A "phosphorus derivative" of aziridines: on the importance of ring strain energy and three heteropolar bonds in azaphosphiridines.

Compared to aziridines, azaphosphiridines, which formally result from the replacement of a carbon atom by phosphorus, have been much less studied. In this work, accurate values for one of the most prominent properties, the ring strain energy (RSE), have been theoretically examined for a wide range of azaphosphiridine derivatives. Strongly related aspects of interest for developing the use of azaphosphiridines in heteroatom and polymer chemistry are ring opening reactions and polymerisations, the latter facilitated by their significantly high RSE.

Oxaphosphiranes: isolable phosphorus-containing epoxide rings.

Combining different heteroatoms in an epoxide-type ring having Lewis basic and acidic characteristics is challenging as it creates an increasing number of polar bonds and high ring strain energy. The first examples of isolable oxaphosphiranes, , epoxide rings with a phosphorus atom, have been synthesized using a facile and effective protocol starting from [pentacarbonyl{dichloro(trityl)phosphane}molybdenum(0)] (trityl = CPh), -butyllithium and commercially available fluorinated benzaldehydes. Reactions with various acids and bases will be described.

A metal and a metalloid Lewis acid bridged by a μ-phosphinidene.

Dinuclear phosphinidene complexes bridging two transition metal centres are now well established. However, a phosphinidene bridging a metal centre and a main group Lewis acid has not yet been reported. Herein, we describe the generation of a highly reactive phosphinidene complex bridging a tungsten and a boron centre.

Access to ligand-stabilized PH-containing phosphenium complexes.

While the chemistry of phosphenium compounds, including metal complexes thereof, is very well established, few derivatives having a P-H bond have been described, yet. This work describes rational access to donor-stabilised phosphenium metal complexes possessing a P-H bond using protonation reactions of stable phosphinidene complex adducts. While most Brønsted-Lowry acids yield formal 1,1-addition products at the phosphorus centre under the loss of the donor, super-strong acids having weakly coordinating anions enable access to donor-stabilised P-H phosphenium complex salts.

Deoxygenation of Oxiranes by λ σ -Phosphorus Reagents: A Computational, Mechanistic, and Stereochemical Study.

Invited for this month's cover is Prof. Arturo Espinosa Ferao at the University of Murcia, Spain. The cover picture shows two different ways of reacting a phosphane (R P) with the oxirane (epoxide) ring.

Challenging an old paradigm by demonstrating transition metal-like chemistry at a neutral nonmetal center.

We describe nonmetal adducts of the phosphorus center of terminal phosphinidene complexes using classical C- and N-ligands from metal coordination chemistry. The nature of the L-P bond has been analyzed by various theoretical methods including a refined method on the variation of the Laplacian of electron density ∇ρ along the L-P bond path. Studies on thermal stability reveal stark differences between N-ligands such as N-methyl imidazole and C-ligands such as tert-butyl isocyanide, including ligand exchange reactions and a surprising formation of white phosphorus.

Deoxygenation of Oxiranes by λ σ -Phosphorus Reagents: A Computational, Mechanistic, and Stereochemical Study.

The deoxygenation of parent and substituted oxiranes by λ σ -phosphorus reagents has been explored in detail, therefore unveiling mechanistic aspects as well as regio- and stereochemical consequences. Attack to a ring C atom is almost always preferred over one-step deoxygenation by direct P-to-O attack. In most cases a carbene transfer occurs as first step, leading to a phosphorane and a carbonyl unit that thereafter react in the usual Wittig fashion via the corresponding λ σ -1,2-oxaphosphetane intermediate.

A novel access to phosphanylidene-phosphorane complexes P-donor substitution and a detailed bonding analysis.

Phospha-Wittig reagents such as phosphanylidene-phosphoranes and their transition metal complexes are of great interest as sources of P building blocks but the access is still limited. Herein, we describe a new access to phosphanylidene-phosphorane complexes starting from the -methylimidazole-to-phosphinidene complex adduct. The complexes were studied electrochemically and theoretically, also with respect to their P NMR data, and the P-P bonds were evaluated by various DFT-derived descriptors.

Ring Strain Energy of Diheteropnictogeniranes El Pn (Pn=N, P, As, Sb)- Accurate versus Additive Approaches.

Accurate ring strain energy (RSE) values for sixty-six parent pnictogeniranes having two other identical p-block elements, El Pn, have been reported. A decrease in RSE was observed to correlate with an increase in the p character of the AO used in endocyclic bonds, which is particularly remarkable on descending the groups 15 and 16. The latter also parallels higher -NICS(1) values, which seems not to be related with an increase in aromaticity, as pointed out by other NICS-related criteria, but to atom-centred diatropic currents mostly arising from the presence of lone pairs.

Anions featuring an aluminium-silicon core with alumanyl silanide and aluminata-silene characteristics.

Molecular species containing multiple bonds to aluminium have long been challenging synthetic targets. Despite recent landmark discoveries in this area, heterodinuclear Al-E multiple bonds (where E is a group-14 element) have remained rare and limited to highly polarized π-interactions (Al=E ↔ Al-E). Here we report the isolation of three alumanyl silanide anions that feature an Al-Si core stabilized by bulky substituents and a Si-Na interaction.

Dehydrogenation reaction of triethylamine by an electrophilic terminal phosphinidene complex.

Reaction of a transiently formed terminal phosphinidene complex with triethylamine resulted in the formation of an sp C-H insertion product, as revealed by P NMR spectroscopy, which was isolated as semi-solid compound. However, if the reaction was continued for 24 h, a primary phosphane complex was obtained eventually. The compounds were characterised by NMR spectroscopy and mass spectrometry.

The quest for unligated oxaphosphiranes with phosphorus in different coordination numbers.

After more than 160 years of oxirane (epoxide) chemistry, the first derivative of a phosphorus analogue, namely oxaphosphirane, has been synthesized. Reactions with borane sulfane, a peroxy compound and elemental sulfur, as well as tetra-chloro--benzoquinone (TOB) reveal a significant destabilization upon increasing the coordination number at phosphorus from σ to σ, thus somehow supporting previous reports on such fleeting species. Theoretical studies provide insight into ring strain energy, ring/ring interconversion and the oxidation pathways.

Ring Strain Energies of Three-Membered Homoatomic Inorganic Rings El and Diheterotetreliranes ElTt (Tt = C, Si, Ge): Accurate versus Additive Approaches.

Accurate ring strain energies (RSEs) for three-membered symmetric inorganic rings El and organic dihetero-monocycles ElC and their silicon ElSi and germanium ElGe analogues have been computed for group 14-16 "El" heteroatoms using appropriate homodesmotic reactions and calculated at the DLPNO-CCSD-(T)/def2-TZVPP//B3LYP-D4/def2-TZVP(ecp) level. Rings containing triels and Sn/Pb heteroatoms are studied as exceptions to the RSE calculation as they either do not constitute genuine rings or cannot use the general homodesmotic reaction scheme due to uncompensated interactions. Some remarkable concepts already related to the RSE such as aromaticity or strain relaxation by increasing the s-character in the lone pair (LP) of the group 15-16 elements are analyzed extensively.

1,2σλ-Oxaphosphetanes and Their -Chalcogenides-A Combined Experimental and Theoretical Study.

Although 1,2σλ-oxaphosphetanes have been known for a long time, the "low-coordinate" 1,2σλ-oxaphosphetanes have only been known since their first synthesis in 2018 via decomplexation. Apart from ligation of this P-heterocycle to gold(I)chloride and the oxidation using -chloranil, nothing on their chemistry has been reported so far. Herein, we describe the synthesis of new 1,2σλ-oxaphosphetane complexes (-) and free derivatives (-), as well as reactions of with chalcogens and/or chalcogen transfer reagents, which yielded the -chalcogenides (-; Ch = O, S, Se).

Accurate Ring Strain Energies of Unsaturated Three-Membered Heterocycles with One Group 13-16 Element.

High-quality ring strain energy (RSE) data for 1unsaturated (CH)X parent rings, where X is a group 13-16 element, are reported in addition to the 2-isomers of the pnictogenirene rings. RSE data are obtained from appropriate homosdesmotic reactions and calculated at the DLPNO-CCSD(T)/def2-TZVPP//B3LYP-D3/def2-TZVP(ecp) level. 1Tallirene and 1plumbirene have unique donor-acceptor structures between an acetylene π(CC) orbital and an empty p orbital of a metallylene subunit (a Dewar-Chatt-Duncanson description) and therefore cannot be described as proper rings but as pseudocyclic structures.

Synthesis of azadiphosphiridine complexes. Theoretical studies on ring formation, the P-to-P' metal shift and the resulting nitrogen geometry.

A set of azadiphosphiridine complexes 3a and 4b,c were synthesized in high selectivity using N-H and P-H deprotonation as key steps and RPCl as substrates (R = NPr (), -Bu (), Ph ()). While complex 3a (-NPr) retained the P-W linkage of the starting material W(CO){PhCP(H)NH}, complexes 4b (-Bu) and 4c (-Ph) revealed that a P-to-P' haptotropic shift of the W(CO) group has occurred. Remarkably, complex 3a, bearing an unligated -NPr unit, displays a planar ring N geometry while 4b,c showed a pyramidal geometry of the ring nitrogen atom.

Toward a 1,4-Diphosphinine-Based Molecular CPS-Ternary Compound.

Synthesis of the tricyclic 1,3-dithiole-2-thione-derived 1,4-dihydro-1,4-diphosphinine is presented using a base-induced ring formation protocol and chloro(diethylamino)(1,3-dithiole-2-thion-4-yl)phosphane as the starting point. P-oxidation reactions of dihydrodiphosphinine by chalcogens led to bis(-oxide), bis(-sulfide), or bis(-selenide), respectively; all tricyclic compounds were obtained as mixtures. 1,4-Dihydro-1,4-diphosphinine was converted into 1,4-dichloro-1,4-dihydro-1,4-diphosphinine.

Azaphosphiridines: challenges and perspectives.

This mini-review describes a broad spectrum of synthetic strategies to access mono- and polycyclic azaphosphiridines; properties and theoretical calculations of free and metal-ligated are discussed. These species are characterized by a highly strained (saturated) CPN ring with three differently polarized endocyclic bonds. The latter causes a high reactivity of aza-phosphiridine complexes towards ring expansion and exchange reactions.

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

Several phosphaquinodimethanes and their M(CO) 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/NH 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).

M/X Phosphinidenoid Metal Complex Chemistry.

ConspectusLike singlet carbenes and silylenes, transient electrophilic terminal phosphinidene complexes enabled highly selective synthetic transformations, but the required multistep synthetic protocols precluded widespread use of these P building blocks. By contrast, nucleophilic M/Cl phosphinidenoid complexes can be easily accessed in one step from [M(CO)(RPCl)] complexes. This advantage and the mild reaction conditions opened broad synthetic applicability that enabled access to a variety of novel compounds.

A case study on the conversion of Li/Cl phosphinidenoid into phosphinidene complexes.

N,N-Diphenylamino- and N,N-dicyclohexylamino-substituted dichlorophosphane W(CO) complexes 1a,b were used to generate thermally very labile Li/Cl phospinidenoid W(CO) complexes 2a,b. The formation of transient complex 2a was confirmed via low-temperature P{H} NMR spectroscopy, but further strong evidence for the formation of transient complexes 2a,b was obtained from reactions with methanol and methylamine as formal E-H insertions (E = O, N) furnished complexes 3a,b and 4a. By using toluene in the absence of donor ligands, the primarily nucleophilic complexes 2a,b were converted into electrophilic terminal phosphinidene complexes 5a,b which was deduced from specific trapping reactions using tolane, 1-pentene and 1-hexene and thus obtained 1H-phosphirene 6 and phosphirane complexes 7 and8.

Terminal Phosphinidene Complex Adducts with Neutral and Anionic O-Donors and Halides and the Search for a Differentiating Bonding Descriptor.

The stability and some characteristic bonding features of a variety of ligand (L)-stabilized phosphinidene complexes derived from adduct formation with halides, and both anionic or neutral O-donor bases were explored. Furthermore, the main features of L → P pnictogen bonding in such adducts were studied not only by using geometric criteria such as L-P bond distances and pyramidalization or planarity at P but also by turning the spotlight on bond-strength-related (including atoms-in-molecules-derived) parameters, thermodynamic stability dependence with electronic characteristics of the free ligand, and dative-bonding participation. We propose the new descriptor, τ, which, together with the sign and magnitude of ∇ρ at the bond critical point, constitutes the required criteria to differentiate L-P linkages as van der Waals interactions, dative bonding, or mostly covalent bonds.

Accurate Ring Strain Energy Calculations on Saturated Three-Membered Heterocycles with One Group 13-16 Element.

Accurate ring strain energy (RSE) data for parent (CH)X rings are reported, where X are group 13-16 elements (El) in their lowest oxidation state, from the second to the sixth row, with their covalence completed by bonds to H. They are obtained from appropriate homodesmotic and hyper-homodesmotic reactions at different levels up to the CCSD(T) level, thus providing a benchmark of high-quality reference RSE values, as well as acceptably accurate faster lower-level options. Derivatives of indium, thallium, and lead cannot be properly described by a three-member ring connectivity, because they display a unique donor-acceptor structure from an ethylene π(C═C) orbital to an empty p orbital of a metallylene subunit.