3 shows irreversible reduction and oxidation. Indeed, two-electron reduction of 3 with potassium graphite (KC8) afforded 1, making a fully reversible 1 ↔ 3 redox system, whereas two-electron oxidation with AuCl produced a boronium [L2PhBCl]OTf 4. Moreover, the reactions of 3 with isonitrile derivatives RNC: under heating conditions gave a cyano-substituted boronium [L2PhBCN]BF4 5 and a 2-boranyl-indole derivative 6, depending on the substituent R. The proposed reaction mechanism involves a borinylium radical 1(•+) which is generated via a homolytic cleavage of the B-B bond of 3.

A zwitterionic boraalkenyl boronium 3 was synthesized by reduction of cyclic (alkyl)(amino)carbene (cAAC) and trimethylphosphine (PMe )-coordinated tetrabromodiborane 2 with KC in the presence of PMe . Further reduction of 3 led to the formation of neutral allenic diborene 4. X-ray diffraction and computational studies revealed that 4 features the cumulated C=B and B=B double bonds. The reaction of 4 with four isonitrile molecules afforded a heterocycle 5 with the B C five-membered ring, via a complete scission of the B=B bond of 4.

Comproportionation of [Ni(cod)(2)] (cod = cyclooctadiene) and [Ni(PPh(3))(2)X(2)] (X = Br, Cl) in the presence of six-, seven- and eight-membered ring N-aryl-substituted heterocyclic carbenes (NHCs) provides a route to a series of isostructural three-coordinate Ni(I) complexes [Ni(NHC)(PPh(3))X] (X = Br, Cl; NHC = 6-Mes 1, 6-Anis 2, 6-AnisMes 3, 7-o-Tol 4, 8-Mes 5, 8-o-Tol 6, O-8-o-Tol 7). Continuous wave (CW) and pulsed EPR measurements on 1, 4, 5, 6 and 7 reveal that the spin Hamiltonian parameters are particularly sensitive to changes in NHC ring size, N substituents and halide. In combination with DFT calculations, a mixed SOMO of ∣3d z 2〉 and ∣3d x 2-y 2〉 character, which was found to be dependent on the complex geometry, was observed and this was compared to the experimental g values obtained from the EPR spectra. A pronounced (31)P superhyperfine coupling to the PPh(3) group was also identified, consistent with the large spin density on the phosphorus, along with partially resolved bromine couplings. The use of 1, 4, 5 and 6 as pre-catalysts for the Kumada coupling of aryl chlorides and fluorides with ArMgY (Ar = Ph, Mes) showed the highest activity for the smaller ring systems and/or smaller substituents (i.e., 1>4≈6≫5).