Analysis of Non-innocence of Phosphaquinodimethane Ligands when Charge and Aromaticity Come into Play

Several phosphaquinodimethanes and their M(CO)5 complexes (M=Cr, Mo, W) and model derivatives have been theoretically investigated regarding the quest of non-innocence. Computed structural and electronic properties of the P-Me/NH2 substituted phosphaquinodimethanes and tungsten complexes revealed an interesting non-innocent ligand behaviour for the radical anion complexes with distonic ion character and a strong rearomatization of the middle phenyl ring. The latter was further probed taking also geometric aromaticity (HOMA) and quinoid distortion parameters (HOMQc) into account, as well as NICS(1). Furthermore, the effect of the P-substitution was investigated for real (or plausible) complexes and their free ligands focusing on the resulting aromaticity at the middle phenyl ring and vertical one-electron redox processes. The best picture of ligand engagement in redox changes was provided by representing NICS(1) values versus HOMA and the new geometric distortion parameter HOMQc8.

η3 -Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)*

We present the η3 -coordination of the 2-phosphaethynthiolate anion in the complex (PN)2 La(SCP) (2) [PN=N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide)]. Structural comparison with dinuclear thiocyanate-bridged (PN)2 La(μ-1,3-SCN)2 La(PN)2 (3) and azide-bridged (PN)2 La(μ-1,3-N3 )2 La(PN)2 (4) complexes indicates that the [SCP]- coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π*-orbital of the [SCP]- ligand to the LUMO of complex 2, rendering it the ideal precursor for the first functionalization of the [SCP]- anion. Complex 2 was therefore reacted with CAACs which induced a selective rearrangement of the [SCP]- ligand to form the first CAAC stabilized group 15-group 16 fulminate-type complexes (PN)2 La{SPC(R CAAC)} (5 a,b, R=Ad, Me). A detailed reaction mechanism for the SCP-to-SPC isomerization is proposed based on DFT calculations.

Rearrangements and reductive cleavage of 3a,6a-diaza-1,4-diphosphapentalenes

Interaction of 1,4-dichloro-3,6a-diaza-1,4-diphosphapentalenes with alkali metals leads to the cleavage of the N–N bond and the formation of isomeric heteropentalenes as intermediates, which further transform into aromatic 1,2,3-azadiphospholides.

The Chemistry of the 2-Phosphaethynolate Anion

In all likelihood the first synthesis of the phosphaethynolate anion, PCO^- , was performed in 1894 when NaPH₂ was reacted with CO in an attempt to make Na(CP) accompanied by elimination of water. This reaction was repeated 117 years later when it was discovered that Na(OCP) and H₂ are the products of this remarkable transformation. Li(OCP) was synthesized and fully characterized in 1992 but this salt proved to be too unstable to allow for a detailed investigation of its chemistry. It was not until the heavier analogues of this lithium salt were isolated, Na(OCP) and K(OCP) (both of which are remarkably stable and can be even dissolved in water), that the chemistry of this new functional group could be explored. Here we review the chemistry of the 2-phosphaethynolate anion, a heavier phosphorus-containing analogue of the cyanate anion, and describe the wide breadth of chemical transformations for which it has been thus far employed. Its use as a ligand, in decarbonylative and deoxygenative processes, and as a building block for novel heterocycles is described. In the mere twenty-six years since Becker first reported the isolation of this remarkable anion, it has become a fascinating reagent for the synthesis of a vast library of, often unprecedented, molecules and compounds.

Simple Synthesis of Functionalized 2-Phosphanaphthalenes

A simple synthesis of sodium 2-phosphanaphthalene-3-olate (1) based on the extrusion of N₂ from phthalazine using Na[OCP] is reported. This heterocycle can be readily functionalized at the negatively charged oxygen center using a variety of electrophilic substrates. The coordination chemistry of both 1 and its neutral derivatives was explored, revealing their facile use as P-donor ligands for late-transition-metal complexes.

Borane-Stabilized Isomeric Dimers of the Phosphaethynolate Anion

The reactions of the phosphaethynolate anion ([PCO]^- ) with a range of boranes were explored. BPh₃ and [PCO]^- form a dimeric anion featuring P-B bonds and is prone to dissociation at room temperature. The more Lewis acidic borane B(C₆ F₅ )₃ yields a less symmetric dimer of [PCO]^- with P-B and P-O bonds. Less sterically demanding HB(C₆ F₅ )₂ and H₂ B(C₆ F₅ ) boranes form a third isomer with [PCO]^- featuring both boranes bound to the same phosphorus atom. Despite the unexpected thermodynamic preference for P-coordination, computational data illustrate that electronic and steric features impact the binding modes of the resulting dianionic dimers.

A Monoanionic Arsenide Source: Decarbonylation of the 2-Arsaethynolate Anion upon Reaction with Bulky Stannylenes

We report fundamental studies on the reactivity of the 2-arsaethynolate anion (AsCO- ), a species that has only recently become synthetically accessible. The reaction of AsCO- with the bulky stannylene Ter2 Sn (Ter=2,6-bis[2,4,6-trimethylphenyl]phenyl) is described, which leads to the unexpected formation of a [Ter3 Sn2 As2 ]- cluster compound. On the reaction pathway to this cluster, several intermediates were identified and characterized. After the initial association of AsCO- to Ter2 Sn, decarbonylation occurs to give an anion featuring monocoordinate arsenic, [Ter2 SnAs]- . Both species are not stable under ambient conditions, and [Ter2 SnAs]- rearranges to form [TerSnAsTer]- , an unprecedented anionic mixed Group 14/15 alkene analogue.

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.

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.