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Although the application of cationic aluminum complexes in catalysis has been extensively investigated, the incorporation of an aluminum cation into a chiral environment is less explored. In this s...

To expand the reactivity scope of divalent germanium, an α-iminopyridine supported dicoordinate germanium complex (2) was prepared from deamination of the corresponding pyridine-coordinated diamido...

The chemistry of the boron cation has been revitalized in the past decade due to its newfound application in stoichiometric and catalytic organic reactions. To extend the frontier of boron cation c...

In an attempt to prepare the heavier analogue of NHC-stabilized borenium cation, we have prepared a silylene-coordinated borenium equivalent (1a), which can be viewed as a contact ion pair of borenium and triflate. The triflate anion coordinates to the oxophilic silicon center, leaving the boron center existing in a trigonal-planar geometry in the solid state and in solution. Nucleophilic substitution reactions of 1a all result in the release of free silylene ligand, demonstrating the borenium-ion-like reactivity of 1a. Chemical reduction of 1a leads to a neutral radical possessing a partial Si–B double bond.

As the synthetic applications of boron monocations as stoichiometric reagents or catalysts have expanded significantly in the past decade, investigation on the molecular electronics and reactivity of the related boron dications remains in its infancy. This mini-review highlights the recent advancements in boron polycations consisting of one or multiple boron centers. The structure–reactivity relationship of these dicationic species will also be discussed.

Bridging-type polydentate N-heterocyclic carbene (NHC) ligands are valuable building blocks for organometallic supramolecules. In order to quickly expand the ligand library of poly-NHC, we have ass...

The reaction mechanism of the [Et3BH]−-induced conversion of a dicationic boron compound ([Cp*B-IMes]2+, [1]2+) to a planar neutral carbene-coordinated borabenzene (2) is investigated experimentally and theoretically. Owing to the steric congestion around the boron center, bulky [Et3BH]− attacks the less encumbered carbon atom of Cp*, leading to a metastable 5-borabicyclo[2.1.1]hex-2-ene borenium cation ([3-CH]+) at low temperature. Upon raising the temperature, the bicyclic-borenium ion undergoes sequential pericyclic reactions, including suprafacial [1,3]-sigmatropic shift, two-electron electrocyclic ring opening, and then [1,2]-hydrogen shift to a planar cyclic borenium ion, [4-CH]+, which can then be deprotonated to yield the neutral aromatic borabenzene. The attack of hydride at the boron center of [1]2+ was excluded through the preparation and isolation of 6-borabicyclo[3.1.0]hexenylium, [3-BH]+, which could not be transformed into [3-CH]+ or [4-CH]+. The borenium ion rearrangement follows first-ord...

A facile synthetic protocol, which utilized dehydrative condensation of phthalic anhydride and primary amines, for symmetrical non-chelating poly-N-heterocyclic carbene ligands was established. With the designed bi-functional building block, poly-NHC ligands having various denticities and geometries could be readily achieved by varying the structure of poly-amino compounds. Examination of catalytic activity of a series of poly-NHC–Ni complexes revealed the lack of electronic interference among NHC–metal units.

A twisted mono-cationic bis-benzimidazolium salt was serendipitously isolated from the dehydrative condensation of 5,6-dihydroxyl-1,3-dimesityl-benzimidazolium and 1,4-benzenediboronic acid. Subsequent deprotonation of the benzimidazolium salt led to the formation of a spiroborate-linked free bis-NHC, which was further transformed into the corresponding diborane adduct and the di-Rh complex.

Main-group metal-based catalysts have attracted considerable attentions due to their complementary reactivities to transition metals. In searching for the catalytic application of heavy divalent Group 14 derivatives, we came to discover that the benzannulated N-heterocyclic plumbylene (1) could serve as an effective catalyst for ring-opening polymerization of l -lactide (L-LA) at room temperature. In the presence of benzyl alcohol (BnOH), 97% conversion of L-LA was accomplished in 10 min under a catalyst loading of merely 0.3 mol% ([LA]:[1]:[BnOH] = 400:1.2:1.2, [1] = 1.2 mM). Compared to the polymeric plumbylene ([Pb(μ-OiPr)2]∞), the excellent catalytic activity of 1 at ambient temperature may be ascribed to the steric and electronic stabilizations of the Pb2+ center by the organic backbone. Thus, thermal activation is no longer required to expose the Lewis acidic metal center for polymerization.

Upon treatment with a molybdenum-carbene with bidentate substituted biaryl-o,o′-diphenoxide ligand 12, norbornene fused with N-aryl-endo-pyrrolidine 9a undergoes ROMP to give exclusively polynorbornene with cis, isotactic-selectivity. Bis(norbornenes) connected with ferrocene 18 or benzene 20 linkers yield the corresponding double-stranded ladderphanes 19 and 21, respectively with isotactic stereochemistry having all double bonds in Z-configuration. Like the corresponding ladderphanes with E-double bonds, ladderphane 19 also assembles on HOPG to give a highly ordered two-dimensional array as revealed by STM images.

Herein, we report the synthesis of boroles that are linked by a conjugated phenylene spacer. The characterization of these compounds was completed by NMR and UV/Vis spectroscopy, as well as X-ray crystal diffraction. Furthermore, the coordination behavior of these oligoboroles towards five electronically and sterically disparate pyridine derivatives was studied and revealed fundamental differences in the properties of the resulting adducts. The experimental results were supported by density functional theory (DFT) calculations that showed a charge-transfer effect upon formation of the pyridine-4-carbonitrile adduct. By chemical reduction of a tris(borolyl)-substituted benzene derivative, a hexaanion was isolated as a result of a two-electron reduction of each borolyl moiety. The interaction of the borolyl units through the aryl spacer, and the possible increase of the Lewis acidity due to the conjugation of the borolyl moieties, were investigated by base transfer reactions.

Borole systems tend to undergo various reactions driven by the disruption of its destabilizing antiaromatic character. As a consequence, the isolation and characterization of free boroles is challenging, especially when the substituents around the C4B framework are sterically less demanding. In the present paper we report the synthesis of 1-bromo-2,3,4,5-tetraphenylborole. The title compound readily undergoes a dimerization/rearrangement reaction in analogy to the previously reported 1-chloro-2,3,4,5-tetraphenyborole to form an isostructural product identified by X-ray crystallography. Additionally we present the formation of Lewis acid–base adducts of the title compound with 3,5-lutidine, PCy3, N-hetrocyclic carbene, cyclic (amino)(alkyl)carbene, and THF. The latter compounds were analyzed by single-crystal X-ray diffraction and compared.

Mes2BF and ArN2BF (ArN = 4-(Me2N)-2,6-Me2-C6H2) react with trimethylsilyltriflate and p-dimethylaminopyridine in chlorobenzene to afford the corresponding borenium salts [Mes2B-DMAP]+ OTf− ([1]+OTf−) and [ArN2B-DMAP]+ OTf− ([2]+OTf−), which have been fully characterized.

Herein, we report on the synthesis of ferrocenylborole [Fc(BC(4)Ph(4))(2)] featuring two borole moieties in the 1,1'-positions. The results of NMR and UV/Vis spectroscopy and X-ray diffraction studies provided conclusive evidence for the enhanced Lewis acidity of the boron centers resulting from the conjugation of two borole fragments. This finding was further validated by the reaction of [Fc(BC(4)Ph(4))(2)] and the 4-Me-NC(5)H(4) adduct of monoborole [Fc(BC(4)Ph(4))], which led to quantitative transfer of the Lewis base. The coordination chemistry of ferrocenylboroles was further studied by examining their reactivity towards several pyridine bases. Accordingly, the strong Lewis acidity of boroles in general was nicely demonstrated by the reaction of [Fc(BC(4)Ph(4))] with 4,4'-bipyridine. Unlike common borane derivatives such as [FcBMe(2)], which only forms a 2:1 adduct, we also succeeded in the isolation of a 1:1 Lewis acid/base adduct, with one nitrogen donor of 4,4'-bipyridine remaining uncoordinated. In addition, the reduction chemistry of ferrocenylboroles [Fc(BC(4)Ph(4))] and [Fc(BC(4)Ph(4))(2)] has been studied in more detail. Thus, depending on the reducing agent and the reaction stoichiometry, chemical reduction of [Fc(BC(4)Ph(4))] might lead to the migration of the borolediide fragment towards the iron center, affording dianions with either η(5)-coordinated C(5)H(4) or η(5)-coordinated BC(4)Ph(4) moieties. In contrast, no evidence for borole migration was observed during reduction of bisborole [Fc(BC(4)Ph(4))(2)], which readily resulted in the formation of the corresponding tetraanion. Finally, our efforts to further enhance the borole ratio in ferrocenylboroles aiming at the synthesis of [Fc(BC(4)Ph(4))(4)] failed and, instead, generated an uncommon ansa-ferrocene containing two borole fragments in the 1,1'-positions and a B(2)C(4) ansa-bridge.

As neutral isoelectronic analogues of the elusive cyclopentadienyl cation, boroles have been of interest for their prospective applications as strong Lewis acids, chromophores, and electron acceptors. Recently our group discovered a π-nucleophilic boryl anion based on the borole system. In an effort to extend borole chemistry, we now report the molecular structure of 1-chloro-2,3,4,5-tetraphenylborole (1) and its corresponding borole dianion resulting from the two-electron reduction of 1 with KC 8 . The thermally induced dimerization of 1 yields an unprecedented boracyclohexadiene/borolene spiro-bicyclic compound and the resulting dimer was fully characterized including a single-crystal X-ray analysis.