Libor Dostál

B ← P coordinated phosphide 1 acts as a nucleophile and reacts with RCH ₂ NC to form a 2-imidazoline, imidazole or an enamine.

The reaction of the P,C,P ‐pincer indium(III) chloride ArInCl ₂ with 2 eq. of K[BEt ₃ H] provided crystalline monomeric indane ArInH ₂ (1) (Ar = 2,6‐(tBu ₂ PO) ₂ C ₆ H ₃ ) bearing two terminal In─H bonds. Indane 1 is a multitalented reagent that serves as a reductant toward dichalcogenides (PhE) ₂ giving ArIn(EPh) ₂ (2E, E = S, Se, Te) or a hydride source in reaction with 4‐CF ₃ ‐C ₆ H ₄ OH that gives mono‐ or disubstituted indium phenolates ArIn(H)(4‐CF ₃ ‐C ₆ H ₄ O) (3), ArIn(4‐CF ₃ ‐C ₆ H ₄ O) ₂ (4) depending on stoichiometry. Most importantly, 1 is an unprecedented double hydroindation agent, as illustrated by its reactions with aldehydes 4‐R‐C ₆ H ₄ CHO (R = OMe, CF ₃ , F) yielding ArIn(4‐R‐C ₆ H ₄ CH ₂ O) ₂ (5R) or ketene Ph ₂ C═C═O providing ArIn(Ph ₂ C═CH─O) ₂ (6).

This contribution provides a detailed mechanistic insight into a remarkably complex reaction of neutral 1-Ph-2-tert-butyl-1H-1,2-benzazaborole (1) with elemental potassium in THF, yielding the known 10π-aromatic 1H-2,1-benzazaborolyl (2,1-Bab⁻) potassium salt (2), an isoelectronic species with indenyl potassium, along with a racemic mixture of a new potassium hydridoborate complex (3), formed together with 2 in ca. 1:1 molar ratio. Unlike derivatives of isoelectronic 1H-indene, which undergo various self-protonation processes under analogous conditions, for 1, we propose a completely different and rather complex, non-linear tandem mechanism. Key species are four enantiomeric pairs of short-lived, dimeric, diamagnetic intermediates, denoted α, β, ω₁ and ω₂, possessing structures related to Gomberg’s dimer and Krause‘s adduct. Based on an exhaustive multinuclear NMR analysis of the reaction mixture, including experiments with C3-methylene deuterium-labelled starting compound 1-d_n (n ∈ {0–2}) and the observation of a primary AKIE (k_H/k_D >> 1), as well as a detailed analysis of full scan mass spectra and observed ions in ultrahigh-resolution LDI-MS data of the resulting mixture of isotopologues of the final product 3-d_n (n ∈ {0–4}), comprising multiple isotopomers, in combination with probabilistic calculations, electrochemical studies, and DFT calculations, we were able to reconstruct the full sequence of reaction steps and pathways. The presented results support the involvement of various H-atom transfer (HAT) processes within pairs of radical-anionic species K⁺1^{● −}, proceeding throught different transition states, and, most notably, reveal an extremely rare boron-targeted HAT. These findings provide a basis for developing synthetic routes to unconventional boron hydrides.

The oxidation of phosphorus atoms in P,C,P-pincer organotin(IV) compounds ArSnCl₃ (1), ArSnPhCl₂ (2) and ArSnPh₂Cl (3) (Ar = 2,6-(tBu₂PO)₂C₆H₃) with Me₃NO (or H₂O₂), S or Se furnished compounds Ar^YSnCl₃ (1^Y), Ar^YSnPhCl₂ (2^Y), and Ar^YSnPh₂Cl (3^Y) (Ar^Y = 2,6-(tBu₂(Y)PO)₂C₆H₃; Y = O, S or Se, except 3^O). Their reactions with Na[BArF] ([BArF] = [3,5-(CF₃)₂C₆H₃]₄B) afforded salts containing organotin cations [Ar^YSnCl₂][BArF] (1^Y+[BArF]^-), [Ar^YSnPhCl][BArF] (2^Y+[BArF]^-), and [Ar^YSnPh₂][BArF] (3^Y+[BArF]^-). The oxidation of compound 3 with 1 equiv of Me₃NO gave compound [Ar^POSnPh₂Cl] (3^PO) (Ar^PO = 2-(tBu₂PO)-6-(tBu₂(O)PO)C₆H₃) and its subsequent oxidation by S or Se allowed the isolation of mixed donor compounds [Ar^OYSnPh₂Cl] (3^OY) (Ar^OY = 2-(tBu₂(O)PO)-6-(tBu₂(Y)PO)C₆H₃; Y = S or Se). Compounds 3^PO and 3^OY were converted to salts [Ar^POSnPh₂][BArF] (3^PO+[BArF]^-) and [Ar^OYSnPh₂][BArF] (3^OY+[BArF]^-; Y = S or Se). All compounds were characterized by multinuclear NMR spectroscopy in solution, and their molecular structures (except 3^OS) were determined by single crystal (sc) X-ray diffraction analysis. The intramolecular P/Y → Sn interactions and their influence on the structures of complexes were analyzed in detail using NMR data and solid-state structures. The experiments were corroborated by a DFT study including NBO and AIM-analysis, which reveals the role of chalcogen centers in tuning the thermodynamic stabilization in the pincer complexes.

Neutral Te(II) species 2-(tBuNCH)C₆H₄TeCl ([I]Cl) as well as tellurenyl Te(II)⁺ cations [2-(tBuNCH)C₆H₄Te][X] (X = OTf or SbF₆), i.e., [I][OTf] and [I][SbF₆], exhibit a wide range of reactivity toward various ortho-quinones. While the reaction of ortho-chloranil leads to the oxidation of Te(II) into Te(IV), 3,5-di-tert-butyl-ortho-benzoquinone leads only to partial oxidation due to an ongoing dynamic reversible reaction, being the first example of a chemically reversible two electron Te(II)/Te(IV) redox couple. By contrast, 9,10-phenanthrenequinone as a very weak oxidant shows no reaction; however, the most Lewis acidic [I][SbF₆] produces a corresponding Lewis adduct interacting by both electrostatic and weak chalcogen bond interactions. The diverse reactivity scope is further complemented by DFT computed thermochemistry data. Furthermore, [I][OTf] is successfully utilized for the catalytic transfer of silanes (Et₃SiH, Ph₃SiH, Ph₂SiH₂, and (EtO)₃SiH) to ortho-quinones via redox single or double Si–H bond activation, yielding silylated catechols, monomeric cyclic catecholatosilanes, or bis(catecholato)silanes. Surprisingly, in the absence of the catalyst [I][OTf], the reactivity spans from no reaction to the formation of hexachloro-dibenzo[1,4]dioxine-2,3-dione. The latter product is an entirely different substance class compared to the one formed during the catalyzed reaction.

A new diphosphine-substituted Ga-based ligand, [(L)Ga(CH₂PPh₂)₂] (1) was prepared as a potential chelator for transition metals complexes. The data indicate that 1 exhibits higher Lewis basicity and donor strength than conventional organic diphosphines due to the presence of the Ga center, which enhances its electronic properties. This ligand demonstrates efficient coordination behavior toward various metal centers as Ru(II), Ir(III), Ni(0), Pt(II), or Cu(I), forming stable bimetallic complexes in various coordination modes. The photophysical study of these complexes revealed the deep-blue emission of 1·CuX complexes with lifetimes in the μs range and quantum yield up to 0.12. The impact of the (pseudo)halogen ligand X (X = Cl, Br, I or SCN) and the metal linker in the ligand framework [(L)M(CH₂PPh₂)₂] (M = Ga vs In) on the photophysical properties are discussed.

The present study demonstrates the high versatility of the P,C,P-pincer ligand in the coordination chemistry of tin(iv) compounds, offering a promising outlook in respect to its future application with other p-block elements.

Oxidation of the arylpnictinidenes 2,6-(Ph ₂ PNMes) ₂ C ₆ H ₃ Pn (Pn = As, Sb, Bi) with the heavier chalcogens (Ch = S, Se, Te) led to the formation of arylpnictinidene chalcogenides (Ph ₂ PNMes) ₂ C ₆ H ₃ PnCh formally containing terminal double bonds, which are best described as bipolar ⁺ Pn–Ch ⁻ single bonds.

The reaction of [2,6‐(DippN = CH)₂C₆H₃]Bi (1Dipp, Dipp = 2,6‐iPrC₆H₃) with CH₂I₂ proceeded via double C─I bond activation yielding [2,6‐(DippN = CH)₂C₆H₃]Bi(μ‐(Bi,N)─CH₂)I₂ (3). By contrast, the reaction of 1Dipp with 1,2‐diiodoethane provided [2,6‐(DippN═CH)₂C₆H₃]BiI₂ (1DippI₂) and ethene. The tert‐butyl analogue [2,6‐(tBuN═CH)₂C₆H₃]Bi (1tBu) reacted with CH₂ClX to give [2,6‐(tBuN═CH)₂C₆H₃]Bi(CH₂Cl)X (X═I (4) or Cl (5)). Further, its reactivity with CH₂I₂ was sensitive towards the stoichiometry since using a 1:1 ratio gave a mixture of dinuclear complex {[2,6‐(tBuN═CH)₂C₆H₃]Bi(I)}₂(μ‐(Bi,Bi)─CH₂) (6) and [2,6‐(tBuN═CH)₂C₆H₃]Bi(CH₂I)I (7). The reaction could be shifted in favor of 7 using an excess of CH₂I₂, but with 0.45 eq. of CH₂I₂ compound 6, as a product of double C─I bond activation mediated by two Bi atoms was isolated as the main product.

The treatment of pnictinidenes [2‐(RNHCH₂)‐6‐(RN=CH)C₆H₃]E (1As/Sb) (where E=As or Sb) with benzoyl peroxide provided compounds [2‐(DippNCH₂)‐6‐(DippN=CH)C₆H₃]E(O₂CPh) (2As/Sb) as a result of two step procedure, i. e. oxidation of the pnictogen centre followed by the elimination of benzoic acid. The reaction between 1As and diphenyl disulfide proceeded in the same vein yielding thiophenol and [2‐(DippNCH₂)‐6‐(DippN=CH)C₆H₃]As(SPh) (3As). Analogous reaction of 1Sb furnished a mixture of [2‐(DippNHCH₂)‐6‐(DippN=CH)C₆H₃]Sb(SPh)₂ (3'Sb), [2‐(DippNCH₂)‐6‐(DippN=CH)C₆H₃]Sb(SPh) (3Sb) and PhSH, while NMR studies proved the existence of a dynamic equilibrium between all three compounds in solution and removal of incipient PhSH was necessary for the isolation of 3Sb. Both 1As/Sb smoothly reacted with 2‐nitrosotoluene leading to [2‐(DippNCH₂)‐6‐(DippN=CH)C₆H₃]E(O‐NH‐2‐Me−Ph) 4As/Sb and with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione giving [2‐(DippNCH₂)‐6‐(DippN=CH)C₆H₃]E[(N(CO)‐NH(CO))N−Ph] 5As/Sb. All compounds were characterized by IR, Raman, NMR spectroscopy, and the molecular structures, except for 3As and 5Sb, were determined by single‐crystal X‐ray diffraction. Furthermore, we scrutinized the thermally induced reductive elimination of benzoic acid and thiophenol from 2–3As/Sb, respectively, and that of 4‐phenylurazole from 5As. These eliminations involve C−H activation at the CH₂N group, and the recovery of the pnictinidene center in [2,6‐(RN=CH)₂C₆H₃]E (6As/Sb). Using DFT calculations a plausible mechanism was suggested for all the investigated reactions, which are in good agreement with the experimental observations.