Designing a visible light-mediated double photoswitch: a combination of biradical and azobenzene structural motifs that can be switched independently.

A new molecular switch is presented that combines both biradical and azobenzene motifs to perform visible light-induced constitutional and stereo-isomerisation within the same molecule. The insertion of isonitrile-functionalised azobenzenes into the four-membered biradical [˙P(μ-NTer)P˙] (1), yielding a phosphorus-centred cyclopentane-1,3-diyl (-4B and -5B), represents a straightforward method to generate the desired double switches (-4B and -5B) in excellent yields (>90%). The switching properties are demonstrated for the fluorinated species -5B and, interestingly, can occur either stepwise or simultaneously, depending on the order in which the sample is irradiated with red and/or green light.

Manipulating the Substituent Sphere of a Bicyclic Silicon(I) Ring Compound Results in Anionic Cubane-Type Clusters and a Tetrahedral Silanide.

The reaction of the bicyclic silicon(I) ring compound Si{N(SiMe)Mes} 1 with strong zwitterionic character and moderate sterical demand of the amido substituents with two equivalents of KC was investigated. This resulted in the unexpected abstraction of two amido substituents from 1 and additionally in dimerization to a dianionic Si 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 cluster 3 with only two unsubstituted silicon atoms.

Tricyanomethane or Dicyanoketenimine-Silylation makes the Difference.

Pseudohalides such as tricyanomethanide, [C(CN)], are well known in chemistry, biochemistry and industrial chemistry. The protonated species HC(CN), a classic hydrogen pseudohalide Brønsted acid, is a very strong acid with a pK value of -5. However, HC(CN) is difficult to handle as it tends to decompose rapidly or, more precisely, to oligo- and polymerize.

A Phosphorus-Centred, Zirconocene-Bridged Tetraradical: Synthesis, Structure and Application as Molecular Double Switch.

Biradicals are important intermediates in the formation and breaking of a chemical bond. Their use as molecular switches is of particular interest. Much less is known about tetraradicals, which can, for example, consist of two biradical(oid) units.

Heteroatom-Based Diradical(oid)s.

Heteroatom-centered diradical(oid)s have been in the focus of molecular main group chemistry for nearly 30 years. During this time, the diradical concept has evolved and the focus has shifted to the rational design of diradical(oid)s for specific applications. This review article begins with some important theoretical considerations of the diradical and tetraradical concept.

Rational Design of Persistent Phosphorus-Centered Singlet Tetraradicals and Their Use in Small-Molecule Activation.

Biradicals are important intermediates in the process of bond formation and breaking. While main-group-element-centered biradicals have been thoroughly studied, much less is known about tetraradicals, as their very low stability has hampered their isolation and use in small-molecule activation. Herein, we describe the search for persistent phosphorus-centered tetraradicals.

On the Dynamic Behavior of Pacman Phosphanes─A Case of Cooperativity and Redox Isomerism.

In solution, the Pacman chlorophosphane () shows fast exchange of the /-orientation of the two P-Cl bonds in the molecule featuring cooperativity. Experimental and quantum mechanical investigations of the inversion on the phosphorus(III) centers reveal a crucial role of chloride ions in the dynamic process. To confirm the results, the homologous Pacman halogen-phosphanes were prepared by halogen exchange reactions (X = F, Br, and I).

Coinage metal complexes of multidentate Pacman phosphane ligands.

We present the extension of Pacman ligands to bidentate phosphane ligands enabling them to bind metals in their sterically protected cavity. The coordination of coinage metals shows the ability of the ligand to adopt different coordination modes by distortion, of which some additionally include the imine nitrogen atoms. Besides the coordinated metal, the substitution on the phosphorus atoms influences the type of coordination.

Synthesis of Benzene Derivatives with Multiple Dichlorophosphino Groups.

The chlorination of 1,2-diphosphinobenzene with PCl to 1,2-bis(dichlorophosphino)benzene was performed with high yields (93 %) despite the high number of P-H functions. The method was further applied to other phosphanes, enabling the first synthesis and complete characterization of 1,2,4-tris(dichlorophosphino)benzene (89 % yield) and 1,2,4,5-tetrakis(dichlorophosphino)benzene (91 % yield), valuable precursors for example for binuclear complexes, coordination polymers, organic wires, or metal-organic frameworks. The application of the chlorophosphanes in base induced ring closure reactions with primary amines is demonstrated.

Access to Benzo- and Naphtho-Azaphospholes via C-H Bond Activation of Aryl-Substituted Isonitriles.

Differently substituted phenyl isonitriles (with C-H bonds in ortho-position) and naphthyl isonitriles were reacted with the cyclic biradical [⋅P(μ-N-Ter) P⋅] (1). Insertion of the isonitrile formed a cyclic five-membered biradical [⋅P(NTer) C(R)P⋅] (2R, R=phenyl, naphthyl) in the first step, followed by C-H activation at the aryl substituent, resulting in novel azaphospholes (5R), which could be isolated and fully characterized. The formation of the azaphospholes can be prevented by the addition of a second equivalent of isonitrile, which causes the blocking of the radical centers in 2R by adduct formation (3R).

Photochemical formation and reversible base-induced cleavage of a phosphagallene.

The reactivity of Cp*Ga (Cp* = CMe) towards phosphanylidenephosphoranes of the type TerP(PMe) (Ter = Ter 2,6-(2,6-iPrCH)CH), Ter 2,6-(2,4,6-iPrCH)CH was investigated. While no thermal reaction was observed (in line with DFT results), irradiation at 405 nm at low temperatures resulted in the formation of phosphagallenes TerP = GaCp* (1a) and TerP = GaCp* (1b) accompanied by release of PMe. When warming the reaction mixture to ambient temperatures without irradiation, the clean re-formation of TerP(PMe) and Cp*Ga in a second-order reaction was observed.

Concerted addition of aldehydes to the singlet biradical [P(μ-NTer)].

The reaction of the singlet biradical [P(μ-NTer)] with various aldehydes selectively yielded the corresponding [2.1.1]-bicyclic addition products in a very fast reaction.

A Lewis Acid Stabilized Ketenimine in an Unusual Variant of the Electrophilic Aromatic Substitution.

Electrophilic aromatic substitution (EAS) can provide a straightforward approach to the efficient synthesis of functionalized complex aromatic molecules. In general, Lewis acids serve as a beneficial stimulus for the formation of a Wheland complex, the intermediate in the classical S Ar mechanism of EAS, which is responsible for H/E (E=electrophile) substitution under formal H elimination. Herein, we report an unusual variant of EAS, in which a complex molecule such as the tricyanomethane, HC(CN) , is activated with a strong Lewis acid (B(C F ) ) to the point where it can finally be used in an EAS.

Radical Reactivity of the Biradical [⋅P(μ-NTer) P⋅] and Isolation of a Persistent Phosphorus-Cantered Monoradical [⋅P(μ-NTer) P-Et].

The activation of C-Br bonds in various bromoalkanes by the biradical [⋅P(μ-NTer) P⋅] (1) (Ter=2,6-bis-(2,4,6-trimethylphenyl)-phenyl) is reported, yielding trans-addition products of the type [Br-P(μ-NTer) P-R] (2), so-called 1,3-substituted cyclo-1,3-diphospha-2,4-diazanes. This addition reaction, which represents a new easy approach to asymmetrically substituted cyclo-1,3-diphospha-2,4-diazanes, was investigated mechanistically by different spectroscopic methods (NMR, EPR, IR, Raman); the results suggested a stepwise radical reaction mechanism, as evidenced by the in-situ detection of the phosphorus-centered monoradical [⋅P(μ-NTer) P-R].< To provide further evidence for the radical mechanism, [⋅P(μ-NTer) P-Et] (3Et⋅) was synthesized directly by reduction of the bromoethane addition product [Br-P(μ-NTer) P-Et] (2 a) with magnesium, resulting in the formation of the persistent phosphorus-centered monoradical [⋅P(μ-NTer) P-Et], which could be isolated and fully characterized, including single-crystal X-ray diffraction.

Synthesis of Bicyclic P,S-Heterocycles via the Addition of Thioketones to a Phosphorus-Centered Open-Shell Singlet Biradical.

Formal addition reactions between the open-shell singlet biradical [P(μ-NTer)] () and xanthione, thioxanthione, as well as ferrocenyl naphthyl thioketone were studied in detail. Reactions were performed at room temperature and led to the formation of strained [2.1.

A Persistent Phosphanyl-Substituted Thioketyl Radical Anion.

Alkali metal salts, M [Ter(iPr)P-C(=S)-P(iPr) S] (M=Na, K; 2_M; Ter=2,6-bis-(2,4,6-trimethylphenyl)phenyl) containing a room-temperature-stable thioketyl radical anion were obtained by reduction of the thioketone precursor, Ter(iPr)P-C(=S)-P(iPr) S (1), with alkali metals (Na, K). Single-crystal X-ray studies as well as EPR spectroscopy revealed the unequivocal existence of a thioketyl radical anion in the solid state and in solution, respectively. The computed Mulliken spin density within 2_M is mainly located at the sulfur (49 %) and the carbonyl carbon (33 %) atoms.

A Phosphorus-Based Pacman Dication Generated by Cooperative Self-Activation of a Pacman Phosphane.

Formal coordination of phosphorus(III) by a calix[4]pyrrole Schiff base ligand was achieved through the reaction of this ligand with PCl under basic conditions. The reaction product adopts a Pacman conformation with two P-Cl moieties, one in exo and one in endo position. It represents the first non-metal compound of calix[4]pyrrole Schiff base ligands and of Pacman ligands in general.

Reaction of potassium phosphide KP(iPr)Ter with chalcogens, heteroallenes and an acyl chloride.

The reactivity of the secondary phosphide KP(Pr)Ter (1) (Ter = 2,6-bis-(2,4,6-trimethylphenyl)phenyl) toward small molecules is reported. Phosphide 1 displays distinct nucleophilic character and reacts selectively with chalcogens (S, Se), heteroallenes (CO, PrNCS), and an acyl chloride (AdCOCl) to give the corresponding dichalcogenophosphinates (2a, 3), phosphanyl formate (5), thiocarbamoylphosphane (6a), or acylphosphane (7a), respectively. Furthermore the follow-up chemistry of these products was investigated.

Lewis Acid-Catalyzed Carbofunctionalization of Uncommon ,-Diacyliminium Ions: Controlling Regio- and Enantioselectivity.

The tricyclic azepino[1,2-]indole acetates , readily accessible by visible-light-driven catalytic photooxygenation of cyclohepta[]indoles , are convenient precursors to novel and uncommon cyclic ,-diacyliminium ions . We report here the first Lewis acid-catalyzed C-C bond forming reactions of these species with TMSCN and silyl enol ethers as nucleophiles and utilizing TIPSOTf as well as Sc(OTf) as catalysts. Employing Sc(OTf)/pybox complexes as a chiral catalyst system, regio- and enantioselective asymmetric alkylations with silyl enol ethers were achieved.

Insertion of CS into a Phosphorus-Arsenic Single Bond and Investigations on Phosphane Arsanyldithiocarboxylates.

The synthesis and reactivity of sterically demanding phosphaarsanes TerRP-AsR () is described. These species were selectively synthesized via metathesis reactions of Ter-stabilized [Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl] potassium phosphides TerRPK () with the N-heterocyclic chloroarsane ClAs{N(Bu)CH} (). Conversion of the -butyl-substituted phosphaarsane with the reactive heterocumulene CS leads to an insertion into the P-As bond, yielding the phosphane arsanyldithiocarboxylate TerRP-C(S)S-AsR () as a new structural motif.

Separation of microplastics from mass-limited samples by an effective adsorption technique.

Microplastic in the environment hides visible and invisible dangers for the ecosystems and domiciled organisms. Due to the large quantities of microplastics already distributed worldwide, comparative studies to investigate the associated hazards, distribution patterns, and abundances are becoming increasingly important. Due to varying efforts and budgets, there is still no homogenized detection method for microplastics in the environment, which severely compromises the comparability and reliability of results between previous studies.

Photoisomerization of a phosphorus-based biradicaloid: ultrafast dynamics through a conical intersection.

As previously reported, photoisomerization of the open-shell singlet biradicaloid [TerNP]CNDmp (2) yields its closed-shell housane-type isomer (3). In the present study, pump-probe spectroscopy was applied to investigate the excited-state dynamics of the photoisomerization, indicating ultrafast de-excitation of the S state through a conical intersection, in agreement with computational predictions. The structural and electronic changes during the isomerization process are discussed to gain an understanding of the reaction pathway and the transformation of the biradicaloid to a closed-shell species.

Hyperpolarization Effects in Parahydrogen Activation with Pnictogen Biradicaloids: Metal-free PHIP and SABRE.

Biradicaloids attract attention as a novel class of reagents that can activate small molecules such as H , ethylene and CO . Herein, we study activation of parahydrogen (nuclear spin-0 isomer of H ) by a number of 4- and 5-membered pnictogen biradicaloids based on hetero-cyclobutanediyl [X(μ-NTer) Z] and hetero-cyclopentanediyl [X(μ-NTer) ZC(NDmp)] moieties (X,Z=P,As; Ter=2,6-Mes -C H , Dmp=2,6-Me -C H ). The concerted mechanism of this reaction allowed observing strong nuclear spin hyperpolarization effects in H and P NMR experiments.