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The chiral spiroborate anions [B

The merger of photoredox catalysis with asymmetric copper catalysis have been realized to convert achiral carboxylic acids into enantiomerically enriched alkyl nitriles. Under mild reaction conditions, the reaction exhibits broad substrate scope, high yields and high enantioselectivities. Furthermore, the reaction can be scaled up to synthesize key chiral intermediates to bioactive compounds.

A borylene cation stabilized by bis(silylene) and carbon monoxide was prepared and structurally characterized via the reaction of bis(silylene)-stabilized bromoborylene with W(CO)

Boroles are important motifs within functional materials. With the aim to prepare a pinacolboryl-substituted derivative, the metallacycle transfer from corresponding zirconium and tin precursors has been explored. We show that the reaction of 1,1-dimethyl-2,3,4,5-tetrapinacolborylstannole with dichloro(phenyl)borane does not provide the desired borole, but instead a stannyl-substituted 1-chloroboracyclopent-3-ene. Spectroscopic and structural details of this highly functionalized boracycle indicate that intramolecular interactions between the tin and oxygen atoms of the boryl substituents may account for the unexpected outcome of the tin-boron exchange reaction.

Boroles can react with CO to give Lewis acid–base adduct 1AD, tricyclic boracycle 1TB or ketene derivative 1KD depending on the substituents on the borole. DFT calculations at the M06-2X level of theory were performed to study systematically the influence of borole substituents on these reactions. It was found that the Lewis acid–base adduct 1AD is a kinetic product, which can further transform to the tricyclic boracycle 1TB or ketene derivative 1KD. The computational results show that strong electron-withdrawing perfluorophenyl substituents significantly stabilise the Lewis acid–base adduct 1AD, allowing its successful isolation. In most cases, the tricyclic boracycle 1TB is both kinetically and thermodynamically more favourable than the ketene derivative 1KD. However, a –B(C6F5)2 substituent at the 4-position and a silyl substituent at the 5-position together are able to lower the barrier leading to the formation of the ketene derivative 1KD.

The purpose of the work described herein is to design highly efficient photosensitizers (PS) for photodynamic therapy (PDT) in theory. A series of expanded Zn porphyrins have been studied as light-activated PS. Their main photophysical properties are systematically calculated by using density functional theory and its time-dependent extension. The mechanisms of PDT are discussed. All the considered candidates exhibit intense absorption in the therapeutic window (600–800 nm), efficient intersystem crossing, and sufficient energy for singlet molecular oxygen production. Accordingly, the designed Zn pentaphyrins and sapphyrins would be proposed as potential PS for PDT. Moreover, the therapeutic effects of Zn pentaphyrins and sapphyrins are better than those of the referenced Zn iso-pentaphyrin. It is expected that the results could provide a new way to design and develop PS for PDT application.

A versatile π-extension reaction was developed based on the three-component cross-coupling of aryl halides, 2-haloarylcarboxylic acids, and norbornadiene. The transformation is driven by the direction and subsequent decarboxylation of the carboxyl group, while norbornadiene serves as an ortho-C-H activator and ethylene synthon via a retro-Diels-Alder reaction. Comprehensive DFT calculations were performed to account for the catalytic intermediates.

Tetra(o-tolyl)diborane(4), 1, was synthesized and characterized experimentally as well as theoretically by density functional theory (DFT) calculations. Exposure of 1 to H2 (1 bar) at room temperature afforded the corresponding di(o-tolyl)hydroborane through cleavage of the H–H and B–B bonds. DFT calculations suggested a diarylboryl anion character for the transition state.

Treatment of Na[Re(CO)5] with methyl 3-(naphthalen-1-yl)propiolate (NpC≡CCO2Me) followed by acetyl chloride and alcohols ROH (R = Me, nPr) afforded the rhenacyclobutadiene complexes Re{-C(Np)═C(CO2Me)C(OR)═}(CO)4. Reactions of these rhenacyclobutadiene complexes with HC≡COEt produced the rhenabenzene complexes Re{-C(Np)═C(CO2Me)C(OR)═CHC(OEt)═}(CO)4 and new rhenacyclobutadienes with a pendant vinyl substituent Re{-C(Np)═C(C(OR)═CH(CO2Et))C(OMe)═}(CO)4. In the vinyl-substituted rhenacyclobutadiene products, the ethyl of the ester group is from the alkyne HC≡COEt, the alkyl of the ReC(OR) group is from the ester group of the starting rhenacyclobutadienes, and the alkyl group of the OR of the vinyl substituent is from the ReC(OR) group of the starting rhenacyclobutadienes. A plausible mechanism for the formation of the vinyl-substituted rhenacyclobutadienes is discussed.

A new organocatalytic transfer hydrogenation strategy for the asymmetric synthesis of 1,1-diarylethanes is described. Under mild conditions, a range of 1,1-diarylethanes substituted with an o-hydroxyphenyl or indole unit could be obtained with excellent efficiency and enantioselectivity. We also extended the protocol to an unprecedented asymmetric hydroarylation of 1,1-diarylalkenes with indoles for the synthesis of a range of highly enantioenriched 1,1,1-triarylethanes bearing acyclic all-carbon quaternary stereocenters. These diaryl- and triarylethanes exhibit impressive cytotoxicity against a number of human cancer cell lines. Preliminary mechanistic studies combined with DFT calculations provided important insight into the reaction mechanism.

DFT calculations have been carried out to study the detailed mechanism of Rh(III)-catalyzed C–H activation/cyclization of 2-acetyl-1-arylhydrazines with alkynes leading to the formation of indoles, in which the hydrazine moiety is used as the internal oxidant. The energy profiles associated with the catalytic cycle, involving N–H deprotonation, C–H activation (a concerted metalation–deprotonation (CMD) process), alkyne insertion, ring rearrangement/isomerization, and finally N–N bond cleavage/reductive elimination to regenerate the active species, are presented and analyzed. Through analysis of the calculation results, we found that the combined processes of the CMD and alkyne insertion contribute to the overall rate-determining step. The N–N bond cleavage step was examined in detail to understand how the internal oxidant interacts with the metal center to facilitate the catalytic reactions. The factor influencing regioselectivity was also investigated. How different types of substrates (alkynes versus al...

DFT calculations have been carried out to study the detailed mechanisms for the nickel-catalyzed reductive carboxylation of ester-substituted styrenes H2C═CHAr using CO2 to form α-carboxylated products. Two possible mechanisms, the oxidative coupling mechanism and the nickel hydride mechanism, were calculated and compared. Our calculations show that, for the oxidative coupling mechanism, a metallacycle thermodynamic sink is generated from oxidative coupling between CO2 and a styrene substrate molecule on the nickel(0) metal center, which should be avoided in order for smooth reductive carboxylation of styrenes. For the nickel hydride mechanism, a nickel hydride species is the active species, from which styrene insertion into the Ni–H bond followed by reductive elimination produces the α-carboxylated product. Calculations show that either of these two steps (insertion and reductive elimination) can be the rate-determining step, and both transition states are only slightly more stable than the oxidative cou...

DFT calculations have been carried out to study the detailed mechanisms for carboxylative-coupling reactions among terminal alkynes, allylic chlorides, and CO2 catalyzed by N-heterocyclic carbene copper(I) complex (IPr)CuCl. The competing cross-coupling reactions between terminal alkynes and allylic chlorides have also been investigated. The calculation results show that a base-assisted metathesis of (IPr)CuCl with PhC≡CH occurs as the first step to give the acetylide (IPr)Cu–C≡CPh, from which CO2 insertion and reaction with an allylic chloride molecule, respectively, lead to carboxylative-coupling and cross-coupling reactions. It was found that both the reactions of (IPr)Cu–C≡CPh and (IPr)CuOCOC≡CPh (a species derived from CO2 insertion) with an allylic chloride molecule occur through an SN2 substitution pathway. The two SN2 transition states (calculated for the carboxylative coupling and cross coupling) are the rate-determining transition states and show comparable stability. How the reaction conditions...

The intramolecular arylation of 2-pyrones, 2-pyridones, coumarins and quinolones is reported using PdII precatalyst sources without added phosphine ligands. The excellent yields and convenient reagents enables the formation of various analogues containing these moieties, and access to potential biologically active candidates. Stoichiometric studies were carried out to provide an insight into the oxidation addition step. A switch in regioselectivity, together with a hydrodebromination process, was observed in the case of a 3-bromo-2-pyrone.

New ruthenium(II) photosensitizers [Ru(dcbpy)(L)(NCS)2] (dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine; L = 4,4′-bis{di[4-(N,N′-dimethylamino)phenyl]amino}-2,2′-bipyridine (1), 4,4′-bis[di(4-methoxyphenyl)amino]-2,2′-bipyridine (2), and 4,4′-bis[di(4-tolyl)amino]-2,2′-bipyridine (3)) were prepared and characterized and their application in dye-sensitized solar cells is presented. The optical absorption of these photosensitizers gives a peak at around 540 nm, which is very similar to that of the standard N719. The maximum incident photon-to-current conversion efficiency (IPCE) of 80.6 % was obtained for 3, which corresponded to a power conversion efficiency (η) of 5.68 % under standard air mass (AM) 1.5 sunlight (versus N719 at 6.76 %). Molecular cosensitization of 3 with an organic dye, QS-DPP-I, yielded higher η values up to 6 % relative to the cells based on individual photosensitizers, and the corresponding IPCE can reach 93.6 % at 549 nm. A preliminary stability test of the devices was also conducted.

The use of various diethynylarene ligands in the synthesis of some metal carbonyl linking clusters is established. New dimeric complexes of osmium [{(μ-CO)Os3(CO)9}2(μ3-η2-diyne)], ruthenium [{(μ-H)Ru3(CO)9}2(μ3-η2,η2-diyne)] or [{(μ-CO)Ru3(CO)9}2(μ3-η2-diyne)] and cobalt [{Co2(CO)6}2(η2-diyne)] (diyne = HC≡CArC≡CH, Ar = 2,7-fluorene, 2,7-fluoren-9-one, bithiazole or bithiophene) have been prepared in good yields from the reaction of [Os3(CO)10(NCMe)2], [Ru3(CO)12] or [Ru3(CO)10(NCMe)2] and [Co2(CO)8] with half an equivalent of the appropriate diethynylarene ligand, respectively. All these cluster compounds have been characterized by IR and 1H NMR spectroscopies and mass spectrometry. The molecular structures of three of them have been determined by X-ray crystallography. For the group 8 osmium and ruthenium analogues, the hexanuclear carbonyl clusters consist of two trinuclear metal cores with the exhibition of the μ3-(η2-||) bonding mode for the acetylene groups when [M3(CO)10(NCMe)2] (M = Ru, Os) was used and the μ3-η2,η2 bonding mode when [Ru3(CO)12] served as the starting cluster. The tetracobalt species possesses two Co2C2 cores adopting the pseudo-tetrahedral geometry having the alkyne bond lying perpendicular to the Co–Co vector in each core. Density functional theory was also used to study the electronic structures of selected molecules.

Treatment of Na[Re(CO)5 ] with RCCCO2 Et (R=phenyl, naphthalen-1-yl, phenanthren-9-yl and pyren-1-yl) followed by reaction with acetyl chloride and ethanol afforded the rhenacyclobutadienes Re{-C(R)C(CO2 Et)C(OEt)}(CO)4 . Reactions of these rhenacyclobutadienes with HCCOEt produced rhenabenzenes Re{-C(R)C(CO2 Et)C(OEt)CHC(OEt)}(CO)4 . Except for R=Ph, new rhenacyclobutadienes with pendant alkenyl substituents Re{-C(R)C(C(OEt)CH(CO2 Et))C(OEt)}(CO)4 were also isolated from these reactions. The NMR spectroscopic and X-ray structural data, as well as the aromatic stabilization energy (ASE) values suggest that the rhenabenzenes are aromatic, with extensive delocalized π character.

Treatment of RuCl2(PPh3)3 with 6-dimethylaminopentafulvene in THF in the presence of water produced (η5-C5H4CHO) RuCl(PPh3)2, which was reduced by NaBH4 to give the Ru-H⋯HO dihydrogen bonded complex (η5-C5H4CH2OH) RuH(PPh3)2. The dihydrogen bonded complex (η5-C5H4CH2OH)RuH(PPh3)2 could also be synthesized by the reduction of complex (η5-C5H4CHO)RuH(PPh3)2, which was obtained by the reaction of RuHCl(PPh3)3 with 6-dimethylaminopentafulvene in the presence of water. The analogous dihydrogen bonded osmium complex (η5-C5H4CH2OH)OsH(PPh3)2 was similarly prepared. Single crystal structures and DFT calculations support the presence of intra-molecular H…H interaction, with separations of around 1.9 to 2.0 A.

New heteroleptic cyclometalated iridium(III) 2-phenylpyridine-type complexes with trifluoromethyl substituents and various main-group moieties were synthesized and their photophysical, electrochemical, and electroluminescent (EL) properties studied. The emission color can be tuned by a facile derivatization of the phenyl moiety of 2-phenylpyridine with various main-group moieties, and we have prepared new yellowishgreen to orange triplet emitters with enhanced charge injection/charge transporting features, which can furnish attractive EL performance in phosphorescent organic light-emitting devices (OLEDs). Attempts were also made to fabricate two-color white-light OLEDs based on a combination of fluorescent blue and phosphorescent orange emitters.

A density functional theory (DFT) study was carried out to elucidate the mechanism of [2 + 2 + 1] cyclotrimerization of o-carboryne with CH2═CHnBu and TMS–≡–Ar mediated by a nickel complex. The calculated results reveal that the commonly proposed mechanism via a nickel vinylidene intermediate is kinetically and thermodynamically disfavored. An unprecedented reaction mechanism involving alkyne insertion, η1-alkenyl to η2-alkenyl rearrangement, and TMS migrations is found to be responsible for the favorable [2 + 2 + 1] cycloaddition. The new mechanism rationalizes well the substituent effect on the stereoselectivity of E/Z [2 + 2 + 1] products 3E/3Z and the chemoselectivity of [2 + 2 + 1] over [2 + 2 + 2] cyclotrimerization.

The detailed reaction mechanisms of the C═O hydrosilylation of isocyanate and the C═S bond cleavage of isothiocyanate mediated by the neutral ruthenium silylene hydride complex Cp*(CO)(H)Ru═Si(H){C(SiMe3)3} have been investigated with the aid of density functional theory calculations. Through the investigation, the difference in reactivity between isocyanate and isothiocyanate toward the ruthenium silylene hydride complex has been examined and discussed. The different bond strengths and π-accepting abilities of C═O and C═S and the different degrees of affinity of O and S toward the Si center in the silylene ligand contribute to the different reactivities of the isocyanate and isothiocyanate substrates observed experimentally.

A mixed ionic liquid system has been developed for the efficient catalysis of CO2 addition to aliphatic epoxides without involving any transition metal catalysts or other additives. The ionic liquid integrated with pyridinium and pyrrolidinium groups (1·(Br)3) together with a non-polar ionic liquid (3·(Ntf)2) effectively transformed non-polar aliphatic epoxides to cyclic carbonates by the reaction with CO2 under mild CO2 pressure (3.0 MPa) and reaction temperature (80 °C). The presence of 3·(Ntf)2 remarkably improved the catalytic activity of 1·(Br)3 towards non-polar epoxides by increasing the miscibility of catalyst with the substrates. The mixed ionic liquid system is robust enough to be recycled without any significant loss of catalytic activity. GC–MS studies were performed to reveal the reaction pathways to the cyclic carbonates and a feasible model accounting for the effective CO2 activation in the ionic liquid system was proposed using density functional theory (DFT) calculations.

Whereas terminal oxo complexes of transition and actinide elements are well documented, analogous lanthanide complexes have not been reported to date. Herein, we report the synthesis and structure of a cerium(IV) oxo complex, [CeO(LOEt )2 (H2 O)]⋅MeC(O)NH2 (1; LOEt (-) =[Co(η(5) -C5 H5 ){P(O)(OEt)2 }3 ](-) ), featuring a short CeO bond (1.857(3) Å). DFT calculations indicate that the hydrogen bond to cocrystallized acetamide plays a key role in stabilizing the CeO moiety of 1 in the solid state. Complex 1 exhibits oxidizing and nucleophilic reactivity.

Density functional theory calculations were carried out to study the Pd-catalysed oxidation reactions of alcohols using phenyl chloride as an oxidant. Our calculations supported that the mechanism mainly involves oxidative addition, β-hydride elimination, reductive elimination, and finally ligand substitution. Through our calculations, we have explained why oxidation of secondary alcohol was experimentally observed but not that of primary alcohol. The oxidation products (ketones) of secondary alcohols bind much more weakly than the oxidation products (aldehydes) of primary alcohols, contributing to the reactivity difference. The mechanism of the Pd-catalysed domino oxidation–arylation reactions of secondary alcohols was also studied. We have explained the experimental observation that α-arylation of the oxidation products (ketones) of secondary alcohols occurs only when the temperature was raised to 80 °C from below 40 °C.

We describe herein the design and synthesis of two new organic regioisomeric D–π–A sensitizers incorporating the dithieno[3,2-b:2′,3′-d]pyran (DTP) unit. The dye-sensitized solar cells (DSSCs) based on these two dyes exhibit impressive power conversion efficiency.

The Low Level radio frequency system long-term stability is critical for the operation of accelerator facilities. The RF cavity field phase drift observed at the Tsinghua Thomson scattering X-ray source showed the correlations with devices temperature characteristic. We proposed a drift compensation technique by time-multiplexing cavity pick-up and phase reference signals, which guaranteed that they shared the same route with the same change. The preliminary ∼84 h Dual-Receiver out-of-loop stability test showed phase drift of 100 fs peak-peak (∼45 fs rms) when the reference signal phase changed ∼40 ps peak-peak.

DFT calculations have been carried out to study the Rh-catalyzed site selective ring-opening reactions of phenylcyclobutabenzenol (1a). Our calculations supported that the mechanism involves β-carbon elimination in a rhodium(I) phenylcyclobutabenzenolato complex followed by alcoholysis. The favorable β-carbon elimination involves the cleavage of the C(sp(2))-C(sp(3))(OH)(Ph) bond in 1a, which determines the site selectivity. The mechanism and regioselectivity of the related Rh-catalyzed insertion reaction of the asymmetric alkyne MeC≡CPh with phenylcyclobutabenzenol (1a) was also investigated. The key step involves the alkyne insertion into the Rh-C σ bond of a species resulting from the favorable β-carbon elimination in the rhodium(I) phenylcyclobutabenzenolato complex. The favorable insertion couples the metal-bonded carbon with the methyl-substituted carbon of MeC≡CPh.

In this paper, DFT calculations have been carried out to study the reaction mechanism of copper-catalyzed hydrocarboxylation of alkynes using CO2 and hydrosilanes. In addition to hydrocarboxylation of alkynes, possible competitive reactions such as hydrosilylation of alkynes, hydrosilylation of CO2, and silacarboxylation of alkynes have also been investigated and compared. Through these DFT calculations, we are able to understand the reason only hydrocarboxylation of alkynes has been observed experimentally.

Three new organic photosensitizers ( HK1 – HK3 ) incorporating functionalized bulky trimer of triarylamine derivatives as the electron donor units, 3,4-ethylenedioxythiophene moiety as the conjugated spacer, and cyanoacrylic acid as the electron acceptor, have been synthesized and the effects of different bulky electron donor substituents on the photovoltaic performances of dye-sensitized solar cells (DSSCs) are investigated accordingly. The DSSC based on HK1 with tris(triphenylamine) electron donor in the absence of the co-adsorbent chenodeoxycholic acid (CDCA) shows the best photovoltaic performance under standard global AM 1.5 sunlight: a short-circuit current density ( J sc ) of 10.41 mA cm −2 , an open-circuit voltage of 0.76 V and a fill factor of 0.65, corresponding to a maximum overall power conversion efficiency (PCE) of 5.11%. However, in the presence of co-adsorbent CDCA, the PCEs of DSSCs based on these photosensitizers, decrease significantly by about 9.7%, which is contrary to the conventional concept that CDCA can improve the efficiency by inhibition of dye aggregation and intermolecular electron recombination. The results demonstrate that the synthesized new organic dyes with bulky dendritic triarylamine and its derivatives as electron-donation units can efficiently suppress dye aggregation without the need of the co-adsorbent and effectively reduce the intramolecular electron recombination in DSSCs.

With the aid of DFT calculations, we have examined the mechanism of the Ni-catalyzed cycloaddition of 3-azetidinone with alkynes. Our DFT results did not support the originally proposed mechanism, which involves a ring expansion through β-carbon elimination. Instead, our calculations supported a mechanism which involves oxidative addition of 1-Boc-3-azetidinone to a Ni(0) center to form an intermediate having both Ni–C(O) and Ni–C(sp3) bonds, then alkyne insertion into either the Ni–C(O) or Ni–C(sp3) bond depending on the alkyne substrates being studied, and finally reductive elimination to give the cycloaddition products. The nature of insertion of alkynes into a Ni–C bond was also discussed. When an alkyne substrate inserts into the Ni–C(O) bond, we found that the alkyne acts as a nucleophile to attack the electron-deficient, metal-bonded C═O carbon center. When an alkyne substrate inserts into the Ni–C(sp3) bond, the alkyne acts as an electrophile to interact with the Ni–C(sp3) bond.

Density functional theory calculations have been performed to investigate the mechanisms of the Pd-catalyzed dearomatization reaction between chloromethylnaphthalene and the cyclic amine morpholine. The calculation results indicate that the reductive elimination leading to the formation of the dearomatic product takes place via an intramolecular C–N bond coupling between the para carbon of an η3-exo-(naphthyl)methyl ligand and the nitrogen atom of the amide ligand. The free energy barrier is calculated to be only 13.1 kcal/mol, significantly lower than that (37.8 kcal/mol) through the η3-endo-(naphthyl)methyl intermediate originally thought. For comparison, various C–N coupling reaction pathways leading to the formation of dearomatic and aromatic products have also been examined.

The synthesis, structural, electrochemical and photophysical studies of a series of cyclometalated iridium(III) complexes with functionalized borylated oligothiophene ligands are reported. The effect of oligothiophene chain length on the photophysical properties of these metal complexes was examined in detail and their excited state properties can be controlled by increasing the number of thienyl rings in the cyclometalating ligand, thus allowing the emission to be tuned from red to near-infrared. All of the iridium(III) complexes were utilized in the fabrication of phosphorescent organic light-emitting diodes and their device performances were investigated. These electrophosphors emit in the red to near-infrared regions. The present work enables the rational design of new borylated iridium phosphors by synthetically tailoring the structure of oligothiophene-based pyridine ring that can permit color tuning toward near-infrared phosphorescence. (C) 2013 Elsevier B.V. All rights reserved.

A multidentate and flexible diolefin-diphosphine ligand, based on the dibenzylidene acetone core, namely dbaphos (1), is reported herein. The ligand adopts an array of different geometries at Pt, Pd and Rh. At Pt(II) the dbaphos ligand forms cis- and trans-diphosphine complexes and can be defined as a wide-angle spanning ligand. (1)H NMR spectroscopic analysis shows that the β-hydrogen of one olefin moiety interacts with the Pt(II) centre (an anagostic interaction), which is supported by DFT calculations. At Pd(0) and Rh(I), the dbaphos ligand exhibits both olefin and phosphine interactions with the metal centres. The Pd(0) complex of dbaphos is dinuclear, with bridging diphosphines. The complex exhibits the coordination of one olefin moiety, which is in dynamic exchange (intramolecular) with the other "free" olefin. The Pd(0) complex of dbaphos reacts with iodobenzene to afford trans-[Pd(II)(dbaphos)I(Ph)]. In the case of Rh(I), dbaphos coordinates to form a structure in which the phosphine and olefin moieties occupy both axial and equatorial sites, which stands in contrast to a related bidentate olefin, phosphine ligand ("Lei" ligand), in which the olefins occupy the equatorial sites and phosphines the axial sites, exclusively.

Recently, many examples of gold nanoclusters have been synthesized due to their exceptional spectroscopic properties and potential applications in nanotechnology. In this work we put forward an approach based on the icosahedral [Au

In the absence of transition metal catalysts, the unsymmetrical diborane(4), pinB-BMes2, reacted with alkynes to afford diborylalkenes. The isomer ratio of the products could be controlled via temperature, solvent, and additive(s). A reaction mechanism was proposed on the basis of two isolated intermediates, and this reaction could furthermore be applied to synthesize a luminescent molecule.

The electronic structure of so-called 'xenophilic' clusters, which contain both organometallic fragments and Werner-type paramagnetic transition metal centres, presents a challenge to simple theories of bonding. Density functional theory shows clearly that the cluster Mn(2)(thf)(4)(Fe(CO)(4))(2) is best described as an exchange-coupled Mn(II)(2) dimer, the closed-shell organometallic [Fe(CO)(4)](2-) fragments acting simply as bridging ligands. The high-spin configuration of the Mn(II) ions leads to single occupation of the Mn-Fe σ* orbitals and therefore substantially weaker metal-metal bonding than in conventional low-valent organometallic clusters. The transition metal fragments are effective mediators of superexchange (J(calc) = -44 cm(-1)), leading to the measured effective magnetic moment of ~5 μ(B) at 300 K, considerably lower than the limiting value of 8.37 μ(B) for two uncoupled S = 5/2 Mn(II) centres.

The (B-Cl)-chloroboroles 2-chloro-1,3-di(4-R-phenyl)-2,4,5,6-tetra-hydrocyclopenta[c]borole (R = H, Br) undergo a novel dimerisation process in CH2Cl2 solution. The resulting unsymmetric dimers are highly fluxional in solution via reversible enantiomerisation through an intermediate with mirror symmetry. DFT calculations suggest an unusual dimerisation mechanism and provide insight into the dynamics of the dimers.

A potassium diboryllithate (B2 LiK) was synthesized and structurally characterized. DFT calculations, including NPA and AIM analyses of B2 LiK, revealed ionic interactions between the two bridging boryl anions and Li(+) and K(+) . Upon standing in benzene, B2 LiK deprotonated the solvent to form a hydroborane and a phenylborane. On the basis of DFT calculations, a detailed reaction mechanism, involving deprotonation and hydride/phenyl exchange processes, is proposed. An NBO analysis of the transition state for the deprotonation of benzene suggests that the deprotonation should be induced by the coordination of benzene to the K(+) .

The reactivity of the cerium(IV) oxo complex [(L-OEt)(2)Ce-IV(=O)(H2O)].MeC(O)NH2 (1; L-OEt(-) = [CoCp{P(O)(OEt)(2)}(3)] (-), where Cp = eta(5)-C5H5) toward electrophiles and Bronsted acids has been investigated. The treatment of 1 with acetic anhydride afforded the diacetate complex [Ce-IV(L-OEt)(2)(O2CMe)(2)] (2). The reaction of 1 with B(C6F5)(3) yielded [Ce-IV(L-OEt)(2)(Me2CONH2)(2)][B(C6F5)(3)(OH)](2) (3), in which the [B-(C6F5)(3)(OH)](-) anions are H-bonded to the O-bound acetamide ligands. The treatment of 1 with HCl and HNO3 afforded [Ce-IV(L-OEt)(2)Cl-2] and [Ce-IV(L-OEt)(2)(NO3)(2)], respectively. Protonation of 1 with triflic acid (HOTf) gave the diaqua complex [Ce-IV(L-OEt)(2)(H2O)(2)](OTf)(2) (4), in which the triflate anions are H-bonded to the two aqua ligands. The treatment of 1 with phenol afforded the phenoxide complex [Ce-IV(L-OEt)2(OPh)(2)] (5). The oxo-bridged bimetallic complex [(L-OEt)(2)(Me2CONH2)Ce-IV(O)NaLOEt] (6) with the Ce-O-oxo and Na-O-oxo distances of 1.953(4) and 2.341(4) angstrom, respectively, was obtained from the reaction of 1 with [NaLOEt]. Density functional theory calculations showed that the model complex [(L-OMe)(2)Ce-IV(Me2CONH2)(O)NaLOMe] (6A; L-OMe(-) = [CoCp{P(O)(OMe)(2)}(3)](-)) contains a polarized Ce=O multiple bond. The energy for dissociation of the {NaLOMe} fragment from 6A in acetonitrile was calculated to be +33.7 kcal/mol, which is higher than that for dissociation of the H-bonded acetamide from [(L-OMe)(2)Ce-IV(=O)(H2O)].MeC(O)NH2 (1A) (calculated to be +17.4 kcal/mol). In hexanes containing trace water, complex 1 decomposed readily to a mixture of a tetranuclear cerium(IV) oxo cluster, [Ce-4(IV)(L-OEt)4(mu(4)-O)(mu(2)-O)(4)(mu(2)-OH)(2)] (7), and a cerium(III) complex, [Ce-III(L-OEt)(2)(H2O)(2)][L-OEt] [8(L-OEt)], whereas the cerium/sodium oxo complex 6 is stable under the same conditions. The crystal structures of 3, 4.H2O, 6, and 8(L-OEt) have been determined.

Many transition-metal complexes and some metal-free compounds are able to bind carbon monoxide, a molecule which has the strongest chemical bond in nature. However, very few of them have been shown to induce the cleavage of its C-O bond and even fewer are those that are able to transform CO into organic reagents with potential in organic synthesis. This work shows that bis(pinacolato)diboron, B2pin2, reacts with ruthenium carbonyl to give metallic complexes containing borylmethylidyne (CBpin) and diborylethyne (pinBC≡CBpin) ligands and also metal-free perborylated C1 and C2 products, such as C(Bpin)4 and C2 (Bpin)6, respectively, which have great potential as building blocks for Suzuki-Miyaura cross-coupling and other reactions. The use of (13)CO-enriched ruthenium carbonyl has demonstrated that the boron-bound carbon atoms of all of these reaction products arise from CO ligands.

Reactions of both terminal and internal alkynols with ReOCl2(OEt)(PPh3)2 (1) are described. Treatment of ReOCl2(OEt)(PPh3)2 (1) with HC≡CC6H4-2-CH2OH and HC≡CCH2CH2CH2OH produced the six-membered ylide complexes ReOCl2(C(═CH(PPh3))-C6H4-CH2O)(PPh3) (2) and ReOCl2(C(═CH(PPh3))CH2CH2CH2O)(PPh3) (3), respectvely, derived from addition of PPh3 to the terminal alkyne carbon. Similarly, phosphine addition to the terminal alkyne carbon occurred in the reactions of ReOCl2(OEt)(PPh3)2 (1) with HC≡CCH2CH(OH)Me and HC≡CCH2CH(OH)CH(OH)CH2C≡CH to give the five-membered ylide complexes ReOCl2(C(═CH(PPh3))CH2CH2CHMeO)(PPh3) (5) and {ReOCl2(C(═CH(PPh3)CH2CHO)(PPh3)}2 (6), respectively. Interestingly, related reactions of ReOCl2(OEt)(PPh3)2 with RC≡CCH2CH2OH (R = Me, Et, Ph) produced the six-membered ylide complexes ReOCl2(CR═C(PPh3)CH2CH2O)(PPh3) (7, R = Me; 8, R = Et; 9, R = Ph), derived from addition of PPh3 to the alkyne carbon closer to the OH group.

Calcium silicate hydrate (C-S-H) is a main product of Portland cement hydration. Although C-S-H is treated as an amorphous phase in macro scale, the atomic-scale structure of C-S-H is considered to be nanocrystalline and short-ordered. Various studies have been carried out and many models have been proposed in the past few decades to describe the structure of C-S-H at nano scale. Tobermorite and jennite are considered as two naturally existing crystalline solids sharing similar structures with C-S-H, especially tobermorite. As a result, tobermorite-based models are predominant in the literature. Besides, combination models with both tobermorite and jennite as well as exceptive models have also been developed in the same period. In this paper, the C-S-H models developed in the past decades are reviewed systematically. The reliability of the models is discussed based on the fundamental requirements of the C-S-H structure from consideration of experimental observations and structural chemistry, including charge balance, Ca/Si (C/S) ratio and Qn distribution. Finally, some considerations on the understanding of C-S-H are put forward for possible development of C-S-H structure in the future.

Reactions of [ReH(5)(PMe(2)Ph)(3)] with alkynols HC≡CC(OH)(R)C≡CSiMe(3) (R=tBu, iPr, 1-adamantyl) in the presence of HCl give the vinylcarbyne complexes [Re{≡CCH=C(R)C≡CSiMe(3)}Cl(2)(PMe(2)Ph)(3)], which react with tBuMgCl to give [Re{≡CCH=C(R)C≡CSiMe(3)}HCl(PMe(2)Ph)(3)]. Treatment of [Re{≡CCH=C(R)C≡CSiMe(3)}HCl(PMe(2)Ph)(3)] with nBu(4)NF gives [Re{≡CCH=C(R)C≡CH}HCl(PMe(2)Ph)(3)], which first isomerizes to the bicyclic complexes [Re{CH=CH-C(R)=CCH=}Cl(PMe(2)Ph)(3)], and then to the rhenabenzynes [Re{≡CCH=C(R)CH=CH}Cl(PMe(2)Ph)(3)]. The NMR spectroscopic and structural data as well as the aromatic stabilization energy (ASE) and nucleus-independent chemical-shift (NICS) values suggest that these rhenabenzynes have aromatic character.

Building bridges: The first m-metallapyridine and the first metallapyridyne were synthesized under mild reaction conditions. The two complexes are metal-bridged polycyclic metallabenzenoid aromatics, in which the transition-metal center is shared by both six-membered rings. The synthetic method permits the use of metallabenzene as a starting material to access higher π-electron metallaaromatics.