Synthesis and Characterization of a Stable Cyclic gem-Bis(phosphaylide): a 4π-Electron Three-Membered Heterocycle

New Insight into the Reactivity of S,S-Bis-ylide

The present work focuses on the reactivity of S,S-bis-ylide 2, which presents a strong nucleophilic character, as evidenced by reactions with methyl iodide and CO₂, affording C-methylated salts 3 and betaine 4, respectively. The derivatization of betaine 4 affords the corresponding ester derivative 6, which is fully characterized by using NMR spectroscopy and X-ray diffraction analysis. Furthermore, an original reaction with phosphenium ions leads to the formation of a transient push-pull phosphino(sulfonio)carbene 8, which rearranges to give stabilized sulfonium ylide derivative 7.

Configurational Lability at Tetrahedral Phosphorus: syn/anti-Isomerization of a P-Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus

Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH₂ CHPh][OTf] (Mes*=2,4,6-(t-Bu)₃ C₆ H₂ ) occurred under mild conditions at 60 °C in CD₂ Cl₂ , resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu₄ ][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C₆ Cl₄ O₂ )₃ ) followed by chromatography on silica removed [NBu₄ ][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH₂ CHPh][Δ-TRISPHAT]⋅x[NBu₄ ][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P-C cleavage to yield a hyperconjugation-stabilized carbocation, pyramidal inversion promoted by σ-interaction of the P lone pair with the neighboring β-carbocation, and ring closure with inversion of configuration at P.

Reappraising Schmidpeter's bis(iminophosphoranyl)phosphides: coordination to transition metals and bonding analysis

The synthesis and characterization of a range of bis(iminophosphoranyl)phosphide (BIPP) group 4 and coinage metals complexes is reported. BIPP ligands bind group 4 metals in a pseudo fac-fashion, and the central phosphorus atom enables the formation of d⁰–d¹⁰ heterobimetallic complexes. Various DFT computational tools (including AIM, ELF and NCI) show that the phosphorus–metal interaction is either electrostatic (Ti) or dative (Au, Cu). A bridged homobimetallic Cu–Cu complex was also prepared and its spectroscopic properties were investigated. The theoretical analysis of the P–P bond in BIPP complexes reveals that (i) BIPP are closely related to ambiphilic triphosphenium (TP) cations; (ii) the P–P bonds are normal covalent (i.e. not dative) in both BIPP and TP.

The synthesis, characterization and computational analysis of a range of bis(iminophosphoranyl)phosphide (BIPP) group 4 and coinage metals complexes is reported. White phosphorus was used to install the central phosphorus atom.

Geminal Dianions Stabilized by Main Group Elements

This review is dedicated to the chemistry of stable and isolable species that bear two lone pairs at the same C center, i.e., geminal dianions, stabilized by main group elements. Three cases can thus be considered: the geminal-dilithio derivative, for which the two substituents at C are neutral, the yldiide derivatives, for which one substituent is neutral while the other is charged, and finally the geminal bisylides, for which the two substituents are positively charged. In this review, the syntheses and electronic structures of the geminal dianions are presented, followed by the studies dedicated to their reactivity toward organic substrates and finally to their coordination chemistry and applications.

Metalated Ylides: A New Class of Strong Donor Ligands with Unique Electronic Properties

The development and design of new ligand systems with special donor properties has been essential for crucial advances made in main-group-element and transition-metal chemistry over the years. This Forum Article focuses on metalated ylides as novel ligand systems. These anionic congeners of bisylides possess likewise two lone pairs of electrons at the central carbon atom and can thus function as X,L-type ligands with strong donor abilities. This article highlights recent efforts in the isolation and application of metalated ylides with a focus on work from this laboratory. We summarize structural and electronic properties and their use in organic synthesis as well as main-group-element and transition-metal chemistry.

Donor-Stabilized Silylene/Phosphine-Supported Carbon(0) Center with High Electron Density

An isolable donor-stabilized silavinylidene phosphorane was synthesized. This molecule, which can also be regarded as a new carbon(0) complex featuring a phosphine and a donor-stabilized silylene ligand, presents a central carbon atom with a remarkably high electron density (-1.82). Furthermore, the experimental electron-density study of this compound demonstrates the delocalization of the σ-lone pair at the central carbon atom toward the silicon center, a feature which is remarkably different from electronic situation of other bent-allene-type molecules. This result clearly demonstrates the powerful electron-donating ability of donor-stabilized silylene ligands, as well as their excellent electron-acceptor properties.

The Bonding Situation in Metalated Ylides

Quantum chemical calculations have been carried out to study the electronic structure of metalated ylides particularly in comparison to their neutral analogues, the bisylides. A series of compounds of the general composition Ph3 P-C-L with L being either a neutral or an anionic ligand were analyzed and the impact of the nature of the substituent L and the total charge on the electronics and bonding situation was studied. The charge at the carbon atom as well as the dissociation energies, bond lengths, and Wiberg bond indices strongly depend on the nature of L. Here, not only the charge of the ligand but also the position of the charge within the ligand backbone plays an important role. Independent of the substitution pattern, the NBO analysis reveals the preference of unsymmetrical bonding situations (P=C-L or P-C=L) for almost all compounds. However, Lewis structures with two lone-pair orbitals at the central carbon atom are equally valid for the description of the bonding situation. This is confirmed by the pronounced lone-pair character of the frontier orbitals. Energy decomposition analysis mostly reveals the preference of several bonding situations, mostly with dative and ylidic electron-sharing bonds (e.g., P→C- -L). In general, the anionic systems show a higher preference of the ylidic bonding situations compared to the neutral analogues. However, in most of the cases different resonance structures have to be considered for the description of the "real" bonding situation.

Carbones as Ligands in Novel Main-Group Compounds E[C(NHC)2 ]2 (E=Be, B+ , C2+ , N3+ , Mg, Al+ , Si2+ , P3+ ): A Theoretical Study

Quantum chemical calculations of the main-group compounds E[C(NHC^Me )₂ ]₂ (E=Be, B⁺ , C²⁺ , N³⁺ , Mg, Al⁺ , Si²⁺ , P³⁺ ) have been carried out using density functional theory at the BP86/def2-TZVPP and BP86-D3(BJ)/def2-TZVPP levels of theory. The geometry optimization at BP86/def2-TZVPP gives equilibrium structures with two-coordinated species E and bending angles C-E-C between 152.5° (E=Be) and 110.5° (E=Al). Inclusion of dispersion forces at BP86-D3(BJ)/def2-TZVPP yields a three-coordinated beryllium compound Be[C(NHC^Me )₂ ]₂ as the only energy minimum form. Three-coordinated isomers are found besides the two-coordinated energy minima for the boron and carbon cations B[C(NHC^Me )₂ ]₂⁺ and C[C(NHC^Me )₂ ]₂²⁺ . The three-coordinated form of the boron compound is energetically lower lying than the two-coordinated form, while the opposite trend is calculated for the carbon species. The theoretically predicted bond dissociation energies suggest that all compounds are viable species for experimental studies. The X-ray structure of the benzoannelated homologue of P[C(NHC^Me )₂ ]₂³⁺ that was recently reported by Dordevic et al. agrees quite well with the calculated geometry of the molecule. A detailed bonding analysis using charge and energy decomposition methods shows that the two-coordinated neutral compounds Be[C(NHC^Me )₂ ]₂ and Mg[C(NHC^Me )₂ ]₂ possess strongly positively charged atoms Be and Mg. The carbodicarbene groups C(NHC^Me )₂ serve as acceptor ligands in the compounds and may be sketched with dative bonds (NHC^Me )₂ C←E→C(NHC^Me )₂ (E=Be, Mg). Dative bonds in which the carbones C(NHC^Me )₂ are donor ligands are suggested for the cations (NHC^Me )₂ C→E←C(NHC^Me )₂ (E=B⁺ , Al⁺ ). The dications and trications possess electron-sharing bonds in which the bonding situation is best described with the formula [(NHC^Me )₂ C]⁺ -E-[C(NHC^Me )₂ ]⁺ (E=C, Si, N⁺ , P⁺ ).