Ravi Yadav

We report a bora(amino)silylene‐coordinated copper metallacycle [{LSi(NDipp(BPin))‐Cu‐Si(N ^t BuC(H)PhN ^t Bu)(NDipp(BPin))}] ( 2 ) (L = PhC(N ^t Bu) ₂ ). Complex 2 was isolated during attempts to prepare a silylene‐coordinated copper hydride. Reaction of a (bis)silylene‐copper‐ tert ‐butoxide intermediate with pinacolborane resulted in the ligand transformation via B─H bond activation and the transfer of a hydrogen atom to the ligand backbone. The complex 2 was characterized by multinuclear NMR spectroscopy and single‐crystal x‐ray diffraction studies. Preliminary theoretical calculations were performed to suggest a possible reaction pathway for the formation of complex 2 .

Experimental assignment of aromaticity in all-metal systems remains challenging, particularly for heavy-element clusters, where local magnetic effects can obscure signatures of circular electron delocalization. Here, we investigate a supramolecularly stabilized, formally tetracationic [Bi4]4+ ring by combining structurally meaningful reference compounds, solid- and solution-state NMR spectroscopy, SQUID magnetometry, and exact two-component relativistic calculations. Comparison with an isostructural [Li4Br]3+-encapsulated analogue and a binuclear Bi(III) reference compound disentangles global ring-current effects from local heavy-atom deshielding and ligand-specific conformational effects. On this basis, the unusually downfield-shifted 1H and 13C NMR signals observed for the Bi4-containing species provide direct spectroscopic evidence for magnetically induced ring currents in the [Bi4]4+ core. By contrast, bulk magnetic measurements do not reveal significant diamagnetic exaltation, indicating that this quantity is not a resolved descriptor of aromaticity in these systems. Stoichiometric studies further identify chemically competent intermediates that provide mechanistic snapshots of [Bi4]4+ ring formation. Complementary calculations support the assignment of a magnetically responsive, σ-delocalized [Bi4]4+ core, reproduce a rare spectroscopically observed puckering motion of the rhomboidal [Bi4]4+, and underscore the critical role of spin–orbit coupling on electronic structure and dynamics. Overall, this work moves the discussion of aromaticity from predominantly computational assignment toward experimentally benchmarked analysis in the heavy-element and all-metal regime.

This work deals with the synthesis of metallocene-phosphorus based radical coordination polymers.

Recently, we discovered that silaiminyl-silylene, [LSi–Si(NDipp)L] (L = PhC(NtBu)₂, Dipp = 2,6-diisopropylphenyl), can be converted from a mono-silylene to bis-silylene by using Lewis acids. This revelation led us to further use silaiminyl-silylene as a silylene-based ligand, which can coordinate to one metal center and later, on demand, release one more silylene center to coordinate to a second metal. Furthermore, an insight into the mechanism of this unusual rearrangement reaction is presented. Initially, mono-silylene complexes [LSi{M(Mes)}–Si(NDipp)L] (M = Ag, Au) were isolated. These complexes were then used as templates to access bis-silylene coordinated homo-dinuclear, [LSi{M(Mes)}–(NDipp)–{M(Mes)}SiL] (M = Ag, Au) and hetero-dinuclear, [LSi{Ag(Mes)}–(NDipp)–{Au(Mes)}SiL] complexes via a Lewis acid triggered ligand rearrangement. Notably, using this silylene, a selective coordination of the two different coinage metals Ag and Au was achieved stepwise. This differs from the reactivity when a conventional bis-silylene is employed. The isolation of [LSi{Ag(Mes)}–(NDipp)–{Au(Mes)}SiL] showcases the utility of strong σ-donor silylene-based switchable ligands. This represents the first example of a heterobimetallic complex ligated by a spacer-separated bis-silylene ligand.

Aromaticity in organic molecules is well defined, but its role in metal-only rings remains controversial. Here we introduce a supramolecular stabilization approach of a cationic {Bi₄} rhomboid within the symmetric charge sphere of two bowl-shaped dianionic calix[4]pyrrolato indinates. Crystallographic and spectroscopic characterization, quantum chemical analysis and magnetically induced ring currents indicate σ-aromaticity in the formally tetracationic 16-valence electron [Bi₄]⁴⁺ ring. Computational screening for other p-block elements identifies the planar rhomboid as the globally preferred structure for 16-valence electron four-atomic clusters. The aromatic [Bi₄]⁴⁺ is isoelectronic to the [Al₄]⁴⁻, a motif previously observed as antiaromatic in Li₃[Al₄]⁻ in the gas phase. Thus, subtle factors such as charge isotropy seem to decide over aromaticity or antiaromaticity, advising for caution in debates based on the Hückel model—a concept valid for second-row elements but less deterministic for the heavier congeners.

Electromerism is a very well‐known phenomenon in transition metal chemistry. In main group chemistry, this concept has only started getting attention recently. We report stimuli responsive low‐valent silicon compounds exhibiting electromerism. A mixed‐valent silaiminyl‐silylene1, [LSi−Si(NDipp)L] (L=PhC(N^tBu)₂), was synthesized in a single step from amidinate‐chlorosilylene. Compound1has two interconnected Si atoms in formally +I and +III oxidation states. Upon treatment with Lewis acidic Cu^IX (X=mesityl, Cl, Br, I), electron redistribution occurs resulting in the formation of [{LSi(NDipp)Si(L)}−CuX], in which both silicon atoms are in the +II formal oxidation state. Removal of the copper center from [{LSi(NDipp)Si(L)}−CuX] by using a Lewis basic carbene led to reformation of the precursor [LSi−Si(NDipp)L]. Thus, the process is fully reversible. This showcases the first example of Lewis acid/base‐induced reversible electromerism in silicon chemistry.

Electromerism is a very well‐known phenomenon in transition metal chemistry. In main group chemistry, this concept has only started getting attention recently. We report stimuli responsive low‐valent silicon compounds exhibiting electromerism. A mixed‐valent silaiminyl‐silylene1, [LSi−Si(NDipp)L] (L=PhC(N^tBu)₂), was synthesized in a single step from amidinate‐chlorosilylene. Compound1has two interconnected Si atoms in formally +I and +III oxidation states. Upon treatment with Lewis acidic Cu^IX (X=mesityl, Cl, Br, I), electron redistribution occurs resulting in the formation of [{LSi(NDipp)Si(L)}−CuX], in which both silicon atoms are in the +II formal oxidation state. Removal of the copper center from [{LSi(NDipp)Si(L)}−CuX] by using a Lewis basic carbene led to reformation of the precursor [LSi−Si(NDipp)L]. Thus, the process is fully reversible. This showcases the first example of Lewis acid/base‐induced reversible electromerism in silicon chemistry.

Lewis superacids enable the activation of highly inert substrates. However, the permanent presence of a Lewis superacidic center comes along with a constantly increased intolerance toward functional groups or ambient conditions. Herein, we describe a strategy to unleash Lewis superacidity by electromerism. Experimental and computational results indicate that coordinating a Lewis base to Δ‐calix[4]pyrrolato‐antimony(III) triggers a ligand redox‐noninnocent coupled transfer into antimony(V)‐state that exhibits Lewis superacidic features. Lewis acidity by electromerism establishes a concept of potential generality for powerful yet robust reagents and on‐site substrate activation approaches.

Lewis superacids enable the activation of highly inert substrates. However, the permanent presence of a Lewis superacidic center comes along with a constantly increased intolerance toward functional groups or ambient conditions. Herein, we describe a strategy to unleash Lewis superacidity by electromerism. Experimental and computational results indicate that coordinating a Lewis base to Δ‐calix[4]pyrrolato‐antimony(III) triggers a ligand redox‐noninnocent coupled transfer into antimony(V)‐state that exhibits Lewis superacidic features. Lewis acidity by electromerism establishes a concept of potential generality for powerful yet robust reagents and on‐site substrate activation approaches.

Fe–Li–Pb heterotrimetallic triple-decker complexes were synthesized by reduction of pentaphospha- and pentarsaferrocene with the dilithioplumbole. Both complexes comprise bent P₅/As₅ middle decks and plumbole as lower decks.