Anionic N-Heterocyclic Dicarbene−Borane Binuclear Complexes

Synthesis of MAuAg (M = Ni, Pd, or Pt) and NiAuCu Heterotrimetallic Complexes Ligated by a Tritopic Carbanionic N-Heterocyclic Carbene

Heterotrimetallic complexes (NiAuAg, PdAuAg, PtAuAg, and NiAuCu) containing a tritopic N-heterocyclic carbene (NHC) have been synthesized for the first time through the deprotonation and metalation of heterodimetallic complexes and were structurally characterized by single-crystal X-ray diffraction. The carbene character of the donor groups in the tritopic NHC complexes was established on the basis of structural and NMR analyses.

Lewis base-complexed magnesium dithiolenes

The first magnesium-based dithiolene, 2, was prepared by reaction of the lithium dithiolene radical, 1˙, with 2-mesitylmagnesium bromide. Reaction of 2 with N-heterocyclic carbenes (in toluene) gave a carbene-stabilized magnesium monodithiolene complex, 3. Complex 3, in turn, is readily converted to a THF-solvated magnesium bis-dithiolene dianion, 4, via partial hydrolysis in polar solvents (i.e., THF/CH3CN). Compounds 2, 3 and 4 have been spectroscopically and structurally characterized and probed by DFT computations.

Cationic abnormal N-heterocyclic carbene ruthenium complexes as suitable precursors for the synthesis of heterobimetallic compounds

Heterobimetallic dicarbene compounds are easily prepared from cationic imidazolyl-based abnormal N-heterocyclic carbene ruthenium complexes which allow facile metallation.

2-Aminophenolate ligands for phosphorus(v): a lithium salt featuring the chiral [P(OC6H4NR)3]- anion

Phosphoranes P(OC6H4NR)2(OC6H4NHR) [R = Me (2a), Ph (2b), C6F5 (2c)] were synthesized by treating PCl5 with the respective 2-aminophenol derivative (1a-c, 3.1 equiv.). In one instance, an intermediate species, P(OC6H4NR)2Cl [R = Me (3a)], was isolated and structurally characterized. Deprotonation of the amine moieties (-NH[combining low line]R) in phosphoranes 2a and 2b with a strong alkali-metal base (e.g. n-BuLi) in the presence of a strong-donor solvent (e.g. THF) afforded salts composed of the hexacoordinate P(v)-anions [P(OC6H4NR)3]- (R = Me, [4a]-; Ph, [4b]-). Employing precursor 2a, the salt Li(THF)3fac-[4a]- was isolated. The X-ray crystal of each enantiomer of [4a]- was determined and, to our knowledge, represents the first structurally characterized example of a salt containing a hexacoordinate P(v)N3O3 anion featuring P(v)-N bonds.

A tritopic carbanionic N-heterocyclic dicarbene and its homo- and heterometallic coinage metal complexes

Homo (Au₃)- and heterotrinuclear coinage metal complexes (Au₂Ag and Au₂Cu) ligated by the first tritopic dicarbanionic NHC have been prepared by deprotonation of ditopic NHC digold complexes.

1,3,2-Diazaborole-derived carbene complexes of boron

Reaction of 2-bromo-1,3,2-diazaborole (1) with excess BBr₃ induces 1,2-hydrogen migration, giving 1,3,2-diazaborole-derived carbene complexes of boron bromide (2). Compound 2 exists in a dynamic solution equilibrium with 1. The ¹H NMR study shows that the equilibrium lies to the right side of the dissociation reaction of 2. Parallel reaction of 1 with excess BI₃ gives the corresponding 1,3,2-diazaborole-derived carbene boron iodide complex (3). Notably, in contrast to 2, the dissociation reaction of 3 largely lies to the left side, favouring the formation of 3. The dynamic solution equilibrium behaviours of 2 and 3 are probed by both experimental and theoretical methods.

Normal-to-abnormal rearrangement of an N-heterocyclic carbene with a silylene transition metal complex

The NHC ligand of the complex 3-W undergoes normal-to-abnormal rearrangement on treatment with CsOH and yields the aNHC-complex 6-W, which is found to be 13.5 kcal mol⁻¹ less stable than its normal counterpart.

Abnormal carbene–silicon halide complexes

Reaction of the anionic NHDC ligand, [:C{[N(2,6-Prⁱ₂C₆H₃)]₂CHCLi}]_n (1), with SiCl₄ gives the trichlorosilyl-substituted NHC ligand (7). Abnormal carbene–SiCl₄ complex (8) can be conveniently synthesized by combining 7 with HCl·NEt₃. Meanwhile, 7 may react with CH₂Cl₂ in warm hexane, giving the abnormal carbene-complexed SiCl₃⁺ cation (9). The structure and bonding of 9 have also been probed by DFT computations.

Carbon-based two electron σ-donor ligands beyond classical N-heterocyclic carbenes

Recent advances in N-heterocyclic carbene-derived carbon-based two electron σ-donor ligands are presented in this perspective.

Ru–Ag and Ru–Au dicarbene complexes from an abnormal carbene ruthenium system

The first complexes containing an anionic dicarbene connected to two different d-block elements are reported. The synthetic pathway entails metalation and transmetalation reactions, starting from a cationic abnormal Ru-NHC complex.

A spiroborate-based anionic bis-N-heterocyclic carbene

A twisted bis-benzimidazolium salt was isolated from the reaction of 5,6-dihydroxyl-benzimidazolium and benzenediboronic acid. Deprotonation of the azolium salt led to the formation of a spiroborate-linked bis-NHC, which was further transformed into the corresponding diborane adduct and the di-Rh complex.

Carbene-stabilized beryllium borohydride

The reaction of N-heterocyclic carbene, L:, with BeCl(2) quantitatively yields L:BeCl(2)1 (L: = :C{N(2,6-Pr(i)(2)C(6)H(3))CH}(2)). The carbene-stabilized beryllium borohydride monomer L:Be(BH(4))(2)2 is prepared by the reaction of 1 with LiBH(4). Compound 3, prepared by the reaction of 2 with Na(2)[Fe(CO)(4)]·dioxane, represents an unusual "dual reduction" of the imidazole ring (i.e., hydroboration of the C═C backbone and hydrogenation of the C2 carbene center).