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.

Synthesis of P-bridged, planar bis(NHC) BCl adducts.

Planar P- or P-bridged bis(NHCs), which have only been employed in transition metal complex chemistry so far, were subjected to BCl-containing solutions targeting the corresponding bis(NHC) BCl adducts. While the P(O)NEt-bridged bis(NHC) showed the expected adduct formation, the PNEt-bridged bis(NHC) reacted not only at the carbene moiety but also at the P-NEt functional group. The latter enabled access to the first 1,4-diphosphinine bis(NHC) main group adduct; its formation and properties were investigated by DFT calculations.

[4 + 1]- and [4 + 2]-cycloadditions of a thiazole-2-thione-based 1,4-diphosphinine - broadening the scope.

A broad study on [4 + 1]- and [4 + 2]-cycloaddition reactions of a thiazole-2-thione-based 1,4-diphosphinine (1) is reported, with a special focus on reversible reactions. Reactions of 1 with group 13 carbenoids NacNacM (M = Al and Ga) afford [4 + 1] adducts that can be classified as Al and Ga phosphides or as 7-metalla-1,4-norbornadienes. Reactions of 1 with alkynes and alkenes result in [4 + 2]-cycloaddition, affording 1,4-diphosphabarrelenes.

Tapping into the coordinative potential of a -functional 1,4-diphosphabarrelene using two sets of complementary ligand centres.

7,8-Dihydro-1,4-diphosphabarrelene diselones and bis(NHCs) were synthesised and employed as multitopic P,Se and P,C ligands in coordination chemistry, benefitting from a unique bent, P-bridged topology, thus being promising new building blocks.

Facile synthesis of five-membered cyclic REP-H iron(0) complexes.

The synthesis of five-membered P-heterocyclic iron(0) complexes possessing a P-H unit and two heteroatoms (E = O, N), directly bound to phosphorus, is described. Initial problems to achieve access "classical" reduction of P-Cl bonds of P-heterocycle complexes, , leading to P-P coupling, could be solved by a "combined two-step" reduction/complexation. The use of K[Fe(CO)H] not only opened access to such heterocyclic phosphane Fe(CO) complexes but also allowed the synthesis of sterically non-shielded 'secondary' heterocyclic phosphane complexes.

Elimination reactions in 1,4-diphosphinine chemistry: mixed-valence intermediates and 1,1- 1,4-elimination pathways.

Reactions of tricyclic 1,4-diphosphinines 1,4 with LiOH, followed by protonation are reported. 1,3-Thiazole-2-thione-derived 1 enabled only observation of the first anionic addition product 2/3. On the other hand, imidazole-2-selone-annelated derivative 4 enabled the identification of the first (5) and second product (6) at low temperature.

Tricyclic 1,4-Diphosphinines: Local vs. Global Aromaticity.

1D and 2D (Sigma only model) calculations were performed on recently established tricyclic 1,4-diphosphinines as well as related benzene and pyrazine derivatives. The study was extended to evaluate the effect of the fused rings on the overall aromatic properties with a special focus on functional groups such as carbenes. The effect of non-aromatic heterocycles on the local ring current of the central ring is small, while aromatic heterocycles (e.

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.

Synthesis of tricyclic 1,4-dihydro-1,4-phosphagermines - trying to establish molecular fencing of reactive centers.

Novel tricyclic 1,4-dihydro-1,4-phosphagermines (3a and 4a) were synthesised from Ge(NR)-bridged 1,3-imidazole-2-thione derivative 2a; all structures were crystallographically confirmed. In going from rather small alkyl substituents (Me, Bu) at the nitrogen centers of the 1,3-imidazole-2-thione units to sterically more demanding R = Mes and changing the employed Ge reagent from (RN)GeCl to RNGeCl we achieved access to mixed functional bis(1,3-imidazole-2-thione)-substituted germanium derivative 2c. The latter was treated with MeLi and, subsequently, with PCl to yield a pentacyclic P,Ge-heterocycle (5); its formation was rationalized using DFT theoretical calculations.

Application of phosphorus-bridged rigid, bent bis(NHCs) as dipodal ligands in main group and transition metal chemistry.

Phosphorus-bridged rigid, bent bis(N-heterocyclic) carbenes have not been reported, so far, despite having structural features that could make them interesting ligands in coordination and main group element chemistry. In previous reports, we had demonstrated that tuning of σ- and σ-phosphorus environments in planarised bis(NHCs) affects electronic properties and can provide additional coordination sites. Herein, we report on first examples of synthesis and conversion of 1,4-diphosphabarrelene-related compounds into rigid bent, doubly P-bridged bis(NHCs).

Arbuzov meets 1,2-oxaphosphetanes: transient 1,2-oxaphosphetan-2-iums as an entry point to beta-halo phosphane oxides and P-containing oligomers.

Herein, we describe the synthesis of a 1,2σλ-oxaphosphetane from ethylene oxide and its reactions with alkyl halides to form β-halo phosphane oxides in an Arbuzov-type reaction. When methyl triflate was used as a hard electrophile, cationic oligomerisation of 1,2-oxaphosphetanes was observed. DFT calculations indicate 1,2-oxaphosphetan-2-iums as intermediates and reveal differences between the Arbuzov and the potential Perkow reaction pathway.

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.

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.

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.

P-Centred redox reactions of a 1,4-dihydro-1,4-phosphasiline.

Tricyclic 1,4-dihydro-1,4-phosphasilines 3a,b were synthesized from Si(NR)-bridged imidazole-2-thione compounds 2a,b. Based on calculated FMOs of 3b, forecasting a possible P-selective P-N bond cleavage reduction, a redox cycle could be established using solutions of P-centred anionic derivative K[4b]. The cycle started with the oxidation of the latter to give the P-P coupled product 5b which could be chemically reduced by KC to yield K[4b], again.

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.

Design of transition metal complexes containing a P-E radical motif.

Recently, we have synthesized phosphane W(CO) complexes containing a -O-TEMP ligand motif as bench-stable precursors of thermally accessible phosphanoxyl complex radicals possessing a ligand with a P-O˙ group. In this work, extensive dispersion-corrected DFT calculations are used to explore both W(CO) and Fe(CO) phosphane complexes containing the -E-TEMP ligands (E = O, S, NMe, and PMe) in order to reach thermally accessible radicals with a P-E˙ motif. Moreover, a more general single-electron transfer (SET) oxidation approach to synthesize such P-E˙ radicals anionic precursors is disclosed.

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.

Catalyst-free CO hydrogenation with BHNH in water: DFT mechanistic insights.

Extensive DFT calculations show that BHNH may transfer dihydrogen as separated hydride and proton to CO rather than HCO in water over a barrier of 25.9 kcal mol, followed by faster hydride transfer from borate anions to either electrophilic CO or protic HO or HCOH, leading to competitive formate production and H release.

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).

On metal coordination of neutral open-shell P-ligands focusing on phosphanoxyls, their electron residence and reactivity.

This feature article highlights the discovery and development of phosphanoxyl complex chemistry starting from (neutral) low-coordinate phosphorus radicals and the quest of metal ligation effects. We describe synthesis and reactions of precursors, namely 2,2,6,6-tetramethylpiperidinoxyl (TEMPO) substituted phosphane tungsten(0) complexes. Trapping reactions of transient phosphanoxyl complexes, formed thermal homolytic N-O bond cleavage, as well as their use in radical polymerisations are illustrated, thus revealing an interesting reactivity dichotomy.

Reversible Redox Chemistry of Anionic Imidazole-2-thione-Fused 1,4-Dihydro-1,4-diphosphinines.

Anionic 1,4-dihydro-1,4-diphosphinines were synthesized from tricyclic 1,4-diphosphinines and isolated as blue powdery salts M[-]. Reaction of solutions of these monoanions with iodomethane led to -methylated compounds -. An oxidation/reduction cycle was examined, starting from solutions of K[] via P-P coupled product and back to K[], and the recyclability and redox chemistry of this cycle were confirmed by experimental and simulated cyclic voltammetry analysis, which is proposed as a potential 2-electron cathode for rechargeable cells.

1,3,2-Diheterophospholane complexes: access to new tuneable precursors of phosphanoxyl complexes and P-functional polymers.

Synthesis of a testbed of P-H functional diheterophospholane complexes (3 and 6a,b) with no or little steric bulk at the α-position was achieved using [NEt][WH(CO)] as a combined reductant and complexation reagent. Reaction with TEMPO leads to P-OTEMP substituted tungsten complexes (4 and 7a,b) possessing different thermostabilities towards N-O bond cleavage. The transient phosphanoxyl complexes obtained were used for the polymerisation of styrene and acrylonitrile.