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The bidentate silicon-based Lewis acid, bis(dimethyl-(trifluoromethylsulfonyl)silylethyl)dimethylsilane, Me 2 Si[(CH 2 ) 2 SiMe 2 OTf] 2 , was prepared in a two-step synthesis starting from dimethyldivinylsilane by hydrosilylation with dimethylchlorosilane and subsequent Lewis acidity enhancement of the terminal silicon atoms by substituting the chlorine with triflate groups using silver triflate. The potential of the resulting Me 2 Si[(CH 2 ) 2 SiMe 2 OTf] 2 for binding of Lewis basic guests was explored in reactions with mono- and bifunctional aromatic nitrogen bases. A 1 : 2-adduct with pyridine and a 2 : 2-adduct with 4,4'-bipyridine was structurally characterised in the solid state. In solution, diffusion NMR spectroscopy revealed the existence of complex dynamic equilibria of oligomers which are formed by the host with bidentate guests. The size of the oligomers is significantly determined by the spatial arrangement of the docking sites within the guests and depends on the host-guest ratio.

An improved synthesis for 1,8-bis(dimethylboranyl)naphthalene (1, hydride sponge) was developed avoiding the use of tin(IV) reagents. The related 1,2-bis(dimethylboranyl)benzene (2) was prepared. 1 combined with 1,8-bis(dimethylamino)naphthalene (3, proton sponge) is a Frustrated Lewis pair (FLP) that forms adducts [1-EH n -1 ][3-H] with the protic compounds EH n = H 2 O, NH 3 , H 2 S, PH 3 , H 2 Se, HCN. Their structures show the chelation of the deprotonated substrates, except for CN - (binds to one B atom of 1). The mechanisms of formation of [1-EH n -1 ][3-H] were explored by NMR spectroscopy. Similar reactions took places for the FLP system 2 + 3, but the adducts [2-EH n -1 ][3-H] are less stable; only the PH 3 adduct was isolated and AsH 3 forms a chelated adduct [2-NC(CD 3 )AsH 2 ][3-H]. FLP 1 + 3 does not react with molecular hydrogen, but the formal adduct [1-H][3-H] was isolated via salt metathesis from K[1-H] and [3-H]Cl; it is stable towards water, atmospheric oxygen and up to 100 °C; its thermal decomposition proceeds without formation of H 2 . The stabilities of both, the mixture 1 + 3 + H 2 and the formal adduct [1-H][3-H], allow concluding that hydrogen activation of FLP 1 + 3 is kinetically prevented.

Mono- and bidentate tri-coordinated boron compounds bearing the yet unexplored para -chlorotetrafluorophenyl substituent have been synthesized and structurally investigated. The acidity of tris( para -chlorotetraphenyl)borane (7) was shown to exceed that of the widely used tris(pentafluorophenyl)borane (BCF) according to the Gutmann-Beckett method. Acid-base adducts of 7 with diethyl ether and triethylphosphine oxide were crystallized. Dihydrogen splitting at room temperature was observed with a Frustrated Lewis Pair consisting of 7 and 2,2,6,6-tetramethylpiperidine (TMP). The hydrogen adduct was isolated and characterized by NMR, SC-XRD and elemental analysis. Its solid-state structure contains a H⋯H distance on the verge of dihydrogen bonding (2.28(6) Å). Bis( para -chlorotetrafluorophenyl)hydridoborane was prepared in situ and shown to be applicable in hydroboration reactions similarly to Piers' borane.

Compounds exhibiting main group elements in low oxidation states were found to mimic the reactivity of transition metal complexes. Like the latter, such main group species show a proclivity of changing their oxidation state as well as their coordination number by +2, therefore fulfilling the requirements for oxidative additions. Prominent examples of such main group compounds that undergo oxidative additions with organohalides R-X (R=alkyl, aryl, X=F, Cl, Br, I) are carbenes and their higher congeners. Aluminyl anions, which like carbenes and silylenes oxidatively add to strong σ-bonds in R-X species, have been recently discovered. We present the first anion based upon a Group 14 element, namely the tris(pentafluoroethyl)silanide anion, [Si(C 2 F 5 ) 3 ] - , which is capable of oxidative additions towards C-F bonds. This enables the isolation of non-chelated tetraorganofluorosilicate salts, which to the best of our knowledge had only been observed as reactive intermediates before., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Equimolar mixtures of pyridine (Py) with para -halotetrafluoropyridine (BrTFP and ITFP) were investigated by VT-diffusion NMR experiments. The formation of a halogen-bond-stabilized ITFP · Py complex was detected upon cooling a solution in methylcyclohexane- d 14 to 260 K; this allows monitoring a halogen-bond-driven aggregation process preceding crystallization in solution.

The chemical investigation of the ethanol/water (7:3) extract of the roots of Detarium microcarpum (Fabaceae) led to the isolation of one new labdane diterpenoid, microcarpin ( 1 ) and one new ceramide derivative, microcarpamide ( 2 ), along with eight known secondary metabolites ( 3-10 ) including, 5-(carboxymethyl)-5,6,8a-trimethyl-3,4,4a,5,6,7,8,8a-octahydronaphthalene-1-carboxylic acid ( 3 ), microcarposide ( 4 ), rhinocerotinoic acid ( 5 ), 1,7-dihydroxy-6-methylxanthone ( 6 ), ursolic acid ( 7 ), 3 β ,23-dihydroxylup-20(29)-en-28-oic acid ( 8 ), alphitolic acid ( 9 ), and stigmasterol glucoside ( 10 ). The structures of these compounds were elucidated based on their spectroscopic data. Although compounds 3 and 4 are known, their crystalline structures are reported here for the first time. These compounds were evaluated in vitro for their antisalmonella activity. The results obtained showed that, microcarpamide ( 2 ), microcarposide ( 4 ), and rhinocerotinoic acid ( 5 ) were moderately active against three salmonella strains: Salmonella typhi , Salmonella enteritidis and Salmonella typhimirium , with minimum inhibition concentration values of 76.7 and 153.5 μM., (© 2022 Walter de Gruyter GmbH, Berlin/Boston.)

The chemical investigation of the total alkaloid extract (TAE) of the stem bark of Araliopsis soyauxii (Rutaceae) afforded an unreported indolopyridoquinazoline (compound 1 ) along with nine previously known alkaloids 2 - 10 . In addition, six semi-synthetic derivatives 3a - c , 4b , 5a and 6a were prepared by allylation and acetonidation of soyauxinium nitrate ( 5 ), edulinine ( 3 ), ribalinine ( 4 ) and arborinine ( 6 ). The structures and spectroscopic data of five of them are reported herein for the first time. The suggested mechanism for the formation of the new N -allylindolopyridoquinazoline 5a is presented. The structures of natural and derived compounds were determined employing extensive NMR and MS techniques. The absolute configuration of stereogenic centers in compounds 2 - 4 were determined using NOESY technique and confirmed by the single-crystal X-ray diffraction (SC-XRD) technique. The use of SC-XRD further enabled us to carry out a structural revision of soyauxinium chloride recently isolated from the same plant to soyauxinium nitrate ( 5 ). The TAE, fractions, compounds 1 - 7 and 9 , and semi-synthetic derivatives 3a - c , 4b , 5a and 6a were evaluated for their cytotoxic activity towards the cervix carcinoma cell line KB-3-1. No significant activity was recorded for most of the compounds except for 9 , which showed moderate activity against the tested cancer cell lines.

Starting with 1,2-dibromobenzene and 1,2,3,4-tetrafluorobenzene, dimethyl(2-(trimethylstannyl)phenyl)phosphane, Me 2 P( o -C 6 H 4 )SnMe 3 , and dimethyl-[2,3,4,5-tetrafluoro-6-(trimethylstannyl)phenyl]phosphane, Me 2 P( o -C 6 F 4 )SnMe 3 , were synthesized and used in tin-gold exchange reactions to prepare two gold(I) dimers, bis[(2-dimethylphosphino)phenyl]di-gold(I), [Au 2 (μ-2-C 6 H 4 PMe 2 ) 2 ], and bis[(2-dimethylphosphino)-3,4,5,6-tetrafluorophenyl]di-gold(I), [Au 2 (μ-2-C 6 F 4 PMe 2 ) 2 ], respectively. Both tin precursor molecules, as well as the gold(I) complexes, were characterized by multinuclear NMR spectroscopy, CHN analysis and X-ray diffraction experiments. Both gold(I) dimers were further investigated by the means of computational as well as photophysical methods.

A new xanthone, mboudiexanthone ( 1 ), together with five known compounds, euxanthone ( 2 ), isogarcinol ( 3 ), garcinol ( 4 ), betulinic acid ( 5 ) and zeorin ( 6 ) were isolated from the leaves of Garcinia nobilis Engl. The structures were determined by 1D and 2D NMR techniques and X-ray diffraction for 6 . The in vitro antiproliferative properties of isolated compounds were evaluated against the human breast cancer cell line MCF-7. All compounds showed an antiproliferative activity with an IC 50 value down to ∼11 µM for isogarcinol.

The phytochemical investigation of the methanolic extracts of roots, stem bark, leaves and twigs of Manilkara obovata has led to the isolation of one new friedelane triterpene, lacefriedelic acid or 3 β ,23-dihydroxy D:A-friedooleanan-28-oic acid ( 1 ) and one new prenylated xanthone, lacexanthone or 4,7-dihydroxy-2,3,3,9,9-pentamethyl-2,2-dihydrofurano[2,3-a]pyrano[2,3-i]xanthen-13( 9H )-one ( 2 ) alongside twenty-four known compounds. Compounds 1 - 11 are reported here for the first time from the genus Manilkara . The structures of all compounds were determined by spectroscopic analyses and X-ray crystallography. The methanolic extracts of twigs and leaves showed anti-oxidant activity of 93.2 and 91.1%, respectively, at 100 µg/mL when measured by DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate), while the twig extract displayed 86.3% at 100 µg/mL against the urease inhibition assay. Some isolated compounds ( 1 - 4 , 15 and 20 ) showed significant to moderate anti-oxidant activity and urease inhibition assay. It is estimated that significantly active anti-oxidants and urease inhibitors metabolized by the plant may find future application in food industry.

The crystal structure and unambiguous absolute configuration of meleagrin ( 1 ) isolated from fungus Emericella dentata Nq45 is reported herein to first time on the bases of single crystal X-ray diffraction. Together with 1 , haenamindole ( 2 ), isorugulosuvine ( 3 ), secalonic acid D ( 4 ), ergosterol ( 5 ) and cerebroside A ( 6 ) were obtained and their structures were determined by ESI MS and NMR data analysis. Diverse biological activity of meleagrin ( 1 ) was investigated. Compound 1 pronounced potent cytotoxicity against the human cervix carcinoma cell line KB-3-1 and its multidrug resistant sub-clone KB-V1 of IC 50 3.07 and 6.07 µM, respectively, in comparison with the reference (+) - griseofulvin (IC 50 19, 19.5 µM). Based on the antibiofilm activity, compound 1 displayed as well potent activity against Staphylococcus aureus with an MIC of 0.25 mg/mL. Isolation of the producing fungus and taxonomical characterization is stated as well.

Despite the fact that different metal tetrafluorophosphoranides, M[PF 4 ] (M = Cs, Ag, K), decompose readily, we successfully enhanced the stability of such species by the replacement of two fluorine atoms with electron withdrawing pentafluoroethyl groups. Thus, AgF adds to P(C 2 F 5 ) 2 F, yielding Ag[P(C 2 F 5 ) 2 F 2 ], which served as a starting material for the synthesis of mono-, bis-, and tris[difluorobis(pentafluoroethyl)phosphoranido]silver complexes. Addition of 2,2'-bipyridine allowed for the isolation of stable [Ag(bipy){P(C 2 F 5 ) 2 F 2 }], whereas the reaction with the chlorides [NMe 4 ]Cl and CoCl 2 afforded the bis- and trisphosphoranidoargentates [NMe 4 ][Ag{P(C 2 F 5 ) 2 F 2 } 2 (OEt 2 )] and [Co(NCMe) 6 ][Ag{P(C 2 F 5 ) 2 F 2 } 3 ]·2MeCN, respectively. Altogether, the difluorobis(pentafluoroethyl)phosphoranido moiety serves as a novel, small, noncyclic phosphoranido ligand. It provided access to the first homoleptic phosphoranidometal complex, [Co(NCMe) 6 ][Ag{P(C 2 F 5 ) 2 F 2 } 3 ]·2MeCN, which itself features the unusual structural motif of an [AgX 3 ] 2- ion.

Unlike silanolates [SiR 3 O] - (R = alkyl, aryl), which have been intensely studied, the heavier derivatives [SiR 3 E] - (E = S, Se, Te) have been much less examined. Among such species, virtually nothing is known about perfluoroalkyl-substituted silylchalcogenolates. In this contribution, a convenient synthesis of tris(pentafluoroethyl)silylchalcogenolate salts [{(Et 2 N) 3 P═N} 3 PN(H) t Bu][Si(C 2 F 5 ) 3 E] (E = S, Se, Te; t Bu = tert -butyl) is presented. All representatives were isolated and fully characterized by multinuclear NMR spectroscopy, IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction studies. Furthermore, first reactivity studies of these novel species toward selected metal halide complexes were performed. In this course, metal complexes [HgPh{SSi(C 2 F 5 ) 3 }] ( 2 ) and [Au(PPh 3 ){SSi(C 2 F 5 ) 3 }] ( 3 ) were isolated and characterized.

Several rigid 1,3,5-tris(phenylethynyl)benzenes with different fluorination patterns were synthesized through selective Sonogashira-Hagihara coupling reactions to analyze the packing behavior in solid-state structures. The aggregation is dominated by various intermolecular interactions between aryl substituents, triple bonds, C-H bonds and H⋅⋅⋅F contacts. Co-crystallization experiments for the analysis of preferred aryl-aryl-interactions led to 1 : 1 complexes. Intermolecular phenyl-perfluorophenyl interactions with short centroid-centroid distances are dominating these co-crystal structures. They lead to melting point increases of up to 49 °C for the co-crystals compared to the pure substances., (© 2021 The Authors. Published by Wiley-VCH GmbH.)

Starting from 1,2-diethynylbenzene, a series of bidentate Lewis acids was prepared by means of hydrometalations, in particular hydrosilylation, hydroboration, hydroalumination and terminal metalation based on group 13 and 14 elements. In the case of terminal alkyne metalation, the Lewis-acidic gallium function was introduced using triethylgallium under alkane elimination. A total of six different Lewis acids based on a semiflexible organic scaffold were prepared, bearing -SiClMe 2 , -SiCl 2 Me, -SiCl 3 , -B(C 6 F 5 ) 2 , -AlBis 2 (Bis=bis(trimethylsilyl)methyl) and -GaEt 2 as the corresponding functional units. In all cases, the Lewis acid functionalisation was carried out twice and the products were obtained in good to excellent yields. In the case of the twofold gallium Lewis acid, a different structural motif in the form of a polymer-like chain was observed in the solid state. All new bidentate Lewis acids were characterised by multinuclear NMR spectroscopy, CHN analysis and X-ray diffraction experiments., (© 2021 The Authors. Published by Wiley-VCH GmbH.)

We synthesized new imidazolium-based tunable aryl alkyl ionic liquids (TAAILs) with the weakly coordinating tetrakis(pentafluoroethyl)gallate anion, [Ga(C 2 F 5 ) 4 ] - . Phenyl and phenyl derivatives (2-Me, 4-OMe, 2,4-F) were combined with varying alkyl chain lengths at the imidazolium core leading to TAAILs, which were investigated with regard to their viscosity, conductivity, and electrochemical window and compared to EMIM and BMIM standard cations. Remarkable low viscosities of 29 cP at 25 °C for [BMIM][Ga(C 2 F 5 ) 4 ] were achieved. However, the EMIM and BMIM gallates show electrochemical instability, releasing pentafluoroethane at a voltage of 1.5 V. The 2-Me-substituted gallate-TAAILs slowly decompose over several weeks, whereas all other gallate-TAAILs showed no decomposition at all. With electrochemical windows of up to 5.15 V and low viscosities in a range of 66-162 cP, the gallate-TAAILs are promising candidates as electrolytes in electrochemical applications., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

While alkyl-substituted siloxanes are widely known, virtually nothing is known about perfluoroalkyl siloxanes and their congener species, the silanols and silanolates. We recently reported on the tris(pentafluoroethyl)silanide ion, [Si(C 2 F 5 ) 3 ] - , which features Lewis amphoteric character deriving from the pentafluoroethyl substituents and their strong electron-withdrawing properties. Transferring this knowledge, we investigated the Lewis amphoteric behavior of the tris(pentafluoroethyl)silanolate, [Si(C 2 F 5 ) 3 O] - . In order to examine such Lewis amphoteric behavior, we first developed a strategy for the synthesis of the corresponding silanol Si(C 2 F 5 ) 3 OH, which readily condenses at room temperature to the hexakis(pentafluoroethyl)disiloxane, (C 2 F 5 ) 3 SiOSi(C 2 F 5 ) 3 . Deprotonation of Si(C 2 F 5 ) 3 OH employing a sterically demanding phosphazene base allows the characterization of the first example of a dimeric triorganosilanolate: the dianionic hexakis(pentafluoroethyl)disilanolate, [{Si(C 2 F 5 ) 3 O} 2 ] 2- , implies Lewis amphoteric character of the monomeric [Si(C 2 F 5 ) 3 O] - anion., (© 2021 The Authors. Published by Wiley-VCH GmbH.)

The renaissance of Brønsted superbases is primarily based on their pronounced capacity for a large variety of chemical transformations under mild reaction conditions. Four major set screws are available for the selective tuning of the basicity: the nature of the basic center (N, P, …), the degree of electron donation by substituents to the central atom, the possibility of charge delocalization, and the energy gain by hydrogen bonding. Within the past decades, a plethora of neutral electron-rich phosphine and phosphazene bases have appeared in the literature. Their outstanding properties and advantages over inorganic or charged bases have now made them indispensable as auxiliary bases in deprotonation processes. Herein, an update of the chemistry of basic phosphines and phosphazenes is given. In addition, due to widespread interest, their use in catalysis or as ligands in coordination chemistry is highlighted., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

1,4-Diarsinine-1,4-diide compound [(ADC Ph )As] 2 (5) (ADC Ph ={C(DippN)} 2 CPh, Dipp=2,6-iPr 2 C 6 H 3 ) with a planar C 4 As 2 ring fused between two 1,3-imidazole scaffolds has been isolated as a red crystalline solid. Compound 5, formally comprising an 8π-electron C 4 As 2 ring, is antiaromatic and undergoes 2e-oxidation with AgOTf to form the 6π-electron aromatic system [(ADC Ph )As] 2 (OTf) 2 (6)., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

According to a first view on the geometrical and electronic structure of the tris(pentafluoroethyl)silanide, this anion appears as a Lewis base. Quantum chemical calculations on perfluoroalkylated silanides show significantly lower HOMO and LUMO energy levels in comparison to their non-fluorinated counterparts, which implies reduced Lewis basicity and increased Lewis acidity of the [Si(C 2 F 5 ) 3 ] - ion. With these findings and a HOMO-LUMO gap of 4.80 eV similar to N-heterocyclic silylenes (NHSis), perfluoroalkyl silanides are predestined to exhibit Lewis-amphoteric character similar to silylenes. Deprotonation of Si(C 2 F 5 ) 3 H with sterically demanding phosphazene bases afforded thermally stable phosphazenium salts of the [Si(C 2 F 5 ) 3 ] - anion, which add to benzaldehyde, benzophenone, CS 2 , and CO 2 in various manners. This behavior also mirrors the reactivity of silylenes towards ketones as well as heterocumulenes and is rationalized by Lewis amphotericity being inherent in these silanides., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Using 2-hydroxypropyl-protecting groups, 1,8-dialkynylanthracene photo-dimers were prepared in head-to-head-configuration by UV irradiation on a multi-gram scale. In non-polar solvents, the combination of non-covalent hydrogen bonds and π-π-interactions induces the formation of the syn -isomer in up to 85% yield. Instead, more polar solvents or irradiation of unprotected 1,8-diethynylanthracene led to formation of the corresponding anti -isomer in large excess. Cleavage of the protecting groups under basic conditions affords a rigid hydrocarbon skeleton with four directional functions. This was used as a building block for a tetradentate boron Lewis acid. Its applicability as a host for Lewis-base substrates was demonstrated by the formation of adducts with various nitrogen bases. Adduct formation with hydrazine leads to impressive networks between the tetraboron host and the substrate molecules., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

In this work, the syntheses of non-coordinated electron-rich phenolate anions via deprotonation of the corresponding alcohols with an extremely powerful perethyl tetraphosphazene base (Schwesinger base) are reported. The application of uncharged phosphazenes renders the selective preparation of anionic phenol-phenolate and phenolate hydrates possible, which allows for the investigation of hydrogen bonding in these species. Hydrogen bonding brings about decreased redox potentials relative to the corresponding non-coordinated phenolate anions. The latter show redox potentials of up to -0.72(1) V vs. SCE, which is comparable to that of zinc metal, thus qualifying their application as organic zinc mimics. We utilized phenolates as reducing agents for the generation of radical anions in addition to the corresponding phenoxyl radicals. A tetracyanoethylene radical anion salt was synthesized and fully characterized as a representative example. We also present the activation of sulfur hexafluoride (SF 6 ) with phenolates in a SET reaction, in which the nature of the respective phenolate determines whether simple fluorides or pentafluorosulfanide ([SF 5 ] - ) salts are formed., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The reaction of the strong monophosphazene base with the weakly acidic phenol leads to the formation of a phenol-phenolate anion with a moderately strong hydrogen bond. Application of the more powerful tetraphosphazene base (Schwesinger base) renders the isolation of the corresponding salt with a free phenolate anion possible. This compound represents the first species featuring the free phenolate anion [H 5 C 6 -O] - . The deprotonation of phenol derivatives with tetraphosphazene bases represents a great way for the clean preparation of salts featuring free phenolate anions and in addition allows the selective syntheses of hydrogen bonded phenol-phenolate salts. This work presents a phosphazenium phenolate salt with a redox potential of -0.72 V and its capability for the selective activation of the chemically inert greenhouse gas SF 6 . The performed two-electron reduction of SF 6 leads to phosphazenium pentafluorosulfanide ([SF 5 ] - ) and fluoride salts., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3-E)GaCl 4 [(3-E) .+ = [{(IPr)C(Ph)E} 2 Fe(CO) 3 ] .+ , E = P or As; IPr = C{(NDipp)CH} 2 , Dipp = 2,6-iPr 2 C 6 H 3 ] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E} 2 (1-E) with Fe 2 (CO) 9 affords [{(IPr)C(Ph)E} 2 Fe(CO) 3 ] (2-E), in which 1-E binds to the Fe atom in an allylic (η 3 -EEC vinyl ) fashion and functions as a 4e donor ligand. Complexes 2-E undergo 1e oxidation with GaCl 3 to yield (3-E)GaCl 4 . Spin density analysis revealed that the unpaired electron in (3-E) .+ is mainly located on the Fe (52-64 %) and vinylic C (30-36 %) atoms. Further 1e oxidation of (3-E)GaCl 4 leads to unprecedented η 3 -EEC vinyl to η 3 -EC vinyl C Ph coordination shuttling to form the dications (4-E)(GaCl 4 ) 2 ., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The first Sn I diradical [(ADC Ph )Sn] 2 (4) based on an anionic dicarbene (ADC Ph ={CN(Dipp)} 2 CPh; Dipp=2,6-iPr 2 C 6 H 3 ) scaffold has been isolated as a green crystalline solid by KC 8 reduction of the corresponding bis-chlorostannylene [(ADC Ph )SnCl] 2 (3). The six-membered C 4 Sn 2 -ring of 4 containing six π-electrons shows a diatropic ring current, thus 4 may also be regarded as the first 1,4-distannabenzene derivative. DFT calculations suggest an open-shell singlet (OS) ground state of 4 with a remarkably small singlet-triplet energy gap (ΔE OS-T =4.4 kcal mol -1 ), which is consistent with CASSCF (ΔE S-T =6.6 kcal mol -1 and diradical character y=37 %) calculations. The diradical 4 splits H 2 at room temperature to yield the bis-hydridostannylene [(ADC Ph )SnH] 2 (5). Further reactivity of 4 has been studied with PhSeSePh and MeOTf., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The reactivity of the geminal frustrated Lewis pair (FLP) (F 5 C 2 ) 3 SnCH 2 P(tBu) 2 (1) was explored by reacting it with a variety of small molecules (PhOCN, PhNCS, PhCCH, tBuCCH, H 3 CC(O)CH=CH 2 , Ph[C(O)] 2 Ph, PhN=NPh and Me 3 SiCHN 2 ), featuring polar or non-polar multiple bonds and/or represent α,β-unsaturated systems. While most adducts are formed readily, the binding of azobenzene requires UV-induced photoisomerization, which results in the highly selective complexation of cis-azobenzene. In the case of benzil, the reaction does not lead to the expected 1,2- or 1,4-addition products, but to the non-stereoselective (tBu) 2 PCH 2 -transfer to a prochiral keto function of benzil. All adducts of 1 were characterised by means of multinuclear NMR spectroscopy, elemental analyses and X-ray diffraction experiments., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Herein, we report the first 1,4-diphosphinine-1,4-diide compound [(ADC Ph )P] 2 (5-Ph) (ADC Ph =PhC{(NDipp)C} 2 ; Dipp=2,6-iPr 2 C 6 H 3 ) derived from an anionic dicarbene (ADC Ph ) as a red crystalline solid. Compound 5-Ph containing a 16π-electron planar fused-tricyclic ring system was obtained by the 4e reduction of [(ADC Ph )PCl 2 ] 2 (4-Ph) with Mg (or KC 8 ) in a quantitative yield. Experimental and computational results imply that the central 8π-electrons C 4 P 2 ring of 5-Ph, which is fused between two 6π-electrons C 3 N 2 aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5-Ph has two electron-lone-pairs, one in a p-type orbital is in conjugation with the C=C bonds of the C 4 P 2 ring, while the second resides in a σ-symmetric orbital. This can be shown with the gold complex [(ADC Ph )P(AuCl) 2 ] 2 (6-Ph) obtained by reacting 5-Ph with (Me 2 S)AuCl. A mixture of 5-Ph and 4-Ph undergoes comproportionation in the presence of MgCl 2 to form the intermediate oxidation state compound [(ADC Ar )P] 2 (MgCl 4 ) (7-Ph), which is an aromatic species., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Intramolecular 1,2-Dipp migration of seven mesoionic carbenes (iMIC Ar ) 2 a-g (iMIC Ar =ArC{N(Dipp)} 2 CHC; Ar=aryl; Dipp=2,6-iPr 2 C 6 H 3 ) under nickel catalysis to give 1,3-imidazoles (IMD Ar ) 3 a-g (IMD Ar =ArC{N(Dipp)CHC(Dipp)N}) has been reported. The formation of 3 indicates the cleavage of an N-C Dipp bond and the subsequent formation of a C-C Dipp bond in 2, which is unprecedented in NHC chemistry. The use of 3 in accessing super-iMICs (5) (S-iMIC=ArC{N(Dipp)N(Me)C(Dipp)}C) has been shown with selenium (6), gold (7), and palladium (8) compounds. The quantification of the stereoelectronic properties reveals the superior σ-donor strength of 5 compared to that of classical NHCs. Remarkably, the percentage buried volume of 5 (%V bur =45) is the largest known amongst thus far reported iMICs. Catalytic studies show a remarkable activity of 5, which is consistent with their auspicious stereoelectronic features., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Tridentate Lewis acids with aligned functions were synthesized based on the rigid framework hexadehydrotribenzo[12]annulene. The backbone and its fluorinated analogue were synthesised in one-pot syntheses, with alkyne deprotection and Sonogashira cross coupling reaction being carried out in one step. Hydrosilylation of the annulene with chlorohydrosilanes proceeded highly selectively and afforded rigid poly-Lewis acids with three SiCl 3 or SiCl 2 Me substituents perfectly oriented to one side of the molecule in a single step. The progress of hydrosilylation was investigated by time-correlated NMR spectroscopic studies. The crystal structures show that the framework is symmetrically functionalised and the silyl substituents are aligned in one direction. To increase the acidity of the Lewis acids the chlorosilyl substituents were fluorinated with SbF 3 . Further investigation of hydrometallation reactions (M=B, Al, Ga, Sn) did not lead to corresponding structures., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

(C 6 F 5 )Te(CH 2 ) 3 NMe 2 (1), a perfluorophenyltellurium derivative capable of forming intramolecular N⋅⋅⋅Te interactions, was prepared and characterized. The donor-free reference substance (C 6 F 5 )TeMe (2) and the unsupported adduct (C 6 F 5 )(Me)Te⋅NMe 2 Et (2 b) were studied in parallel. Molecular structures of 1, 2 and 2 b were determined by single-crystal X-ray diffraction and for 1 and 2 by gas-phase electron diffraction. The structure of 1 shows N⋅⋅⋅Te distances of 2.639(1) Å (solid) and 2.92(3) Å (gas). Ab initio plus NBO and QTAIM calculations show significant charge transfer effects within the N⋅⋅⋅Te interactions and indicate σ-hole interactions., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The cyclic Ge(I) compound [(ADC Ph )Ge] 2 ( 4 ) (ADC Ph = {CN(Dipp)} 2 CPh, Dipp = 2,6- i Pr 2 C 6 H 3 ) containing a 6π-electron C 4 Ge 2 framework has been isolated as a red crystalline solid. CASSCF calculations reveal a closed-shell singlet ground state for 4 with a considerable diradical character ( y = 34%). Thus, the diradicaloid 4 readily splits dihydrogen at room temperature to yield the elusive bis-hydridogermylene [(ADC Ph )GeH] 2 ( 5 ).

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol-silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol-silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate-oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol-silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol-silanolate chains in the solid state., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The phytochemical exploration of the Entandrophragma candollei stem bark extract led to the isolation and identification of twenty compounds including three undescribed phragmalin-class limonoids named encandollens C-E (1-3), the undescribed protolimonoid 5 together with sixteen known compounds. The structures of all the isolated compounds were determined by interpretation of their spectroscopic and spectrometric data including HRMS, 1D and 2D NMR analyses. The assignment of the absolute and relative stereochemistry of the undescribed compounds was achieved using SC-XRD analyses as well as NOESY experiments. The previously reported structure of odoratone (5a) was corrected as 23 R,24 S-dihydroxy-22 S,25-epoxytirucall-7-en-3-one (5) based on its NMR and SC-XRD data. Prieurianin (4) exhibited high cytotoxic activity on KB3-1 cell lines with an IC 50 of 1.47 μM compared to the reference griseofulvin (IC 50  = 17-21 μM). The results of the in silico docking of compound 4 supported and delivered further insights on its cytotoxicity., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The reactivity of the frustrated Lewis pair (FLP) (F 5 C 2 ) 3 SnCH 2 P(tBu) 2 (1) was investigated with respect to the activation of elemental hydrogen. The reaction of 1 at elevated hydrogen pressure afforded the intramolecular phosphonium stannate(II) (F 5 C 2 ) 2 SnCH 2 PH(tBu) 2 (3). It was characterized by means of multinuclear NMR spectroscopy and single crystal X-ray diffraction. NMR experiments with the two isotopologues H 2 and D 2 showed it to be formed via an H 2 adduct (F 5 C 2 ) 3 HSnCH 2 PH(tBu) 2 (2) and the subsequent formal reductive elimination of pentafluoroethane; this is supported by DFT calculations. Parahydrogen-induced polarization experiments revealed the formation of a second product of the reaction of 1 with H 2 , [HP(tBu) 2 Me][Sn(C 2 F 5 ) 3 ] (4), in 1 H NMR spectra, whereas 2 was not detected due to its transient nature., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Several ethylenedioxy-bridged bisarenes with a variety of type and number of aryl groups were synthesized to study non-covalent dispersion-driven inter- and intramolecular aryl-aryl interactions in the solid state and gas phase. Intramolecular interactions are preferably found in the gas phase. DFT calculations with and without dispersion correction show larger interacting aromatic groups increase the stabilization energy of folded conformers and decrease the intermolecular centroid-centroid distance. Single-molecule structures generally adopt folded conformations with short intramolecular aryl-aryl contacts. Gas electron diffraction experiments were performed exemplarily for 1-(pentafluorophenoxy)-2-(phenoxy)ethane. A new procedure for structure refinement was developed to deal with the conformational complexity of such molecules. The results are an experimental confirmation of the existence of folded conformations of this molecule with short intramolecular aryl-aryl distances in the gas phase. Solid-state structures are dominated by stretched structures without intramolecular aryl-aryl interactions but interactions with neighboring molecules., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Phosphinidene complexes of the general formula RPM(CO) n (R = an alkyl or aryl group; M = a transition metal) are electrophilic and thermally unstable. Thus, the isolation of these elusive species for structural elucidations remains a challenge. Herein, we report the first terminal phosphinidene complexes [{(NHC)C(Ph)}P]Fe(CO) 4 [NHC = IPr = C{(NDipp)CH} 2 for 3 ; Me-IPr = C{(NDipp)CMe} 2 for 4 ; Dipp = 2,6- i Pr 2 C 6 H 3 ; NHC = N-heterocyclic carbene] as red crystalline solids containing a π-donor N-heterocyclic vinyl (NHV) substituent at the phosphorus atom. Calculations reveal donor-acceptor type bonding between phosphorus and iron atoms in 3 and 4 . The P → Fe donation represents ∼70% of the orbital interaction, whereas the Fe → P π-back-donation corresponds to ∼15% of the orbital interaction. The phosphorus atoms in 3 and 4 carry charges of +0.65e and +0.64e, respectively, indicating the electrophilic character of the phosphinidene {(NHC)C(Ph)}P moiety. Accordingly, 3 reacts with an NHC nucleophile (IMe 4 ) to yield the Lewis adduct [{(NHC)C(Ph)}P(IMe 4 )]Fe(CO) 4 ( 5 ) [IMe 4 = C(NMeCMe) 2 ]. The coordination of an electron-rich NHC (IMe 4 ) to the phosphorus atom in 5 precludes the π-electron density transfer from the NHV to the phosphorus atom. Thus, the C IPr -C vinyl and C vinyl -P bonds of 5 become shorter and longer, respectively, compared to those of 3 .

While perfluorinated aryl, aryloxy and alkoxy aluminum species are well-established as weakly coordinating anions (WCAs), corresponding perfluoroalkyl aluminum derivatives are virtually unknown. Reaction of Si(C 2 F 5 ) 3 CH 3 with Li[AlH 4 ] afforded the tetrakis(pentafluoroethyl)aluminate, [Al(C 2 F 5 ) 4 ] - . Several salts of the [Al(C 2 F 5 ) 4 ] - ion were synthesized and characterized by NMR spectroscopic methods, mass spectrometry, X-ray diffraction studies and elemental analysis., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The geminal frustrated Lewis pair (F 5 C 2 ) 3 SnCH 2 P(tBu) 2 (1) reacted with N-sulfinylaniline PhNSO to afford the first sulfur monoxide adduct of a main group metal, (F 5 C 2 ) 3 SnCH 2 P(tBu) 2 ⋅SO (2), which contains a SnCPSO ring. The second product is a phenylnitrene adduct of 1. The surprising stability of 2 was compared with the stabilities of the so far inaccessible O 2 and S 2 adducts of 1. Attempts to prepare these from 1 and the elemental chalcogens (O 2 , S 8 , Se ∞ , Te ∞ ) led to four-membered SnCPE ring systems. Quantum-chemical investigations of 2 demonstrate the bond polarity of the SO unit to stabilize 2., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The refrigerant trans- 1,3,3,3-tetrafluoropropene (HFO-1234ze) is used as a replacement for former cooling agents that have been phased-out due to their global warming potential or ozone depleting potential. Although it is used on a large scale, only a few vibrational data and no structural data of HFO-1234ze are known. We report structure determinations based on low-temperature single-crystal X-ray diffraction data as well as gas-phase diffraction data of HFO-1234ze and HFO-1234yf (2,3,3,3-tetrafluoropropene). Furthermore, vibrational spectra of HFO-1234ze in all phases are described. The results are discussed together with quantum-chemical calculations on the PBE0/cc-pVTZ level of theory. Combustion experiments of HFO-1234ze show carbonyl difluoride, carbon dioxide and hydrogen fluoride to be the main combustion products., Competing Interests: The authors declare no conflict of interest., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Difluorothiophosphoryl isocyanate, F 2 P(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar-matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas electron diffraction (GED) and single crystal X-ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum-chemical calculations. Theoretically, the C s symmetric syn -conformer is predicted to be the most stable conformation. Rotation about the P-N bond requires about 9 kJ mol -1 and the predicted existence of an anti -conformer is dependent on the quantum-chemical method used. This syn- orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of F 2 P(S)NCO to form CO, F 2 P(S)N, and F 2 PNCO is observed in the solid Ar-matrix., Competing Interests: The authors declare no conflict of interest., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Crystalline 1,4-distannabarrelene compounds [(ADC Ar ) 3 Sn 2 ]SnCl 3 (3-Ar) (ADC Ar ={ArC(NDipp) 2 CC}; Dipp=2,6-iPr 2 C 6 H 3 , Ar=Ph or DMP; DMP=4-Me 2 NC 6 H 4 ) derived from anionic dicarbenes Li(ADC Ar ) (2-Ar) (Ar=Ph or DMP) have been reported. The cationic moiety of 3-Ar features a barrelene framework with three coordinated Sn II atoms at the 1,4-positions, whereas the anionic unit SnCl 3 is formally derived from SnCl 2 and chloride ion. The all carbon substituted bis-stannylenes 3-Ar have been characterized by NMR spectroscopy and X-ray diffraction. DFT calculations reveal that the HOMO of 3-Ph (ϵ=-6.40 eV) is mainly the lone-pair orbital at the Sn II atoms of the barrelene unit. 3-Ar readily react with sulfur and selenium to afford the mixed-valence Sn II /Sn IV compounds [(ADC Ar ) 3 SnSn(E)](SnCl 6 ) 0.5 (E=S 4-Ar, Ar=Ph or DMP; E=Se 5-Ph)., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Isoshamixanthone ( 1 ), a new stereoisomeric pyrano xanthone together with the previously known fungal metabolites, epiisoshamixanthone ( 2 ), sterigmatocystin ( 3 ), arugosin C ( 4 ), norlichexanthone ( 5 ), diorcinol ( 6 ), ergosterol and methyllinoleate, were obtained from the endophytic fungal strain Aspergillus sp. ASCLA isolated from leaf tissues of the medicinal plant Callistemon subulatus . The chemical structure of the new xanthone ( 1 ) was elucidated by extensive 1D, 2D NMR, and ESI HR mass measurements, and by comparison with literature data. The constitutions and absolute configurations of 1 and epiisoshamixanthone ( 2 ) were additionally confirmed by X-ray crystallography. Compounds 1,2 were evaluated for their potential anticancer activity using the human cervix carcinoma cell line (KB-3-1). The antimicrobial activities of the fungal extract and compounds 1,2 were studied using a panel of pathogenic microorganisms as well.

We report on the first examples of isolated silanol-silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol-silanolate anions are postulated intermediates in the hydroxide-mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

2-Arsa-1,3-butadienes (L)As(cAACR) (L = PhC[double bond, length as m-dash]C{(NDipp)CH}2, Dipp = 2,6-iPr2C6H3; cAACR = C{(NDipp)CMe2CH2C(R)}, R = Me22a, R = cyclohexyl (Cy) 2b) and the corresponding radical cations [(L)As(cAACR)]GaCl4 (R = Me23a, Cy 3b) and dications [(L)As(cAACR)](GaCl4)2 (R = Me 4a, Cy 4b) featuring a C[double bond, length as m-dash]C-As[double bond, length as m-dash]C π-conjugated framework are reported.

Non-covalent aryl-aryl interactions for the molecular structures of three 1,2-diaryltetramethyldisilanes X5C6-(SiMe2)2-C6Y5 (X ≠ Y; X, Y = H, F, Cl) were studied by single crystal X-ray and gas electron diffraction as well as by SAPT calculations. Aryl-aryl interactions cause all to adopt exclusively rather untypical eclipsed syn-conformers in the gas phase, and C6F5-(SiMe2)2-C6Cl5 also in the solid state.

Three 1,2-diaryltetramethyldisilanes X 5 C 6 -(SiMe 2 ) 2 -C 6 X 5 with two C 6 H 5 , C 6 F 5 , or C 6 Cl 5 groups were studied concerning the importance of London dispersion driven interactions between their aryl groups. They were prepared from 1,2-dichlorotetramethyldisilane by salt elimination. Their structures were determined in the solid state by X-ray diffraction and for free molecules by gas electron-diffraction. The solid-state structures of the fluorinated and chlorinated derivatives are dominated by aryl-aryl interactions. Unexpectedly, Cl 5 C 6 -(SiMe 2 ) 2 -C 6 Cl 5 exists exclusively as an eclipsed syn-conformer in the gas phase with strongly distorted Si-C 6 Cl 5 units due to strong intramolecular interactions. In contrast, F 5 C 6 -(SiMe 2 ) 2 -C 6 F 5 reveals weaker interactions. The contributions to the total interaction energy were analyzed by SAPT calculations., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The first C5-protonated 1,3-imidazol-based mesoionic carbene iMICBp (2) (iMICBp = :C{CH(NDipp)2C(Bp)}; Dipp = 2,6-iPr2C6H3; Bp = 4-PhC6H4) has been reported as a crystalline solid. Spectroscopic, X-ray diffraction, and computational studies clearly support the carbenic nature of 2, which has been further corroborated by its reactions with Ni(CO)4, (Me2S)AuCl, white phosphorus, and CO2.

The title compound, [Bi(C 9 H 6 NS 2 ) 3 ], was prepared by reacting BiCl 3 and 2-mercapto-4-phenyl-thia-zole ( L H) at room temperature in a stoichiometric ratio of 1:4. The mol-ecular structure reveals a slightly distorted square-pyramidal environment around the Bi III atom. Two of the three monoanionic ligands L - coordinate in an N , S -bidentate mode, while one shows a monodentate mode through an S atom. There are no significant inter-molecular inter-actions present in the crystal., (© Stammler and Imran 2020.)

A synthetic strategy for the 2-phospha-1,3-butadiene derivatives [{(IPr)C(Ph)}P(cAAC Me )] ( 3a ) and [{(IPr)C(Ph)}P(cAAC Cy )] ( 3b ) (IPr = C{(NDipp)CH} 2 , Dipp = 2,6-iPr 2 C 6 H 3 ; cAAC Me = C{(NDipp)CMe 2 CH 2 CMe 2 }; cAAC Cy = C{(NDipp)CMe 2 CH 2 C(Cy)}, Cy = cyclohexyl) containing a C[double bond, length as m-dash]C-P[double bond, length as m-dash]C framework has been established. Compounds 3a and 3b have a remarkably small HOMO-LUMO energy gap ( 3a : 5.09; 3b : 5.05 eV) with a very high-lying HOMO (-4.95 eV for each). Consequently, 3a and 3b readily undergo one-electron oxidation with the mild oxidizing agent GaCl 3 to afford radical cations [{(IPr)C(Ph)}P(cAAC R )]GaCl 4 (R = Me 4a , Cy 4b ) as crystalline solids. The main UV-vis absorption band for 4a and 4b is red-shifted with respect to that of 3a and 3b , which is associated with the SOMO related transitions. The EPR spectra of compounds 4a and 4b each exhibit a doublet due to coupling of the unpaired electron with the 31 P nucleus. Further one-electron removal from the radical cations 4a and 4b is also feasible with GaCl 3 , affording the dications [{(IPr)C(Ph)}P(cAAC R )](GaCl 4 ) 2 (R = Me 5a , Cy 5b ) as yellow crystals. The molecular structures of compounds 3-5 have been determined by X-ray diffraction and analyzed by DFT calculations., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)