Non-conventional Behavior of a 2,1-Benzazaphosphole: Heterodiene or Hidden Phosphinidene?

The titled 2,1-benzazaphosphole (1) (i. e. ArP, where Ar=2-(DippN=CH)C6 H4 , Dipp=2,6-iPr2 C6 H3 ) showed a spectacular reactivity behaving both as a reactive heterodiene in hetero-Diels-Alder (DA) reactions or as a hidden phosphinidene in the coordination toward selected transition metals (TMs). Thus, 1 reacts with electron-deficient alkynes RC≡CR (R=CO2 Me, C5 F4 N) giving 1-phospha-1,4-dihydro-iminonaphthalenes 2 and 3, that undergo hydrogen migration producing 1-phosphanaphthalenes 4 and 5. Compound 1 is also able to activate the C=C double bond in selected N-alkyl/aryl-maleimides RN(C(O)CH)2 (R=Me, tBu, Ph) resulting in the addition products 7-9 with bridged bicyclic [2.2.1] structures. The binding of the maleimides to 1 is semi-reversible upon heating. By contrast, when 1 was treated with selected TM complexes, it serves as a 4e donor bridging two TMs thus producing complexes [μ-ArP(AuCl)2 ] (10), [(μ-ArP)4 Ag4 ][X]4 (X=BF4 (11), OTf (12)) and [μ-ArP(Co2 (CO)6 )] (13). The structure and electron distribution of the starting material 1 as well as of other compounds were also studied from the theoretical point of view.

Hydrostibination of Alkynes: A Radical Mechanism*

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring open-shell neutral intermediates. Density-functional theory (DFT) calculations are consistent with this model, predicting an activation barrier that is in agreement with the experimental value (Eyring analysis) and a rate limiting step that is congruent with the experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring Sb^II and Sb^III intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a synthetic methodology.

Hydrostibination

A rigid naphthalenediamine framework has been used to prepare antimony hydrides that feature LUMO shapes and energies similar to those found in secondary boranes. By exploiting this feature, we introduce the first examples of uncatalyzed hydrostibination reactions of robust C≡C, C=C, C=O, and N=N bonds as new elementary hydrometalation reactions analogous to hydroboration. These results endorse the notion of a diagonal relationship between the lightest p-block element and the heaviest Group 15 elements and may lead to the conception of novel reaction chemistry.

Synthesis, structure and dispersion interactions in bis(1,8-naphthalendiyl)distibine

Naph₂Sb₂1 was synthesized by a reaction of 1,8-dilithionaphthalene NaphLi₂ with SbCl₃ and its solid state structure is reported on. 1 shows intermolecular interactions in the solid state, which were studied by quantum chemical calculations with dispersion corrected density functional theory, supermolecular ab initio approaches and symmetry adapted perturbation theory. The same methods were employed to compare the solid state interactions in the crystal of 1 to those in real (for E = P) and hypothetical (for E = As and Bi) crystal structures of Naph₂E₂. Dispersion interactions were found to provide the most important stabilising contribution in all cases, seconded by electrostatic attraction between pnictogen atoms and π-systems of neighbouring naphthyl groups.

Homolytic, Heterolytic, Mesolytic - As You Like It: Steering the Cleavage of a HC(sp3 )-C(sp3 )H Bond in Bis(1H-2,1-benzazaborole) Derivatives

A set of (3,3')-bis(1-Ph-2-R-1H-2,1-benzazaborole) compounds, in which R=tBu (Bab-tBu)₂ , R=Dipp (Bab-Dipp)₂ or R=tBu and Dipp (Bab-Dipp)(Bab-tBu), was synthesized and fully characterized using ¹ H, ¹¹ B, ¹³ C, and ¹⁵ N NMR spectroscopy as well as single-crystal X-ray diffraction analysis. The central HC(sp³ )-C(sp³ )H bond with restricted rotation at the junction of both 1H-2,1-benzazaborole rings displayed an intriguing reactivity. It was demonstrated that this bond is easily mesolytically cleaved using alkali metals to form the respective aromatic 1Ph-2R-1H-2,1-benzazaborolyl anions M⁺ (THF)_n (Bab-tBu)^- (M=Li, Na, K) and K⁺ (THF)_n (Bab-Dipp)^- . Furthermore, the central HC(sp³ )-C(sp³ )H bond of bis(1H-2,1-benzazaborole)s is also homolytically cleaved either by heating or photochemical means, giving corresponding 1Ph-2R-1H-2,1-benzazaborolyl radicals (Bab-tBu)^. and (Bab-Dipp)^. , which rapidly self-terminate. Nevertheless, their formation was unambiguously established by NMR analysis of the reaction mixtures containing products of the self-termination of the radicals after heating or irradiation. (Bab-Dipp)^. radical was also characterized using EPR spectroscopy. Importantly, it turned out that the essentially non-polarized HC(sp³ )-C(sp³ )H bond in (Bab-tBu)₂ is also cleaved heterolytically with 2 equiv of MeLi, giving the mixture of Li⁺ (SOL)_n (Bab-tBu)^- (SOL=THF or Et₂ O) and lithium methyl-substituted borate complex Li⁺ (SOL)_n (Bab-tBu-Me)^- in a diastereoselective fashion.

Antimony(III) and bismuth(III) amides containing pendant N-donor groups--a combined experimental and theoretical study

N,N- and N,N,N-chelated antimony(III) and bismuth(III) chlorides L(1-3)MCl2 1-4 [for L(1): M = Sb (1), for L(2): M = Sb (2) and for L(3): M = Sb (3) and Bi (4)], containing ligands L(1-3) derived from the pyrrole ring (where L(1) = C4H3N-2-(CH[double bond, length as m-dash]N-2',6'-iPr2C6H3), L(2) = C4H2N-2,5-(CH2NMe2)2, L(3) = C4H2N-2,5-(CH2NC4H8)2), were prepared by the treatment of lithium precursors with SbCl3 or BiCl3. Molecular structures 1-4 of were described both in solution (NMR spectroscopy) and in the solid state (single-crystal X-ray diffraction analysis). Structures of 1-4 were also subjected to a density functional theory study.

Hypervalent diorganoantimony(iii) fluorides via diorganoantimony(iii) cations – a general method of synthesis

A new general synthesis method for hypervalent diorganoantimony(iii) fluorides with pendant arm ligands is ​ based on treatment with [Bu₄N]F·3H₂O of ​ cationic species e.g. [{2-(2′,6′-ⁱPr₂C₆H₃NCH)C₆H₄}₂Sb]⁺[PF₆]⁻ or [{2-(Me₂NCH₂)C₆H₄}PhSb]⁺[SbF₆]⁻.

Synthesis and structure of N,C-chelated organoantimony(v) and organobismuth(v) compounds

The reaction of N,C-intramolecularly coordinated organoantimony(iii) and organobismuth(iii) compounds LMCl2 (M = Sb () or Bi () and L = [o-(CH[double bond, length as m-dash]N-2,6-iPr2C6H3)C6H4]) with phenyllithium in a 1 : 1 or 1 : 2 molar ratio gave compounds LM(Ph)Cl (M = Sb () or Bi ()) and LMPh2 (M = Sb () or Bi ()) in moderate to good yields. Compound could also be prepared by the treatment of the lithium compound LLi with in situ prepared PhSbCl2. Oxidation of the antimony(iii) compounds , and with one equivalent of SO2Cl2 proceeded smoothly with formation of organoantimony(v) compounds LSbCl4 (), LSb(Ph)Cl3 () and LSbPh2Cl2 () in nearly quantitative yields. Compounds are yellowish solids that are stable for a long time even in the presence of air. In contrast, only organobismuth(iii) compounds and could be successfully oxidized using SO2Cl2 to give compounds LBi(Ph)Cl3 () and LBiPh2Cl2 (). Compound is stable, but compound readily decomposed in solution and could not be isolated and stored for a longer period. All attempts to prepare compound LBiCl4 by the oxidation of with SO2Cl2 failed and resulted only in a mixture of products. All studied compounds were characterized by electrospray ionization (ESI) mass spectrometry, and (1)H and (13)C NMR spectroscopy. The molecular structures of , and were unambiguously established using single-crystal X-ray diffraction analysis.