Air-Stable Thermoluminescent Carbodicarbene-Borafluorenium Ions

Borenium ions, originally synthesized as fundamentally important laboratory curiosities, have attracted significant attention due to their applications in catalysis and frustrated Lewis pair chemistry. However, investigations of the materials properties of these types of compounds are exceptionally rare. Herein, we report the synthesis, molecular structures, and optical properties of a new class of air-stable borenium ions, stabilized by the strongly donating carbodicarbene (CDC) ligand (2, 3, 6). Notably, CDC-borafluorenium ions exhibit thermoluminescence in solution, a result of a twisted intramolecular charge transfer process. The temperature responsiveness, which is observable by the naked eye, is assessed over a 20 to -60 °C range. Significantly, compound 2 emits white light at lower temperatures. In the solid state, these borocations exhibit increased quantum yields due to aggregation-induced emission. CDC-borafluorenium ions with two different counteranions (Br^-, BPh₄^-) were investigated to evaluate the effect of anion size on the solution and solid-state optical properties. In addition, CDCs containing both symmetrical and unsymmetrical N-heterocycles (bis(1-isopropyl-3-methylbenzimidazol-2-ylidene)methane and bis(1,3-dimethyl-1,3-dihydro-2H-benzo[d]imidazol-2-ylidene)methane) were tested to understand the implications of free rotation about the CDC ligand carbon-carbon bonds. The experimental work is complemented by a comprehensive theoretical analysis of the excited-state dynamics.

Facile access to halogenated cationic BC-centered organoborons isoelectronic with alkenyl halides

A facile strategy to prepare halogenated cationic BC-centered organoboron analogues of alkenyl halides via the reaction between carbodiphosphoranes (CDPs) and aryl dihaloboranes is reported. Structural comparison of the halogen and alkoxy derivatives, as well as detailed computational studies, corroborates the polarized double dative bonding nature of the central BC double bonds.

Isolation of a Uranium(III)-Carbon Multiple Bond Complex

Low-valent uranium-element multiple bond complexes remain scarce, though there is burgeoning interest regarding to their bonding and reactivity. Herein, isolation of a uranium(III)-carbon double bond complex [(Cp*)2 U(CDP)](BPh4 ) (1) comprising a tridentate carbodiphosphorane (CDP) was reported for the first time. Oxidation of 1 afforded the corresponding U(IV) complex [(Cp*)2 U(CDP)](BPh4 )2 (2). The distance between U and C in 2 is 2.481 Å, indicating the existence of a typical U=C double bond, which is further confirmed by quantum chemical calculations. Bonding analysis suggested that the CDP also serves as both σ- and π-donor in complex 1, though a longer U-C bond (2.666(3) Å) is observed. It implies that 1 is the first isolable mononuclear uranium(III) carbene complex. Moreover, these results suggest that CDPs are promising ligands to establish other low-valent f-block metal-carbon multiple bond complexes.

Flexible coordination of carbodiphosphorane-based pincer ligands in chromium(0) carbonyl complexes

A series of chromium(0) complexes was obtained by subsequent irradiation of [Cr(CO)6] in the presence of [(Ph2P-CH2-PPh2)2CH]+. Depending on the reaction conditions and the duration of irradiation, complexes with different coordination modes of the potentially tridentate ligand can be isolated. Shorter irradiation times lead to the coordination of the terminal PPh2 groups and the formation of [(κ2P,P′-{Ph2P-CH2-PPh2}CH)Cr(CO)4]+ (2), whereas after longer irradiation duration, the formation of fac- and mer-[(κ3P,C,P′-{Ph2P-CH2-PPh2}CH)Cr(CO)3]+ (3) can be observed. In the presence of base, the neutral complex [(κ3P,C,P′-{Ph2P-CH2-PPh2}C)Cr(CO)3] (4) can be isolated, enabling the analysis of the central CDP group’s net donor strength through the C–O stretching vibration. Finally, the utilization of reductants like potassium graphite lead to the loss of hydrogen and generation of an anionic chromium(0) complex (5). Using quantum chemical methods, the stability of possible isomers is explored.

Comparison of Chemical and Interpretative Methods: the Carbon-Boron π-Bond as a Test Case*

Quantum chemical calculations and NBO, ETS-NOCV, QTAIM and ELF interpretative approaches have been carried out on C-donor ligand-stabilized dihydrido borenium cations. Numerous descriptors of the C-B π-bond strength obtained from orbital localization, energy partitioning or topological methods as well as from structural and chemical parameters have been calculated for 39 C-donor ligands including N-heterocyclic carbenes and carbones. Comparison of the results allows the identification of relative and absolute descriptors of the π interaction. For both families of descriptors excellent correlations are obtained. This enables the establishment of a π-donation capability scale and shows that the interpretative methods, despite their conceptual differences, describe the same chemical properties. These results also reveal noticeable shortcomings in these popular methods, and some precautions that need to be taken to interpret their results adequately.

Cationic Phosphorus Compounds Based on a Bis(1-piperidinyl)-Substituted Carbodiphosphorane: Syntheses, Structures, and Csp3–H Activation

The use of the bis(1-piperidinyl)-substituted carbodiphosphorane (Ph₂(Pip)P)₂C (1) as an NCN ligand for the stabilization of phosphorus cations was studied. A simple ligand for halide exchange allowed the synthesis and isolation of a series of phosphorus monocations of the type [1-PR₂]⁺ (with R = Cl, Br, I, CyCl, Ph). These cations exhibit characteristic NMR and structural properties which nicely correlate with the charge at the central phosphorus atom and the interaction between the ligand and the PR₂ moiety. Halide abstraction from the monocations does not result in isolable dicationic compounds but in an unexpected intramolecular C_sp³–H activation in the piperidinyl group. DFT studies show that the selective activation of the CH₂ group next to the nitrogen atom instead of a CH group at the phenyl substituents proceeds via an iminium intermediate formed by hydride transfer from the carbon atom to the cationic phosphorus center. This observation clearly demonstrates the pronounced π acidity of the dicationic phosphorus species in comparison to compounds with a further π-donor substituent.

Double donation in trigonal planar iron-carbodiphosphorane complexes - a concise study on their spectroscopic and electronic properties

We present the syntheses of trigonal planar coordinated Fe(ii) carbodiphosphorane (CDPR) complexes, starting from iron(ii)-bis(trimethylsilylamide) [Fe{N(SiMe3)2}2] and hexaphenyl-(CDPPh) and sym-dimethyltetraphenyl-carbodiphosphoranes (CDPMe), respectively. Both complexes [CDPPh-Fe{N(SiMe3)2}2] (1) and [CDPMe-Fe{N(SiMe3)2}2] (2) were examined in solution and in the solid state. 1 shows a dissociation equilibrium in solution which we monitored by variable temperature 1H-NMR spectroscopy. Magnetic measurements of 1 and 2 yielded a high spin configuration (S = 2) for both complexes. Quantum chemical calculations were performed to analyze the bonding situation in compound 1.

Hexaphenyl carbodiphosphorane adducts of heavier group 15 element trichlorides: syntheses, properties and reactivities

Herein, we present a series of hexaphenyl carbodiphosphorane (CDP^Ph) adducts of heavier group 15 trichlorides ECl₃ (E = P-Bi). The reaction with PCl₃ yields the known salt [CDP^Ph-PCl₂][Cl] ([1][Cl]), the heavier element trichlorides ECl₃ (E = Sb (4), Bi (5)) give the neutral adducts CDP^Ph-ECl₃ which were characterised crystallographically and spectroscopically. The reaction of CDP^Ph with AsCl₃ does not yield CDP^Ph-AsCl₃ (2), but in the presence of GaCl₃ the corresponding salt [CDP^Ph-AsCl₂][GaCl₄] ([3][GaCl₄]) is formed. DFT (density functional theory) calculations were carried out to examine the molecular frontier orbitals in 1⁺-5. Additional reactivity studies revealed an intramolecular electrophilic aromatic substitution (S_EAr) in 1⁺, which represents an excellent starting point for further selective C-P bond formation reactions.

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.

Synthesis, Electronic Structure, and Reactivities of Two-Sulfur-Stabilized Carbones Exhibiting Four-Electron Donor Ability

Bis(sulfane)carbon(0) (BSC; Ph₂ S→C←SPh₂ (1)) is successfully synthesized by deprotonation of the corresponding protonated salt 1⋅HTfO. The diprotonated salt 1⋅(HTfO)₂ as the starting material can be also easily accessed by the deimination of iminosulfane(sulfane)carbon(0) (iSSC)⋅HBF₄ . Density functional theory calculations revealed the peculiar electronic structure of 1, which has two lone pairs of electrons at the central carbon atom. The largest proton affinities (PA(1): 297.5 kcal mol^-1 ; PA(2): 183.7 kcal mol^-1 ) and the highest energy levels of the HOMOs (HOMO: -4.89 eV; HOMO-1: -5.02 eV) for 1 among the two-sulfur-stabilized carbones clearly indicate the strong donor ability of carbon center stabilized by two S^II ligands. The donating ability of these lone pairs of electrons is demonstrated by the C-diaurated and C-proton-aurated complexes, which provide the first experimental evidence for two-sulfurstabilized carbones behaving as four-electron donors. Furthermore, the syntheses and application of Ag^I carbone complexes as carbone transfer agents are also reported.

Donor–acceptor interactions in tri(phosphonio)methanide dications [(Ph3P)2CP(X)Ph2]2+(X = H, Me, CN, NCS, OH, Cl, OTf, F)

The impact of the strongly electron donating carbodiphosphorane moiety in the series of tri(phosphonio)methanide dications as triflate salts [(Ph₃P)₂CP(X)Ph₂][OTf]₂(X = H, Me, CN, NCS, OH, Cl, OTf, F) deriving from [(Ph₃P)₂CPPh₂][OTf] (19[OTf]) is presented.