Fusing Triphenylbismuth and PnPh3 (Pn = P-Bi): Synthesis, Isolation, and Characterization of 9-Bisma-10-Pnictatriptycenes.

The first series of 9-bisma-10-pnictatriptycenes Bi(C6H4)3Pn (2-Pn, Pn = P-Bi; see graphic) has been synthesized in a two-step procedure via suitable tris(2-bromophenyl)pnictanes 1-Pn and characterized in solution as well as in the solid state. DFT calculations suggest preferential interactions between 2-Pn and soft Lewis acids via the lighter pnictogen donor atom. Experimental studies demonstrate that even the weakest Lewis base in the series of 2-Pn, namely the dibismatriptycene 2-Bi, interacts with Lewis acidic [BiMe2(SbF6)] in solution. Analytical techniques include (VT-)NMR spectroscopy, DOSY NMR spectroscopy, high-resolution mass spectrometry, single-crystal X-ray diffraction analyses, and DFT calculations.

Small molecule activation by well-defined compounds of heavy p-block elements.

The creative design and exploration of new bonding motifs and molecular architectures in main group chemistry have pushed the boundaries of reactivity in this field of research. In this context, the activation of small molecules represents a set of benchmark reactions and offers valuable opportunities for the development of innovative synthetic methods. In addition to significant progress by use of transition metal complexes and compounds of lighter p-block elements, compounds based on heavy p-block elements (with the principle quantum number n > 4) have seen major advances in recent years. Fundamental properties originating from their high atomic number (such as the size, energy, and polarizability of atomic orbitals) set them apart from more established species in small molecule activation. Challenges and opportunities arising from this scenario are analyzed and highlighted.

Insertion of CO2 and CS2 into Bi-N bonds enables catalyzed CH-activation and light-induced bismuthinidene transfer.

The uptake and release of small molecules continue to be challenging tasks of utmost importance in synthetic chemistry. The combination of such small molecule activation with subsequent transformations to generate unusual reactivity patterns opens up new prospects for this field of research. Here, we report the reaction of CO2 and CS2 with cationic bismuth(iii) amides. CO2-uptake gives isolable, but metastable compounds, which upon release of CO2 undergo CH activation. These transformations could be transferred to the catalytic regime, which formally corresponds to a CO2-catalyzed CH activation. The CS2-insertion products are thermally stable, but undergo a highly selective reductive elimination under photochemical conditions to give benzothiazolethiones. The low-valent inorganic product of this reaction, Bi(i)OTf, could be trapped, showcasing the first example of light-induced bismuthinidene transfer.

Reactivity of a Cationic Bismuth Amide towards Unsymmetric Heterocumulenes.

Invited for this month's cover is the Lichtenberg group of the Philipps-University Marburg (Germany). The front cover picture shows "bismuth" dressed in colors reminiscent of those found on the surface of this element. In the graphic, bismuth is craving for soft ice cream. This represents the preference of Lewis acidic bismuth centers for soft donor atoms, as demonstrated in the insertion of heterocumulenes into the Bi-N bond of a cationic bismuth amide. More information can be found in the Research Article by Crispin Lichtenberg and co-workers.

Reactivity of a Cationic Bismuth Amide towards Unsymmetric Heterocumulenes.

The reactivity of a literature-known, ring-strained bismuth amide cation towards a range of unsymmetric heterocumulene substrates has been investigated. Reactions with ketenes R2 C=C=O (R=Me, Ph), isocyanates R'N=C=O, and isothiocyanates R'N=C=S (R'=Ph, 4-CF3 -C6 H4 ) proceed via facile insertion of the heterocumulene in the Bi-N bond of the cationic bismuth amide. Unexpectedly pronounced differences in the regioselectivity of these insertion reactions have been observed, yielding a rich variety of heterocycle motifs (BiC2 NC2 , BiC2 NCO, BiC2 NCS, BiC2 NCN), some of which are unprecedented. Parameters that control the regioselectivity of the insertion reactions have been identified and are discussed based on experimental and theoretical investigations. Analytical techniques applied in this work include heteronuclear and two-dimensional NMR spectroscopy, IR spectroscopy, elemental analysis, single-crystal X-ray diffraction analyses, and DFT calculations.

CH Activation of Cationic Bismuth Amides: Heteroaromaticity, Derivatization, and Lewis Acidity.

Cationization of Bi(NPh2)3 has recently been reported to allow access to single- and double-CH activation reactions, followed by selective transformation of Bi-C into C-X functional groups (X = electrophile). Here we show that this approach can successfully be transferred to a range of bismuth amides with two aryl groups at the nitrogen, Bi(NRaryl2)3. Exchange of one nitrogen-bound aryl group for an alkyl substituent gave the first example of a homoleptic bismuth amide with a mixed aryl/alkyl substitution pattern at the nitrogen, Bi(NPhiPr)3. This compound is susceptible to selective N-N radical coupling in its neutral form and also undergoes selective CH activation when transformed into a cationic species. The second CH activation is blocked due to the absence of a second aryl moiety at nitrogen. The Lewis acidity of neutral bismuth amides is compared with that of cationic species "[Bi(aryl)(amide)(L)n]+" and "[Bi(aryl)2(L)n]+" based on the (modified) Gutmann-Beckett method (L = tetrahydrofuran or pyridine). The heteroaromatic character of [Bi(C6H3R)2NH(triflate)] compounds, which are iso-valence-electronic with anthracene, is investigated by theoretical methods. Analytical methods used in this work include nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction, mass spectrometry, and density functional theory calculations.

Bismuth Amides Mediate Facile and Highly Selective Pn-Pn Radical-Coupling Reactions (Pn=N, P, As).

The controlled release of well-defined radical species under mild conditions for subsequent use in selective reactions is an important and challenging task in synthetic chemistry. We show here that simple bismuth amide species [Bi(NAr2 )3 ] readily release aminyl radicals [NAr2 ]. at ambient temperature in solution. These reactions yield the corresponding hydrazines, Ar2 N-NAr2 , as a result of highly selective N-N coupling. The exploitation of facile homolytic Bi-Pn bond cleavage for Pn-Pn bond formation was extended to higher homologues of the pnictogens (Pn=N-As): homoleptic bismuth amides mediate the highly selective dehydrocoupling of HPnR2 to give R2 Pn-PnR2 . Analyses by NMR and EPR spectroscopy, single-crystal X-ray diffraction, and DFT calculations reveal low Bi-N homolytic bond-dissociation energies, suggest radical coupling in the coordination sphere of bismuth, and reveal electronic and steric parameters as effective tools to control these reactions.

Toward Transition-Metal-Templated Construction of Arylated B4 Chains by Dihydroborane Dehydrocoupling.

The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH2 ] (Dur=2,3,5,6-Me4 C6 H) and [(Me3 Si)2 NBH2 ] led to the formation of bridging borylene complexes of the form [(Cp*RuH)2 BR] (Cp*=C5 Me5 ; 1 a: R=Dur; 1 b: R=N(SiMe3 )2 ) through oxidative addition of the B-H bonds with concomitant hydrogen liberation. Employing the more electron-deficient dihydroborane [3,5-(CF3 )2 -C6 H3 BH2 ] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF)4 [(Cp*Ru)2 B4 H5 (3,5-(CF3 )2 C6 H3 )4 ] (4), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido-[1,2(Cp*Ru)2 (µ-H)B4 H9 ] (I) indicates that there appear to be no classical σ-bonds between the boron atoms in complex I, whereas in the case of 4 the B4 chain better resembles a network of three B-B σ bonds, the central bond being significantly weaker than the other two.