When Electrons Step in: Polarizing Effects Explored with Triisobutylaluminum.

High-resolution X-ray diffraction data of triisobutylaluminum were collected, and unexpected structural features were observed, hinting toward yet unnoticed polarization effects. To approach these, a multipole refinement using the Hansen and Coppens method, followed by a topological analysis using Bader's quantum theory of atoms in molecules, was employed. The electron localization function based on density functional theory calculations supported the experimental findings. Thereby, unobserved electron shifts within the isobutyl group become detectable. It is shown that the impact of this electron shift is dependent mainly on whether the iBu substituent of the homoleptic triisobutylaluminum dimer [AliBu3]2 (1) is connected by a directional (σ) or a multicenter (µ) bond to the metal. The effect found is assumed not only to be of paramount importance for organoaluminum compounds, widely used in synthesis and in the industrial value chain, but also to be present in organometallic chemistry in general.

Tetraimido Sulfuric Acid H2 S(NtBu)4 -Valence Isoelectronic to H2 SO4.

The valence isoelectronic imido analog H2 S(NtBu)4 (1) of sulfuric acid H2 SO4 was synthesized, isolated, and characterized by NMR spectroscopy and high-resolution X-ray charge density analysis. The latter reveals strongly polarized Sδ+ -Nδ- bonds with virtually no double bond character. The easy-to-polarize S-N bonds are an advantageous and versatile feature of sulfur nitrogen ligands, which enables them to adapt to different electron requirements of various metal cations.

Synthesis and Coordination Behavior of a New Hybrid Bidentate Ligand with Phosphine and Silylene Donors.

This work describes the synthesis and coordination behavior of a new mixed-donor ligand PhC(NtBu)2 SiC6 H4 PPh2 (1) containing both silylene and phosphine donor sites. Ligand 1 was synthesized from a reaction of ortho-lithiated diphenylphosphinobenzene (LiC6 H4 PPh2 ) with chlorosilylene (PhC(NtBu)2 SiCl). Treatment of 1 with Se and GeCl2 resulted in SiIV compounds 2 and 3 by selective oxidation of the silylene donor. This strong σ-donor ligand induces dissociation of CuCl and PhBCl2 leading to formation of ionic complexes 4 and 5 respectively. The reaction of 1 with ZnCl2 and AlCl3 resulted in the formation of chelate complexes 5 and 7, respectively, while treatment with EtAlCl2 and GaCl3 forms monodentate complexes 8 and 9. X-ray analysis of 4 showed that the copper is in the spiro center of the two five-membered rings. Moreover, the copper(I)chloride has not been oxidized but dissociates to Cu+ and [CuCl2 ]- . All the compounds are well characterized by mass spectrometry, elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction studies.

A Neutral Three-Membered 2π Aromatic Disilaborirane and the Unique Conversion into a Four-Membered BSi2 N-Ring.

We report the design, synthesis, structure, bonding, and reaction of a neutral 2π aromatic three-membered disilaborirane. The disilaborirane is synthesized by a facile one-pot reductive dehalogenation of amidinato-silylene chloride and dibromoarylborane with potassium graphite. Despite the tetravalent arrangement of atoms around silicon, the three-membered silicon-boron-silicon ring is aromatic, as evidenced by NMR spectroscopy, nucleus independent chemical shift calculations, first-principles electronic structure studies using density functional theory (DFT) and natural bond orbital (NBO) based bonding analysis. Trimethylsilylnitrene, generated in situ, inserts in the Si-Si bond of disilaborirane to obtain a four-membered heterocycle 1-aza-2,3-disila-4-boretidine derivative. Both the heterocycles are fully characterized by X-ray crystallography.

Insight into the Bonding and Aggregation of Alkyllithiums by Experimental Charge Density Studies and Energy Decomposition Analyses.

In this Article, the organolithiums [((-)-sparteine)LitBu] (1), [(ABCO)LitBu]2 (2), and [(ABCO)2(LiiPr)4] (3) are investigated by means of experimental and theoretical charge density determination to elucidate the nature of the Li-C and Li-N bonds. Furthermore, the valence shell charge concentrations (VSCCs) in the nonbonding region of the deprotonated Cα-atom will provide some insight on the localization of the carbanionic lone pair. Analysis of the electron density (ρ(rBCP)), Laplacian (∇2ρ(rBCP)), and the energy decomposition (EDA) confirmed that the Li-C/N bond exhibits astonishingly similar characteristics, to reveal an increasingly polar contact with decreasing aggregate size. This explains former observations on the incorporation of halide salts in organolithium reagents. Furthermore, it could be shown that the bonding properties of the iPr group are similar to those of the tBu substituent. The accuracy of fit to all previously determined properties in organolithiums is remarkable.

Treatment of Silylene-Phosphinidene with Chalcogens Resulted Exclusively in the Formation of Silicon-Bonded Chalcogens.

Chalcogen-bonded silicon phosphinidenes LSi(E)-P-Me cAAC (E=S (1); Se (2); Te (3); L=PhC(NtBu)2 ; Me cAAC=C(CH2 )(CMe2 )2 N-2,6-iPr2 C6 H3 )) were synthesized from the reactions of silylene-phosphinidene LSi-P-Me cAAC (A) with elemental chalcogens. All the compounds reported herein have been characterized by multinuclear NMR, elemental analyses, LIFDI-MS, and single-crystal X-ray diffraction techniques. Furthermore, the regeneration of silylene-phosphinidene (A) was achieved from the reactions of 2-3 with L'Al (L'=HC{(CMe)(2,6-iPr2 C6 H3 N)}2 ). Theoretical studies on chalcogen-bonded silicon phosphinidenes indicate that the Si-E (E=S, Se, Te) bond can be best represented as charge-separated electron-sharing σ-bonding interaction between [LSi-P-Me cAAC]+ and E- . The partial double-bond character of Si-E is attributed to significant hyperconjugative donation from the lone pair on E- to the Si-N and Si-P σ*-molecular orbitals.

Silanylidene and Germanylidene Anions: Valence-Isoelectronic Species to the Well-Studied Phosphinidene.

The reduction of TipMCl3 (Tip=2,4,6-triisopropylphenyl) (M=Si, Ge) with KC8 in the presence of cyclic alkyl(amino) carbene (cAAC) afforded the acyclic silanylidene and germanylidene anions in the form of potassium salt [K(cAAC)MTip]2 (M=Si (1); Ge (2)). The silanylidene and germanylidene anions are valence-isoelectronic to the well-studied phosphinidene and are a new class of acyclic anions of Group 14. Compounds 1 and 2 were isolated and well characterized by NMR and single-crystal X-ray structure analysis. Furthermore, the structure and bonding of compounds 1 and 2 was investigated by computational methods.

Manganese-Catalyzed Carbonylative Annulations for Redox-Neutral Late-Stage Diversification.

An inexpensive, nontoxic manganese catalyst enabled unprecedented redox-neutral carbonylative annulations under ambient pressure. The manganese catalyst outperformed all other typically used base and precious-metal catalysts. The outstanding versatility of the manganese catalysis manifold was reflected by ample substrate scope, setting the stage for effective late-stage manipulations under racemization-free conditions of a wealth of marketed drugs and natural products, including alkaloids, amino acids, steroids, and carbohydrates.

Methylenecyclopropane Annulation by Manganese(I)-Catalyzed Stereoselective C-H/C-C Activation.

C-H/C-C functionalizations with methylenecyclopropanes (MCPs) were accomplished with a versatile base-metal catalyst. A robust manganese(I) complex enabled the expedient annulation of MCPs by synthetically meaningful ketimines to deliver, upon one-pot hydroarylation, densely substituted polycylic anilines in a step-economical fashion. Mechanistic studies provided strong support for a facile organometallic C-H manganation, while typical cobalt, ruthenium, rhodium, and palladium catalysts were found completely ineffective.