Hypervalent Silicon Compounds by Coordination of Diphosphine–Silanes to Gold

Coordination of ambiphilic diphosphine–silane ligands [o‐(iPr₂P)C₆H₄]₂Si(R)F (R=F, Ph, Me) to AuCl affords pentacoordinate neutral silicon compounds in which the metal atom acts as a Lewis base. X‐ray diffraction analyses, NMR spectroscopy, and DFT calculations substantiate the presence of Au→Si interactions in these complexes, which result in trigonal‐bipyramidal geometries around silicon. The presence of a single electron‐withdrawing fluorine atom is sufficient to observe coordination of the silane as a σ‐acceptor ligand, provided it is positioned trans to gold. The nature of the second substituent at silicon (R=F, Ph, Me) has very little influence on the magnitude of the Au→Si interaction, in marked contrast to N→Si adducts. According to variable‐temperature and 2D EXSY NMR experiments, the apical/equatorial positions around silicon exchange in the slow regime of the NMR timescale. The two forms, with the fluorine atom in trans or cis position to gold, were characterized spectroscopically and the activation barrier for their interconversion was estimated. The bonding and relative stability of the two isomeric structures were assessed by DFT calculations.     

Facile Modulation of FLP Properties: A Phosphinylvinyl Grignard Reagent and Ga/P‐ and In/P2‐Based Frustrated Lewis Pairs

An Al/P‐based frustrated Lewis pair (FLP) reacted with PhMgCl by an unexpected transmetalation and formation of a phosphinylvinyl Grignard reagent. This compound is well suited for the transfer of the basic FLP component to other Lewis acidic metal atoms and allowed the generation of a Ga/P and an In/P₂ FLP. The Ga FLP showed a behavior different to that of the corresponding Al FLP, the In FLP allowed the chelating coordination of an Au atom by Au−Cl bond activation.     

A Stable but Highly Reactive Phosphine‐Coordinated Borenium: Metal‐free Dihydrogen Activation and Alkyne 1,2‐Carboboration

Borenium cations have been found to be valuable analogues of boranes as a result of their cationic character which imparts high electrophilicity. Herein, we report the synthesis, characterization, and reactivity of a new type of borenium cation employing a naphthyl bridge and a strong intramolecular P→B interaction. The cation reacts with H₂ in the presence of PtBu₃ (frustrated Lewis pair (FLP) approach) but also on its own. The mechanism of the reaction between the borenium cation and H₂ in the absence of PtBu₃ has been investigated using deuterium‐labeling experiments and DFT calculations. Both experiments and calculations imply the side‐on coordination of H₂ to the B center, followed by heterolytic splitting and B? C bond cleavage. An uncommon syn 1,2‐carboboration has also been observed upon reaction of the borenium ion with 3‐hexyne.     

Designing Tunable White‐Light Emission from an Aurophilic CuI/AuI Coordination Polymer with Thioether Ligands

White‐light emitters have attracted considerable attention due to their importance in current and future technologies. By incorporating molecular fragments that independently emit in the blue, green/yellow, and red visible regions, specifically Cu‐NC, Au???Au interactions, and Cu‐SR₂, respectively, into a single material, new white‐light‐emitting systems have been targeted. With this goal, three new Cu^I/thioether‐based coordination polymers containing bridging [Au(CN)₂]^? units have been synthesized and structurally characterized, and their photoluminescence properties (at room and low temperatures) have been delineated. Using this approach, white‐light emission (tunable from slightly yellow to slightly blue, depending on λ_ex) is generated from Cu(Me₂S)[Au(CN)₂], a feature uncommon in such simple coordination compounds.     

Coordination Polymer Flexibility Leads to Polymorphism and Enables a Crystalline Solid–Vapour Reaction: A Multi‐technique Mechanistic Study

Despite an absence of conventional porosity, the 1D coordination polymer [Ag₄(O₂C(CF₂)₂CF₃)₄(TMP)₃] ( 1 ; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into Ag?O bonds to yield coordination polymers [Ag₄(O₂C(CF₂)₂CF₃)₄(TMP)₃(ROH)₂] ( 1‐ROH ; R=Me, Et, iPr). The reactions are reversible single‐crystal‐to‐single‐crystal transformations. Vapour‐solid equilibria have been examined by gas‐phase IR spectroscopy (K=5.68(9)×10^?5 (MeOH), 9.5(3)×10^?6 (EtOH), 6.14(5)×10^?5 (iPrOH) at 295 K, 1 bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two‐step reactions 1‐ROH → 1 → 2 , in which 2 is the 2D coordination polymer [Ag₄(O₂C(CF₂)₂CF₃)₄(TMP)₂] formed by loss of TMP ligands exclusively from singly‐bridging sites. Four polymorphic forms of 1 ( 1‐A^LT , 1‐A^HT , 1‐B^LT and 1‐B^HT ; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X‐ray diffraction (PXRD) studies of the 1‐ROH → 1 → 2 transformations indicate the role of the HT polymorphs in these reactions. The structural relationship between polymorphs, involving changes in conformation of perfluoroalkyl chains and a change in orientation of entire polymers (A versus B forms), suggests a mechanism for the observed reactions and a pathway for guest transport within the fluorous layers. Consistent with this pathway, optical microscopy and AFM studies on single crystals of 1‐MeOH / 1‐A^HT show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.     

Platinum Oxoboryl Complexes as Substrates for the Formation of 1:1, 1:2, and 2:1 Lewis Acid–Base Adducts and 1,2‐Dipolar Additions

The oxoboryl complex trans‐[(Cy₃P)₂BrPt(B?O)] ( 2 ) reacts with the Group 13 Lewis acids EBr₃ (E=Al, Ga, In) to form the 1:1 Lewis acid–base adducts trans‐[(Cy₃P)₂BrPt(B?OEBr₃)] ( 6 – 8 ). This reactivity can be extended by using two equivalents of the respective Lewis acid EBr₃ (E=Al, Ga) to form the 2:1 Lewis acid–base adducts trans‐[(Cy₃P)₂(Br₃Al‐Br)Pt(B?OAlBr₃)] ( 18 ) and trans‐[(Cy₃P)₂(Br₃Ga‐Br)Pt(B?OGaBr₃)] ( 15 ). Another reactivity pattern was demonstrated by coordinating two oxoboryl complexes 2 to InBr₃, forming the 1:2 Lewis acid–base adduct trans‐[{(Cy₃P)₂BrPt(B?O)}₂InBr₃] ( 20 ). It was also possible to functionalize the B?O triple bond itself. Trimethylsilylisothiocyanate reacts with 2 in a 1,2‐dipolar addition to form the boryl complex trans‐[(Cy₃P)₂BrPt{B(NCS)(OSiMe₃)}] ( 27 ).     

Ligand‐Stabilized and Atomically Precise Gold Nanocluster Catalysis: A Case Study for Correlating Fundamental Electronic Properties with Catalysis

We present results from our investigations into correlating the styrene‐oxidation catalysis of atomically precise mixed‐ligand biicosahedral‐structure [Au₂₅(PPh₃)₁₀(SC₁₂H₂₅)₅Cl₂]²⁺ (Au₂₅‐bi) and thiol‐stabilized icosahedral core–shell‐structure [Au₂₅(SCH₂CH₂Ph)₁₈]^? (Au₂₅‐i) clusters with their electronic and atomic structure by using a combination of synchrotron radiation‐based X‐ray absorption fine‐structure spectroscopy (XAFS) and ultraviolet photoemission spectroscopy (UPS). Compared to bulk Au, XAFS revealed low Au–Au coordination, Au? Au bond contraction and higher d‐band vacancies in both the ligand‐stabilized Au clusters. The ligands were found not only to act as colloidal stabilizers, but also as d‐band electron acceptor for Au atoms. Au₂₅‐bi clusters have a higher first‐shell Au coordination number than Au₂₅‐i, whereas Au₂₅‐bi and Au₂₅‐i clusters have the same number of Au atoms. The UPS revealed a trend of narrower d‐band width, with apparent d‐band spin–orbit splitting and higher binding energy of d‐band center position for Au₂₅‐bi and Au₂₅‐i. We propose that the differences in their d‐band unoccupied state population are likely to be responsible for differences in their catalytic activity and selectivity. The findings reported herein help to understand the catalysis of atomically precise ligand‐stabilized metal clusters by correlating their atomic or electronic properties with catalytic activity.     

Characterising lone-pair activity of lead(II) by 207Pb solid-state NMR spectroscopy: coordination polymers of [N(CN)2]- and [Au(CN)2]- with terpyridine ancillary ligands

A series of lead(II) coordination polymers containing [N(CN)₂]^? (DCA) or [Au(CN)₂]^? bridging ligands and substituted terpyridine (terpy) ancillary ligands ([Pb(DCA)₂] ( 1 ), [Pb(terpy)(DCA)₂] ( 2 ), [Pb(terpy){Au(CN)₂}₂] ( 3 ), [Pb(4′‐chloro‐terpy){Au(CN)₂}₂] ( 4 ) and [Pb(4′‐bromo‐terpy)(μ‐OH₂)_0.5{Au(CN)₂}₂] ( 5 )) was spectroscopically examined by solid‐state ²⁰⁷Pb MAS NMR spectroscopy in order to characterise the structural and electronic changes associated with lead(II) lone‐pair activity. Two new compounds, 2 and [Pb(4′‐hydroxy‐terpy){Au(CN)₂}₂] ( 6 ), were prepared and structurally characterised. The series displays contrasting coordination environments, bridging ligands with differing basicities and structural and electronic effects that occur with various substitutions on the terpyridine ligand (for the [Au(CN)₂]^? polymers). ²⁰⁷Pb NMR spectra show an increase in both isotropic chemical shift and span (Ω) with increasing ligand basicity (from δ_iso=?3090 ppm and Ω=389 ppm for 1 (the least basic) to δ_iso=?1553 ppm and Ω=2238 ppm for 3 (the most basic)). The trends observed in ²⁰⁷Pb NMR data correlate with the coordination sphere anisotropy through comparison and quantification of the Pb? N bond lengths about the lead centre. Density functional theory calculations confirm that the more basic ligands result in greater p‐orbital character and show a strong correlation to the ²⁰⁷Pb NMR chemical shift parameters. Preliminary trends suggest that ²⁰⁷Pb NMR chemical shift anisotropy relates to the measured birefringence, given the established correlations with structure and lone‐pair activity.     

Front Cover: Reactivity of a Free Aluminylene towards Boron Lewis Acids: Accessing Aluminum-Boron-Bonded Species (Eur. J. Inorg. Chem. 25/2023)

The reactivity of the free aluminylene [N]-Al ( 1 ) ([N]=1,8-bis(3,5-di-tert-butylphenyl)-3,6-di-tert-butylcarbazolyl) towards boron Lewis acids is investigated. A facile oxidative addition reaction of 1 with Ph₂BOBPh₂ furnishes an exceedingly scarce example of the free alumaborane [N]-Al(BPh₂)(OBPh₂) ( 2 ) with an Al−B electron-sharing bond. By contrast, complexation of 1 with B(C₆F₅)₃ and HB(C₆F₅)₂ gives rise to the corresponding Lewis adducts [N]-Al→B(C₆F₅)₃ ( 3 ) and [N]-Al→BH(C₆F₅)₂ ( 4 ), respectively, with an Al→B dative bond. Crystallization of 4 in Et₂O produces the adduct [N]-Al(Et₂O)→BH(C₆F₅)₂ ( 5 ). Quantum chemical calculations are carried out to understand the formation of 2 as well as the bonding situation of 3 and 5 .     

Theoretical study of the decomposition mechanism of a series of group III triazides X(N3)3 (X = B,Al, Ga)

Density functional theory method is used to examine a series of group III triazides X(N₃)₃ (X = B, Al, Ga). These compounds, except for the C_3h planar B(N₃)₃ and Al(N₃)₃, are first reported here. C_3h planar structures are the most energetically favored for all singlet X(N₃)₃ systems. Potential‐energy surfaces for unimolecular decompositions of the C_3h and C_S planar X(N₃)₃ species have been investigated. Results show that decomposition of B(N₃)₃ obeys sequential fashion and follows a four‐step mechanism: (1) B(N₃)₃ → NB(N₃)₂ + N₂; (2) NB(N₃)₂ → cyc‐N₂BN₃ + N₂; (3) cyc‐N₂BN₃ → trigonal‐BN₃ + N₂; (4) trigonal‐BN₃ → linear‐NBNN. Decomposition of Al(N₃)₃ follows a two‐step mechanism: (1) Al(N₃)₃ → NAl(N₃)₂ + N₂; (2) NAl(N₃)₂ → linear‐AlN₃ + 2N₂. The dissociation of Ga(N₃)₃ follows only one‐step mechanism: Ga(N₃)₃ → angular‐GaN₃ + 3N₂. These findings may be helpful in understanding the decomposition mechanisms of group III triazides as well as the possible mechanism for XN film generation. © 2014 Wiley Periodicals, Inc.     

Room‐Temperature Activation of H2 by a Surface Frustrated Lewis Pair

Surface frustrated Lewis pairs (SFLPs) have been implicated in the gas‐phase heterogeneous (photo)catalytic hydrogenation of CO₂ to CO and CH₃OH by In₂O_3?x(OH)_y. A key step in the reaction pathway is envisioned to be the heterolysis of H₂ on a proximal Lewis acid–Lewis base pair, the SFLP, the chemistry of which is described as In???In‐OH + H₂ → In‐OH₂⁺???In‐H^?. The product of the heterolysis, thought to be a protonated hydroxide Lewis base In‐OH₂⁺ and a hydride coordinated Lewis acid In‐H^?, can react with CO₂ to form either CO or CH₃OH. While the experimental and theoretical evidence is compelling for heterolysis of H₂ on the SFLP, all conclusions derive from indirect proof, and direct observation remains lacking. Unexpectedly, we have discovered rhombohedral In₂O_3?x(OH)_y can enable dissociation of H₂ at room temperature, which allows its direct observation by several analytical techniques. The collected analytical results lean towards the heterolysis rather than the homolysis reaction pathway.     

Nickel as a Lewis Base in a T‐Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand

Flexible, chelating bis(NHC) ligand 2 , able to accommodate both cis‐ and trans‐coordination modes, was used to synthesize ( 2 )Ni(η²‐cod), 3 . In reaction with GeCl₂, it produced ( 2 )NiGeCl₂, 4 , featuring a T‐shaped Ni⁰ and a pyramidal Ge center. Complex 4 could also be prepared from [( 2 )GeCl]Cl, 5 , and Ni(cod)₂, in a reaction that formally involved Ni–Ge transmetalation, followed by coordination of the extruded GeCl₂ moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ‐donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)₂Ni(cod) complexes 9 and 10 , as well as (NHC)₂GeCl₂ derivative 11 , incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni–Ge complexes. The isolation of ( 2 )Ni(η²‐Py), 12 , provides further evidence for the reluctance of the ( 2 )Ni⁰ fragment to act as a σ‐Lewis acid.     

Structure of Framework Aluminum Lewis Sites and Perturbed Aluminum Atoms in Zeolites as Determined by 27Al{1H} REDOR (3Q) MAS NMR Spectroscopy and DFT/Molecular Mechanics

Zeolites are highly important heterogeneous catalysts. Besides Brønsted SiOHAl acid sites, also framework Al_FR Lewis acid sites are often found in their H‐forms. The formation of Al_FR Lewis sites in zeolites is a key issue regarding their selectivity in acid‐catalyzed reactions. The local structures of Al_FR Lewis sites in dehydrated zeolites and their precursors—“perturbed” Al_FR atoms in hydrated zeolites—were studied by high‐resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)₃AlOH groups and are characterized by a broad ²⁷Al NMR resonance (δ_i=59–62 ppm, C_Q=5 MHz, and η=0.3–0.4) with a shoulder at 40 ppm in the ²⁷Al MAS NMR spectrum. Dehydroxylation of (SiO)₃AlOH occurs at mild temperatures and leads to the formation of Al_FR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)₃Al Lewis sites exhibit an extremely broad ²⁷Al NMR resonance (δ_i≈67 ppm, C_Q≈20 MHz, and η≈0.1).     

Hydride Transfer to Gold: Yes or No? Exploring the Unexpected Versatility of Au⋅⋅⋅H−M Bonding in Heterobimetallic Dihydrides

The potential for coordination and H-transfer from Cp₂MH₂ (M=Zr, W) to gold(I) and gold(III) complexes was explored in a combined experimental and computational study. [(L)Au]⁺ cations react with Cp₂WH₂ giving [(L)Au(κ²-H₂WCp₂)]⁺ (L=IPr ( 1 ), cyclic (alkyl)(amino)carbene ( 2 ), PPh₃ ( 3 ) and Dalphos-Me ( 4 ) [IPr=1,3-bis(diisopropylphenyl)imidazolylidene; Dalphos-Me=di(1-adamantyl)-2-(dimethylamino)phenyl-phosphine], while [Au(DMAP)₂]⁺ (DMAP=p-dimethylaminopyridine) affords the C₂-symmetric [Au(κ-H₂WCp₂)₂]⁺ ( 5 ). The Dalphos complex 4 can be protonated to give the bicationic adduct 4 H, showing Au^I⋅⋅⋅H⁺−N hydrogen bonding. The gold(III) Lewis acid [(C^N−CH)Au(C₆F₅)(OEt₂)]⁺ binds Cp₂WH₂ to give an Au-H-W σ-complex. By contrast, the pincer species [(C^N^C)Au]⁺ adds Cp₂WH₂ by a purely dative W→Au bond, without Au⋅⋅⋅H interaction. The biphenylyl-based chelate [(C^C)Au]⁺ forms [(C^C)Au(μ-H)₂WCp₂]⁺, with two 2-electron-3-centre W−H⋅⋅⋅Au interactions and practically no Au−W donor acceptor contribution. In all these complexes, strong but polarized W−H bonds are maintained, without H-transfer to gold. On the other hand, the reactions of Cp₂ZrH₂ with gold complexes led in all cases to rapid H-transfer and formation of gold hydrides. Relativistic DFT calculations were used to rationalize the striking reactivity and bonding differences in these heterobimetallic hydride complexes along with an analysis of their characteristic NMR parameters and UV/Vis absorption properties.     

Infinite Gold Zig‐Zag Chains as Structural Motif in Ca3Au3In – A Ternary Ordered Variant of the Ni4B3 Type

New auride Ca₃Au₃In was synthesized from the elements in a sealed tantalum tube in a high‐frequency furnace. Ca₃Au₃In was investigated by X‐ray powder and single crystal diffraction: ordered Ni₄B₃ type, Pnma, a = 1664.1(6), b = 457.3(2), c = 895.0(3) pm, wR2 = 0.0488, 1361 F² values, and 44 variables. The three crystallographically independent boron positions of the Ni₄B₃ type are occupied by the gold atoms, while the four nickel sites are occupied by calcium and indium in an ordered manner. All gold atoms have trigonal prismatic coordination, i.e. Ca₆ prisms for Au1 and Au2 and Ca₄In₂ prisms for Au3. While the Au3 atoms are isolated, we observe Au1–Au1 and Au2–Au2 zig‐zag chains at Au–Au distances of 292 and 284 pm. These slabs resemble the CrB type structure of CaAu. Consequently Ca₃Au₃In can be considered as a ternary auride. Together the Au2, Au3 and indium atoms build up a three‐dimensional [Au₂In] polyanionic network (281–293 pm Au–In) in which the chains of Au1 centered trigonal prisms are embedded. The crystal chemical similarities with the structures of Ni₄B₃, CaAuIn, and CaAu are discussed.     

Ultra‐wideline 27Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Ultra‐wideline ²⁷Al NMR experiments are conducted on coordination compounds with ²⁷Al nuclei possessing immense quadrupolar interactions that result from exceptionally nonspherical coordination environments. NMR spectra are acquired using a methodology involving frequency‐stepped, piecewise acquisition of NMR spectra with Hahn‐echo or quadrupolar Carr–Purcell Meiboom–Gill (QCPMG) pulse sequences, which is applicable to any half‐integer quadrupolar nucleus with extremely broad NMR powder patterns. Despite the large breadth of these central transition powder patterns, ranging from 250 to 700 kHz, the total experimental times are an order of magnitude less than previously reported experiments on analogous complexes with smaller quadrupolar interactions. The complexes examined feature three‐ or five‐coordinate aluminum sites: trismesitylaluminum (AlMes₃), tris(bis(trimethylsilyl)amino)aluminum (Al(NTMS₂)₃), bis[dimethyl tetrahydrofurfuryloxide aluminum] ([Me₂‐Al(μ‐OTHF)]₂), and bis[diethyl tetrahydrofurfuryloxide aluminum] ([Et₂‐Al(μ‐OTHF)]₂). We report some of the largest ²⁷Al quadrupolar coupling constants measured to date, with values of C_Q(²⁷Al) of 48.2(1), 36.3(1), 19.9(1), and 19.6(2) MHz for AlMes₃ , Al(NTMS₂)₃ , [Me₂‐Al(μ‐OTHF)]₂ , and [Et₂‐Al(μ‐OTHF)]₂ , respectively. X‐ray crystallographic data and theoretical (Hartree–Fock and DFT) calculations of ²⁷Al electric field gradient (EFG) tensors are utilized to examine the relationships between the quadrupolar interactions and molecular structure; in particular, the origin of the immense quadrupolar interaction in the three‐coordinate species is studied via analyses of molecular orbitals.     

Supramolecular Assembly of Bis(benzimidazole)pyridine: An Extended Anisotropic Ligand For Highly Birefringent Materials

Four new bis(benzimidazole)pyridine (BBP)‐containing compounds Zn(BBP)Cl[Au(CN)₂], Mn(BBP)[Au(CN)₂]₂?H₂O, Mn(BBP)Br₂(MeOH) and Mn(BBP)Cl₂(MeOH)?MeOH have been synthesized and structurally characterized and their birefringence values (Δn) determined. The structure of Zn(BBP)Cl[Au(CN)₂] contains a hydrogen‐bonded dimer of Zn(BBP)Cl[Au(CN)₂] units which propagate into a 1D chain through Au–Au interactions, although the crystals are of poor optical quality. The supramolecular structure of Mn(BBP)[Au(CN)₂]₂?H₂O forms a 1D coordination polymer through chains of Mn(BBP)[Au(CN)₂]₂ units, each containing one bridging Au(CN)₂ and one forming a 2D sheet through Au–Au interactions. The supramolecular structures of Mn(BBP)Br₂(MeOH) and Mn(BBP)Cl₂(MeOH)?MeOH are very similar, consisting of a complex hydrogen‐bonded network between NH imidazole, methanol and halide groups to align BBP building blocks. In the plane of the primary crystal growth direction, the birefringence values of the three Mn‐containing materials were Δn=0.08(1), 0.538(3) and 0.69(3), respectively. The latter two birefringence values are larger than in the related 2,2′;6′2′′‐terpyridine systems, placing them among the most birefringent solids reported. These compounds illustrate the utility of extending the π‐system of the building block and incorporating hydrogen‐bonding sites as design elements for highly birefringent materials and also illustrates the effect on the measurable birefringence of the crystal quality, growth direction and structural alignment of the anisotropic BBP building blocks.     

Evaluation of Electron Donation as a Mechanism for the Stabilisation of Chalcogenate‐Protected Gold Nanoclusters

Models based on Au(111) face have been extensively used to describe self‐assembled monolayers, as well nanoparticles and nanoclusters. However, for very small clusters (<2 nm), the chemisorption of ligands leads to surface reconstruction, making necessary the use of a more reliable model that is able to simulate the main electronic and geometrical features of these small systems. In this work, a simple model to describe the geometries and the metal–ligand bonding in chalcogenate‐protected gold nanoclusters is proposed. Three different models with Au_n⁺ and [XCH₃]^? (n=10, 15, 19, 22 and X=S, Se, Te) are used in this work. The obtained structures are in close agreement not only with the available crystallographic data, but also with much more expensive computational procedures, confirming that the proposed models are robust enough to describe the metal–ligand bonding. The results reveal that the Au–X distances are dependent on both the nature of the chalcogen and the coordination mode. The shortest Au–X distances are observed in the face‐centred cubic mode, indicating that the central gold atom seems to play a role in determining the adsorption strength. The proposed models show unambiguously chalcogen→cluster σ‐donation, as supported by energy decomposition analysis coupled with the natural orbitals for chemical valence and natural bond orbital analyses. In all cases, the metal–ligand interactions are characterised as being more covalent than electrostatic.     

Chemistry of Stannylene‐Based Lewis Pairs: Dynamic Tin Coordination Switching Between Donor and Acceptor Character

The coordination chemistry of cyclic stannylene‐based intramolecular Lewis pairs is presented. The P→Sn adducts were treated with [Ni(COD)₂] and [Pd(PCy₃)₂] (COD=1,5‐cyclooctadiene, PCy₃=tricyclohexylphosphine). In the isolated coordination compounds the stannylene moiety acts either as an acceptor or a donor ligand. Examples of a dynamic switch between these two coordination modes of the P?Sn ligand are illustrated and the structures in the solid state together with heteronuclear NMR spectroscopic findings are discussed. In the case of a Ni⁰ complex, ¹¹⁹Sn Mössbauer spectroscopy of the uncoordinated and coordinated phosphastannirane ligand is presented.     

Oleanane Saponins from Rhizome of Anemone raddeana

Two new oleanolic acid‐type triterpenoid saponins, raddeanosides R₂₂ and R₂₃ ( 1 and 2 , resp.), together with four known saponins were isolated from the rhizome of Anemone raddeana Regel. The structures of the new compounds were elucidated as oleanolic acid 3‐O‐β‐D ‐glucopyranosyl(1→2)[β‐D ‐glucopyranosyl(1→4)]‐α‐L ‐arabinopyranoside ( 1 ) and oleanolic acid 3‐O‐α‐L ‐arabinopyranosyl(1→3)‐α‐L ‐rhamnopyranosyl(1→2)[β‐D ‐glucopyranosyl(1→4)]‐α‐L ‐arabinopyranoside ( 2 ). The four known compounds were identified as oleanolic acid 3‐O‐α‐L ‐arabinopyranoside ( 3 ), oleanolic acid 3‐O‐β‐D ‐glucopyranosyl(1→4)‐α‐L ‐arabinopyranoside ( 4 ), hederasaponin B ( 5 ), and hederacholchiside E ( 6 ) on the basis of chemical and spectral evidences. Compound 4 is reported for the first time from the Anemone genus, while the other three known compounds have been already found in this plant.