The 2-Phosphaethynolate Anion: A Convenient Synthesis and [2+2] Cycloaddition Chemistry

Insertion of phenyl isothiocyanate into a P-P bond of a nickel-substituted bicyclo[1.1.0]tetraphosphabutane

A new reaction mode for bicyclo[1.1.0]tetraphosphabutanes is reported. The C[double bond, length as m-dash]S and C[double bond, length as m-dash]N bonds of phenyl isothiocyanate reversibly insert into a P-P bond of [{CpNi(IMes)}2(μ-η(1):η(1)-P4)] (, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene), forming isomers and . X-ray crystallography and (31)P{(1)H} NMR spectroscopy revealed similar bicyclo[3.1.0]heterohexane structures for these compounds.

The 2-Arsaethynolate Anion: Synthesis and Reactivity Towards Heteroallenes

The synthesis and isolation of the 2-arsaethynolate anion, AsCO(-) , and its subsequent reactivity towards heteroallenes is reported. Reactions with ketenes and carbodiimides afford four-membered anionic heterocycles in formal [2+2] cycloaddition reactions. By contrast, reaction with an isocyanate yielded a 1,4,2-diazaarsolidine-3,5-dionide anion and the unprecedented cluster anions As10 (2-) and As12 (4-) . These preliminary reactivity studies hint at the enormous potential synthetic utility of this novel anion, which may be employed as an arsenide (As(-) ) source.

Ambient-Temperature Synthesis of 2-Phosphathioethynolate, PCS-, and the Ligand Properties of ECX- (E = N, P; X = O, S)

A synthesis of the 2-phosphathioethynolate anion, PCS-, under ambient conditions is reported. The coordination chemistry of PCO-, PCS- and their nitrogen-containing congeners is also explored. Photolysis of a solution of W(CO)6 in the presence of PCO- [or a simple ligand displacement reaction using W(CO)5(MeCN)] affords [W(CO)5(PCO)]- (1). The cyanate and thiocyanate analogues, [W(CO)5(NCO)]- (2) and [W(CO)5(NCS)]- (3), are also synthesised using a similar methodology, allowing for an in-depth study of the bonding properties of this family of related ligands. Our studies reveal that, in the coordination sphere of tungsten(0), the PCO- anion preferentially binds through the phosphorus atom in a strongly bent fashion, while NCO- and NCS- coordinate linearly through the nitrogen atom. Reactions between PCS- and W(CO)5(MeCN) similarly afford [W(CO)5(PCS)]-; however, due to the ambidentate nature of the anion, a mixture of both the phosphorus- and sulfur-bonded complexes (4a and 4b, respectively) is obtained. It was possible to establish that, as with PCO-, the PCS- ion also coordinates to the metal centre in a bent fashion.

Isolation of Au-, Co-η1PCO and Cu-η2PCO complexes, conversion of an Ir-η1PCO complex into a dimetalladiphosphene, and an interaction-free PCO anion

Sodium phosphaethynolate reacts with [MCl(PDI)] (M = Co, Ir; PDI = pyridinediimine) to give metallaphosphaketenes, which in the case of iridium rearranges into a dimetalladiphosphene.

Sodium phosphaethynolate reacts with [MCl(PDI)] (M = Co, Ir; PDI = pyridinediimine) to give metallaphosphaketenes, which in the case of iridium rearranges into a dimetalladiphosphene, via CO migration from phosphorus to the metal. Two different bonding modes of the PCO anion to CAAC-coinage metal complexes [CAAC: cyclic (alkyl)(amino)(carbene)] are reported, one featuring a strong Au–P bond and the other an η² coordination to copper. The gold complex appears to be mostly unreactive whereas the copper complex readily reacts with various organic substrates. A completely free PCO anion was structurally characterized as the [Cu(L_a)₂]⁺ (OCP)^– salt. It results from the simple displacement of the PCO unit of the cationic (CAAC)Cu(PCO) complex by a second equivalent of CAAC.

Simple access to ionic liquids and organic salts containing the phosphaethynolate (PCO−) and Zintl (Sb113−) anions

A simple and almost quantitative synthesis of the first salts of the PCO⁻ anion with organic cations is presented. Moreover, we discovered a simple synthesis for [P(nBu)₃Me]⁺₃[Sb₁₁]³⁻, the first organic cation salt comprising the Zintl-anion [Sb₁₁]³⁻.

N-Heterocyclic carbene phosphaketene adducts as precursors to carbene–phosphinidene adducts and a rearranged π-system

Sodium phosphaethynolate, Na(OCP), is demonstrated to be successful for the synthesis of NHC–phosphinidene adducts and a linear π-conjugated molecule.

Uranium and thorium complexes of the phosphaethynolate ion

New tris-amidinate actinide (Th, U) complexes containing a rare O-bound terminal phosphaethynolate (OCP ^- ) ligand were synthesized and fully characterized. The cyanate (OCN ^- ) and thiocyanate (SCN ^- ) analogs were prepared for comparison and feature a preferential N-coordination to the actinide metals. The Th(amid)₃(OCP) complex reacts with Ni(COD)₂ to yield the heterobimetallic adduct (amid) ₃ Th(μ-η ¹ (O):η ² (C,P)-OCP)Ni(COD) featuring an unprecedented reduced (OCP ^- ) bent fragment bridging the two metals.

The phosphaethynolate anion reacts with unsaturated bonds: DFT investigations into [2+2], [3+2] and [4+2] cycloadditions

Density functional theory (DFT) calculations were carried out to investigate the [2+2], [3+2] and [4+2] cycloadditions of the phosphaethynolate anion (PCO(-)). The results reveal that the electronic properties of different unsaturated compounds play a crucial role in reactivity and regioselectivity.

Exploiting the Brønsted acidity of phosphinecarboxamides for the synthesis of new phosphides and phosphines

We demonstrate that the synthesis of new N-functionalized phosphinecarboxamides is possible by reaction of primary and secondary amines with PCO(-) in the presence of a proton source. These reactions proceed with varying degrees of success, and although primary amines generally afford the corresponding phosphinecarboxamides in good yields, secondary amines react more sluggishly and often give rise to significant decomposition of the 2-phosphaethynolate precursor. Of the new N-derivatized phosphinecarboxamides available, PH2C(O)NHCy (Cy = cyclohexyl) can be obtained in sufficiently high yields to allow for the exploration of its Brønsted acidity. Thus, deprotonating PH2C(O)NHCy with one equivalent of potassium bis(trimethylsilyl)amide (KHMDS) gave the new phosphide [PHC(O)NHCy](-). In contrast, deprotonation with half of an equivalent gives rise to [P{C(O)NHCy}2](-) and PH3. These phosphides can be employed to give new phosphines by reactions with electrophiles, thus demonstrating their enormous potential as chemical building blocks.

Cyclo-oligomerization of isocyanates with Na(PH2) or Na(OCP) as "P-" anion sources

We show that the 2-phosphaethynolate anion, OCP^-, is a simple and efficient catalyst for the cyclotrimerization of isocyanates. This process proceeds step-wise and involves five-membered heterocycles, namely 1,4,2-diazaphospholidine-3,5-dionide anions and spiro-phosphoranides as detectable intermediates, both of which were also found to be involved in the catalytic conversion. These species can be considered as adducts of a phosphide anion with two and four isocyanate molecules, respectively, demonstrating that the OCP^- anion acts as a formal "P^-" source. The interconversion between these anionic species was found to be reversible, allowing them to serve as reservoirs for unique phosphorus-based living-catalysts for isocyanate trimerization.

Synthesis of anionic phosphorus-containing heterocycles by intramolecular cyclizations involving N-functionalized phosphinecarboxamides

We report that the 2-phosphaethynolate anion (PCO(-)) reacts with propargylamines in the presence of a proton source to afford novel N-derivatized phosphinecarboxamides bearing alkyne functionalities. Deprotonation of these species gives rise to novel five- and six-membered anionic heterocycles resulting from intramolecular nucleophilic attack of the resulting phosphide at the alkyne functionality (via 5-exo-dig or 6-endo-dig cyclizations, respectively). The nature of the substituents on the phosphinecarboxamide can be used to influence the outcome of these reactions. This strategy represents a unique approach to phosphorus-containing heterocylic systems that are closely related to known organic molecules with interesting bio-active properties.

Phosphide delivery to a cyclotrisilene

The reactivity of the 2-phosphaethynolate anion (PCO⁻) towards a cyclic trisilene (cSi₃(Tip)₄) is reported. The result is the net activation of the P=C and Si=Si multiple bonds of the precursors affording a heteroatomic bicyclo[1.1.1]pentan-2-one analogue ([P(CO)Si₃(Tip)₄]⁻; 1). This reaction can be interpreted as the formal addition of a phosphide and a carbonyl across the Si=Si double bond. Photolytic decarbonylation of 1 results in the incorporation of the phosphide vertex into the cyclotrisilene scaffold, yielding a congener of the cyclobutene anion with considerable allylic character.

Carbonyl migration from phosphorus to the metal in binuclear phosphaketenyl metal carbonyl complexes to give bridging diphosphido complexes

Carbonyl groups from bridging phosphaketenyl ligands in Mn₂(CO)₈(μ-PCO)₂ are predicted to migrate from phosphorus to manganese upon decarbonylation, giving the diphosphido Mn₂(CO)_n+2(μ-P₂) derivatives.

A stable phosphanyl phosphaketene and its reactivity

A phosphanyl phosphaketene undergoes a hetero-Cope-rearrangement to a highly reactive heterocyclic diphosphene which can be trapped.

Is the phosphaethynolate anion, (OCP)(-), an ambident nucleophile? A spectroscopic and computational study

The reactivity of Na(OCP) was investigated towards triorganyl compounds of the heavier group 14 elements (R3EX R = Ph or (i)Pr; E = Si, Ge, Sn, Pb; X = Cl, OTf). In the case of E = Si two constitutional isomers were formed and characterised in situ: R3Si-O-C[triple bond, length as m-dash]P is the kinetic and R3Si-P[double bond, length as m-dash]C[double bond, length as m-dash]O is the thermodynamic product, representing experimental evidence of the ambident character of the (OCP)(-) anion. Applying theoretical calculations and spectroscopic methods, the compound previously reported as (i)Pr3Si-O-C[triple bond, length as m-dash]P can now unambiguously be identified as (i)Pr3Si-P[double bond, length as m-dash]C[double bond, length as m-dash]O. The heavier analogues form exclusively the phosphaketene isomer R3E-P[double bond, length as m-dash]C[double bond, length as m-dash]O (E = Ge, Sn, Pb). DFT calculations were performed to gain deeper insight into the bonding and thermodynamic stability of these compounds.

Sodium phosphaethynolate, Na(OCP), as a “P” transfer reagent for the synthesis of N-heterocyclic carbene supported P3and PAsP radicals

From Na(OCP) as a “P” transfer reagent, the radicals (NHC–P–E–P–NHC) (E = P, As) were synthesized and characterized as donor–acceptor adducts by EPR spectroscopy and DFT computations.

The 2-phosphaethynolate anion: convenient synthesis and the reactivity

New members in the family of organophosphorus compounds: convenient synthesis and reactivity of the 2-phosphaethynolate anion are highlighted.

Coulomb repulsion versus cycloaddition: formation of anionic four-membered rings from sodium phosphaethynolate, Na(OCP)

Carbon dioxide and two equivalents of Na(OCP) form, in an equilibrium reaction, a CO2 adduct of the composition Na2(P2C3O4). The anion of this salt, [O2C-P(CO)2P](2-), is built up by a four-membered 1,3-diphosphetane-2,4-dione ring and a carboxylate unit attached to one of the phosphorus atoms. A remarkable π-delocalization was observed within the OCPCO moiety. The stepwise reaction mechanism leading to Na2(P2C3O4) was investigated with quantum chemical calculations. Accompanied by the release of CO2, Na2(P2C3O4) reacts with both 2-iodopropane and 4,4',4''-trimethoxytriphenylmethyl chloride to form four-membered cyclic anions. For comparison the analogous reactions were performed with Na(OCP) instead of Na2(P2C3O4) and the results are discussed in detail.