Search

The reaction of the bicyclic silicon(I) ring compound Si 4 {N(SiMe 3 )Mes} 4 1 with strong zwitterionic character and moderate sterical demand of the amido substituents with two equivalents of KC 8 was investigated. This resulted in the unexpected abstraction of two amido substituents from 1 and additionally in dimerization to a dianionic Si 8 cluster compound 2 with four unsubstituted silicon atoms and two [K([18]crown-6)] + counter cations. Performing this reaction in the absence of [18]crown-6 results in release of only one amido substituent from 1 and dimerization to a dianionic Si 8 cluster 3 with only two unsubstituted silicon atoms. This reaction with KC 8 was repeated and trapping agents such as SiMe 3 Cl and tBuCl were added in-situ whereupon the second isolated homocyclic silylene 4 and a monoanionic hydride and tBu substituted Si 8 cluster 5 with one unsubstituted silicon atom were isolated. Furthermore, 1 was reacted with KOtBu which resulted in the selective abstraction of one SiMe 3 group and formation of the tetrahedral silanide 6 with one imido substituent bridging an edge of the tetrahedron., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

Transition metal complexes are archetypal luminescent probes that are widely used for various applications ranging from optoelectronics to biomedicine. However, they face significant challenges such as photobleaching and photooxidative stress, which limit their performance. Herein, we introduce a photosystem-inspired concept based on the use of a vitamin (ascorbic acid, Asc-Ac) to adaptively suppress photobleaching of molecular luminophores. As a proof-of-concept compound, we have selected a new bis-cyclometalated Pt(II) complex (Pt- t Bu) and investigated its adaptive photoluminescence resulting from singlet dioxygen ( 1 O 2 ) photoproduction in the presence of Asc-Ac. Interestingly, the excited state quenching and subsequent photobleaching of Pt- t Bu in aerated solutions is suppressed by addition of Asc-Ac, which scavenges the 1 O 2 photosensitized by Pt- t Bu upon irradiation and results in an adaptive oxygen depletion with enhancement of luminescence. The adaptation is resilient for successive irradiation cycles with oxygen replenishment, until peroxidation overshooting leads to the degradation of Pt- t Bu by formation of a dark Pt(iv) species. The complexity-related adaptation with initial overperformance (luminescence boost) relies on the external energy input and cascaded feedback loops, thus biomimicking inflammation, as the repeated exposure to a stressor leads to a final breakdown. Our antioxidative protection mechanism against photobleaching can be successfully extended to multiple coordination compounds ( e.g. , Ir(iii), Ru(ii) and Re(i) complexes), thus demonstrating its generality. Our findings broaden the scope of molecular adaptation and pave the way for enhancing the stability of molecular luminophores for multiple applications., Competing Interests: The authors declare no competing interests., (This journal is © The Royal Society of Chemistry.)

In this study, it is demonstrated that the radiative rate constant of phosphorescent metal complexes can be substantially enhanced using monodentate ancillary ligands containing heavy donor atoms. Thus, the chlorido coligand from a Pt(II) complex bearing a monoanionic tridentate C^N*N luminophore ([ PtLCl ]) was replaced by triphenylphosphane (PPh 3 ) and its heavier pnictogen congeners (i.e., PnPh 3 to yield [ PtL(PnPh 3 ) ]). Due to the high tridentate-ligand-centered character of the excited states, the P-related radiative rate is rather low while showing a significant boost upon replacement of the P donor by heavier As- and Sb-based units. The syntheses of the three complexes containing PPh 3 , AsPh 3 , and SbPh 3 were completed by unambiguous characterization of the clean products using exact mass spectrometry, X-ray diffractometry, bidimensional NMR, and 121 Sb- Mössbauer spectroscopy (for [ PtL(SbPh 3 ) ]) as well as steady state and time-resolved photoluminescence spectroscopies. Hence, it was shown that the hybridization defects of the V th main-group atoms can be overcome by complexation with the Pt center. Notably, the enhancement of the radiative rate constants mediated by heavier coligands was achieved without significantly influencing the character of the excited states. A rationalization of the results was achieved by TD-DFT. Even though the Bi-based homologue was not accessible due to phenylation side reactions, the experimental data allowed a reasonable extrapolation of the structural features whereas the hybridization defects and the excited state properties related to the Bi-species and its phosphorescence rate can be predicted by theory. The three complexes showed an interesting antiprotozoal activity, which was unexpectedly notorious for the P-containing complex. This work could pave the road toward new efficient materials for optoelectronics and novel antiparasitic drugs.

In this work, we have explored Re(I) complexes featuring triphenylpnictogen ( PnPh 3 , Pn = P , As , or Sb )-based coligands and bidentate (neutral or monoanionic) luminophores derived from 1,10-phenantroline ( phen ), as well as from 2-(3-( tert -butyl)-1 H -1,2,4-triazol-5-yl)pyridine ( H(N- t Bu) ). The effect of the increasingly heavy elements on the structural parameters, photoexcited-state properties, and electrochemical behavior as well as the hybridization defects and polarization of the Pn atoms was related to the charges of the main luminophores (i.e., phen vs N- t Bu ) and explored in terms of photoluminescence spectroscopy, X-ray diffractometry, and quantum-chemical methods. Therefore, an in-depth analysis of the bonding, crystal packing, excited-state energies, and lifetimes was assessed in liquid solutions, frozen glassy matrices, and crystalline phases along with a semiquantitative photoactivation study. Notably, by changing the main ligand from phen to N- t Bu , an increase in radiative and radiationless deactivation rates ( k r and k nr , respectively) at 77 K together with a faster photoinduced CO release and fragmentation at room temperature was detected. In addition, a progressively red-shifted phosphorescence was observed with the growing atomic number of the pnictogen atom, along with a boost in k r and k nr at 77 K. Down the V th main group and upon coordination of the Pn atom to the Re(I) center, an increasingly prominent jump of s-orbital participation on the binding s x p 3.00 -orbitals of the Pn atoms is evidenced. Based on these findings, the ability of these complexes to act as tunable photoluminescent labels able to perform as light-driven CO-releasing molecules is envisioned.

This work reports on a battery of coordination compounds featuring a versatile dianionic luminophore adopting three different coordination modes (mono, bi, and tridentate) while chelating Pd(II), Pt(II), Au(III), and Hg(II) centers. An in-depth structural characterization of the ligand precursor (H 2 L) and six transition metal complexes ([HLPdCNtBu], [LPtCl], [LPtCNtBu], [LPtCNPhen], [HLHgCl], and [LAuCl]) is presented. The influence of the cations and coordination modes of the luminophore and co-ligands on the photophysical properties (including photoluminescence quantum yields (Φ L ), excited state lifetimes (τ), and average (non-)radiative rate constants) are evaluated at various temperatures in different phases. Five complexes show interesting photophysical properties at room temperature (RT) in solution. Embedment in frozen glassy matrices at 77 K significantly boosts their luminescence by suppressing radiationless deactivation paths. Thus, the Pt(II)-based compounds provide the highest efficiencies, with slight variations upon exchange of the ancillary ligand. In the case of [HLPdCNtBu] , both Φ L and τ increase over 30-fold as compared to RT. Furthermore, the Hg(II) complex achieves, for the first time in its class, a Φ L exceeding 60% and millisecond-range lifetimes. This demonstrates that a judicious ligand design can pave the way toward versatile coordination compounds with tunable excited state properties., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Metal phthalocyaninates and their higher homologues are recognized as deep-red luminophores emitting from their lowest excited singlet state. Herein, we report on the design, synthesis, and in-depth characterization of a new class of dual-emissive (visible and NIR) metal naphthalocyaninates. A 4- N , N -dimethylaminophen-4-yl-substituted naphthalocyaninato zinc(II) complex ( Zn-NMe 2 Nc ) and the derived water-soluble coordination compound ( Zn-NMe 3 Nc ) exhibit a near-infrared fluorescence from the lowest ligand-centered state, along with a unique push-pull-supported luminescence in the visible region of the electromagnetic spectrum. An unprecedentedly broad structural (2D-NMR spectroscopy and mass spectrometry) as well as photophysical characterization (steady-state state and time-resolved photoluminescence spectroscopy) is presented. The unique dual emission was assigned to two independent sets of singlet states related to the intrinsic Q-band of the macrocycle and to the push-pull substituents in the molecular periphery, respectively, as predicted by TD-DFT calculations. In general, the elusive chemical aspects of these macrocyclic compounds are addressed, involving both reaction conditions, thorough purification, and in-depth characterization. Besides the fundamental aspects that are investigated herein, the photoacoustic properties were exemplarily examined using phantom gels to assess their tomographic imaging capabilities. Finally, the robust luminescence in the visible range arising from the push-pull character of the peripheral moieties demonstrated a notable independence from aggregation and was exemplarily implemented for optical imaging (FLIM) through time-resolved multiphoton micro(spectro)scopy.

The bicyclic silicon(I) ring compound Si 4 {N(SiMe 3 )Mes} 4 (2) was used as starting material in reactions with chalcogens and chalcogen transfer agents at low temperatures. This resulted in the selective formation of new cage compounds. With Me 3 NO, a silicon oxide with adamantane-type cage 3 was isolated that represents the first isolated T 4 silsesquioxane. Reactions with propylenesulfide and red selenium gave direct access to defect heterocubane-type cages 4 and 5 with three Si-Si bonds wherein the silicon atoms adopt different low oxidation states of +I and +III. A reaction with elemental tellurium even occurs below room temperature to provide ditelluro-tetrasila-tricyclohexane 6., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A series of [2]catenanes has been prepared from di-NHC building blocks by utilizing solvophobic effects and/or π⋅⋅⋅π stacking interactions. The dinickel naphthobiscarbene complex syn-[1] and the kinked biphenyl-bridged bipyridyl ligand L 2 yield the [2]catenane [2-IL](OTf) 4 by self-assembly. Solvophobic effects are pivotal for the formation of the interlocked species. Substitution of the biphenyl-linker in L 2 for a pyromellitic diimide group gave ligand L 3 , which yielded in combination with syn-[1] the [2]catenane [3-IL](OTf) 4 . This assembly exhibits enhanced stability in diluted solution, aided by additional π⋅⋅⋅π stacking interactions. The π⋅⋅⋅π stacking was augmented by the introduction of a pyrene bridge between two NHC donors in ligand L 4 . Di-NHC precursor H 2 -L 4 (PF 6 ) 2 reacts with Ag 2 O to give the [Ag 2 L 4 2 ] 2 [2]catenane [4-IL](PF 6 ) 4 , which shows strong π⋅⋅⋅π stacking interactions between the pyrene groups. This assembly was readily converted into the [Au 2 L 4 2 ] 2 gold species [5-IL](PF 6 ) 4 , which exhibits exceptional stability based on the strong π⋅⋅⋅π stacking interactions and the enhanced stability of the Au-C NHC bonds., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Depending on the chelate ring present, cyclometalated complexes are useful catalysts for various reactions. The reactivity of Ir III and Rh III NHC complexes bearing aliphatic or aromatic N,N'-substituents and thus featuring various metalation sites toward cyclometalation has been investigated. The Rh III complex bearing an N -mesityl- N '-benzyl-NHC does not participate in any cyclometalation, while the Ir III complex reacts under metalation of an ortho -methyl group of the Mes substituent to give complex [ 3 ] with a six-membered chelate ring. The Rh III and Ir III complexes bearing an N - o -tolyl, N -benzyl-NHC undergo sp 2 -CH activation to yield the cyclometalated complexes [ 4 ] and [ 5 ] featuring a five-membered C NHC ∧ C chelate ring. Density functional theory (DFT) studies corroborated the experimental findings., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

In this study, the insertion of different monodentate co-ligands on Pt(II) complexes bearing a monoanionic C^N*N luminophore as a tridentate chelator was achieved beyond the previously reported chlorido- ([ PtCl(L) ]) and cyanido-decorated ([ PtCN(L) ]) analogues. To investigate the impact of the auxiliary ligand on the photophysical properties, we introduced a neutral carbonyl-ligand and observed a lower photoluminescence quantum yield ( Φ L ) than with a cyanido moiety. However, the direct substitution of the chlorido co-ligand by a NO-related derivative was not successful. Interestingly, the attempted reduction of the successfully inserted nitrito- N -ligand in [ PtNO 2 (L) ] resulted in the oxidation of the Pt(II)-center to Pt(IV), as demonstrated by X-ray diffractometry. For comparison, the trifluoroacetato Pt(II) and chlorido Pt(IV) complexes ([ PtTFA(L) ] and [ PtCl 3 (L) ], respectively) were also synthesized. The photophysical characterization revealed similar photoluminescence profiles for all complexes, indicating a weak effect of the co-ligand on the excited state; in fact, all complexes display emission from metal-perturbed ligand-centered states (even the Pt(IV) species). Nonetheless, longer excited state lifetimes ( τ av ) suggest a reduced thermally-activated radiationless deactivation via metal-centered states upon exchange of the chlorido units for other monodentate entities, yet without significantly improving the overall Φ L at room temperature. The irreversible oxidation waves (measured via cyclic voltammetry) mostly stem from the Pt(II)-center; the co-ligand-related drop of these potentials correlates with the increasing σ -donating capacities of the ancillary ligand. In summary, an enhanced π -acceptor capacity does not necessarily improve the Φ L and can even impair radiative rates by compromising the perturbative participation of the metal center on the emissive triplet state; in addition, strong σ -donor abilities improve the phosphorescence efficiencies by hampering the thermal population of dissociative electronic configurations related to the participation of antibonding d *-orbitals at the metal center.

A series of four regioisomeric Pt(II) complexes ( PtL a -n and PtL b -n ) bearing tetradentate luminophores as dianionic ligands were synthesized. Hence, both classes of cyclometallating chelators were decorated with three n -hexyl ( n = 6) or n -dodecyl ( n = 12) chains. The new compounds were unambiguously characterized by means of multiple NMR spectroscopies and mass spectrometry. Steady-state and time-resolved photoluminescence spectroscopy as well quantum chemical calculations show that the effect of the regioisomerism on the emission colour and on the deactivation rate constants can be correlated with the participation of the Pt atom on the excited state. The thermal properties of the complexes were studied by DSC, POM and temperature-dependent steady-state photoluminescence spectroscopy. Three of the four complexes ( PtL a -12 , PtL b -6 and PtL b -12 ) present an intriguing thermochromism resulting from the responsive metal-metal interactions involving adjacent monomeric units. Each material has different transition temperatures and memory capabilities, which can be tuned at the intermolecular level. Hence, dipole-dipole interactions between the luminophores and disruption of the crystalline packing by the alkyl groups are responsible for the final properties of the resulting materials., Competing Interests: The authors declare no conflicts of interest.

The reaction of the six-vertex amido-substituted silicon cluster Si 6 {N(SiMe 3 )Ph} 6 1 with two equiv. of KC 8 results in the abstraction of K{N(SiMe 3 )Ph} and leads to the contact ion pair 2 including an anionic silicon cluster with two unsubstituted pyramidal vertices. Facile functionalization of 2 was achieved with MeI, SiCl 4 and SiBr 4 and results in neutral two-fold functionalized silicon clusters.

We report herein a series of organometallic Borromean rings (BRs) and [2]catenanes prepared from benzobiscarbene ligands. The reaction of dinickel complexes of the benzobiscarbenes 1 a-1 c with a thiazolothiazole bridged bipyridyl ligand L 2 led by self-assembly to a series of organometallic BRs. Solvophobic effects played a crucial role in the formation and stability of the interlocked species. The stability of BRs is related to the N-alkyl substituents at the precursors 1 a-1 c, where longer alkyl substitutes improve stability and inter-ring interactions. Solvophobic effects are also important for the stability of [2]catenanes prepared from 1 a-1 c and a flexible bipyridyl ligand L 3 . In solution, an equilibrium between the [2]catenanes and their macrocyclic building blocks was observed. High proportions of [2]catenanes were obtained in concentrated solutions or polar solvents. The proportion of [2]catenanes in solution could be further enhanced by lengthening of the N-alkyl substitutes., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

In this work, we explored coordination compounds featuring caffeine-based carbene co-ligands and tridentate dianionic pincer luminophores derived from 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine (N), as well as from 2-phenyl-6-(1H-1,2,4-triazol-5-yl)pyridine (C), bearing either Ad (adamantyl) or tBu (tertiary butyl) substituents. The new 2-phenyl-6-(1H-1,2,4-triazol-5-yl)pyridine-based ligand precursors along with four Pt(II) complexes, namely Pt(C-tBu), Pt(C-Ad), Pt(N-tBu) and Pt(N-Ad) were characterized. Further on, the influence of the different substituents at the chelating luminophores and of the caffeine-based NHC-co-ligand on the photophysical properties (including photoluminescence quantum yields (Φ L ), excited-state lifetimes (τ), radiative (k r ), and non-radiative (k nr ) deactivation rate constants) was assessed in fluid solutions at room temperature (RT) and in frozen glassy matrices at 77 K. All four luminophores perform equivalently well within the experimental uncertainty. In deoxygenated fluid solutions at RT, photoluminescence quantum yields reaching up to 24 ± 2% and excited-state lifetimes of around 12 μs were found. The generally long excited-state lifetimes and only minor blue shift upon cooling to 77 K along with mostly well-resolved vibrational progressions point to metal-perturbed ligand-centered excited states. Notably, the yield of the complexation reaction in case of Pt(C-tBu) and Pt(C-Ad) was almost two times higher compared to Pt(N-tBu) and Pt(N-Ad). Cyclometallation is not an essential feature to achieve high photoluminescence quantum yields, but it can improve the synthetic efficiency. In summary, it can be observed that coordination chemical concepts based on natural products can lead to stable phosphorescent species with interesting excited-state properties., (© 2022 The Authors. Photochemistry and Photobiology published by Wiley Periodicals LLC on behalf of American Society for Photobiology.)

The synthesis as well as the structural and photophysical characterization of two isoleptic bis-cyclometalated Pt(II) and Pd(II) complexes, namely [ PtL ] and [ PdL ], bearing a tailored dianionic tetradentate ligand ( L 2- ) are reported. The isostructural character and intermolecular interactions of [ PtL ] and [ PdL ] were assessed by NMR spectroscopy and X-ray diffraction analysis. Both complexes show fully ligand-controlled aggregation, demonstrating that a judicious molecular design can tune the photophysical properties. In fact, by introduction of fluorine atoms on defined positions and methoxy groups on complementary sites, metal-metal interactions can be forced by a head-to-tail stacking. Hence, [ PtL ] shows luminescence from metal-perturbed ligand-centered or from metal-metal-to-ligand charge-transfer triplet states in diluted solutions, in frozen glasses and in crystals, with high photoluminescence quantum yields and long lifetimes in the microsecond range. At room temperature (RT) in concentrated fluid solutions, the palladium analogue [ PdL ] surprisingly emits luminescence from aggregated species involving supramolecular interactions. Time-resolved photoluminescence and transient absorption spectroscopies demonstrated that ultrafast intersystem crossing occurs for both metals, which outruns any competitive relaxation pathway from the photoexcited singlet state. Furthermore, we demonstrate that the radiationless deactivation can be suppressed in frozen glassy matrices at 77 K and by intermolecular interactions in fluid solutions at RT. In both cases and as indicated by density functional theory calculations, the lowest emissive state acts as an energy trap from which the thermal population of dissociative states with formal occupation of an antibonding Pd-centered 4d x 2 - y 2 orbital is suppressed. This occurs as the energy gap between the emissive and the dark states surpasses kT .

In this work, we describe the synthesis as well as structural, photophysical, and theoretical investigation of a new coordination chemical concept involving rhenium(I) complexes bearing monoanionic 1,2,4-triazolylpyridine-based bidentate chromophores. The X-ray diffractometric analysis of single crystals revealed particular packing features: the trifluoromethylated exemplar displayed two kinds of arrangements of the coordination centers, where the bidentate ligands at the edges of the unit cell are staggered parallel to each other, whereas those inside show antiparallel stacking with respect to the external ligands. On the other hand, the complexes bearing an adamantyl substituent yield a linear arrangement, where the bulky moiety of one luminophore points to the pyridine center of the adjacent ligand of the neighboring complex while including methanol molecules hydrogen-bonded to the triazolato unit. We observed that the photophysical properties of the complexes (photoexcited-state lifetimes, photoluminescence maxima and quantum yields) can be adjusted by tuning of the substitution pattern at the bidentate luminophore as well as by variation of the monodentate coligand. The photoluminescence spectra and photoexcited-state lifetimes of the crystalline phases were measured by phosphorescence lifetime micro(spectro)scopy. Interestingly, the vibrationally resolved emission spectra of the crystals closely resemble those of diluted frozen glassy matrixes at 77 K, in contrast with the broad bands observed in amorphous solids and in fluid solutions, where the charge-transfer character is enhanced. While the photoluminescence quantum yields (Φ L ) reach up to 15%, the complexes are able to attain up to 55% efficiency regarding the photosensitization of 1 O 2 (Φ Δ ), depending on the combination of luminophore and coligand. Theoretical calculations showed that the photoexcited triplet (T 1 ) state has a metal-ligand-to-ligand charge-transfer character, where promotion to the excited electronic configuration shortens the Re(I)-N bond involving the bidentate triazolylpyridine while stretching the three fac -CO-Re(I) bonds as well as the linkage to the axial monodentate coligand. The calculated vertical ( E vl ) and 0-0 ( E (0-0) ) radiative transition energies are in very good agreement with the experimental values ( E exp lum ).

The silanide [Si 4 {N(SiMe 3 )Dipp} 3 ] - (1) transforms into the anionic siliconoid cluster [Si 7 {N(SiMe 3 )Dipp} 3 ] - (2) with four unsubstituted silicon atoms as a contact ion pair with [K([18]crown-6)] in C 6 D 6 at room temperature within five weeks. Anion 2 was investigated by natural population analysis and visualization of intrinsic atomic orbitals. Magnetically induced current-density calculations of 2 revealed two distinct strong diatropic vortices that sum up in one direction and create a strongly shielded apical silicon atom in 2., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The synthesis of mixed silicon and germanium clusters Si x Ge 6- x {N(SiMe 3 )Dipp} 4 1-3 ( x = 3.7, 3.1, 2.1) with amido-substituents and two unsubstituted germanium atoms was achieved in co-reductions using the tribromosilane {N(SiMe 3 )Dipp}SiBr 3 and the tribromogermane {N(SiMe 3 )Dipp}GeBr 3 in three different ratios. The ratio of Si and Ge used for the synthesis of 1-3 approximately corresponds to that in the final products. All compounds were characterized by single crystal X-ray diffraction and EI mass spectrometry. In addition, 1 and 2 were characterized by solid-state 29 Si{ 1 H} CP/MAS NMR spectroscopy and multinuclear NMR spectroscopy in solution.

A family of Pt(II) complexes bearing monoanionic C^N^N ligands as luminophoric units as well as a set of monodentate ligands derived from allenylidene and carbene species were synthesized and characterized in terms of structure and photophysical properties. In addition, we present the extraordinary molecular structure of a phosphorescent complex carrying an allenylidene ligand. Depending on the co-ligand, an effect can be observed in the photoluminescence lifetimes and quantum yields as well as in the radiative and radiation less deactivation rate constants. Their correlation with the substitution pattern was analyzed by comparing the photoluminescence in fluid solution at room temperature and in frozen glassy matrices at 77 K. Moreover, in order to gain a deeper understanding of the electronic states responsible for the optical properties, density functional theory calculations were performed. Finally, the cytotoxicity of the complexes was evaluated in vitro , showing that the cationic complexes exhibit strong effects at low micromolar concentrations. The calculated half-maximum effective concentrations (EC 50 values) were 4 times lower in comparison to the established antitumor agent oxaliplatin. In contrast, the neutral species are less toxic, rendering them as potential bioimaging agents.

Reductive debromination of the tribromoamidosilane 2 gave the tetracyclic silaheterocycle 3 through a unique reaction cascade involving unprecedented two-fold intramolecular cycloaddition by transient silylenes. Experimental and computational analyses of the reaction mechanism allowed the identification of the key intermediates that lead to the silaheterocycle 3 or, alternatively, to the cyclotrisilene 19.

The reductive debromination of {N(SiMe 3 )Ph}SiBr 3 1 with Rieke magnesium yields the six-vertex amido-substituted silicon cluster 2 with zwitterionic character that represents an unprecedented isomer of hexasilabenzene. The topology of Si1 and Si2 in 2 has bonding features of a highly twisted disilene and resembles that of a buckled dimer of Si(100)2 × 1 reconstructed surfaces. Cluster 2 forms the adducts 3 and 4 with NHC Me4 and DMAP, respectively. The NHC adduct 4 additionally coordinates to BH 3 which affords the saturated cluster BH 3 NHC Me4 Si 6 {N(SiMe 3 )Ph} 6 (5). Furthermore, 2 undergoes addition with MeI and iodine to form the halogenated silicon clusters 6 and 7, respectively.

Isolation of the neutral homocyclic silylene 2 is possible via amine ligand abstraction with potassium graphite (KC 8 ) and subsequent reaction with SiMe 3 Cl from a bicyclic silicon(I) amide J. This reaction proceeds via an anionic homoaromatic silicon ring compound 1 as an intermediate. The twofold-coordinated silicon atom in the homocyclic silylene 2 is stabilized by an allyl-type π-electron delocalization. 2 reacts in an oxidative addition with two equivalents of MeOH and in cycloadditions with ethene, phenylacetylene, diphenylacetylene and with 2,3-dimethyl-1,3-butadiene to afford novel functionalized ring compounds., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The bicyclic amido-substituted silicon(I) ring compound Si 4 {N(SiMe 3 )Mes} 4 2 (Mes=Mesityl=2,4,6-Me 3 C 6 H 2 ) features enhanced zwitterionic character and different reactivity from the analogous compound Si 4 {N(SiMe 3 )Dipp} 4 1 (Dipp=2,6- i Pr 2 C 6 H 3 ) due to the smaller mesityl substituents. In a reaction with the N-heterocyclic carbene NHC Me 4 (1,3,4,5-tetramethyl-imidazol-2-ylidene), we observe adduct formation to give Si 4 {N(SiMe 3 )Mes} 4  ⋅ NHC Me 4 (3). This adduct reacts further with the Lewis acid BH 3 to yield the Lewis acid-base complex Si 4 {N(SiMe 3 )Mes} 4  ⋅ NHC Me 4  ⋅ BH 3 (4). Coordination of AlBr 3 to 2 leads to the adduct 5. Calculated proton affinities and fluoride ion affinities reveal highly Lewis basic and very weak Lewis acidic character of the low-valent silicon atoms in 1 and 2. This is confirmed by protonation of 1 and 2 with Brookharts acid yielding 6 and 7. Reaction with diphenylacetylene only occurs at 111 °C with 2 in toluene and is accompanied by fragmentation of 2 to afford the silacyclopropene 8 and the trisilanorbornadiene species 9., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Reductive debromination of {N(SiMe 3 ) 2 }SiBr 3 with Rieke magnesium results in the formation of the five-vertex silicon cluster with one bromine substituent Si 5 {N(SiMe 3 ) 2 } 5 Br, 1, and the cyclobutadiene analogue 2 in a 1:1 ratio. The latter features a planar four-membered silicon ring with a charge-separated electronic situation. Two silicon atoms in 2 are trigonal planar and the other two trigonal pyramidal. In cycloadditions with ethylene, diethylacetylene, 1,5-cyclooctadiene, and 2,3-dimethyl-1,3-butadiene cyclic unsaturated ring compounds (3-6) were formed at room temperature in quantitative reactions. Two of the products (3 and 6) show photochemical isomerization with LED light (λ=405 nm) to afford saturated ring compounds 4 e and 6'., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Guanine quadruplexes are tetra-stranded nucleic acid structures currently raising significant interest in the context of the development of potential anticancer therapeutics with a new mode of action. They are composed of planar guanine tetrads, allowing a high-affinity targeting by using molecules with a large π surface. However, the extreme topological versatility of guanine quadruplexes impedes a straightforward targeting of particular preselected guanine-rich sequences. We report here a systematic study of a family of luminescent platinum(II) complexes devised to overcome this challenge. By attaching a pendant adenine or thymine nucleobase as a substituent to one of the ligands at the platinum center, an additional recognition site is introduced with the aim of modulating the affinity of the metal complex to different DNA sequences. By comparing different attached nucleobases and a series of linker moieties, first conclusions are drawn with respect to the scope of this approach., (© 2021 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

CAAC precursors 2-chloro-3,3-dimethylindole 1 and 2-chloro-1-ethyl-3,3-dimethylindolium tetrafluoroborate 2BF 4 have been prepared and oxidatively added to [M(PPh 3 ) 4 ] (M=Pd, Pt). Salt 2BF 4 reacts with [Pd(PPh 3 ) 4 ] in toluene at 25 °C over 4 days to yield complex cis-[3]BF 4 featuring an N-ethyl substituted CAAC, two cis-arranged phosphines and a chloro ligand. Compound trans-[3]BF 4 was obtained from the same reaction at 80 °C over 1 day. Salt 2BF 4 reacts with [Pt(PPh 3 ) 4 ] to give cis-[4]BF 4 . The neutral indole derivative 1 adds oxidatively to [Pt(PPh 3 ) 4 ] to give trans-[5] featuring a CAAC ligand with an unsubstituted ring-nitrogen atom. This nitrogen atom has been protonated with py⋅HBF 4 to give trans-[6]BF 4 bearing a protic CAAC ligand. The Pd II complex trans-[7]BF 4 bearing a protic CAAC ligand was obtained in a one-pot reaction from 1 and [Pd(PPh 3 ) 4 ] in the presence of py⋅HBF 4 ., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The redox behaviour of sterically constrained tricyclic phosphine 3a was investigated by spectroelectrochemistry. The data suggested a highly negative reduction potential with the reversible formation of a dianionic species. Accordingly, 3a reacted with two equivalents of Li/naphthalene by reductive cleavage of a P-C bond of one of the PC 4 heterocycles. The resulting dilithium compound 5 represents a phosphaindole derivative with annulated aromatic C 6 and PC 4 rings. It is an interesting starting material for the synthesis of new heterocyclic molecules, as was shown by treatment with Me 2 SiCl 2 and PhPCl 2 . The structures of the products ( 6 and 7 ) formally reflect ring expansion by insertion of silylen or phosphinidene fragments into a P-C bond of 3a . Treatment of 3a with H 2 O 2 did not result in the usually observed transfer of a single O atom to phosphorus, but oxidative cleavage of a strained PC 4 ring afforded a bicyclic phosphinic acid, R 2 PO 2 H., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

3H-Phosphaallenes, R-P=C=C(H)C-R' (3), are accessible in a multigram scale on a new and facile route and show a fascinating chemical reactivity. BH 3 (SMe 2 ) and 3 a (R=Mes*, R'=tBu) afforded by hydroboration of the C=C bonds of two phosphaallene molecules an unprecedented borane (7) with the B atom bound to two P=C double bonds. This compound represents a new FLP based on a B and two P atoms. The increased Lewis acidity of the B atom led to a different reaction course upon treatment of 3 a with H 2 B-C 6 F 5 (SMe 2 ). Hydroboration of a C=C bond of a first phosphaallene is followed in a typical FLP reaction by the coordination of a second phosphaallene molecule via B-C and P-B bond formation to yield a BP 2 C 2 heterocycle (8). Its B-P bond is short and the B-bound P atom has a planar surrounding. Treatment of 3 a with tBuLi resulted in deprotonation of the β-C atom of the phosphaallene (9). The Li atom is bound to the P atom as demonstrated by crystal structure determination, quantum chemical calculations and reactions with HCl, Cl-SiMe 3 or Cl-PtBu 2 . The thermally unstable phosphaallene Ph-P=C=C(H)-tBu gave a unique trimeric secondary product by P-P, P-C and C-C bond formation. It contains a P 2 C 4 heterocycle and was isolated as a W(CO) 4 complex with two P atoms coordinated to W (15)., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

In this work, a series of γ-substituted diphenylnaphthalonitriles were synthesized and characterized. They show efficient emission in solution and in the aggregated state and their environment responsiveness is based on having variable substituents at the para -position of the two phenyl moieties. The excited state properties were fully investigated in tetrahydrofuran (THF) solutions and in THF/H 2 O mixtures. The size of the aggregates in aqueous media were measured by dynamic light scattering (DLS). The steady-state and time-resolved photoluminescence spectroscopy studies revealed that all the molecules show intense fluorescence both in solution and in the aggregated state. In THF solutions, a blue emission was observed for the unsubstituted (H), methyl- (Me) and tert -butyl- ( t -Bu) substituted γ-diphenylnaphthalonitriles, which can be attributed to a weak π-donor capability of these groups. On the other hand, the methoxy- (OMe), methylsulfanyl- (SMe) and dimethylamino- (NMe 2 ) substituted compounds exhibit a progressive red-shift in emission compared to H, Me and t -Bu due to a growing π-electron donating capability. Interestingly, upon aggregation in water-containing media, H, Me and t -Bu show a slight red-shift of the emission and a blue-shift is observed for OMe, SMe and NMe 2 . The crystal structure of Me allowed a detailed discussion of the structure-property relationship. Clearly, N-containing substituents such as NMe 2 possess more electron-donating ability than the S-based moieties such as SMe. Moreover, it was found that NMe 2 showed higher luminescence quantum yields (Φ F ) in comparison to SMe, indicating that N-substituted groups could enhance the fluorescence intensity. Therefore, the π-donor nature of the substituents on the phenyl ring constitutes the main parameter that influences the photophysical properties, such as excited state lifetimes and photoluminescence quantum yields. Hence, a series of highly luminescent materials from deep blue to red emission depending on substitution and environment is reported with potential applications in sensing, bioimaging and optoelectronics., (Copyright © 2020, Thulaseedharan Nair Sailaja et al.; licensee Beilstein-Institut.)

3H-Phosphaallenes are accessible on a new and facile route and show a fascinating chemical behavior. The thermally induced rearrangement of Mes*P═C═C(H)R' (R' = t Bu, Ad) afforded by C-H activation, isobutene elimination, and C-C and P-H bond formation bicyclic 1-benzo-dihydrophosphetes ( 2 ) with PC 3 heterocycles. DFT calculations suggest a mechanism with intramolecular nucleophilic aromatic substitution and replacement of an alkyl group by the nucleophilic α-C atom of the phosphaallene. These bicycles formed W(CO) 5 complexes ( 3 ) or afforded 1,2-dihydrophosphetes with P-bound alkenyl groups by catalyst-free hydrophosphination of alkynes ( 4 and 5 ). The resulting bulky phosphines formed complexes with IrCp*Cl 2 , RuCl 2 , AuCl, or CuO 3 SCF 3 . The Ru atom is coordinated by the P atom and a phenyl group. Irradiation of TripP═C═C(H) t Bu led by the insertion of the central C atom of the P═C═C group into the α-C-H bond of an i Pr substituent and by C-C and P-C bond formation to a new isomer of phosphaallenes, 10 , which features a strained PC 2 heterocycle. It formed adducts with M(CO) 5 (M = Cr, Mo, W) and AuCl and reacted with SO 2 Cl 2 by cleavage of one of the phosphirane P-C bonds to yield PC 4 or PC 5 heterocycles. Hydrolysis yielded a PC 5 compound with a P(O)Cl group.

Bis-NHC precursors composed of an azolium and a 2-halogenoazole group connected by different linkers have been site-selectively metallated to give heterobimetallic complexes from a single-frame bis-NHC ligand. The azolium group reacts with a base and oxidized metal centers to give NHC complexes with no participation of the halogenoazole, while the halogenoazole reacts in an oxidative addition with low-valent transition metals to give azolato complexes with no participation of the azolium group.

The NHC-coordinated trisilacyclopropylidene (A) is shown to behave as the basic component of an FLP used in combination with the Lewis acid B(C6F4H)3 (i.e. B(2,3,5,6-C6F4H)3). This FLP cleaves dihydrogen highly selectively at room temperature giving rise to the ionic compound [(NHC)SiH(Mes2SiSiMes2)][HB(C6F4H)3] 1 in 90% isolated yield. Further reaction of the FLP with Ph2NH and acetone yielded compounds [(NHC)SiH(Mes2SiSiMes2)][Ph2NB(C6F4H)3] 2 and [(NHC)SiH(Mes2SiSiMes2)][MeC(CH2)OB(C6F4H)3] 3 in 75% and 80% yield, respectively. Reaction of the FLP with N2O results in the oxidation of the silylene center affording [((NHC)SiOB(C6F4H)3)(Mes2SiSiMes2)] 4 in 53% yield. These products are spectroscopically characterized and an X-ray structure of 4 is reported.

The unsaturated metalloid germanium cluster Ge 6 {N(SiMe 3 )Dipp} 4 2 with two ligand-free germanium atoms and only four amine substituents was obtained starting from the base-coordinated germylene {N(SiMe 3 )Dipp}GeCl·DMAP 1 in 50% yield (DMAP = 4-(dimethylamino)-pyridine). This cluster reacts as a masked digermyne in cycloadditions with ethylene, diphenylacetylene and 2,3-dimethyl-1,3-butadiene in toluene at 100 °C to yield 3-5.

The tetrakisimidazolium salt H 4 -2(Br) 4 , featuring a central benzene linker and 1,2,4,5-(nBu-imidazolium-Ph-CH=CH-) substituents reacts with Ag 2 O in the presence of AgBF 4 to yield the tetranuclear, oktakis-NHC assembly [3](BF 4 ) 4 . Cation [3] 4+ features four pairs of olefins from the two tetrakis-NHC ligands perfectly arranged for a subsequent [2+2] cycloaddition. Irradiation of [3](BF 4 ) 4 with a high pressure Hg lamp connects the two tetra-NHC ligands through four cyclobutane linkers to give compound [4](BF 4 ) 4 . Removal of the template metals yields the novel oktakisimidazolium salt H 8 -5(BF 4 ) 8 . The tetrakisimidazolium salt H 4 -2(BF 4 ) 4 and the oktakisimidazolium salt H 8 -5(BF 4 ) 8 have been used as multivalent anion receptors and their anion binding properties towards six different anions have been compared., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The Ir III hydrido complexes [ 1 ] and [ 2 ] have been synthesized by the regioselective oxidative addition of the N7-H bond of 8-halogenotheophyllines to [IrCl(coe) 2 ] 2 in the presence of PPh 3 . The use of dppf in this reaction yielded the bimetallic Ir III /Fe II hydrido complexes [ 3 ] and [ 4 ]. X-ray diffraction studies confirmed that complexes [ 1 ]-[ 4 ] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe) 2 ] 2 in the presence of PPh 3 to form the Ir III hydrido complex [ 5 ] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [ 5 ] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Thermal treatment of the bicyclo[1.1.0]tetrasilatetraamide [Si 4 {N(SiMe 3 )Dipp} 4 ] 1 resulted in the formation of a highly unsaturated six-vertex silicon cluster [Si 6 {N(SiMe 3 )Dipp} 4 ] 2 with only four amine-substituents and two ligand-free silicon atoms. In solution, a major and a minor conformer of this cluster are in equilibrium according to multinuclear NMR spectroscopy, lineshape analysis, DFT calculations and molecular dynamics simulations. The bonding situation in the highly unsaturated cluster features lone pair type character at the ligand-free silicon atoms and partial single and double bond character in the upper butterfly-shaped ring of 2 . This allows to consider 2 as the silicon analogue of a butalene isomer., (This journal is © The Royal Society of Chemistry 2020.)

The trilithium compound 1,3-[PhMe 2 Si-C(Li)═C(H)] 2 C 6 H 3 Li ( 2b ) reacted with BCl 3 , AlCl 3 , or GaCl 3 by salt elimination to yield dinuclear heptacyclic compounds ( 4 ). Two tridentate tricarbanionic ligands coordinate two B, Al, or Ga atoms and adopt a helical arrangement of the ligands around a central E 2 unit. The unusual structures comprise E 2 C 2 heterocycles with two 3c-2e (three-center-two-electron) E-C-E bonds and two C atoms of aromatic rings in the bridging positions. While such a bonding situation is well-documented in Al chemistry, it is rare for B and Ga compounds. Insight into the bonding situation of the molecules is provided by DFT calculations.

Addition of :P[triple bond, length as m-dash]C-tBu to the NHC-coordinated trisilacyclopropylidene Si3Mes4NHCiPr2Me2 afforded a heavier analogue of a bicyclo[2.1.0]pentane, a so-called "housane", that rearranges under irradiation with a high-pressure mercury lamp or at 60 °C to an NHC-stabilized cyclopentenyl anion isomer with a three-center four-electron (3c-4e) π-bond.

Tetrasilasilylone N is composed of a silicon(0) atom, two NHC-coordinated silylenes, and a silaimine (Si═N) group. It reacts rapidly and selectively with the chalcogens selenium and tellurium to afford corresponding dichalcogenides 1 and 2 in high yields of 69-79%. In these compounds, one chalcogen atom is connected to the silicon(0) atom with a short bond in the range of Si═E double bonds. The second chalcogen atom adopts the bridging position between the Si(0) atom and the Si═N group. Using only 1 equiv of tellurium affords the selective formation of monotelluride 3 in 84% yield. In this monotelluride, the tellurium atom adopts a bridging position between the silylone functionality and the Si═N group.

Different N3-substituted derivatives of the new ligand 3H-imidazo[4,5-f]quinolin-5-ol were synthesized. The three pKa values of its nucleoside derivative 1 were determined as 2.72 ± 0.09, 5.2 ± 0.2 and 9.7 ± 0.2. Sophisticated computational methods were used to explain these experimental acidity constants. The artificial nucleoside analogue 1 containing the new ligand was introduced into various DNA duplexes. Upon the addition of Cu(ii) ions to the DNA, highly stabilizing 1-Cu(ii)-1 base pairs were formed, with an increase in the DNA melting temperature upon Cu(ii) insertion of up to 38 °C. The ligand represents the largest artificial nucleobase used for Cu(ii)-mediated base pairing. It was also applied in Cu(ii)-mediated base pairing with the smallest Cu(ii)-binding nucleoside 2, involving the ligand 4-carboxyimidazole. The thermal duplex stabilization upon 2-Cu(ii)-1 base pair formation is smaller than that of 1-Cu(ii)-1 and comes close to that of the previously reported 2-Cu(ii)-2. Important design principles for Cu(ii)-mediated base pairs can be derived by comparing the homoleptic complexes of the largest and the smallest Cu(ii)-binding nucleosides with the heteroleptic complexes comprising both nucleosides.

Al/P- and Ga/P-based frustrated Lewis pairs (FLPs) reacted with an azirine under mild conditions under cleavage of the heterocycle on two different positions. Opening of the C-C bond yielded an unusual nitrile-ylide adduct in which a C-N moiety coordinated to the FLP backbone. Cleavage of a C-N bond afforded the thermodynamically favored enamine adduct with the N atom bound to P and Al or Ga atoms. Ring closure was observed upon treatment of an Al/P FLP with electronically unsaturated substrates (4-(1-cyclohexenyl)-1-aza-but-1-en-3-ynes) and yielded by C-N bond formation hexahydroquinoline derivatives, which coordinated to the FLP through P-C and Al-C bonds. Diphenylcyclopropenone showed a diverse reactivity, which depending on steric shielding and the polarizing effect of Al or Ga atoms afforded different products. An AltBu 2 /P FLP yielded an adduct with the C=O group coordinated to P and Al. The dineopentyl derivative gave an equilibrium mixture consisting of a similar product and a simple adduct with O bound to Al and a three-coordinate P atom. Both compounds co-crystallize. The Ga/P FLP only formed the simple adduct with the same substrate. Rearrangement resulted in all cases in C 3 -ring cleavage and migration of a mesityl group from P to a former ring C atom by C-C bond formation. Diphenylthiocyclopropenone (evidence for the presence of P=C bonds) and an imine derivative afforded similar products., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A facile method for the efficient synthesis of 3H-phosphaallenes, R-P=C=C(H)-R', is presented, which comprises treatment of dialkynylphosphines with dialkylaluminium hydrides (hydroalumination) and elimination of aluminium alkynides from intermediate alkenyl-alkynylphosphines. The stability of the phosphaallenes depends on steric shielding by the substituents at phosphorus (aryl or CH(SiMe 3 ) 2 groups). Only supermesityl compounds are persistent at room temperature in solution. This simple method starting with easily accessible dialkynylphosphines and commercially available aluminium hydrides (HAlEt 2 , HAliBu 2 ) allows the generation of transient species, which were trapped by coordination to transition metals. The η 1 -coordination via a P-W bond was observed for tungsten, while the side-on coordination via the P=C bond resulted with platinum. Decomposition of the mesityl derivative yielded an unprecedented product, which may be formed by 1,3-H shift to the P atom, hydrophosphination of the P=C bond of a second phosphaallene and formation of a P-P bond., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reaction of the bicyclo[1.1.0]tetrasilatetraamide Si 4 {N(SiMe 3 )Dipp} 4 1 (Dipp=2,6-diisopropylphenyl) with 5 equiv of the N-heterocyclic carbene NHC Me4 (1,3,4,5-tetramethylimidazol-2-ylidene) affords a bifunctional carbene-coordinated four-membered-ring compound with a Si=N group and a two-coordinate silicon atom Si 4 {N(SiMe 3 )Dipp} 2 (NHC Me4 ) 2 (NDipp) 2. When 2 reacts with 0.25 equiv sulfur (S 8 ), two sulfur atoms add to the divalent silicon atom in plane and perpendicular to the plane of the Si 4 ring, which confirms the silylone character of the two-coordinate silicon atom in 2., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The use of imidazole-4-carboxylate (X) as an artificial nucleobase in metal-mediated base pairing is reported. Towards this end, the corresponding deoxyribonucleoside was synthesized and structurally characterized as its sodium salt (sodium 1,2-dideoxy-1-(4-carboxyimidazol-1-yl)-d-ribofuranose). The deoxyribonucleoside was incorporated into different DNA duplexes (parallel-stranded and antiparallel-stranded), and their Cu(II)- and Ag(I)-binding behavior was investigated. It was shown that both X-Cu(II)-X and X-Ag(I)-X base pairs can be formed, with the former being more stabilizing than the latter. The formation of an X-Cu(II)-X base pair is accompanied by an increase in the duplex melting temperature of approximately 20 °C for antiparallel-stranded duplexes and of 12 °C for the parallel-stranded duplex under investigation. Imidazole-4-carboxylate represents the first imidazole-based nucleoside for Cu(II)-mediated base pairing. Moreover, it is the smallest nucleoside known to form stable Cu(II)-mediated base pairs. Structures of the X-Cu(II)-X and X-Ag(I)-X base pairs are proposed, too, based on molecular structures obtained using the model nucleobase 1-benzyl-1H-imidazole-4-carboxylate., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The Al/P-based frustrated Lewis pair (FLP) Mes 2 P-C(AltBu) 2 =C(H)Ph (1; Mes=mesityl) reacted as an efficient two-electron reductant with benzil to afford a cis-enediolate that was coordinated to the FLP through P-O and Al-O bonds and the formation of a seven-membered heterocycle (2). The phosphorus atom is oxidised from +III to +V. Similar heterocycles (3 a to 3 f) were formed if 1 was treated with various enones (acrolein, acrylate, acrylamide). The resulting enolates are bound to the FLP through P-C and Al-O bonds. Cyclopropenone gave an adduct (4) with the C=O bond coordinated by P and Al. Ynones gave a fascinating variety of different structures. 1,3-Diphenylprop-2-yn-1-one afforded a remarkable allene-type moiety with two cumulated C=C bonds (5); 3-hexyn-2-one yielded a ligand with two conjugated C=C bonds by C-H bond activation at the carbonyl methyl group (7); and 4-(trimethylsilyl)-3-butyn-2-one reacted by C-H bond cleavage, formation of an enolate group with a terminal C=C bond, and shift of the proton to the P atom (8). The C≡C bond was not affected. Allene compound 5 rearranged at elevated temperature and in daylight through the formation of a tricyclic compound by C-H bond activation and C-C bond formation. DFT calculations on this unusual rearrangement suggest insertion of the central allene C atom into the C-H bond of a methyl group and the intermediate formation of a C 3 ring., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

With a co-reduction procedure using 2 equivalents Mes 2 SiCl 2 and 1 equivalent NHC iPr2Me2 →SiCl 4 an NHC-adduct of a trisilacyclopropylidene (SiMes 2 ) 2 SiNHC iPr2Me2 1 was synthesized. Addition of NHC Me4 to 1 results in quantitative carbene exchange under release of NHC iPr2Me2 to yield (SiMes 2 ) 2 SiNHC Me4 2. Both NHC-coordinated trisilacyclopropylidenes coordinate to BH 3 . In reaction of 1 with SiMe 3 N 3 a NHC-coordinated trisilane with an exocyclic Si=N double bond is formed. With diphenylacetylene 1 undergoes a ring expansion at room temperature to afford a five-membered ring compound with an NHC-coordinated silylene functionality., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydroalumination of R-P(H)-C[triple bond, length as m-dash]C-tBu with bulky H-Al[CH(SiMe3)2]2 afforded the new P-H functionalized Al/P-based frustrated Lewis pair R-P(H)-C[[double bond, length as m-dash]C(H)-tBu]-AlR2 [R = CH(SiMe3)2; FLP 7]. A weak adduct of 7 with benzonitrile (8) was detected by NMR spectroscopy, but could not be isolated. tert-Butyl isocyanide afforded a similar, but isolable adduct (9), in which the isocyanide C atom was coordinated to aluminium. The unique reactivity of 7 became evident from its reactions with the heteroatom substituted nitriles PhO-C[triple bond, length as m-dash]N, PhCH2S-C[triple bond, length as m-dash]N and H8C4N-C[triple bond, length as m-dash]N. Hydrophosphination of the C[triple bond, length as m-dash]N triple bonds afforded imines at room temperature which were coordinated to the FLP by Al-N and P-C bonds to yield AlCPCN heterocycles (10 to 12). These processes depend on substrate activation by the FLP. Diphenylcyclopropenone and its sulphur derivative reacted with 7 by addition of the P-H bond to a C-C bond of the strained C3 ring and ring opening to afford the fragment (Z)-Ph-C(H)[double bond, length as m-dash]C(Ph)-C-X-Al (X = O, S). The C-O or C-S groups were coordinated to the FLP to yield AlCPCX heterocycles (13 and 14). The thiocarbonyl derived compound 14 contains an internally stabilized phosphenium cation with a localized P[double bond, length as m-dash]C bond, a trigonal planar coordinated P atom and a short P[double bond, length as m-dash]C distance (168.9 pm). Insight into formation mechanisms, the structural and energetic properties of FLP 7 and compounds 13 and 14 was gained by quantum chemical DFT calculations.

Prion diseases have been linked to impaired copper homeostasis and copper induced-oxidative damage to the brain. Divalent metal ions, such as Cu2+ and Zn2+, bind to cellular prion protein (PrPC) at octapeptide repeat (OR) and non-OR sites within the N-terminal half of the protein but information on the impact of such binding on conversion to the misfolded isoform often derives from studies using either OR and non-OR peptides or bacterially-expressed recombinant PrP. Here we created new transgenic mouse lines expressing PrP with disrupted copper binding sites within all four histidine-containing OR's (sites 1-4, H60G, H68G, H76G, H84G, "TetraH>G" allele) or at site 5 (composed of residues His-95 and His-110; "H95G" allele) and monitored the formation of misfolded PrP in vivo. Novel transgenic mice expressing PrP(TetraH>G) at levels comparable to wild-type (wt) controls were susceptible to mouse-adapted scrapie strain RML but showed significantly prolonged incubation times. In contrast, amino acid replacement at residue 95 accelerated disease progression in corresponding PrP(H95G) mice. Neuropathological lesions in terminally ill transgenic mice were similar to scrapie-infected wt controls, but less severe. The pattern of PrPSc deposition, however, was not synaptic as seen in wt animals, but instead dense globular plaque-like accumulations of PrPSc in TgPrP(TetraH>G) mice and diffuse PrPSc deposition in (TgPrP(H95G) mice), were observed throughout all brain sections. We conclude that OR and site 5 histidine substitutions have divergent phenotypic impacts and that cis interactions between the OR region and the site 5 region modulate pathogenic outcomes by affecting the PrP globular domain.

The reduction of the tribromoamidosilane {N(SiMe 3 )Dipp}SiBr 3 (Dipp=2,6-iPr 2 C 6 H 3 ) with potassium graphite or magnesium resulted in the formation of [Si 4 {N(SiMe 3 )Dipp} 4 ] (1), a bicyclo[1.1.0]tetrasilatetraamide. The Si 4 motif in 1 does not adopt a tetrahedral substructure and exhibits two three-coordinate and two four-coordinate silicon atoms. The electronic situation on the three-coordinate silicon atoms is rationalized with positive and negative polarization based on EPR analysis, magnetization measurements, and DFT calculations as well as 29 Si CP MAS NMR and multinuclear NMR spectroscopy in solution. Reactivity studies with 1 and radical scavengers confirmed the partial charge separation. Compound 1 reacts with sulfur to give a novel type of silicon sulfur cage compound substituted with an amido ligand, [Si 4 S 3 {N(SiMe 3 )Dipp} 4 ] (2)., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Several tridentate hydrazone-based ligands, synthesized by a condensation reaction of either 2-(1-methylhydrazinyl)pyridine or 2-(1-methylhydrazinyl)quinoline with an aldehyde (picolinaldehyde, 1H-pyrrole-2-carbaldehyde, 2-mercaptobenzaldehyde, 2-aminobenzaldehyde) have been reacted with palladium(II) and platinum(II) salts and precursor complexes to yield nine new metal complexes. These planar complexes were investigated with respect to their capability to interact with guanine quadruplex DNA. Two sequences (H-telo, derived from the human telomeric sequence, and c-myc, representing an excerpt of the promoter region of the c-Myc oncogene) were investigated. Circular dichroism (CD) spectroscopy, temperature-dependent CD spectroscopy, UV-Vis spectroscopy and a fluorescent intercalator displacement (FID) assay were applied in this respect. The spectroscopic data show that the complexes indeed interact with guanine quadruplex DNA. According to the FID assay, some of the complexes belong to the highest-affinity metal-containing quadruplex binders reported so far. Their affinity towards quadruplex DNA is up to 80-fold higher than to a reference double helix. These findings make the metal complexes good candidates as anticancer drugs, as guanine quadruplexes have been proposed as potential targets in anticancer drug design., (Copyright © 2017 Elsevier Inc. All rights reserved.)