The Group 15 open‐shell singlet biradicaloid P(μ‐NTer)2 (Ter=2,6‐bis(2,4,6‐trimethylphenyl)phenyl) was utilized in the activation of stable small molecules. Fast reactions with H2, CO2, and NH3 were ...observed. Dihydrogen easily added to P(μ‐NTer)2 , yielding HP(μ‐NTer)2 under ambient conditions whereas reversible release of molecular hydrogen was observed at slightly elevated temperatures (T>60 °C). As P(μ‐NTer)2 is a species with phosphorus in the unusual formal oxidation state +II, it is capable of reducing carbon dioxide to afford a zwitterionic compound, OP(μ‐NTer)2P, and carbon monoxide. The reaction of P(μ‐NTer)2 with ammonia led to the formation of an azadiphosphiridine after rearrangements of the central P2N2 heterocycle.
Don't wait for activation: The singlet biradicaloid P(μ‐NTer)2 readily reacts with H2, CO2, or NH3 at ambient temperature. The addition of H2 is reversible whereas CO2 is reduced to CO with formation of “biradicaloid monoxide”. Activation of ammonia causes the P2N2 scaffold to rearrange to give an azadiphosphiridine.
A Mixed Arsenic-Phosphorus Centered Biradicaloid Hinz, Alexander; Schulz, Axel; Villinger, Alexander
Angewandte Chemie (International ed.),
January 7, 2015, Letnik:
54, Številka:
2
Journal Article
Recenzirano
Main‐group singlet biradicaloids have been thoroughly investigated in the past two decades, especially derivatives of cyclobutane‐1,3‐diyl. However, in each of the known examples, the radical centers ...are identical. Therefore, we sought to prepare a mixed dipnictadiazanediyls with P and As bearing the radical character. To achieve this goal, the unprecedented cyclodichloro arsaphosphadiazane ClP(μ‐NTer)2AsCl had to be prepared first. Treatment of ClP(μ‐NTer)2AsCl with a halide‐ing agent led to the novel cyclic cation P(μ‐NTer)2AsCl+, while reduction with magnesium afforded the first arsaphosphadiazanediyl P(μ‐NTer)2As.
When you are two you cannot be too radical: The first biradicaloid with different radical centers, heteroatomic biradicaloid P(μ‐NR)2As, was obtained by reducing the corresponding dichloroarsaphosphadiazane with magnesium. Structure elucidation revealed a kite‐shaped planar four‐membered N2PAs ring with two equal PN and AsN distances (see scheme, note in German the word for kite is Drachen, and dragon is Drache).
Ullazines and their π-expanded derivatives have gained much attention as active components in various applications, such as in organic photovoltaic cells or as photosensitizers for CO
photoreduction. ...Here, we report the divergent synthesis of functionalized diazaullazines by means of two different domino-reactions consisting of either a Povarov/cycloisomerization or alkyne-carbonyl metathesis/cycloisomerization protocol. The corresponding quinolino-diazaullazine and benzoyl-diazaullazine derivatives were obtained in moderate to good yields. Their optical and electronic properties were studied and compared to related, literature-known compounds to obtain insights into the impact of nitrogen doping and π-expansion.
Synthesis and Properties of Aza‐ullazines Boldt, Sebastian; Parpart, Silvio; Villinger, Alexander ...
Angewandte Chemie International Edition,
April 10, 2017, Letnik:
56, Številka:
16
Journal Article
Recenzirano
A range of aza‐ullazines, which represent a new heterocyclic core structure, were synthesized through a scalable four‐step reaction, including a Sonogashira reaction and metal‐free cyclization ...promoted by p‐toluenesulfonic acid. The optical and electrochemical properties of selected derivatives were investigated, they were found to have similar absorption and emission spectra but a higher oxidation potential than the parent ullazine core.
Ring, ring: Aza‐ullazines, which represent a new heterocyclic core structure, were synthesized through a four‐step reaction, including a Sonogashira reaction and metal‐free cyclization promoted by p‐toluenesulfonic acid. The optical and electrochemical properties of selected derivatives were investigated, and they were found to have similar absorption and emission spectra but a higher oxidation potential than the parent ullazine core.
Stable Heterocyclopentane-1,3-diyls Hinz, Alexander; Schulz, Axel; Villinger, Alexander
Angewandte Chemie,
February 23, 2015, Letnik:
54, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Diphosphadiazanediyl, (μ‐NR)P2 (R=Ter=2,6‐dimesitylphenyl), is known to readily activate small molecules with multiple bonds. CO is an especially intriguing species for activation, because either ...1,1‐ or 1,2‐bridging mode would lead to a 1.1.1bicycle or a carbene, respectively. The activation of CO with diphosphadiazanediyl already occurs at ambient temperatures (1 bar, 25 °C). However, CO is involved in an unprecedented ring expansion reaction under preservation of the biradical character, which leads to the formation of the first stable cyclopentane‐1,3‐diyl analogue displaying photochromic molecular switch characteristics.
There is a house in UV light: By an unprecedented ring expansion reaction, diphosphadiazanediyls were utilized to activate carbon monoxide, leading to the first stable cyclopentane‐1,3‐diyl, which can be transformed into a housane by UV irradiation. Cyclopentane‐1,3‐diyl displays typical biradicaloid reactivity, such as activation of small molecules bearing single or multiple bonds. Ter=2,6‐dimesitylphenyl.
A variety of thienoquinolones were synthesized from readily accessible thiophene derivatives by regioselective acylations and subsequent two‐fold Buchwald–Hartwig–amination. This cyclization allows a ...convenient synthesis of biologically and pharmaceutically important thienoquinolones. Several thienoquinolones were synthesized in good to very good yields. The optical properties of the products were studied in detail.
Different Thienoquinolones have been synthesized by a two‐fold Buchwald–Hartwig reaction. This ring‐closing reaction allows the introduction of various functional groups at any position of the heterocyclic scaffold in good to very good yield. Steady state UV/Vis‐ and fluorescence studies were performed for selected compounds and show a high dependency of the quantum yield on the employed solvent.
New pyranocoumarin and coumarin-sulfonamide derivatives were prepared and evaluated for their antioxidant, antimicrobial, and/or anti-inflammatory activities. Coumarin-sulfonamide compounds
...demonstrated significant antioxidant activity, while
,
,
,
, and
,
exhibited antimicrobial activity equal to or higher than the standard antimicrobials against at least one tested microorganism. Regarding the anti-inflammatory testing, pyranocoumarins
,
,
and
and coumarin-sulfonamide compound
showed more potent antiproteinase activity than aspirin in vitro; however, five compounds were as potent as aspirin. The anti-inflammatory activity of the promising compounds was further assessed pharmacologically on formaldehyde-induced rat paw oedema and showed significant inhibition of oedema. For in vitro COX-inhibitory activity of coumarin derivatives, pyranocoumarin derivative
was the most selective (SI = 152) and coumarin-sulfonamide derivative
was most active toward COX-2 isozyme. The most active derivatives met the in silico criteria for orally active drugs; thus, they may serve as promising candidates to develop more potent and highly efficient antioxidant, antimicrobial, and/or anti-inflammatory agents.
The reaction of HN3 with the strong Lewis acid B(C6F5)3 led to the formation of a very labile HN3⋅B(C6F5)3 adduct, which decomposed to an aminoborane, H(C6F5)NB(C6F5)2, above −20 °C with release of ...molecular nitrogen and simultaneous migration of a C6F5 group from boron to the nitrogen atom. The intermediary formation of azide–borane adducts with B(C6F5)3 was also demonstrated for a series of organic azides, RN3 (R=Me3Si, Ph, 3,5‐(CF3)2C6H3), which also underwent Staudinger‐like decomposition along with C6F5 group migration. In accord with experiment, computations revealed rather small barriers towards nitrogen release for these highly labile azide adducts for all organic substituents except R=Me3Si (m.p. 120 °C, Tdec=189 °C). Hydrolysis of the aminoboranes provided C6F5‐substituted amines, HN(R)(C6F5), in good yields.
Boron on a Staudinger trip: HN3 reacts with the strong Lewis acid B(C6F5)3 to give a highly labile HN3⋅B(C6F5)3 adduct, which readily decomposes above −20 °C to the aminoborane H(C6F5)NB(C6F5)2 and N2. This Staudinger‐like reaction, which involves a C6F5 group migration from boron to the attached nitrogen atom, was transferred to a variety of organic azides, enabling the synthesis of C6F5‐substituted aminoboranes and amines of the type H(R)N(C6F5).
The activation of C−Br bonds in various bromoalkanes by the biradical ⋅P(μ‐NTer)2P⋅ (1) (Ter=2,6‐bis‐(2,4,6‐trimethylphenyl)‐phenyl) is reported, yielding trans‐addition products of the type ...Br−P(μ‐NTer)2P−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)2P‐R.< To provide further evidence for the radical mechanism, ⋅P(μ‐NTer)2P‐Et (3Et⋅) was synthesized directly by reduction of the bromoethane addition product Br‐P(μ‐NTer)2P‐Et (2 a) with magnesium, resulting in the formation of the persistent phosphorus‐centered monoradical ⋅P(μ‐NTer)2P‐Et, which could be isolated and fully characterized, including single‐crystal X‐ray diffraction. Comparison of the EPR spectrum of the radical intermediate in the addition reaction with that of the synthesized new ⋅P(μ‐NTer)2P‐Et radical clearly proves the existence of radicals over the course of the reaction of biradical ⋅P(μ‐NTer)2P⋅ (1) with bromoethane. Extensive DFT and coupled cluster calculations corroborate the experimental data for a radical mechanism in the reaction of biradical ⋅P(μ‐NTer)2P⋅ with EtBr. In the field of hetero‐cyclobutane‐1,3‐diyls, the demonstration of a stepwise radical reaction represents a new aspect and closes the gap between P‐centered biradicals and P‐centered monoradicals in terms of radical reactivity.
Revealing a radical route: The radical reactivity of the biradical ⋅P(μ‐NTer)2Ṗ has been investigated. It was possible to synthesize the persistent phosphorus‐centered monoradical ⋅P(μ‐NTer)2P−Et and identify it as a radical intermediate during the addition of bromoethane to ⋅P(μ‐NTer)2Ṗ. A possible stepwise mechanism of this reaction was formulated and is supported by both detailed quantum chemical calculations and experimental results.
Cyclic Group 15 Radical Cations Brückner, Angelika; Hinz, Alexander; Priebe, Jacqueline B. ...
Angewandte Chemie (International ed.),
June 15, 2015, Letnik:
54, Številka:
25
Journal Article
Recenzirano
Singlet cyclo‐1,3‐dipnicta‐2,4‐diazane‐1,3‐diyls of the type E(μ‐NTer)2E (2, E=P, As, Ter=2,6‐dimesitylphenyl) can undergo a one‐electron‐oxidation utilizing silver salts of weakly coordinating ...anions such as AgLnB(C6F5)4 (L=donor solvents) to afford the novel cyclic radical cations, E(μ‐NTer)2E+. (3+.). When smaller and more basic anions were employed in the reaction, the anions were found to form covalent bonds to the radical centers yielding dipnictadiazanes, FP(μ‐NTer)2PF (5) and (CF3CO2)P(μ‐NTer)2P(CF3CO2) (6). A two‐electron oxidation process, resulting in the formation of dications of the type E(μ‐NTer)2E2+, could not be observed. Computational and EPR data revealed that the spin density is almost completely localized at the two heavier pnictogen centers E of the former 1,3‐dipnictadiazane‐1,3‐diyls. The bonding situation in the radical cations features a rare example of a transannular one‐electron π bond without having a σ bond.
Positively radical: New radical cations of the type E1(μ‐NTer)2E2 (E1,2=P, As and E1=P, E2=As) were obtained by one‐electron oxidation of Group 15 biradicaloids with silver salts. The structural features remain nearly unchanged upon oxidation. EPR and DFT studies show that there is an unpaired electron residing primarily on the heavy pnictogen atoms P and As, but in mixed species (see picture) it is to a larger extent at the As atom.
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