The reactivity of pnictinidenes 2‐(DippN=CH)‐6‐(DippNHCH2)C6H3E (where E=As (1) or Sb (2)) toward substituted ortho‐ and para‐quinones is reported. The central pnictogen atom is easily oxidized by ...ortho‐quinones closing five‐membered EO2C2 ring. The oxidized antimony derivatives are stable species, while in the case of arsenic compounds the hydrogen of the pendant amino NHCH2 group cleaves one newly formed As−O bonds leading to the closure of a new azaarsole ring. Furthermore, a heating of these arsenic heterocycles resulted in a C−H bond activation at the NCH2 group involved in this heterocycle followed by a reductive elimination of corresponding catechols and arsinidene 2,6‐(DippN=CH)C6H3As. Using of para‐quinones, resulted in the oxidation of the central atom with a concomitant hydrogen migration from NHCH2 group even in the case of the antimony derivatives. The reductive elimination of hydroquinones is in this case feasible for all compounds. Studied compounds were characterized by multi‐nuclear NMR, IR and Raman spectroscopy and single‐crystal X‐ray diffraction analysis. The theoretical study focusing the key compounds and reactions is also included.
A remarkable element‐ligand cooperation allowing a step‐wise oxidative addition‐tautomerization‐reductive elimination reaction sequence is reported in this work, and shows promise for further applications of these pnictinidenes in activation and conversion of other substrates.
Phosphorus‐containing heterocycles have evolved from laboratory curiosities to functional components, such as ligands in catalytically active metal complexes or molecular constituents in electronic ...devices. The straightforward synthesis of functionalized heterocycles on a larger scale remains a challenge. Herein, we report the use of the phosphaethynolate (OCP)− anion as a building block for various sterically unprotected and functionalized hydroxy substituted phosphorus heterocycles. Because the resulting heterocycles are themselves anions, they are building blocks in their own right and allow further facile functionalization. This property may be of interest in coordination chemistry and material science.
Small, but effective—such is the nature of the OCP− anion of the sodium phosphaethynolate salt. In atom‐economic cycloadditions, several five‐ and six‐membered phosphorus heterocycles are accessed, all of which are useful building blocks in their own right.
Carbon phosphides, CnPm, may have highly promising electronic, optical, and mechanical properties, but they are experimentally almost unexplored materials. Phosphaheteroallenes stabilized by ...N‐heterocyclic carbenes undergo a one‐electron reduction to yield compounds of the type (L)2C2P2 with diverse structures. The use of imidazolylidenes as ligands L give complexes with a central four‐membered ring C2P2, while more electrophilic cyclic diamidocarbenes (DAC) give a compound with an acyclic π‐conjugated CP−PC unit. Cyclic C2P2 compounds are best described as non‐Kekulé molecules that are stabilized by coordination to the NHC ligands NHC→(C2P2)←NHC. These species can be easily oxidized to give stable radical cations (NHC)2C2P2+.. The remarkably stable molecules with an acylic C2P2 core are best described with electron‐sharing bonds (DAC)=C=P−P=C=(DAC).
Hope for CP? Carbonphosphides, CnPm, are scarcely known but are predicted to have interesting properties. The non‐Kekulé molecule NHC→C2P2←NHC and the classical DAC=C=P−P=C=DAC could now be synthesized and may allow the development of CnPm chemistry (NHC=N‐heterocyclic carbene, DAC=diamidocarbene).
The concept of isomerism is essential to chemistry and allows defining molecules with an identical composition but different connectivity (bonds) between their atoms (constitutional isomers) and/or a ...different arrangement in space (stereoisomers). The reaction of phosphanyl ketenes, (NHP)−P=C=O (NHP=N‐heterocyclic phosphenium) with N‐heterocyclic carbenes (NHCs) leads to phosphaheteroallenes (NHP)−O−P=C=NHC in which the PCO unit has been isomerized to OPC. Based on the isolation of several intermediates and DFT calculations, a mechanism for this fundamental isomerisation process is proposed.
Stable phosphaketenes react with N‐heterocyclic carbenes to give phosphaheteroallenes. The PCO unit is converted to its constitutionally isomeric OPC group in this process (see scheme).
Molecules which change their structures significantly and reversibly upon an oxidation or reduction process have potential as future components of smart materials. A prerequisite for such an ...application is that the molecules should undergo the redox‐coupled transformation within a reasonable electrochemical window and lock into stable redox states. Sodium phosphaethynolate reacts with two equivalents of dicyclohexylcarbodiimide (DCC) to yield an anionic, imino‐functionalized 1,3,5‐diazaphosphinane 3 a−. The oxidation of this anion with elemental iodine causes an intramolecular rearrangement reaction to give a bicyclic 1,3,2‐diazaphospholenium cation 6+. This umpolung of electronic properties from non‐aromatic to highly aromatic is reversible, and the cation 6+ is reduced with elemental magnesium to reform the 1,3,5‐diazaphosphinanide anion 3 a−. Theoretical calculations suggest that phosphinidene species are involved in the rearrangement processes.
Turning a negative into a positive: The fully reversible conversion between an anionic six‐membered phosphorus–nitrogen heterocycle and a bicyclic diazaphospholenium cation as stable redox states leads to an “umpolung” of the electronic properties which is of interest for smart materials.
Phosphorus heterocycles find applications in the synthesis of π‐conjugated compounds and as precursors for optoelectronic materials such as organic light‐emitting diodes (OLEDs), electronic switches, ...and transistors. A high‐yield, one‐pot synthesis of anionic annulated 1,3,4‐azadiphospholides from Na(OCP) and 2‐chloropyridines is presented. The synthesis proceeds without the use of transition metals and tolerates a wide range of substrates. Cyano‐substituted compounds are especially deeply colored and have absorption maxima which range from λmax=525 to 596 nm. The optical properties are dominated by the spatial separation of an electron acceptor and donor unit within one molecule (push–pull chromophore). The anionic 1,3,4‐azadiphospholides are silylated to neutral siloxy compounds with a strong blue‐shifted absorption. This reaction can be reversed by addition of fluoride ions, which allows fluoride ions to be detected in optically low concentrations.
Substitution matters: A high‐yield, multi‐gram, one‐pot synthesis of benzo‐annulated 1,3,4‐azadiphospholides was successfully developed. These new heterocycles exhibit tunable optical properties, which allow their use as a chemical fluoride sensor.
A new synthetic route to functionalized neutral and anionic azadiphospholes from easily accessible starting materials is described. Equimolar reaction of Na(OCP) and ...N‐(2,6‐dimethylphenyl)pivalimidoyl chloride 2 a cleanly affords the imidoxy‐functionalized 1,2,4‐azadiphosphole 3 a. Using Na(OCP) and imidoyl chloride in a 2:1 ratio leads to an anionic four‐membered ring Na4 a, which has been structurally characterized. During 16 h at room temperature, Na4 a rearranges to the anionic 1,3,4‐azadiphospholide Na5 a with release of carbon monoxide. Applying the more sterically demanding N‐(2,6‐diisopropylphenyl)pivalimidoyl chloride allows isolation of the 1,3,4‐azadiphospholide Na5 b in good yield (>70 %). Possible mechanisms leading to the new isomeric azadiphospholides have been investigated with the aid of high‐level composite calculations.
Atom efficient on a preparative scale: A convenient synthetic route to functionalized neutral and anionic 1,2,4‐ and 1,3,4‐azadiphospholes from sodium phosphaethnyolate Na(OCP) and imidoyl chloride (IMCl) has been developed. The reaction proceeds via the formation of an anionic four‐membered ring intermediate (see graphic; counter cations are not shown in the scheme.)
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