Activation of boryl-, borylene and metalloborylene complexes by isonitriles.

The reactions of isonitriles with a variety of metalloboryl and metalloborylene species are shown to yield a range of products, none of which display the typical Lewis acid-base reactivity previously observed between such metal complexes and other Lewis bases. Insertions of one, or several, isonitriles into the metal-boron bond give cyclic and spiro compounds with bonding controlled by the electron count at the metal and in the ring.

sp(2)-sp(3) diboranes: astounding structural variability and mild sources of nucleophilic boron for organic synthesis.

Despite the widespread use of organoborane reagents in organic synthesis and catalysis, a major challenge still remains: very few boron-centered nucleophiles exist for the direct construction of B-C bonds. Perhaps the most promising emerging solution to this problem is the use of sp(2)-sp(3) diboranes, in which one boron atom of a conventional diborane(4) is quaternised by either a neutral or anionic nucleophile. These compounds, either isolated or generated in situ, serve as relatively mild and convenient sources of the boryl anion [BR2](-) for use in organic synthesis and have already proven their efficacy in metal-free as well as metal-catalysed borylation reactions.

Silver(I) and thallium(I) cations as unsupported bridges between two metal bases.

Stirring Lewis-basic transition metal complexes with the salts M[BAr(Cl)4] (M = Ag, Tl; Ar(Cl) = 3,5-C6H3Cl2) resulted in the formation of diplatinum complexes [{(Cy3P)2Pt}2(μ-Ag)][BAr(Cl)4] (3) and [{(Cy3P)2Pt}2(μ-Tl)][BAr(Cl)4] (4) and the diiron compound [{(OC)3(Me3P)2Fe}2(μ-Ag)] (5) featuring bridging, unsupported metal cations. Their properties were investigated by multinuclear NMR spectroscopy, as well as X-ray diffraction and infrared measurements.

Synthesis of catechol-, pinacol-, and neopentylglycolborane through the heterogeneous catalytic B-B hydrogenolysis of diboranes(4).

A new synthetic approach to hydroboranes catechol-, pinacol-, and neopentylglycolborane has been developed. Starting from diboranes(4) B2cat2, B2pin2, or B2neop2, the respective boranes were obtained by heterogeneously catalyzed cleavage of the B-B bond in the respective diboranes with hydrogen. Group 10 metals were found to be effective catalysts for this reaction.

Boryl-functionalized σ-alkynyl and vinylidene rhodium complexes: synthesis and electronic properties.

The synthesis, reactivity, and properties of boryl-functionalized σ-alkynyl and vinylidene rhodium complexes such as trans-[RhCl(=C=CHBMes2)(PiPr3)2] and trans-[Rh(C≡CBMes2)(IMe)(PiPr3)2] are reported. An equilibrium was found to exist between rhodium vinylidene complexes and the corresponding hydrido σ-alkynyl complexes in solution. The complex trans-[Rh(C≡CBMes2)(IMe)(PiPr3)2] (IMe=1,3-dimethylimidazol-2-ylidene) was found to exhibit solvatochromism and can be quasireversibly oxidized and reduced electrochemically.

Diverse reactions of N-heterocyclic carbenes with an alkynylborane and isolation of a reactive zwitterionic borataallene.

Ethynyldimesitylborane (1) is synthesised via salt elimination and its reactivity towards NHCs is studied. Depending on their size, NHCs attack either at the boron atom or at the β-alkynyl carbon atom. Steric control over the reaction was probed by reactions with N-heterocyclic carbenes yielding a carbene-borane adduct (2), a 1-boraindane (3), and the first structurally characterised borataallene (4).

Multiple reduction of 2,5-bis(borolyl)thiophene: isolation of a negative bipolaron by comproportionation.

The 2,5-bis(borolyl)thiophene 2, a conjugated acceptor-π-acceptor system, can be reduced to the monoradical anion [2](.-) , the dianion [2](2-) , and the tetraanion [2](4-) . The dianion [2](2-) was also prepared by a comproportionation reaction and features an absorption maximum in the near-IR region (λmax =800 nm), which is characteristic of a bipolaron with a quinoidal structure.

σ-Coordination of metal-boryl bonds to gold(I).

The first examples of σ-coordinated metal-haloboryl complexes have been synthesised. The haloboryl moiety may be functionalized by nucleophilic substitution reactions, by which more electron-withdrawing substituents may be installed at the boron center.

Synthesis and structure of the first heterodinuclear bis(borylene) complexes.

We report a facile synthesis of the first heterodinuclear bis(borylene) complex by reaction of an iron bis(borylene) complex with [Pt(PCy3)2], and its fully-reversible CO uptake and liberation reaction.

Cyclic (amino)(imino)carbene complexes by borylene transfer to isocyanides.

Here we report the facile formation of boron-containing cyclic (amino)(imino)carbene complexes by reaction of a chromium borylene complex [(OC)(5)Cr=B=N(SiMe(3))(2)] with isocyanides.

σ-Donor-σ-acceptor plumbylene ligands: synergic σ-donation between ambiphilic Pt(0) and Pb(II) fragments.

Mono- and diplatinum plumbylene complexes are prepared in which the bonding comprises synergic σ donation between the Pt and Pb atoms. The bonding distinguishes the complexes from both the classical Fischer carbene bonding model and M→Pb dative-only bonding. The Pt-Pb bond of the monoplatinum complex is stable, while the diplatinum complex reversibly loses one Pt fragment.

Borylene transfer from an iron bis(borylene) complex: synthesis of 1,4-diboracyclohexadiene and 1,4-dibora-1,3-butadiene complexes.

Diene to be made: By tuning the size of acetylenic substituents, 1,4-diboracyclohexadiene and unprecedented 1,4-dibora-1,3-butadiene complexes were generated in a controlled manner by borylene transfer from an iron bis(borylene) complex to alkynes (see scheme).

High yield synthesis of a neutral and carbonyl-rich terminal arylborylene complex.

High yield synthesis of trans-[(Me(3)P)(OC)(3)Fe = BDur] (Dur, "Duryl" = 2,3,4,6-Me(4)C(6)H) is achieved by salt elimination and subsequent liberation of trimethylsilylbromide from K[Fe(CO)(3)(PMe(3))SiMe(3)] and Br(2)BDur.

Transition-metal-catalyzed synthesis of diboranes(4).

The diboranes(4) bis(catecholato)diborane (B(2)Cat(2)) and bis(pinacolato)diborane (B(2)Pin(2)) are important precursors for organoboronic esters, which are versatile reagents for the formation of carbon-carbon bonds. A new catalytic synthesis for these compounds starts from catecholborane or pinacolborane and gives the dehydrocoupling products B(2)Cat(2) and B(2)Pin(2) with turnover numbers of up to 11,600 (see scheme).

Sterically demanding hetero-substituted [2]borametallocenophanes of group IV metals: synthesis, structure and reactivity.

We report the synthesis and characterisation of unprecedented unstrained [2]diborametallocenophanes of zirconium and hafnium that bear the bulky octamethylfluorenyl (η(5)-C(29)H(36)) system, the proligands of which were pre-constructed by a two-step synthesis. The compounds were fully characterised by NMR spectroscopy, MALDI-TOF mass spectrometry and X-ray diffraction analysis. Typical reactivities relevant to olefin polymerisation such as methylation and chloride abstraction were also investigated.

Borido complexes via intermetallic metalloborylene transfer.

Intermetallic borylene transfer has been applied to synthesise new borido complexes. Starting from [{(η(5)-C(5)Me(5))Fe(CO)(2))}(μ-B){Cr(CO)(5)}] (1) the borylene moiety has been transferred successfully to different transition metal fragments. In the manner described, two new compounds have been fully characterised in solution and by X-ray crystallography.

Recent developments in the chemistry of antiaromatic boroles.

First isolated in 1969, most progress in the chemistry of the antiaromatic 4π electron borole system has been made during the 1980s. However, besides the fundamental aspects of the electronic structure and reactivity, boroles have not encountered serious research efforts for a rather long timeframe. This is somewhat surprising given the fact that boroles feature a unique combination of antiaromaticity, strong electrophilicity and unusual electronic properties.

Synthesis and coordination chemistry of 1-cymantrenyl-2,3,4,5-tetraphenylborole.

In this contribution, we report the synthesis of base-free 1-cymantrenyl-2,3,4,5-tetraphenylborole and two of its Lewis base adducts. In addition, the structural characterization and investigation of the photophysical properties are provided.

NHC-stabilized 1-hydro-1H-borole and its nondegenerate sigmatropic isomers.

Electrophilic quenching of a carbene-stabilized π-boryl anion with the Brønsted acid Et(3)NHCl provides a convenient synthetic route to the parent NHC-stabilized 1-hydroborole, which isomerizes to the corresponding 3-hydroborole via two successive nondegenerate [1,5]-sigmatropic hydrogen migrations. Molecular structures of both isomers have been determined by X-ray crystallography.