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Stabilization of low oxidation gold anions as aurate or auride by organic ligands has long been a synthetic challenge, owing to the proneness of low-valent gold centres to cluster. Despite being the most electronegative metal, isolable gold(I) aurate complexes have only been obtained from a few σ-withdrawing organo- and organo-main group ligands. Stabilization of highly-reduced gold complexes by π-modulating redox active ligands has only been achieved by cyclic (amino)(alkyl)carbene (CAAC), which is limited to 1e

To stabilize S

In this study, we afford explicit characterizations of electronic and geometrical structures of recently reported hypervalent penta-coordinate carbon compounds by using gas-phase characterization techniques: photodissociation spectroscopy (PDS) and ion mobility-mass spectrometry (IM-MS). In particular for a compound with moderately electron donating ligand bearing p-methylthiophenyl substituents, the coexistence of tetra- and penta-coordinate isomers are confirmed, consistent with the solution characterizations. It is in sharp contrast to the exclusive tetra-coordinate form (with normal valence of the central carbon atom) in the single crystal. This suggests that non-polar environment makes penta-coordinate structure thermodynamically most stable. This delicate difference between the tetra- and penta-coordinate structures dependent on environments is a close reflection of the lower activation barrier of SN2 reaction found under neutral solvent or gas-phase reactions.

Meridional tridentate N-heterocyclic carbene (NHC)-based pincer ligands contribute to a substantial growth in modern organometallic chemistry in both homogeneous catalysis and luminescence materials. Among all NHC-based pincer ligands, the dianionic LX2-type CCC-pincer ones constitute the smallest subcategory owing to their limited ligand frameworks suitable for complexation. This work reports a one-pot, high-yield synthesis of a homoleptic anionic all-carbon bis-pincer iridium(III) complex (4) directly from a bis(aryl)-substituted dipyrido-annulated (dpaAr2) imidazolium salt and [Ir(COD)Cl]2 via a cascade of deprotonation/C-H activation processes. Both experimental complexation chemistry and computational mechanistic investigation suggest that the large bite angle and π-rich character of the dpaAr2 NHC are responsible for its facile complexation as a dianionic LX2-type CCC-pincer ligand precursor. The all-carbon ligated iridium(III) complex (4) bearing a π-conjugated ligand scaffold showed remarkably low oxidation potentials, which allows future investigations in its redox chemistry and photophysical properties.

We investigated the complexes of Cram's hexa(p-anisole) spherands (SPR, 1) with Li+ and Na+ ions (1·Li+ and 1·Na+) isolated in the gas phase. Despite the small conformational difference between 1·Li+ and 1·Na+ owing to the rigid framework of 1, ultraviolet photodissociation (UVPD) spectroscopy under cryogenic (∼10 K) conditions yielded clearly distinguishable absorption edges: ∼34 000 and ∼34 500 cm−1 for 1·Li+ and 1·Na+, respectively. The spectral assignment and the preorganization characteristics of the host molecule were compared with those of dibenzo-18-crown-6-ether (DB18C6) complexes, which have more flexible frameworks. Furthermore, we revealed the characteristic unimolecular dissociation of the 1·Li+ complex using UVPD and collision-induced dissociation (CID); the formation of fragment ions with dibenzofuran moieties was detected. This dissociation pattern was ascribed to the efficient release of dimethyl ether molecule(s) from the 1·Li+ complex, which is characteristic of the cyclic skeleton formed with six methoxy groups in the SPR.

A new efficient metal-based frustrated Lewis pair constructed by (Pt Bu3 )2 Pt and B(C6 F5 )3 was designed through density functional theory calculations for the catalytic dehydrogenation of ammonia borane (AB). The reaction was composed by the successive dehydrogenation of AB and H2 liberation, which occurs through the cooperative functions of the Pt(0) center and the B(C6 F5 )3 moiety. Two equivalents of H2 were predicted to be liberated from each AB molecule. The generation of the second H2 is the rate-determining step, with a Gibbs energy barrier and reaction energy of 27.4 and 12.8 kcal/mol, respectively.

The reaction of Power’s digalladeltacyclane with Au(PPh3)Cl led to formation of a digallium gold complex (2) with both chloride and gold bridging between two gallium atoms. The bonding parameters f...

An addition of two equivalents of Lewis acid with Lewis basic 9,10-dicyanoanthracene enabled tuning of the spatial and electronic properties of the parent molecule. An investigation on optical prop...

Dipyrrolyldiketone difluoroboron complexes (BONEPYs) were synthesized by condensation of the corresponding pyrroles and malonyl chloride followed by treatment with BF3·OEt2. The aryl-substituted pyrrole is introduced to form a cyclic system in order to investigate anion binding studies. In BONEPYs 1–3 the o-H of the aryl group forms hydrogen bonding with F− to give a more table complex. In contrast, the intramolecular hydrogen-bonded BONEPY endo-4 is more stable than its exo isomer. While adding F−, the hydrogen bonds must be broken first to give 4·(3)F−. Owing to the electron-rich group (-OMe), the o-H of the phenyl group can hardly interact with F− via hydrogen bonding to give the less stable complex 4·(5)F−. The energy differences between the different conformations were calculated using DFT methods, which is consistent to the experimental observations.

We investigated the complexes of Cram's hexa(

Generation of dihydrogen from water splitting, also known as water reduction, is a key process to access a sustainable hydrogen economy for energy production and usage. The key step is the selective reduction of a protic hydrogen to an accessible and reactive hydride, which has proven difficult at a p-block element. Although frustrated Lewis pair (FLP) chemistry is well known for water activation by heterolytic H–OH bond cleavage, to the best of our knowledge, there has been only one case showing water reduction by metal-free FLP systems to date, in which silylene (SiII) was used as the Lewis base. This work reports the molecular design and synthesis of an ortho-phenylene linked bisborane-functionalized phosphine, which reacts with water stoichiometrically to generate H2 and phosphine oxide quantitatively under ambient conditions. Computational investigations revealed an unprecedented multi-centered electron relay mechanism offered by the molecular framework, shuttling a pair of electrons from hydroxide (OH−) in water to the separated proton through a borane-phosphonium-borane path. This simple molecular design and its water reduction mechanism opens new avenues for this main-group chemistry in their growing roles in chemical transformations., A (bisborane)triarylphosphine was developed to spontaneously generate H2 from water under ambient conditions, revealing an unprecedented multi-centered electron relay mechanism for a metal-free umpolung of proton to hydride.

Halogen–lithium exchange reaction of o-(silyl)bromobenzene 5 with tert-BuLi afforded o-(silyl)lithiobenzene 6, which was reacted with (alkoxy)diarylboranes 7 to form borate intermediates 8. Treatment of 8 with chlorotrimethylsilane formed o-(alkoxysilyl)(diarylboryl)benzenes 4. The C–O bond in 4 was activated by intramolecular interaction between the oxygen atom and the boron atom. 4a readily reacted with MeOH and EtOH to afford the corresponding alkoxysilanes 10 and 11, respectively. Treatment of 10 with 1,4-diazabicyclo[2.2.2]octane (DABCO) afforded the silyloxyborate complex 13.

The coordination chemistry of our recently isolated bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC (N-heterocyclic carbene), dpaP2-NHC, towards copper(I) and silver(I) has been studied. Based on dpaP2-NHC, two dinuclear silver and copper complexes [2, (Ag2L2) and 3, (Cu2L2)], two tetranuclear copper complexes {4, [Cu4L2(NCMe)2] and 6, (Cu4LBr4)} and a pentanuclear copper complex [5, (Cu5L2Br3)] exhibiting strong intramolecular metal–metal interactions were achieved and characterized. All the complexes exhibited dynamic behavior in solution, in which the NMR coalescence of 2 was well resolved at low temperature (below 208 K) and dissociation for 2 was observed according to the calculated Eyring plot. Ag2L2 (2) shows a similar coordination sphere to that of our previously reported gold complex Au2L2; Cu2L2 (3) features a rare μ2-bridging carbene and a terminal carbene; Cu4LBr4 (6) is neutral and monomeric, in which four copper atoms were rigidly fixed by the tridentate dpaP2-NHC ligand and bromide anions. All the complexes (2–6) were luminescent at room temperature, in which 4–6 provided phosphorescence at 77 K. Based on the comparison of the emission bands with dpaP2-NHC, we conclude that the electronic transitions of 2–6 can be attributed to the ligand-centered (LC) transitions.

Phosphine-functionalized N-heterocyclic carbene (NHC) ligands are known to complex group 11 metal centers to form multinuclear complexes with photoluminescence properties. This study reports a structurally rigid ortho-substituted dipyrido-annulated NHC with T-shape coordination geometry and its di- and tetranuclear gold(I) complexes. The free ligand as well as all metal complexes are found luminescent at room temperature and phosphorescent at 77 K. Although metal d10–d10 interactions are evident based on their solid-state structures, their effect on the photoemission is limited, most likely due to the weak coordination of the ligand to the metal centers in solution.

Heteroatomic derivatives of Chichibabin's hydrocarbon are explored theoretically to highlight the relationship between the electronic structure and nonlinear optical (NLO) properties. The results show that the systems are divided into two classes: one that has intermediate electronic structure between two main contributing resonance structures, and a second with an electronic structure that is approximated by only one resonance structure. It is found that the former class of derivatives exhibits approximately one-order larger static second hyperpolarizability (γ) than the latter class, because of either their intermediate diradical or charge-transfer (CT) characteristics. The asymmetric systems are further scrutinized by using the static electric field model, which shows that the intermediate CT character is essential for the very large enhancement of γ in the asymmetric systems. These results not only clarify the structure–property relationships of open-shell singlet NLO compounds with redox switching properties, but also shed light on a new and unexplored class of closed-shell NLO systems generated by the introduction of intermediate CT nature into open-shell singlet systems.

The new sterically hindered piperidine analog, dispiro[cyclohexane-2,2′-piperidine-6′,2″-cyclohexane] (CPC(H), 2), and its N-methylated derivative CPC(Me) (3) were synthesized from commercially available starting materials in short steps. The N-lithiated amide LiCPC (4) was also isolated from 2 as a cyclictrimer in single crystals and showed slightly larger steric hindrance than that of lithium 2,2,6,6-tetramethylpiperidide (LiTMP) in the competitive methylation reaction with methyl trifluoromethanesulfonate. In addition, the heterobimetallic heteroleptic zincate complexes [Li(μ-NR2)(μ-Et)Zn(Et)] (NR2 = CPC, 5, and NR2 = TMP, 6) were obtained as THF- and TMEDA-coordinated monomer 5·(THF)2, 6·(THF)2, 5·TMEDA, and 6·TMEDA (THF = tetrahydrofuran, TMEDA = N,N,N′,N′-tetramethylethylenediamine). These molecular structures bearing different amido ligands in single crystals showed little structural differences from crystallographic studies. Diffusion-ordered spectroscopy (DOSY) revealed that the solution structur...

Pyridazines with amino groups positioned para to each aromatic ring nitrogen and fixed in six-membered rings were prepared. The representative symmetric amino N-Et derivative was found to slightly exceed DMAP in catalytic activity in the acetylation reaction of a tertiary alcohol in C6D6. Nucleophilicity eclipsing that of DMAP was established in competitive reactions using phenacyl bromide as the electrophile, and the unsymmetric N-Et derivative was revealed to have even higher nucleophilicity.

A new pentacene-type silaborin, in which three benzene rings are bridged by silicon and boron atoms, has been synthesized and characterized by using NMR spectroscopy and X-ray crystallographic analysis. The precursor, 1,4-bis(dimesitylboryl)-2,5-bis(phenylsilyl)benzene (4), was prepared by stepwise introduction of a silyl group and a boryl group to a benzene ring starting from 1,4-dibromobenzene. Double cyclization of 4 proceeds by a H-Mes exchange and a B-H/C-H dehydrogenative condensation to afford pentacene-type silaborin 5. X-ray crystal structure analysis reveals that 5 adopts a bent structure rather than a planar one. UV/Vis spectra and DFT calculations for 5 reveal a lowering of the LUMO energy level compared with corresponding anthracene-type 3.

The donor properties of five different PCcarbeneP ligands are assessed by evaluation of the CO stretching frequencies in iridium(i) and rhodium(i) carbonyl cations. The ligands feature dialkyl phosphine units (R = (i)Pr or (t)Bu) linked to the central benzylic carbon by either an ortho-phenylene bridge, or a 2,3-benzo[b]thiophene linker; in the former, substituent patterns on the phenyl linker are varied. The carbonyl complexes are synthesized from the (PCcarbeneP)M-Cl starting materials via abstraction of the chlorides in the presence of CO gas. In addition to the expected mono carbonyl cations, products with two carbonyl ligands are produced, and for the rhodium example, a novel product in which the second carbonyl ligand adds reversibly across the Rh[double bond, length as m-dash]C bond to give an η(2) ketene moiety was characterized. The IR data for the complexes shows the 2,3-benzo[b]thiophene linked system to be the poorest overall donor, while the phenyl bridged ligands incorporating electron donating dialkyl amino groups para to the anchoring carbene are very strongly donating pincer arrays.

Dimerization of [2,5-bis(fluorodimethylsilyl)phenyl]lithium (8) afforded 9,10-dihydro-9,10-disilaanthracene 9 bearing fluorodimethylsilyl groups at the 2- and 6-positions. Tetrahydrotetrasilapentac...

Direct structural evidence for group 11 metal-mediated B–B bond activation was obtained from reactions of tri(tert-butyl)azadiboriridine (1) with AuCl(L) complexes. The AuCl(SMe2) reaction afforded [η2-B,B-B(tBu)N(tBu)B(tBu)]AuCl (2) by ligand displacement. More donating phosphines as co-ligands led to B–B bond cleavage accompanied by either halide or L migration to form boron–gold complexes 3 (L = PPh3) and 4 (L = PMe3). A similar product 5, which is isostructural to 4, was obtained by the addition of dimethylaminopyridine (DMAP) to 2–4. Complexes 2–5 constitute rare examples of metal complexes bearing two Lewis acidic centres. The effect of the boryl ligand was demonstrated in the formation of a gold(I) complex 6 bearing a 5-membered heterocycle from 3 and tert-butylisonitrile. Plausible reaction mechanisms that led to these complexes and their bonding situation were explored computationally at the DFT level.

A family of 7-6-7 ring-based PCP pincer iridium/rhodium complexes has been applied to the transfer dehydrogenation of isopropanol to give acetone using tert -butylethylene (TBE) as the hydrogen acceptor. For the iridium complexes, high initial activity was achieved with the turnover number (TON) being as high as 6000 after 2 h at 200 °C, even when TBE was present in high concentration (6000 equivalents). The inhibition effect of TBE was found to be somewhat weaker than in the case of alkane dehydrogenation using the same catalysts. Whereas the corresponding rhodium complex was inactive in alkane dehydrogenation, it was unexpectedly found to have a catalytic activity of 2000 TONs (3000/1 TBE/catalyst ratio) after 2 h at 200 °C in the same transfer dehydrogenation. The bonding properties of the reactive complexes were investigated through natural bond orbital (NBO) analysis and compared.

A method for the introduction of various substituents at the 4 and 8 positions of 2,10-di-tert-butyldipyrido[1,2-c;2′,1′-e]imidazolium salts, is described. The new imidazolium salts bearing substituents (R′ = Cl, SPh) at the 4 and 8 positions are synthesized in three-step procedures, and carbenes generated from the imidazolium salts can be used to give the corresponding rhodium complexes. The role of the 4,8-substituents can be either bystanders or coordinating ligands according to the nature of the metal moiety.

For use as an electrode material, a new synthetic route to a Martin-type tridentate ligand and hypervalent sulfur anions bearing this ligand has been developed. A battery containing the anions bear...

A triaminotriborane(3) was isolated as purple crystals through a reduction of (TMP)BCl2 (TMP = 2,2,6,6- tetramethylpiperidino) by sodium naphthalenide. Single-crystal X-ray diffraction and computational studies of the obtained triaminotriborane(3) revealed a bent structure of the [B(NR2)]3 chain. The bond lengths between the central and terminal boron atoms were similar to those observed in neutral diborene species. The multiple-bonding character may be best described by a three-center two-electron π-bond along the B3 chain. The distance between the two terminal boron atoms (2.177 A) in the solid state structure implies a weak interaction in between. When an excess amount of Li was used as the reducing agent, the reaction yielded an unusual dianionoic species. The isolation and characterization of these two reduction products are reported herein.

The isolation and study of carbenes with σ-donating and π-accepting properties stronger than those of N-heterocyclic carbenes (NHCs) have been regarded as one of the big challenges in carbene chemistry. We have investigated the properties of 1,8-disubstituted xanthylidene-based compounds by using two different approaches: The photolysis-induced formation of free carbenes and the synthesis of the corresponding metal–carbene complexes by oxidative addition. The former study revealed that the carbene unsubstituted at the 1- and 8-positions is kinetically more reactive than the parent xanthylidene and that the substituents at the 1- and 8-positions are less effective in generating carbenes by photolysis. However, oxidative addition of palladium(0) to the 1,8-diphenyl-substituted precursor successfully afforded a low-coordinate 14-electron palladium(II)–carbene complex. This unusual complex is stabilized by agnostic interactions involving an adjacent phenyl group. This complex is the second example of a stable cationic 14-electron palladium(II)–carbene complex to have been reported so far.

New allene compounds, 5c and 5d, bearing 1,8-dichloroacridene moieties were synthesized, and the oxidation of 5c and 5d was performed to generate thermally stable triplet carbenes. Since the oxidation resulted in the formation of decomposition products, the photolysis of brominated allene compound 18 was performed. UV–vis measurement at low temperatures indicated the generation of intermediates with decreasing starting material 18, although the efficiency of photolysis was quite low. ESR and electron spin transient nutation (ESTN) spectra suggested that the multiplicity of intermediates is triplet, probably the target triplet carbene 6d is generated. In terms of |D| values of the intermediates, ESR showed that unpaired electrons are more effectively delocalized in 6d by the introduction of nitrogen atoms in the skeleton (biradical character in Scheme 1). The observed triplet species 6d was not stable enough to isolate. Copyright © 2014 John Wiley & Sons, Ltd.

A rarely investigated octaisopropylporphyrin (OiPP) was successfully prepared by an alternative synthetic route with organic reactions. Introduction of an electron-donating butyl group at the meso-position of OiPP nickel(II) and copper(II) complexes induced structural perturbation on the porphyrin cores. Structural distortion of nickel(II) complexes decreased slightly upon introduction of a butyl group; however, structural change of the copper complexes showed opposite behavior. These results indicate that structural deformation of the OiPP metal complexes with a meso-substituent was determined by the central metal.

The most anti-aromatic 16π porphyrin, an octaethylporphyrin (OEP) zinc(II) complex with no substituents at the meso-positions was generated as a highly unstable species from the reaction of the corresponding 18π porphyrin using strong oxidants such as AgSbF 6/ I 2 or SbF 5. The porphyrin showed a significant blue-shift unique to 16π porphyrins in its UV-vis spectrum. 1 H NMR measurements revealed an evident high-field shift of the meso-protons of the porphyrin ring, thereby establishing that the novel 16π porphyrin has the strongest anti-aromaticity reported so far.

A bit borane: Silicon-functionalized dibenzosilaborins were prepared by intramolecular B-H/C-H dehydrogenative cyclization of o-(silyl)(hydroboryl)benzenes. The hydrosilyl derivative (X=H) can be converted into the fluorosilane (X=F) and chlorosilane (X=Cl). UV/Vis and fluorescence spectra are influenced by the functional groups X on the silicon atom through σ*-π* conjugation.

In order to elucidate the electronic nature of our recently reported first hexacoordinated carbon (12-C-6), density functional theory (DFT) calculations of sulfide precursor, sulfone derivative, and S+-F derivative were carried out and compared with those of the reported S+-Me hexacoordinated carbon. Computations on the hexacoordinated carbon, indicating that four attractive C–O interactions with the central hexacoordinate carbon atom exist, also revealed that the interactions consist of two different types of three-center four-electron bonds, which can be regarded as electron donation by the lone pairs of the oxygen atoms to the empty low-lying π*-orbitals of the allene. The optimized structures of the sulfide, sulfone, S+-F, and the original S+-Me suggested that the introduction of electron-withdrawing groups at the sulfur atoms would make the C–O attractive interactions stronger by a larger contribution of the carbon dication resonance structure. Thus, allene compounds (sulfide, sulfone, sulfonium) with two different thioxanthene ligands (one with 1,8-dimethoxy groups as in the S+-Me compound and the other with 1,8-diphenoxy groups) were synthesized to confirm the predicted substituent effects on the C(central)–O interactions. Electron-withdrawing substituents at the sulfur atoms were found to give rise to strong C(central)–O attractive interactions; the average values of the four C–O distances were smaller as the electron-withdrawing ability of the sulfur atoms rose. Additionally, C(central)···OMe distances were shorter than the corresponding C(central)···OPh distances, reflecting the higher electron-donating ability of the oxygen atoms at these 1,8-positions of the thioxanthene skeleton.

A series of Rh-PCP pincer complexes (iPrPCP)Rh(L) bearing a novel alkyl–aryl mixed “7-6-7” ring skeleton has been synthesized and fully characterized. The 7-6-7 ring skeleton in the hydrido-chloro and carbonyl species was found to assume the cis and trans conformations, respectively, in solid state as determined by single crystal X-ray diffraction analysis. This suggested a flexibility of the backbone compared with the similar but strictly fixed anthracene backbone. Electron density on the central rhodium atom was investigated by IR experiments and by DFT computations. NMR monitoring of the reaction of the hydrido-chloro complex with base followed by application of H2 showed the presence of what are likely to be the active 14e− species and the dihydride derivative. Especially, noteworthy is the former that was found to be relatively stable, in contrast to the corresponding iridium complex. [Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, ...

The countercation effect on the reactivity of ambiphilic o-(fluorodimethylsilyl)phenyl anion was investigated by replacing Li in 1 with Cu (4 and 5), Mg (6), and Zn (7). The reactivity of the aryl metal species was estimated by the yields of dimerized product 3, which were monitored by GC. X-ray crystallographic analysis, DFT calculations, and AIM analysis of bis(aryl)zinc 7 were performed. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 24:53–57, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.21062

o-C(6)H(4)(SiR(3-n)H(n))(BMes(2)) (1; R=Me, Ph; n=1, 2) undergo Mes-H (Mes=mesityl) ligand exchange between the silicon atom and the boron atom to form o-C(6)H(4)(SiMesR(3-n)H(n-1))(BMesH) (6) upon heating. The resulting hydroborane intermediates (6) immediately react with benzaldehyde to afford their corresponding benzyloxyboranes (5). A DFT study of model compounds reveals the transition states of the ligand exchange. A hydride abstraction from the silicon atom by the boron center is key to reaching the transition states, which include the tricoordinate silyl-cation moiety and the tetracoordinate hydridoborate moiety.

Previously unreported octaisopropyltetraphenylporphyrin (OiPTPP) was prepared from 3,4-diisopropylpyrrole, an unstable previously unisolated heterocyclic compound. Purification of the free-base 18π porphyrin required conversion to its 18π zinc(II) complex, chromatographic separation, and acid mediated demetalation. Oxidation of the 18π porphyrin with SbCl5 furnished metal-free 16π octaisopropyltetraphenylporphyrin (OiPTPP). X-ray structural determination revealed that the novel species is the most distorted 16π porphyrin to date. The time course of decomposition of the oxidized species monitored by UV-vis spectra implied that the introduction of high steric repulsion was effective for enhancing stability of the 16π porphyrin. The reaction of metal-free 16π OiPTPP with LiBF4 followed by Pd2(dba)3 gave the corresponding 18π OiPTPP palladium(II) complex via reduction of the OiPTPP lithium(I) complex as previously reported for 16π octaisobutyltetraphenylporphyrin (OiBTPP). The new 18π porphyrin system could be characterized by the X-ray analysis of the 18π OiPTPP palladium(II) complex. The X-ray structure of the 18π metal complex also indicated that the distortion of the porphyrin ring had become larger than that of previously known 18π porphyrins

Computational analysis on the dicationic species generated upon two-electron oxidation of the corresponding allenic compounds bearing two thioxanthene (7a) or two acridene (7b) moieties indicated that the ground-state multiplicity would be of the triplet state (ΔEST = ECS − ET = 12.6 and 14 kcal/mol, respectively). Under this premise, oxidation reactions of 7a and 7b were carried out. In the case of 7b, oxidation with (p-BrC6H4)3N•+SbCl6− gave a dimer (13), which could be presumed to have formed by dimerization of the corresponding carbene. Oxidation of 7b in the presence of tetramethylpiperidine N-oxide afforded the corresponding ketone derivative (14), thus implying the likelihood of a triplet carbene being the reactive intermediate. These results suggest that double oxidation of heterocyclic allene compounds is viable as a new approach for generating triplet carbenes. Copyright © 2011 John Wiley & Sons, Ltd.

A series of the monocyclic organophosphorus compounds ([o-OC(CH3)2C6H4]PPh(CH2 Ph)X) bearing a halogen (X = F, Cl, and Br) or a tetrafluoroborate (X = BF4) were synthesized. The solid-state structures of the bromide, the tetrafluoroborate, and an analogous fluoride ([o-OC(CF3)2C6H4]PPh(CH2 Ph)F) were determined by single crystal X-ray crystallography. The geometry of the fluoride was almost an ideal trigonal bipyramid (TBP). On the other hand, the bromide and tetrafluoroborate were essentially phosphonium salts with phosphorane character to some extent for the former. In CD3 CN, the bromide, the chloride, and the tetrafluoroborate were found to exist as phosphonium salts. However, it was suggested that in CDCl3, the bromide and the chloride have structures rapidly equilibrating or averaged between the phosphorane and the phosphonium forms. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:523–530, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20717

Reactions of o-(HSiR2)(BMes2)C6H4 (R = Me (3a), Ph (3b)) with a fluoride ion afford [o-(FSiR2)(HBMes2)C6H4]− (R = Me (5a), Ph (5b)), which involve the FSi⋅⋅⋅HB interaction to render the silicon atom pentacoordinate. The FSi⋅⋅⋅HB interaction in 5a was confirmed by X-ray crystallographic analysis and “atoms-in-molecules” (AIM) analysis. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:471–475, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20709

Neutral hexacoordinate organoantimony compounds LSb(Xyl)C6H4 (o-Y) [L = tridentate ligand; Xyl = C6H3 (3,5-Me2); Y = CH2 OMe (4), CH2 NMe2 (5), and 2-pyridyl (6)] with intramolecular coordination were synthesized. Single crystal X-ray crystallography revealed that the donor atom (N or O) of 4–6 was coordinated trans to one of the two carbon atoms of the tridentate ligand. Variable temperature (VT) NMR measurements of compounds 4 and 5 indicated that the stereomutations proceeded via dissociation of the Sb-donor (N or O) bond followed by SbC bond rotation. Compound 4 was found to have a stereomutation barrier of ca. 12 kcal mol−1. In the case of 5, dissociation of the SbN bond was found to be distinguishable from the stereomutation. Energies of SbN dissociation 5 and interconversion of enantiomers were estimated to be ca. 15 and ca. 19 kcal mol−1, respectively, from the VT-NMR measurements. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:553–561, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20721

Tetrakis(2-pyridyl)stannane (o-Py4Sn), which bears only weakly nucleophilic and Lewis basic pyridines, and a weakly acidic tetraaryltin moiety, was found to efficiently catalyze the reaction betwee...

The reaction of cis-4-oxo-2-pentenal and 8-phenylmenthyl 2-oxocyclopentane-1-carboxylate in the presence of a fluorinated cosolvent afforded the corresponding furan product with a high diastereosel...

A new dipyrido-annulated N-heterocyclic carbene with phosphorus substituents at the 4 and 8 positions and the corresponding Rh(I) and Rh(III) complexes prepared from the carbene are reported. The X...