Base‐Stabilized [PO] + /[PO 2 ] + Cations

A remarkably stable acyclic phosphamethine cyanine dye

While cyanine dyes enjoy a multitude of uses in science and technology, their phosphorus analogues, phosphamethine cyanine dyes, have not yet found benchtop applications primarily because of their sensitivity to air and moisture. We are excited to report full characterization of an extraordinarily stable acyclic phosphamethine cyanine dye. Nitrile substituents on the N-heterocyclic framework afford air and water stability as well as resistance to methylation and sulfuration even under forcing conditions. Cyclic voltammetry confirms a high oxidation potential of the compound and computational investigations reveal stabilized orbitals. The unusual orbital stability appears to render the normally electron-rich P^I site an extremely poor nucleophile and difficult to oxidize. From a practical perspective, this dye is prepared in a one-pot method under mild conditions.

Recent Developments in the Chemistry of Pn(I) (Pn=N, P, As, Sb, Bi) Cations

The Group 15 Pn(I) cations (Pn=N, P, As, Sb and Bi), which are isoelectronic with the donor-stabilized carbones, have emerged recently. Despite the presence of two lone pair of electrons, the Pn(I) cations are weakly nucleophilic due to their inherent positive charge. Strongly electron-donating supporting ligands including zwitterionic forms have been used to enhance their Lewis basicity. Furthermore, the chelating effect of cyclic ligand systems proved effective in increasing their nucleophilicity. The strategies involved in successfully isolating the fleeting Sb(I) and Bi(I) cations as the recent most achievements in this field have been discussed. The syntheses, structure, bonding situations and reactivity of the Pn(I) cations are discussed. An outlook on the periodic trends and future applications of these electronically unique electron-rich cationic moieties have been provided.

The Metaphosphite (PO2 - ) Anion as a Ligand

The utilization of monomeric, lower phosphorous oxides and oxoanions, such as metaphosphite (PO2 - ), which is the heavier homologue of the common nitrite anion but previously only observed in the gas phase and by matrix isolation, requires new synthetic strategies. Herein, a series of rhenium(I-III) complexes with PO2 - as ligand is reported. Synthetic access was enabled by selective oxygenation of a terminal phosphide complex. Spectroscopic and computational examination revealed slightly stronger σ-donor and comparable π-acceptor properties of PO2 - compared to homologous NO2 - , which is one of the archetypal ligands in coordination chemistry.

The Triplet Hydroxyl Radical Complex of Phosphorus Monoxide

Phosphorus monoxide (^. PO) is a key intermediate in phosphorus chemistry, and its association with the hydroxyl radical (^. OH) to yield metaphosphorous acid (cis-HOPO) contributes to the chemiluminescence in the combustion of phosphines. When photolyzing cis-HOPO in an Ar-matrix at 2.8 K, the simplest dioxophosphorane HPO₂ and an elusive hydroxyl radical complex (HRC) of ^. PO form. This prototypical radical-radical complex reforms into cis-HOPO at above 12.0 K by overcoming a barrier of 0.28±0.02 kcal mol^-1 . The vibrational spectra of this HRC and its D- and ¹⁸ O-isotopologues suggest a structure of ^. OH⋅⋅⋅OP^. , for which a triplet spin multiplicity with a binding energy of -3.20 kcal mol^-1 has been computed at the UCCSD(T)-F12a/aug-cc-pVTZ level.