The atomic level mechanism of white phosphorous demolition by di-iodine

Unravelling White Phosphorus: Experimental and Computational Studies Reveal the Mechanisms of P4 Hydrostannylation

The hydrostannylation of white phosphorus (P4) allows this crucial industrial precursor to be easily transformed into useful P1 products via direct, 'one pot' (or even catalytic) procedures. However, a thorough mechanistic understanding of this transformation has remained elusive, hindering attempts to use this rare example of successful, direct P4 functionalization as a model for further reaction development. Here, we provide a deep and generalizable mechanistic picture for P4 hydrostannylation by combining DFT calculations with in situ 31P NMR reaction monitoring and kinetic trapping of previously unobservable reaction intermediates using bulky tin hydrides. The results offer important insights into both how this reaction proceeds and why it is successful and provide implicit guidelines for future research in the field of P4 activation.

Halogen-Bonding-Mediated Radical Reactions: The Unexpected Behavior of Piperazine-Based Dithiooxamide Ligands in the Presence of Diiodine

N,N'-Dialkylpiperazine-2,3-dithiones (R2pipdt) were recognized as a class of hexa-atomic cyclic dithiooxamide ligands with peculiar charge-transfer donor properties toward soft electron-acceptors such as noble metal cations and diiodine. The latter interaction is nowadays better described as halogen bonding. In the reaction with diiodine, R2pipdt unexpectedly provides the corresponding triiodide salts, differently from the other dithiooxamides, which instead typically achieve ligand·nI2 halogen-bonded adducts. In this paper, we report a combined experimental and theoretical study that allows elucidation of the nature of the cited products and the reasons behind the unpredictable behavior of these ligands. Specifically, low-temperature single-crystal X-ray diffraction measurements on a series of synthetically obtained R2pipdt (R = Me, iPr, Bz)/I3 salts, complemented by neutron diffraction experiments, were able to experimentally highlight the formation of [R2pipdtH]+ cations with a -S-H bond on the dithionic moiety. Differently, with R = Ph, a benzothiazolylium cation, resulting from an intramolecular condensation reaction of the ligand, is obtained. Based on density functional theory (DFT) calculations, a reasonable reaction mechanism where diiodine plays the fundamental role of promoting a halogen-bonding-mediated radical reaction has been proposed. In addition, the comparison of combined experimental and computational results with the corresponding reactions of N,N'-dialkylperhydrodiazepine-2,3-dithione (R2dazdt, a hepta-atomic cyclic dithiooxamide), which provide neutral halogen-bonded adducts, pointed out that the difference in the torsion angle of the free ligands represents the structural key factor in determining the different reactivities of the two systems.

Halogenation of the Hexaphosphabenzene Complex [(Cp*Mo)2 (μ,η6 :η6 -P6 )]: Snapshots on the Reaction Progress

The oxidation of [(Cp*Mo)2 (μ,η6 :η6 -P6 )] (1) with halogens or halogen sources was investigated. The iodination afforded the ionic complexes [(Cp*Mo)2 (μ,η3 :η3 -P3 )(μ,η1 :η1 :η1 :η1 -P3 I3 )][X] (X=I3 - , I- ) (2) and [(Cp*Mo)2 (μ,η4 :η4 -P4 )(μ-PI2 )][I3 ] (3), while the reaction with PBr5 led to the complexes [(Cp*Mo)2 (μ,η3 :η3 -P3 )(μ-Br)2 ][Cp*MoBr4 ] (4) [(Cp*MoBr)2 (μ,η3 :η3 -P3 )(μ,η1 -P2 Br3 )] (5) and [(Cp*Mo)2 (μ-PBr2 )(μ-PHBr)(μ-Br)2 ] (6). The reaction of 1 with the far stronger oxidizing agent PCl5 was followed via time- and temperature-dependent 31 P{1 H} NMR spectroscopy. One of the first intermediates detected at 193 K was [(Cp*Mo)2 (μ,η3 :η3 -P3 )(μ-PCl2 )2 ][PCl6 ] (8) which rearranges upon warming to [(Cp*Mo)2 (μ-PCl2 )2 (μ-Cl)2 ] (9), [(Cp*MoCl)2 (μ,η3 :η3 -P3 )(μ-PCl2 )] (10) and [(Cp*Mo)2 (μ,η4 :η4 -P4 )(μ-PCl2 )][Cp*MoCl4 ] (11), which could be isolated at room temperature. All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy and their electronic structures were elucidated by DFT calculations.

A Reinterpretation of the Imidazolate Au(I) Cyclic Trinuclear Compounds Reactivity with Iodine and Methyl Iodide with the Perspective of the Inverted Ligand Field Theory

Coinage metal cyclic trinuclear compounds (CTCs) are an emerging class of metal coordination compounds that are valuable for many fine optoelectronic applications, even though the reactivity dependence by the different bridging ligands remains somewhat unclear. In this work, to furnish some hints to unravel the effect of substituents on the chemistry of Au(I) CTCs made of a specific class of bridging ligand, we have considered two imidazolate Au(I) CTCs and the effect of different substituents on the pyrrolic N atoms relative to classic metal oxidations with I₂ or by probing electrophilic additions. Experimental suggestions depict a thin borderline between the addition of MeI to the N-methyl or N-benzyl imidazolyl CTCs, which afford the oxidized CTC in the former and the ring opening of the CTC and the formation of carbene species in the latter. Moreover, the reactions with iodine yield to the oxidation of the metal centers for the former and just of a metal center in the latter, even in molar excess of iodine. The analysis of the bond distances in the X-ray crystal structures of the oxidized highlights that Au(III)-C and Au(III)-N bonds are longer than observed for Au(I)–C and Au(I)–N bonds, as formally not expected for Au(III) centers. Computational studies converge on the attribution of these discrepancies to an additional case of inverted ligand field (ILF), which solves the question with a new interpretation of the Au(I)–ligand bonding in the oxidized CTCs, which furnishes a new interpretation of the Au(I)-ligand bonding in the oxidized CTCs, opening a discussion about addition/oxidation reactions. Finally, the theoretical studies outputs depict energy profiles that are compatible with the experimental results obtained in the reaction of the two CTCs toward the addition of I₂, MeI, and HCl.

A revisitation of some classic oxidation reactions of gold centers in cyclic trinuclear compounds (CTCs) provides experimental results leading to the opportunity to delineate the effect of imidazole substituents in different outcomes from the reactions of CTCs with I₂ or MeI. Moreover, with the match between experimental and theoretical results, a new interpretation of the oxidation states of tetracoordinate gold as cases of inverted ligand field (ILF) is discussed.

Fragmentation Mechanism of White Phosphorus: A Theoretical Insight into Multiple Cleavage/Formation of P-P and P-C Bonds

Molecular-level understanding of metal-mediated white phosphorus (P₄ ) activation is meaningful but challenging because of its direct relevance to the conversion of P₄ into useful organophosphorus compounds as well as the complicated and unforeseeable cleavage process of P-P bonds. The related study, however, has still rarely been achieved to date. Here, a theoretical insight into the step-by-step process of three P-P bond cleavage/four P-C bond formation for [P₃ +P₁ ]-fragmentation of P₄ mediated by lutetacyclopentadienes is reported. The unique charge-separated intermediate and the intermolecular cooperation between two lutetacyclopentadienes play a vital role in the subsequent P-P/P-C bond breaking/forming. It is found that, although the first P-C formation is involved in the assembly of the cyclo-P₃ [R₄ C₄ P₃ ]^- unit, the construction of the aromatic five-membered P₁ heterocycle [R₄ C₄ P]^- is completed prior to the cyclo-P₃ formation. The reaction mechanism has been carefully elucidated by analyses of the geometric structure, frontier molecular orbitals, bond index, and natural charge, which greatly broaden and enrich the general knowledge of the direct functionalization of P₄ .

Iodination of cyclo-E5 -Complexes (E=P, As)

In a high‐yield one‐pot synthesis, the reactions of [Cp*M(η⁵‐P₅)] (M=Fe (1), Ru (2)) with I₂ resulted in the selective formation of [Cp*MP₆I₆]⁺ salts (3, 4). The products comprise unprecedented all‐cis tripodal triphosphino‐cyclotriphosphine ligands. The iodination of [Cp*Fe(η⁵‐As₅)] (6) gave, in addition to [Fe(CH₃CN)₆]²⁺ salts of the rare [As₆I₈]²⁻ (in 7) and [As₄I₁₄]²⁻ (in 8) anions, the first di‐cationic Fe‐As triple decker complex [(Cp*Fe)₂(μ,η^5:5‐As₅)][As₆I₈] (9). In contrast, the iodination of [Cp*Ru(η⁵‐As₅)] (10) did not result in the full cleavage of the M−As bonds. Instead, a number of dinuclear complexes were obtained: [(Cp*Ru)₂(μ,η^5:5‐As₅)][As₆I₈]_0.5 (11) represents the first Ru‐As₅ triple decker complex, thus completing the series of monocationic complexes [(Cp^RM)₂(μ,η^5:5‐E₅)]⁺ (M=Fe, Ru; E=P, As). [(Cp*Ru)₂As₈I₆] (12) crystallizes as a racemic mixture of both enantiomers, while [(Cp*Ru)₂As₄I₄] (13) crystallizes as a symmetric and an asymmetric isomer and features a unique tetramer of {AsI} arsinidene units as a middle deck.

On the comparison of oxygen and sulfur transfer reactivities in phosphine and phosphorene: the case of R3Sb(X) carriers (X = O or S)

Functionalization is one of the most powerful tools in materials science for the development of new and innovative materials with tailored properties purposefully designed to enhance the overall stability of the system. This is particularly true for exfoliated black phosphorus, which suffers from easy decomposition by air and moisture, hampering its highly desirable applications, especially in electronics. The present work suggests an innovative approach to the functionalization process of this 2D-material based on the selective introduction of chalcogen atoms on the material surface through a reaction with suitable molecular precursors such as stibine chalcogenides (R3Sb(X), X = O or S; R = organyl group). These molecules may readily act as chalcogen-transfer agents and, upon releasing the chalcogen atom atop the bP surface, leave stable stibines (R3Sb) as byproducts, which may be easily removed from the functionalized bP surface. The work provides an overview of all the possible structural, electronic and energy aspects associated with the chalcogen-atom transfer from the stibine to phosphorus based compounds, exemplified by trialkyl phosphines and single layer exfoliated black phosphorus, i.e. phosphorene, Pn. In both cases the oxygen transfer is more exergonic than the sulfur transfer, with the associated free energy barrier for the phosphine process being higher. Although the sulfur transfer for the Pn is found to be endergonic (ca. +3.6 kcal mol-1), the process may surely occur at high temperature. The evolution of the band structure upon the chalcogen transfer has been depicted in detail.

Noncovalent Functionalization of 2D Black Phosphorus with Fluorescent Boronic Derivatives of Pyrene for Probing and Modulating the Interaction with Molecular Oxygen

We studied the chemical-physical nature of interactions involved in the formation of adducts of two-dimensional black phosphorus (2D BP) with organoboron derivatives of a conjugated fluorescent molecule (pyrene). Time-resolved fluorescence spectroscopy showed a stabilization effect of 2D BP on all derivatives, in particular for the adducts endowed with the boronic functionalities. Also, a stronger modulation of the fluorescence decay with oxygen was registered for one of the adducts compared to the corresponding organoboron derivative alone. Nuclear magnetic resonance experiments in suspension and density functional theory simulations confirmed that only noncovalent interactions were involved in the formation of the adducts. The energetic gain in their formation arises from the interaction of P atoms with both C atoms of the pyrene core and the B atom of the boronic functionalities, with a stronger contribution from the ester with respect to the acid one. The interaction results in the lowering of the band gap of 2D BP by around 0.10 eV. Furthermore, we demonstrated through Raman spectroscopy an increased stability toward oxidation in air of 2D BP in the adducts in the solid state (more than 6 months). The modification of the electronic structure at the interface between 2D BP and a conjugated organic molecule through noncovalent stabilizing interactions mediated by the B atom is particularly appealing in view of creating heterojunctions for optoelectronic, photonic, and chemical sensing applications.

A Perspective on Recent Advances in Phosphorene Functionalization and Its Applications in Devices

Phosphorene, the 2D material derived from black phosphorus, has recently attracted a lot of interest for its properties, suitable for applications in materials science. The physical features and the prominent chemical reactivity on its surface render this nanolayered substrate particularly promising for electrical and optoelectronic applications. In addition, being a new potential ligand for metals, it opens the way for a new role of the inorganic chemistry in the 2D world, with special reference to the field of catalysis. The aim of this review is to summarize the state of the art in this subject and to present our most recent results in the preparation, functionalization, and use of phosphorene and its decorated derivatives. We discuss several key points, which are currently under investigation: the synthesis, the characterization by theoretical calculations, the high pressure behavior of black phosphorus, as well as its decoration with nanoparticles and encapsulation in polymers. Finally, device fabrication and electrical transport measurements are overviewed on the basis of recent literature and the new results collected in our laboratories.

Modelling strategies for the covalent functionalization of 2D phosphorene

This paper is a comparative outline of the potential acid-base adducts formed by an unsaturated main group or transition metal species and P atoms of phosphorene (Pn), which derives from black phosphorus exfoliation. Various possibilities of attaining a realistic covalent functionalization of the 2D material have been examined via DFT solid state calculations. The distribution of neighbor P atoms at one side of the sheet and the reciprocal directionalities of their lone pairs must be clearly understood to foreshadow the best possible acceptor reactants. Amongst the latter, the main group BH3 or I2 species have been examined for their intrinsic acidity, which favors the periodic mono-hapto anchoring at Pn atoms. The corresponding adducts are systematically compared with other molecular P donors from a phosphine to white phosphorus, P4. Significant variations emerge from the comparison of the band gaps in the adducts and the naked phosphorene with a possible electronic interpretation being offered. Then, the Pn covalent functionalization has been analyzed in relation to unsaturated metal fragments, which, by carrying one, two or three vacant σ hybrids, may interact with a different number of adjacent P atoms. For the modelling, the concept of isolobal analogy is important for predicting the possible sets of external coligands at the metal, which may allow the anchoring at phosphorene with a variety of hapticities. Structural, electronic, spectroscopic and energy parameters underline the most relevant pros and cons of some new products at the 2D framework, which have never been experimentally characterized but appear to be reasonably stable.