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The history of the cyaphide anion and all literature known preparations are reviewed. Furthermore, new theoretical insights to the cyaphide ion are presented and complemented with additional calculations. Moreover, several novel cyaphido complexes synthesized by two innovative preparation protocols are demonstrated. The first method takes advantage of a light induced C(sp2)-C(sp) cleavage reaction in a platinum(0) coordinated arylphosphaalkyne to generate the cyaphido ligand. The second method introduces the well-known trimethylsilylphosphaalkyne as cyaphide anion transfer reagent by fluorodesilylation to build new cyaphido gold(I) complexes. Finally, the reactivity of the cyaphido complexes were investigated towards consecutive reactions on the cyaphido moiety, especially by means of [3+2] cycloaddition reactions with organic azides to yield the corresponding triazaphospholato complexes.

Oxidative addition of the P-P single bond of an ortho-carborane-derived 1,2-diphosphetane (1,2-C-2(PMes)(2)B10H10) (Mes = 2,4,6-Me3C6H2) to cobalt(-i) and nickel(0) sources affords the first heteroleptic complexes of a carborane-bridged bis(phosphanido) ligand. The complexes also incorporate labile ligands suitable for further functionalisation. Thus, the cobalt(i) complex [K([18]crown-6)][Co{1,2-(PMes)(2)C2B10H10}(cod)] (cod = 1,5-cyclooctadiene) bearing a labile cyclooctadiene ligand undergoes facile ligand exchange reactions with isonitriles and tert-butyl phosphaalkyne with retention of the bis(phosphanido) ligand. However, in the reaction with one equivalent of P-4, the electron-rich bis(phosphanido) moiety abstracts a single phosphorus atom with formation of a new P-3 chain, while the remaining three P atoms derived from P-4 form an eta(3)-coordinating cyclo-P-3 ligand. In contrast, when the same reaction is performed with two equivalents of the cobalt(i) complex, a dinuclear product is formed which features an unusual P-4 chain in its molecular structure., Chemical Science, 12 (33), ISSN:2041-6520, ISSN:2041-6539

We report on the reactivity of a boryloxy-functionalized phosphaalkyne, [B]OCP ([B] = N,N′-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaboryl), toward a series of tungsten(0) reagents to afford the novel complex W(η2-PCO[B])3(CO). As with related organometallic complexes of alkynes, the C3v symmetry adopted by this complex imposes that, of the three coordinated phosphaalkyne ligands, two act as four-electron donors while the remaining species donates two electrons to the tungsten metal center. W(η2-PCO[B])3(CO) readily loses carbon monoxide in the presence of Lewis bases to afford W(η2-PCO[B])3(L) (where L = PMe3, CNtBu).

The remarkable ‘mixed’ diphosphatetrahedrane (tBuCP)2 (1) – which is both the elusive dimeric form of the phosphaalkyne tBuCP and an isolobal analogue of the important industrial feedstock P4 – was recently isolated for the first time; however, its chemistry remains unexplored. Herein we report that treatment of 1 with various N-heterocyclic carbenes readily yields unusual, unsaturated organophosphorus motifs. These results demonstrate the significant potential of 1 as a building block for the synthesis of previously unknown organophosphorus compounds.

A series of dibenzo-7-phosphanorbornadiene compounds, Ph3PC(R)PA (1-R; A = C14H10, anthracene; R = Me, Et, iPr, sBu), are reported to be capable of thermal fragmentation to generate alkyl-substituted phosphaalkynes (RC≡P) concomitant with triphenylphosphine and anthracene. Facile preparation of these molecular precursors proceeds by treatment of ClPA with the appropriate ylide Ph3P═CHR (2 equiv). For methyl, ethyl, and isopropyl substituents, the phosphaalkyne conversions are measured to be 56–73% in solution by quantitative 31P NMR spectroscopy. In the case of compound 1-Me, the kinetic profile of its spontaneous unimolecular fragmentation is investigated by an Eyring analysis. The resulting 1-phosphapropyne is directly detected by solution NMR spectroscopy and gas phase rotational microwave spectroscopy. The latter technique allows for the first time measurement of the phosphorus-31 nuclear spin-rotation coupling tensor. The nuclear spin-rotation coupling provides a link between rotational and NMR spect...

The mononuclear niobium methylidyne [(PNP)(ArO)Nb≡CH] (1; PNP– = N[2-PiPr2-4-methylphenyl]2–, Ar = 2,6-iPr2C6H3) reacts with the isocyanate O═C═NtBu to form a mononuclear niobium oxo species with a rare example of an azaallenyl ligand, namely [(PNP)(ArO)Nb═O(CH═C═NtBu)] (2). When 1 is treated with the phosphaalkyne P≡CAd (Ad = 1-adamantyl), P≡C bond cleavage occurs to form a mononuclear complex where P–P coupling has occurred between the formal phosphaalkyne phosphorus atom and one phosphine arm from the PNP ligand, namely [(PNPP)(ArO)Nb(η2-AdCCH)] (3). Solid-state structural studies and isotopic labeling experiments confirm C–C bond formation of the methylidyne group as well as provide conclusive evidence for the oxo ligand in 2 being terminal and the fate of the phosphorus atom from P≡CAd in complex 3. Computational studies have been applied to understand the pathway involving the P–P bond forming reaction of 1 and P≡CAd.

The reaction of 1-adamantylphosphaalkyne with 9-phenyl-9-borafluorene resulted in the insertion of the P≡C unit into the endocyclic B–C bond, generating a seven-membered 1,3-boraphosphaalkene. The mechanism was investigated computationally, indicating that the reaction proceeds via a bond metathesis pathway.

Coordination of the diazadiene diolefin ligand (trop2dad) to ruthenium leads to various complexes of composition [Ru(trop2dad)(L)]. DFT studies indicate that the closed‐shell singlet (CSS), open‐shell singlet (OSS), and triplet electronic structures of this species are close in energy, with the OSS spin configuration being the lowest in energy for all tested functionals. Singlet‐state CASSCF calculations revealed a significant multireference character for these complexes. The closed‐shell singlet wavefunction dominates, but these complexes have a significant (≈8–16 %) open‐shell singlet [d7‐RuI(L)(trop2dad.−)] contribution mixed into the ground state. In agreement with their ambivalent electronic structure, these complexes reveal both metal‐ and ligand‐centered reactivity. Most notable are the reactions with AdN3, diazomethane, and a phosphaalkyne leading to scission of the C−C bond of the diazadiene (dad) moiety of the trop2dad ligand, resulting in net (formal) nitrene, carbene, or P≡C insertion in the dad C−C bond, respectively. Supporting DFT studies revealed that several of the ligand‐based reactions proceed via low‐barrier radical‐type pathways, involving the dad.− ligand radical character of the OSS or triplet species., Chemistry - A European Journal, 24 (21), ISSN:0947-6539, ISSN:1521-3765

A dicopper complex featuring a symmetrically bridging nitrile ligand and supported by a binucleating naphthyridine-based ligand was treated with phosphaalkynes to yield dicopper complexes that exhibit phosphaalkynes in rare μ-η2:η2 binding modes., A dicopper complex featuring a symmetrically bridging nitrile ligand and supported by a binucleating naphthyridine-based ligand, [Cu2(μ-η1:η1-MeCN)DPFN](NTf2)2, was treated with phosphaalkynes (RC 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 P, isoelectronic analogues of nitriles) to yield dicopper complexes that exhibit phosphaalkynes in rare μ-η2:η2 binding coordination modes. X-ray crystallography revealed that these unusual “tilted” structures exist in two isomeric forms (R “up” vs. R “sideways”), depending on the steric profile of the phosphaalkyne's alkyl group (R = Me, Ad, or tBu). Only one isomer is observed in both solution and the solid state for R = Me (sideways) and tBu (up). With intermediate steric bulk (R = Ad), the energy difference between the two geometries is small enough that both are observed in solution, and NMR spectroscopy and computations indicate that the solid-state structure corresponds to the minor isomer observed in solution. Meanwhile, treatment of [Cu2(μ-η1:η1-MeCN)DPFN](NTf2)2 with 2-butyne affords [Cu2(μ-η2:η2-(MeC 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CMe))DPFN](NTf2)2: its similar ligand geometry demonstrates that the tilted μ-η2:η2 binding mode is not limited to phosphaalkynes but reflects a more general trend, which can be rationalized via an NBO analysis showing maximization of π-backbonding.

The trans bromide of 2,2-dibromo-1-(2,4,6-tri-t-butylphenyl)-1-phosphaethene (Mes*P=CBr2; Mes*=2,4,6-tBu3C6H2) can be successfully substituted with an aryl group by using a palladium version of the Kumada-Tamao-Corriu cross-coupling process. Predominant formation of the 2-aryl-2-bromo-1-phosphaethene [(Z)-Mes*P=C(Br)Ar] required suitable conditions including optimization of the ancillary phosphine ligand, thereby retarding the dual elimination of bromides leading to phosphaalkyne (Mes*C≡P). The 2-aryl-2-bromo-1-phosphaethenes hold promise as versatile synthons for functional π-conjugated molecules, and stereospecific transformations of the bromine atom by halogen-metal exchange and palladium-catalyzed arylations were demonstrated.

The synthesis of novel functionalized 3H-1,2,3,4-triazaphosphole derivatives is presented, making use of the modular [3+2] dipolar cycloaddition reaction between an azide and a phosphaalkyne. These...

This chapter discusses the different methods for synthesis of phosphaalkynes and arsaalkynes and covers the literature from 1995 to 2003. Elimination and rearrangement reactions are the most important methods for phosphaalkyne synthesis. The most frequently employed method for the preparation of kinetically stabilized phosphaalkynes is the elimination of hexamethyldisiloxane from readily available phosphaalkenes. This protocol was first described in 1981 by Becker and was optimized and generalized by Regitz in 1986. A further important method was described by Denis who prepared substituted phosphaalkynes by elimination of HCl from α-dichlorophosphines. The base-induced elimination at low temperature or the vacuum gas–solid reaction (VGSR) are the most efficient protocols for this synthetic method. Only very few examples of arsaalkynes are described and covered in Section 5.31.2.

The reaction of a terphenyl tin(ii) compound bearing an η(3) coordinating allyl ligand with adamantyl phosphaalkyne is reported. The quantitative stochiometric reaction towards one product involves an addition of one Sn-Ar bond across the C[triple bond, length as m-dash]P triple bond and formation of a phosphadistannacyclobutene ring. This kinetically favoured product can be isolated in the solid state, however, in solution, it shows rearrangement towards a new tin-phosphorus molecule over a period of five days.

The reactions of pentaarylboroles with 1-adamantylphosphaalkyne led to the formation of unique 1-phospha-6-boratricyclo-hept-3-enes. A rational mechanism for this transformation is proposed and supported by DFT calculations.

Through-conjugation of two phosphaalkyne moieties within an isolable molecule is demonstrated for the first time with the synthesis of [{Ru(dppe)2}2{μ-(CC)2C6H4-p}(CP)2], via base-induced desilylation of [{Ru(dppe)2}2{μ-(CC)2C6H4-p}(η1-PCSiMe3)2]2+. The nature of the cyaphide ligands and their influence upon the bimetallic core are studied electrochemically.

The phosphorus analogues of cyclopentadienone, tricyclopentanone, and housene were accessed from bis(cyclopropenyl)diphosphetanedione 3, which was prepared by mixing 1,2,3‐tris‐tert‐butylcyclopropenium tetrafluoroborate (1) and sodium phosphaethynolate [Na(OCP)(dioxane)n]. While photolysis of 3 results in decarbonylation, yielding bis(cyclopropenyl)diphosphene 4 and after rearrangement diphosphahousene 5, thermolysis of 3 leads to phosphatricyclo[2.1.0.0]pentanone 7. Metal‐mediated valence isomerization of 7 and subsequent demetalation provides access to phosphacyclopentadienone 12.

Cationic gold(I) complexes of phosphaalkynes are formed by the interaction of [PtBu2(o-biphenyl)AuCl] with AgSbF6 and an excess amount of RC≡P in CH2Cl2 at room temperature. Free and coordinated phosphaalkyne readily exchange through an associative mechanism. In the solid state, the phosphaalkyne binds in a π fashion and slips towards the carbon end of the triple bond.

We have developed methods for installing aryl substituents directly on the phosphino groups of the 1,3-diphosphacyclobutane-2,4-diyl system. The aryl substituents tuned the electronic and structural characteristics of the biradical unit both in solution and in the solid state. 1-tert-butyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobuten-4-yl anion, prepared from phosphaalkyne (Mes*C≡P; Mes* = 2,4,6-tBu3C6H2) and t-butyllithium, was allowed to react with an electron-deficient N-heterocyclic reagent. The corresponding N-heteroaryl-substituted P-heterocyclic biradicals were produced via SNAr reactions. Biradicals bearing perfluorinated pyridyl substituents exhibited photoabsorption properties comparable to those of previously reported derivatives because the highest occupied and lowest unoccupied molecular orbit levels were reduced by a similar amount. In contrast, the triazine substituent reduced the band gap of the biradical unit, and the large red shift in the visible absorption and high oxidation potential were further tuned via subsequent SNAr and Negishi coupling reactions. The amino-substituted triazine structure provided a strongly electron-donating biradical chromophore, which produced unique p-type semiconducting behavior even though there was no obvious π-overlap in the crystalline state. The single-electron transfer reaction involving Mes*C≡P, phenyllithium, and iodine afforded 1,3-diphenyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl via the intermediate P-heterocyclic monoradical. The tetraaryl-substituted symmetric biradical product was used to determine the electron density distribution from the X-ray diffraction data. The data show highly localized radicalic electrons around the skeletal carbon atoms, moderately polarized skeletal P-C bonds in the four-membered ring, and no covalent transannular interaction.

The diphosphacyclobutadiene sandwich compounds (η4-But2C2P2)2Mz (M = Ni, z = 0; M = Co, z = −1, 0; M = Fe, z = −1, 0) as well as the iron carbonyl derivative (η4-But2C2P2)Fe(CO)3 have recently (2008) been synthesized by Lammertsma and co-workers using the dimerization of the phosphaalkyne ButC P: on suitable reactive transition metal sites. The structures and energetics of the closely related dimethyl derivatives (Me2C2P2)Fe(CO)n (n = 3, 2, 1) and (Me2C2P2)2Fe2(CO)n (n = 5, 4, 3, 2) have now been investigated by density functional theory. For (Me2C2P2)2Fe2(CO)5 a structure with a bridging η1,η4-Me2C2P2 ring and no iron–iron bond is energetically preferred by more than 24 kcal/mol over an alternative structure with only terminal η4-Me2C2P2 rings and an iron–iron single bond. The lowest energy singlet and triplet (Me2C2P2)2Fe2(CO)4 structures have at least one bridging η1,η4 ligand, which in one case is in the form of an (η4-Me2C2P2)2Fe(CO) sandwich bidentate ligand chelating to an Fe(CO)3 unit through two ring phosphorus atoms. In contrast to (Me2C2P2)2Fe2(CO)n (n = 5, 4), the lowest energy structures for (Me2C2P2)2Fe2(CO)3 have only terminal η4-Me2C2P2 ligands, three carbonyl groups, and an Fe Fe triple bond. Interesting structures for the dicarbonyl (Me2C2P2)2Fe2(CO)2 include a structure with a (η4-Me2C2P2)2Fe sandwich ligand chelating to an Fe(CO)2 group and a structure with exclusively terminal η4-Me2C2P2 ligands and a short Fe–Fe distance of ∼2.16 A, suggesting a formal quadruple bond.

We report herein an efficient synthesis of a Dewar-triphosphabenzene derived from [2+2+2] cycloaddition of three phosphaalkyne molecules promoted by an amino olefin Ni-0 complex as the catalyst. Amino diolefin Ni-I complex 1 serves as a precursor complex that reacts with triphenylmethylphosphaethyne under reducing conditions at low temperature to give Ni-0 complex 3 with a coordinated phosphaalkyne in a (2)-mode. The structure of 3 was determined by X-ray diffraction methods and suggests a bonding situation for the phosphaalkyne that is between a side-on coordinated CP molecule and a metallaphosphacyclopropene structure. The reaction of 3 with a 10-fold excess of phosphaethylene under reducing conditions at room temperature resulted in the formation of 2,4,6-tris(triphenylmethyl)-Dewar-1,3,5-triphosphabenzene (4) in good yield.

The reactivity of a [1],[1]disilamolybdenocenophane (1) towards several unsaturated substrates has been studied. Treatment of 1 with N-heterocyclic carbene afforded an ansa-metallocene carbene complex. The cleavage of the P=S bond of a phosphane sulfide was observed, resulting in the incorporation of sulfur into the disila-bridging unit and coordination of the phosphane moiety to Mo. Reactions of 1 with carbodiimide and phosphaalkyne led to side-on coordinated products. All products were fully characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction studies.

The facile two-electron reduction of the phosphaalkyne tBuC=P by the U III cyclopentadienyl-pentalene mixed-sandwich complex [U(η5-C5Me5){η8-C 8H4(SiiPr3)2}] is reported. A single-crystal X-ray structural analysis of the diuranium(IV) product [(U{η5-C5Me5}{η8-C 8H4(SiiPr3)2})2(μ- tBuCP)] shows that it contains a slightly unsymmetrical, bridging μ-η2:η1- ligated phosphaalkene dianion.

The yttrium carbene complex [Y(BIPM)(I)(THF)2] (1; BIPM = C(PPh2NSiMe3)2) was reacted with a range of unsaturated substrates. The reaction of 1 with the phosphaalkyne PCBut afforded the [2 + 2] cyc...

Utilizing phosphorus version of the Fritsch-Buttenberg-Wiechell (FBW) reaction, arylphosphaalkynes are prepared from 2,2-dihalo-1-aryl-1-phosphaalkenes, and theoretical calculations were carried out to obtain some basic insight into intramolecular rearrangement in the phosphorus system of interest. [Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Density functional theory (DFT) and ab initio MP2 calculations.] [Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon for the following free supplemental files: Additional tables, figures, and references.]

By employing silver salts with a weakly coordinating anion Ag[A] ([A]=[FAl{OC12F15}(3)], [Al{OC(CF3)(3)}(4)]), two phosphaalkynes could be coordinated side-on to a bare silver-(I) center to form the unprecedented homoleptic complexes [Ag(eta(2)-P equivalent to CtBu)(2)][FAl{OC12F15}(3)] (1) and [Ag(eta(2)-P equivalent to CtBu)(2)]-[Al{OC(CF3)(3)}(4)] (2). DFT calculations show that the perpendicular arrangement in 1 is the minimum energy structure of the coordination of the two phosphaalkynes to a silver atom, whereas for 2 a unique square-planar coordination mode of the phosphaalkynes at Ag+ was found. Reactions with donor molecules yield the trigonally planar coordinated silver salts [((CH3)(2)CO) Ag(eta(2)-P equivalent to CtBu)(2)][FAl{OC12F15}(3)] (3) and [(C7H8)(2)Ag(eta(2)-P equivalent to CtBu)][FAl{OC12F15}(3)] (4). All of the compounds were comprehensively characterized in solution and in the solid state.

A high yield of the tetraphosphaladderene, anti-tetraphosphatricyclo[4.2.0.0(2,5)]octa-3,7-diene, is obtained from reaction of the zirconocene 1,3-diphosphabicyclo[1.1.0]butane with Ph(2)SbCl(3) in THF or CH(2)Cl(2). Exploration of the reaction pathway using density functional theory suggests that an envelope-type adduct of Ph(2)SbCl and 1,3-diphosphabicyclo[1.1.0]butane plays a pivotal role in the reaction. The zwitterionic character of this intermediate species allows it to act simultaneously as both an ene and an eneophile, and a symmetry-allowed bimolecular reaction leads to the tetraphosphaladderene species via a spirocyclic intermediate.

Don't count on counterions: The cyclic five-membered CSi(3)P cation 1 is synthesized in the reaction of benzamidinato-stabilized chlorosilylene and methyl phosphaalkyne. The presence of four π electrons in 1 means it can be considered as a formal, heavier analogue of the cyclopentadienyl cation. Surprisingly the small counteranion (Cl(-)) does not contribute to the ring stability.

The β-diketiminato germanium(II) chloride complex [(ButMesNacnac)GeCl] (ButMesNacnac = [{N(Mes)C(But)}2CH]−, Mes = mesityl) has been prepared and spectroscopically characterized. Treating this compound and a less bulky system, [(MeMesNacnac)GeCl] (MeMesNacnac = [{N(Mes)C(Me)}2CH]−), with K[HBEt3] led to differing outcomes, namely, the formation of the novel diamido germylene [(ButMesNacnacH)Ge:] (ButMesNacnacH = [N(Mes)C(H)(But)C(H)C(But)N(Mes)]2-) and the germanium(II) hydride [(MeMesNacnac)GeH], both of which were crystallographically characterized. The former product forms via a 1,3-hydrogen migration reaction involving [(ButMesNacnac)GeH] as an unstable reaction intermediate. Reactions of [(MeMesNacnac)GeH] with CO2 and P≡CBut proceed at or below ambient temperature, in the absence of a catalyst, to give the crystallographically characterized hydrogermylation products [(MeMesNacnac)GeOC(═O)H] and [(MeMesNacnac)GeC(But)═PH], with complete regioselectivity. When a solution of the latter was gently heate...

The first examples of sulfides of a 1,3,5-triphosphabenzene were synthesized by the sulfurization of parent 1,3,5-triphosphabenzene 2. Disulfide 7 was found to be remarkably thermally stable, the stability likely coming from the contribution of resonance forms 7A and 7B. In addition to two hydrolysis products of trisulfide 8, which can be anticipated in unsaturated phosphorus chemistry, a new and not trivial bicyclic bridgehead five-membered heterocycle 10 was isolated among the decomposition products of 8. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:114–118, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20664

A cyclic phosphaallyl anion generated from a phosphorus-carbon triple bond (phosphaalkyne) was allowed to react with dimethyl- and di-p-tolyl disulfide to afford the corresponding 1,3-diphosphacyclobutane-2,4-diyls bearing the sulfanyl substituent on phosphorus. The sulfanyl-bearing P-heterocyclic biradicals showed high stability permitting easy handling under ambient conditions. UV-vis spectra and electrochemical properties of the compounds indicated that the sulfanyl groups behave as electron-withdrawing groups to affect electronic properties of the cyclic biradical moiety. X-ray analysis of the p-tolylsulfanyl derivative indicated that the sulfanyl group causes no significant modification in the metric parameters around the central 4-membred biradical skeleton.

Organophosphorus chemistry is organized around σ 3 and σ 4 phosphorus compounds and their derivatives. For a long time, this represented the core of phosphorus chemistry and, still today, the bulk of the work on phosphorus concerns this domain. Starting in the 1960s, a new realm of P-chemistry started to emerge. It concerns σ 1 and σ 2 phosphorus compounds. The aim of this concise review is to summarize the main advances in this new field.