A Base-Stabilized Neutral BB Bond: Closing a Gap by Filling the Void

Non-classical covalent bonds

The possibility of multiple bond formation between Periodic Table Group 13 – 15 elements is considered. The ways of triple bond formation between these elements are discussed; particular attention is paid to the B≡B triple bonds. New non-linear compounds with triple bonds and their molecular structures are considered. The causes are given for the formation of compounds with unusually short distances between chemically non-bonded atoms. The grounds of the theory of two-centre three-electron bonds are presented and conditions of existence of isolated square planar carbon clusters are analyzed.

The bibliography includes 181 references.

Use of Single-Metal Fragments for Cluster Building: Synthesis, Structure, and Bonding of Heterometallaboranes

The synergic property of the CO ligand, in general, can stabilize metal complexes at lower oxidation states. Utilizing this feature of the CO ligand, we have recently isolated and structurally characterized a highly fluxional molybdenum complex [{Cp*Mo(CO)₂}₂{μ-η²:η²-B₂H₄}] (2; Cp* = η⁵-C₅Me₅) comprising the diborane(4) ligand. Compound 2 represents a rare class of bimetallic diborane(4) complex corresponding to a singly bridged C _s structure. In an attempt to isolate the tungsten analogue of 2, [{Cp*W(CO)₂}₂{μ-η²:η²-B₂H₄}], we have isolated a rare vertex-fused cluster, [(Cp*W)₃WB₉H₁₈] (5). Having a structural likeness with the dimolybdenum alkyne complex [{CpMo(CO)₂}₂C₂H₂], we have further explored the chemistry of 2 with CO gas that yielded a homoleptic trimolybdenum complex, [(Cp*Mo)₃(μ-H)₂(μ₃-H)(μ-CO)₂B₄H₄] (4). In an attempt to replace the 16-electron {Cp*MoH(CO)₂} moiety in 4 with isolobal fragment {W(CO)₅}, we treated the intermediate, obtained from the reaction of Cp*MoCl₄ and LiBH₄, with the monometal carbonyl fragment {W(CO)₅·THF}. The reaction indeed yielded two bimetallic clusters, [(Cp*Mo)₂B₄H₈W(CO)₄] (7) and [(Cp*Mo)₂B₄H₆W(CO)₅] (8), that seem to have been generated by the replacement of one {BH} or {BH₃} vertex from [(Cp*Mo)₂B₅H₉], respectively. All of the compounds have been characterized by various spectroscopic analyses and single-crystal X-ray diffraction studies. Electron-counting rules and molecular orbital analyses provided further insight into the electronic structure of all of these molecules.

CuOTf-mediated intramolecular diborene hydroarylation

CuOTf-mediated intramolecular diborene hydroarylation, followed by a σ-bond metathesis between the resulting B–H bond and CuOTf, gives a cyclic sp²–sp³ boryl-substituted boronium triflate.

Synthesis and reactions of N-heterocyclic carbene boranes

Boranes are widely used Lewis acids and N-heterocyclic carbenes (NHCs) are popular Lewis bases, so it is remarkable how little was known about their derived complexes until recently. NHC-boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes. They do not exhibit "borane chemistry", but instead are proving to have a rich chemistry of their own as reactants, as reagents, as initiators, and as catalysts. They have significant potential for use in organic synthesis and in polymer chemistry. They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry. Many of their reactions occur through new classes of reactive intermediates including borenium cations, boryl radicals, and even boryl anions. This Review provides comprehensive coverage of the synthesis, characterization, and reactions of NHC-boranes.

A viable anionic N-heterocyclic dicarbene

The first anionic N-heterocyclic dicarbene, polymeric [:C{[N(2,6-Pr(i)(2)C(6)H(3))](2)CHCLi(THF)}](n) 1, containing both normal (C2) and abnormal carbene (C4) centers in the same five-membered imidazole ring (III), has been prepared by lithiation of the imidazole monocarbene, :C{N(2,6-Pr(i)(2)C(6)H(3))CH}(2). The dicarbene nature of 1 was unambiguously demonstrated by the formation of the group 13 Lewis acid adducts (THF)(2)Li:C{[N(2,6-Pr(i)(2)C(6)H(3))](2)CHC(LA)}, where LA = AlMe(3) [2·(THF)(2)] and BEt(3) [3·(THF)(2)].

Unique homonuclear multiple bonding in main group compounds

Significant progress in the chemistry of main group compounds (group 13, 14, and 15) containing homonuclear multiple bonds has been made over the past three decades. This feature article addresses the unique structural and bonding motifs of these compounds, with a particular emphasis on both iconic molecules and recent novel discoveries.