Expanding the Landscape of Phosphorous-Based Open Shell Species: Stable Mono-, Di-, and Trianionic Radicals Based on a Contorted Triphosphaalkene.

The stepwise reduction of the highly contorted truxene-based triphosphaalkene 1 using KC8 led to the isolation of mono-, di-and tri-anionic species. The solid-state molecular structures of mono- and diradical anionic species were elucidated by single crystal X-ray diffractions, revealing elongated P-C bonds and a pronounced "indene" aromatization compared to the parent system. All three radical species displayed distinct Electron Paramagnetic Resonance (EPR) spectra, providing compelling evidence for the open-shell electronic configuration of both the diradical and triradical species-an observation unprecedented in any previously reported phosphorous-based anionic polyradicals. Mulliken spin density calculations revealed a dominant localization of radical spin on a single phosphorous atom in the monoanion. In the dianion, spin localization is observed on two phosphorous atoms (~34% each), with a minor contribution from the third phosphorous (0.13%), while the trianion demonstrates a uniform distribution of spin density (~30%) across each phosphorous atom.

Bioactive Abietenolide Diterpenes from Suregada procera.

The phytochemical investigation of the leaves and the roots of Suregada procera afforded the new ent-abietane diterpenoid sureproceriolide A (1) along with the known secondary metabolites 8,14ß:11,12α-diepoxy-13(15)-abietane-16,12-olid (2), jolkinolide A (3), jolkinolide E (4), ent-pimara-8(14),15-dien-19-oic acid (5), sitosterol (6), oleana-9(11):12-dien-3ß-ol (7), and oleic acid (8). Their structures were elucidated by NMR spectroscopic and mass spectrometric analyses, and the structure of jolkinolide A (3) was confirmed by single-crystal X-ray diffraction analysis. Sureproceriolide A (1) showed modest activity against the Gram-positive bacterium Staphylococcus lugdunensis (MIC = 31.44 µM), and sitosterol (6) against the Gram-negative bacterium Porphyromonas gingivalis (IC50 = 45.37 µM). Jolkinolide A (3) and E (4) as well as sitosterol (6) inhibited the release of NOS (IMR-90 cells), TNF-α (HaCaT cells) and NF-κB (HaCaT cells), with IC50 values of 0.43, 3.21, and 10.32 µM, respectively. Compound 6 showed antitumoral activity against SK-MEL-28 (IC50 = 20.66 µM) and CCD-13Lu (IC50 = 24.70 µM) cell lines, with no cytotoxic effect against the prostate cells PrEC (CC50 > 300 µM).

Introducing Phosphorus into the Overcrowded Thiele's hydrocarbon Family: Unveiling Contorted Main Group Diradicaloids with Dynamic Redox Behavior.

Thiele's Hydrocarbons (THs) featuring a 9,10-anthrylene core with switchable geometric and electronic configurations offer exciting possibilities in advanced functional materials. Despite significant advances in main group-based diradicaloids in contemporary chemistry, main group THs containing an anthrylene cores have remained elusive, primarily due to the lack of straightforward synthetic strategies and the inherent high reactivity of these species. In this study, we utilize an anthracene-based phosphine synthon to demonstrate, for the first time, a facile and high-yielding synthetic strategy for robust P-functionalized overcrowded ethylenes (OCEs) within the TH family. These OCEs feature a non-symmetric environment, incorporating (thio)xanthyl and phosphaalkene termini. We systematically probe the electronic structures of these derivatives to illustrate the impact of the isolobal phosphaalkene motif on the quinoidal/diradicaloid character. Notably, the compounds exhibit dynamic redox behavior, leading to orthogonally twisted conformational changes upon oxidation, with a kinetically locked redox-couple.

Main Group Pentafulvenes: Challenges and Opportunities in Heavy Main Group Isolobal Substitution of Pentafulvene.

Heterofulvenes based on isolobal substitution of carbon fragments by (heavier) main group motifs provide a rich source of structurally interesting building blocks with electronic situations that can vastly differ from all-carbon congeners. Group 13, heavier 14 & 16 fulvenes are rare and pose significant stability challenges, while group 15 derivatives, particularly phosphorus and arsenic, have led to many derivatives with intriguing opto-electronic properties.

Tetrazole-Functionalized Organoboranes Exhibiting Dynamic Intramolecular N→B-Coordination and Cyanide-Selective Anion Binding.

Starting from two different cyano-functionalized organoboranes, we demonstrate that 1,3-dipolar [3+2] azide-nitrile cycloaddition can serve to generate libraries of alkyl-tetrazole-functionalized compounds capable of intramolecular N→B-Lewis adduct formation. Due to the relatively low basicity of tetrazoles, structures can be generated that exhibit weak and labile N→B-coordination. The reaction furnishes 1- and 2-alkylated regio-isomers that exhibit different effective Lewis-acidities at the boron centers, and vary in their optical absorption and fluorescence properties. Indeed, we identified derivatives capable of selectively binding cyanide over fluoride, as confirmed by 11B NMR. This finding demonstrates the potentialities of this synthetic strategy to systematically fine-tune the properties of lead structures that are of interest as chemical sensors.

Derivatization of 2,1,3-Benzothiadiazole via Regioselective C-H Functionalization and Aryne Reactivity.

Despite growing interest in 2,1,3-benzothiadiazole (BTD) as an integral component of many functional molecules, methods for the functionalization of its benzenoid ring have remained limited, and many even simply decorated BTDs have required de novo synthesis. We show that regioselective Ir-catalyzed C-H borylation allows access to versatile 5-boryl or 4,6-diboryl BTD building blocks, which undergo functionalization at the C4, C5, C6, and C7 positions. The optimization and regioselectivity of C-H borylation are discussed. A broad reaction scope is presented, encompassing ipso substitution at the C-B bond, the first examples of ortho-directed C-H functionalization of BTD, ring closing reactions to generate fused ring systems, as well as the generation and capture reactions of novel BTD-based heteroarynes. The regioselectivity of the latter is discussed with reference to the Aryne Distortion Model.

Access to long-lived room temperature phosphorescence through auration of 2,1,3-benzothiadiazole.

A series of 2,1,3-benzothiadiazole-Au(I)-L complexes have been synthesised, structurally characterised and investigated for their photophysical properties. These are the first organometallic Au(I) complexes containing a C-Au bond on the highly electron-deficient benzothiadiazole unit. The complexes exhibit solution-phase phosphorescence at room temperature, assigned to the intrinsic triplet state of the benzothiadiazole unit that is efficently populated through its attachment to gold. Comparison with routinely reported Au(I) complexes, which include intervening alkenyl linkers, suggests that previous assignments of their phosphorescence as 1π → π*(CCR) might be incomplete. Our observations affirm that, in addition to the heavy atom effect, breaking symmetry in the involved aryl motif may be of importance in controlling the luminescence properties.

Synthesis and crystal structures of boryl ortho-silylaryl tri-fluoro-methane-sulfonates.

We report the synthesis and structural characterization of three crystalline borylated ortho-silylaryl tri-fluoro-methane-sulfonates: 5-(4,4,5,5-tetra-methyl-1,3,2-dioxaborolan-2-yl)-2-(tri-methyl-sil-yl)phenyl tri-fluoro-methane-sulfonate, C16H24BF3O5SSi (1a), 4-(4,4,5,5-tetra-methyl-1,3,2-dioxaborolan-2-yl)-2-(tri-methyl-sil-yl)phenyl tri-fluoro-methane-sulfonate, C16H24BF3O5SSi (1b), and 2-methyl-4-(4,4,5,5-tetra-methyl-1,3,2-dioxaborolan-2-yl)-6-(tri-methyl-silyl)phen-yl tri-fluoro-methane-sulfonate, C17H26BF3O5SSi (2), which are versatile aryne precursors. For all three compounds, the heteroatom substituents are almost coplanar with the central aromatic moiety. C-heteroatom bonding metrics are unexceptional and fall withing the typical range of C-B, C-Si, and C-O single bonds. Despite numerous electronegative sites, only weak inter-molecular inter-actions are observed in the solid state.

Precursors for the Development of π-Conjugated Low-Coordinate Phosphorus Compounds.

The synthesis of a novel monomeric precursor and its butadiyne-bridged dimeric form for the preparation of novel π-conjugated organophosphorus compounds is presented. The precursors are synthesized from commercially available starting materials, and based on a Dmp (2,6-dimesitylphenyl) group for kinetic stabilization of the P-functionality, a bromo substituent for the introduction of the phosphorus center, and an acetylene unit at the para position of the Dmp moiety. Such acetylenic units are synthetically versatile, and can be explored for the construction of larger phosphorus-containing π-conjugates. The precursors are utilized to prepare Dmp-stabilized C,C-dibromophosphaalkenes, and butadiyne-bridged dimeric species thereof. The effect of the low-coordinate phosphorus centers and the extent of π-conjugation on the spectroscopic and electronic properties is evaluated by NMR and UV/Vis spectroscopy, as well as cyclic voltammetry. In addition to the phosphaalkenes, the successful syntheses of two new diphosphenes are presented, indicating a broad applicability of the precursor.

Benzo[b]naphtho[2,1-d]furans and 2-Phenylnaphthalenes from Streblus usambarensis.

Three new benzo[b]naphtho[2,1-d]furans, usambarins A-C (1-3), five new 2-phenylnaphthalenes, usambarins D-H (4-8), a new flavan (9), and a new phenyl-1-benzoxepin (10) as well as two known compounds (11 and 12) were isolated from the extract of the stem and roots of Streblus usambarensis (Moraceae). The structures were deduced using NMR spectroscopic and mass spectrometric analyses, and those of compounds 1 and 4 were confirmed by X-ray crystallography. Usambarin D (4) demonstrated moderate antibacterial activity (MIC 9.0 µM) against Bacillus subtilis, while none of the tested compounds were effective against Escherichia coli.

1-Phospha-Butadienes and 1H-Phospholes via Alkynylation of Acetylenic Phosphaalkenes.

Carbon-rich motifs are important building blocks for the fabrication of functional and opto-electronic materials. Electronic tuning can be achieved by alteration of bonding topologies but also via incorporation of heteroelements, for example phosphorus. Herein we present the palladium/copper mediated formation of branched 1-phospha-butadiene derivatives through an unusual alkynylation of a phospha-enyne fragment. Structural and NMR studies provide mechanistic insights into this alkynylation. Furthermore, we disclose a complex cyclisation of the thus obtained 3-yne-1-phosphabutadiene motifs to give highly substituted phosphole derivatives identified by 2D NMR and SC-XRD analysis.

One, Two Three - Phosphaalkene Decoration Tailoring Solubility and Electronic Properties of Truxene-Based Electron Acceptors.

We report the functionalization and deplanarization of truxenes using pnictaalkene fragments. Selective introduction of one, two, or three Mes*-Pn fragments provides up to three fully reversible reductions based on the Pn=C fragments. The incorporation of the unsaturated heteroelement fragment as well as the contortion of the truxene core result in significantly red-shifted absorption spectra and interesting opto-electronic properties which are studied by electrochemistry and spectro-electrochemistry. Incorporation of arsaalkene (As=C) motifs gives significantly milder reduction potentials and red-shifted absorption, while phosphaalkene decorated truxene P3 can be functionalized using Au(I)Cl coordination. Furthermore, solubility is markedly increased upon incorporation of the Pn-Mes* fragments which renders these materials suitable for solution processing.

Modified ent-Abietane Diterpenoids from the Leaves of Suregada zanzibariensis.

The leaf extract of Suregada zanzibariensis gave two new modified ent-abietane diterpenoids, zanzibariolides A (1) and B (2), and two known triterpenoids, simiarenol (3) and ß-amyrin (4). The structures of the isolated compounds were elucidated based on NMR and MS data analysis. Single-crystal X-ray diffraction was used to establish the absolute configurations of compounds 1 and 2. The crude leaf extract inhibited the infectivity of herpes simplex virus 2 (HSV-2, IC50 11.5 µg/mL) and showed toxicity on African green monkey kidney (GMK AH1) cells at CC50 52 µg/mL. The isolated compounds 1-3 showed no anti-HSV-2 activity and exhibited insignificant toxicity against GMK AH1 cells at ≥100 µM.

Carbene chemistry of arsenic, antimony, and bismuth: origin, evolution and future prospects.

The discovery of the first isolable N-heterocyclic carbene in 1991 ushered in a new era in coordination chemistry. The remarkable bonding properties of carbenes have led to their rapid proliferation as auxiliary ligands for a wide range of transition metals and main group elements. In the case of group 15, while carbene-stabilized nitrogen and phosphorus compounds are extensively studied, the scope of research has shrunk significantly from arsenic to bismuth. This is essentially attributed to the decrease in stability of the C-E bond upon descending the group. Even so, modulating the carbene backbone or introducing alternative synthetic strategies not only alleviates the stability issues but also offers promising results in terms of the bonding and reactivities of these compounds. The purpose of the present perspective is to provide a comprehensive overview of the origins and development of carbene chemistry of arsenic, antimony, and bismuth, as well as to highlight the future prospects of this field.

Tuning the photophysical properties of luminescent lanthanide complexes through regioselective antenna fluorination.

Carbostyrils monofluorinated in the 3, 5, or 6 positions were synthesised from olefinic precursors via a photochemical isomerisation-cyclisation route, and incorporated into octadentate cyclen triacetate ligands that formed luminescent complexes with Tb(III) and Eu(III). The photophysical properties of the emitters were strongly dependent on the position of the fluorination.

Analysis of molecular ligand functionalization process in nano-molecular electronic devices containing densely packed nano-particle functionalization shells.

Molecular electronic devices based on few and single-molecules have the advantage that the electronic signature of the device is directly dependent on the electronic structure of the molecules as well as of the electrode-molecule junction. In this work, we use a two-step approach to synthesise functionalized nanomolecular electronic devices (nanoMoED). In first step we apply an organic solvent-based gold nanoparticle (AuNP) synthesis method to form either a 1-dodecanethiol or a mixed 1-dodecanethiol/ω-tetraphenyl ether substituted 1-dodecanethiol ligand shell. The functionalization of these AuNPs is tuned in a second step by a ligand functionalization process where biphenyldithiol (BPDT) molecules are introduced as bridging ligands into the shell of the AuNPs. From subsequent structural analysis and electrical measurements, we could observe a successful molecular functionalization in nanoMoED devices as well as we could deduce that differences in electrical properties between two different device types are related to the differences in the molecular functionalization process for the two different AuNPs synthesized in first step. The same devices yielded successful NO2gas sensing. This opens the pathway for a simplified synthesis/fabrication of molecular electronic devices with application potential.

Catalytic Asymmetric ß-Oxygen Elimination.

A catalytic enantioselective ß-O-elimination reaction is reported in the form of a zirconium-catalyzed asymmetric opening of meso-ketene acetals. Furthermore, a regiodivergent ß-O-elimination is demonstrated. The reaction proceeds under mild conditions, at low catalyst loadings, and produces chiral monoprotected cis-1,2-diols in good yield and enantiomeric excess. The combination with a Mitsunobu reaction or a one-pot hydroboration/Suzuki reaction sequence then gives access to additional diol and aminoalcohol building blocks. A stereochemical analysis supported by DFT calculations reveals that a high selectivity in the hydrozirconation step is also important for achieving high enantioselectivity, although it does not constitute the asymmetric step. This insight is crucial for the future development of related asymmetric ß-elimination reactions.

Preparation of Structurally and Electronically Diverse N → B-Ladder Boranes by [2 + 2 + 2] Cycloaddition.

We report the synthesis of a series of eight N → B-ladder boranes through cobalt-mediated cyclotrimerization of (2-cyanophenyl)-dimesitylborane with different dialkynes. The resulting tetracoordinate boranes show variable electrochemical and optical properties depending on the substitution pattern in the backbone of the coordinating pyridine-derivatives. While boranes containing alkyl-substituted pyridines show lower electron affinities than the known parent compound, boranes featuring π-extended pyridine derivatives show higher electron affinities in the range of acceptor substituted triarylboranes. All derivatives show larger Stokes shifts (8790-6920 cm-1) compared to the N → B-ladder borane coordinated by an unsubstituted pyridine.

Studies on gold(I) and gold(III) alcohol functionalised NHC complexes.

Five pairs of novel chiral alcohol functionalised gold(i) and gold(iii) NHC complexes derived from chiral amino alcohols, were synthesized and characterised (NMR, IR, HRMS). Single crystal X-ray diffraction data of gold(i) and gold(iii) complexes are reported and discussed. The chiral imidazolium preligands were readily synthesized via the oxalamides, subsequent reduction and final orthoformate condensation. An improved method was used for generation of gold(i) NHC complexes (up to 92%) and further oxidation afforded the corresponding gold(iii) NHC complexes (up to 99%). All the Au(i) and Au(iii) NHC complexes proved far more catalytically active in a 1,6-enyne alkoxycyclization test reaction than our previously tested N,N- and P,N-ligated Au(iii) complexes. Comparative gold(i) and gold(iii) catalytic studies demonstrated different catalytic ability, depending on the NHC ligand flexibility and bulkiness. Excellent yields (92-99%) of target alkoxycyclization product were obtained with both gold(i) and gold(iii) complexes with the bulky N1-Mes-N2-ethanol based NHC ligand.

Mechanochemical Solvent-Free Catalytic C-H Methylation.

The mechanochemical, solvent-free, highly regioselective, rhodium-catalyzed C-H methylation of (hetero)arenes is reported. The reaction shows excellent functional-group compatibility and is demonstrated to work for the late-stage C-H methylation of biologically active compounds. The method requires no external heating and benefits from considerably shorter reaction times than previous solution-based C-H methylation protocols. Additionally, the mechanochemical approach is shown to enable the efficient synthesis of organometallic complexes that are difficult to generate conventionally.