Synthesis, Reactivity, and Complexation with Fe(0) of a Tight-bite Bis(N-heterocyclic silylene).

The synthesis, reactivity, and complexation with Fe(0) precursor of a tight-bite bis(N-heterocyclic silylene) (bis(NHSi)) ligand 1 are reported. The reaction of 1 with p-toluidine led to the activation of both N-H bonds across Si(II) atoms to afford a four-membered heterocyclic cyclodisilazane 2, with hydride substituents attached to five-coordinate Si atoms. A 1 : 2 reaction of 1 with Fe(CO)5 led to an intriguing dinuclear complex 3 featuring a five-membered (N-Si-Fe-Fe-Si) ring with a Fe-Fe bond distance of 2.6892(13) Å. All compounds (1-3) were thoroughly characterized by various spectroscopic methods and X-ray diffraction studies conclusively established their molecular structures. DFT calculations were carried out to shed light on bonding and energetic aspects in 1-3.

Preparation of a Compound with a SiII -SiIV -SiII Bonding Arrangement.

Herein, we report the synthesis of a rare bis-silylene, 1, in which two SiII atoms are bridged by a SiIV atom. Compound 1 contains an unusual SiII -SiIV -SiII bonding arrangement with SiII -SiIV bond distances of 2.4212(8) and 2.4157(7) Å. Treatment of 1 with Fe(CO)5 afforded a dinuclear Fe0 complex 2 with two unusually long Si-Si bonds (2.4515(8) and 2.4488(10) Å). We have also carried out a detailed computational study to understand the nature of the Si-Si bonds in these compounds. Natural bond orbital (NBO) and energy decomposition analysis-natural orbital for chemical valence (EDA-NOCV) analyses reveal that the Si-Si bonds in 1 and 2 are of an electron-sharing nature.

En Route to a Molecular Terminal Tin Oxide.

In the pursuit of terminal tin chalcogenides, heteroleptic stannylenes bearing terphenyl- and hexamethyldisilazide ligands were reacted with carbodiimides to yield the respective guanidinato complexes. Further supported by quantum chemical calculations, this revealed that the iso-propyl-substituted derivative provides the maximum steric protection achievable. Oxidation with elemental selenium produced monomeric terminal tin selenides with four-coordinate tin centers. In reactions with N2O as oxygen transfer reagent, silyl migration toward putative terminal tin oxide intermediates gave rise to tin complexes with terminal ─OSiMe3 functionality. To prevent silyl migration, the silyl groups were substituted with cyclohexyl moieties. This analogue exhibited distinctively different reactivities toward selenium and N2O, yielding a 1,2,3,4,5-tetraselenastannolane and chalcogenide-bridged dimeric compounds, respectively.

Correspondence to "Structure of Violet Phosphorus and Its Phosphorene Exfoliation".

The structure described in the publication "Structure of Violet Phosphorus and Its Phosphorene Exfoliation" (Angew. Chem. Int. Ed. 2020, 59, 1074-1080) is identical to the structure by Thurn and Krebs determined already in 1969 and therefore by no means a new modification.

Stabilization of NH- Group Adjacent to Naked Silicon(II) Atom in Base Stabilized Aminosilylenes.

Aminosilylene, comprising reactive NH- and Si(II) sites next to each other, is an intriguing class of compounds due to its ability to show diverse reactivity. However, stabilizing the reactive NH- group next to the free Si(II) atom is challenging and has not yet been achieved. Herein, we report the first examples of base stabilized free aminosilylenes Ar*NHSi(PhC(Nt Bu)2 ) (1 a) and Mes*NHSi(PhC(Nt Bu)2 ) (1 b) (Ar*=2,6-dibenzhydryl-4-methylphenyl and Mes*=2,4,6-tri-tert-butylphenyl), tolerating a NH- group next to the naked Si(II) atom. Remarkably, 1 a and 1 b exhibited interesting differences in their reactivity upon heating. With 1 a, an intramolecular C(sp3 )-H activation of one of the benzhydryl methine hydrogen atoms to the Si(II) atom produced the five-membered cyclic silazane 2. However, with 1 b, a rare 1,2-hydrogen shift to the Si(II) atom afforded a silanimine 3, with a hydride ligand attached to an unsaturated silicon atom. Further, the coordination capabilities of 1 a were also tested with Ru(II) and Fe(0) precursors. Treatments of 1 a with [Ru(η6 -p-cymene)Cl2 ]2 led to the isolation of a η6 -arene tethered complex [RuCl2 {Ar*NHSi(PhC(t BuN)2 )-κ1 -Si-η6 -arene}] (4), whereas with the Fe(CO)5 precursor a Fe(0) complex [Fe(CO)4 {Ar*NHSi(PhC(t BuN)2 )-κ1 -Si}] (5) was obtained. Density functional theory (DFT) calculations were conducted to shed light on the structural, bonding, and energetic aspects in 1-5.

A Neutral Planar Four-Membered Si2B2 2π-Aromatic Ring.

The synthesis of the first inorganic four-membered neutral 2π-aromatic compound 2 is reported. This unique ring has been synthesized from a simple and straightforward reaction of amidinato-silylene with dichlorophenylborane, followed by the reduction with KC8 in THF. Compound 2 has been fully characterized by single-crystal X-ray diffraction (SC-XRD), NMR spectroscopy, and mass spectrometry. The computational calculations reveal that the Si2B2 ring is a π-delocalized system resulting from the interaction of pπ orbital of B and Si-N σ* orbitals having pseudo π symmetry. Compound 2 is the first known example of a neutral planar inorganic analogue of cyclobutenyl dication.

Structure Elucidation of Lithium Compounds Using 7 Li Residual Quadrupolar Couplings.

A new NMR method for the structure elucidation of lithium compounds under solution-like conditions is presented. It is based on the measurement of 7 Li residual quadrupolar couplings (RQCs) in a stretched polystyrene (PS) gel, and comparison to RQCs predicted from crystal or DFT-derived model structures in combination with alignment tensors derived from one-bond 1 H,13 C residual dipolar couplings (RDCs). The method was applied to five lithium model complexes containing monoanionic, bidentate bis(benzoxazole-2-yl)methanide, bis(benzothiazole-2-yl)methanide and bis(pyridyl)methanide ligands, of which two are first introduced in this work. In agreement with the crystalline state, four complexes are monomeric with Li coordinated fourfold by two additional THF molecules, whereas in one complex bulky tBu groups only provide space for one additional THF molecule.

Reactivity of Silylene with Gallium- and Boron Trihalide at Reductive Conditions Resulting in Unforeseen Products.

Herein, we report a one-pot reaction of gallium and boron halides with potassium graphite in the presence of benzamidinate stabilized silylene LSi-R, (L=PhC(Nt Bu)2 ). The reaction of LSiCl with an equivalent amount of GaI3 in the presence of KC8 leads to the direct substitution of one chloride group by gallium diiodide simultaneously additional coordination of silylene resulted in L(Cl)Si→GaI2 -Si(L)→GaI3 (1). In compound 1, the structure comprises two differently coordinated gallium atoms where one gallium presents between two silylenes and the other gallium is only coordinated by one silylene. In this Lewis acid-base reaction the oxidation states of the starting materials remain unchanged. The same is valid in the silylene boron adduct formation of L(t Bu)Si-BPhCl2 (2) and L(t Bu)Si-BBr3 (3). This new route provides access to galliumhalosilanes challenging to synthesize by any other method.

Synthesis and Characterization of Substituted Phosphasilenes and its Rare Homologue Stibasilene >Si=Sb.

Herein we report the reduction of R-EX2 (E=P, Sb) with two equivalents of KC8 in the presence of silylene (LSiR; L=PhC(NtBu)2 ) to give Trip-P=SiL(C6 H4 PPh2 ) (1), Ter Ph-P=(tBu)SiL (2) and Ter Ph-Sb=(tBu)SiL (3). The last (3) belongs to a new class of heavier analogues of Schiff bases (>C=N-), containing a formal >Si=Sb- double bond. The theoretical calculations suggest that lone pairs on the dicoordinated group-15 centers are stabilized by hyperconjugative interactions resulting in pseudo-Si-P/Si-Sb multiple bonds which are highly reactive as indicated by the high first and second proton affinities.

Coordination and Stabilization of a Lithium Ion with a Silylene.

Herein, we report the stabilization of lithium-ion as the source of lithium to use as a trans-metalation reagent [{PhC(Nt Bu)2 Si(t Bu)Li}2 I(t BuN)2 CPh] (1). The reaction of 3 equivalents of the LSit Bu (L=PhC(Nt Bu)2 ) and lithium iodide at low temperature leads to a silylene stabilized lithium-ion with an additional coordination of amidinate ligand. Compound 1 shows two four membered and one six membered ring as confirmed by QTAIM calculations. Whereas the reaction of the LSiCl with 1.5 equivalents of carbodiimide (CyN)2 C at room temperature affords compound [PhC(Nt Bu)2 Si(Cl)(NCy)2 NCy] (2) with the CN2 SiN2 C skeleton containing silicon as a central atom. Both the compounds were fully characterized by NMR, mass spectrometry, X-ray crystallographic analysis, and quantum mechanical calculations.

[2+4] Cycloaddition Product of an Amidinate Substituted Dialumene with Toluene.

Reduction of LAlI2 (L=PhC(Ni Pr2 C6 H3 )2 ) with two equivalents of KC8 in toluene affords the [2+4]cycloaddition product of a dialumene with toluene. The mechanism for the formation of product complex was investigated using density functional theory (DFT) methods.

Compounds with Alternating Single and Double Bonds of Antimony and Silicon; Isoelectronic to Ethane-1,2-diimine.

We present an approach for preparing chain-type unsaturated molecules with low oxidation state Si(I) and Sb(I) supported by amidinato ligands that exploit to generate heavy analogues of ethane 1,2-diimine. The reduction of antimony dihalide (R-SbCl2) with KC8 in the presence of silylene chloride afforded L─(Cl)Si═Sb─Tip (1) and L(Cl)Si═Sb─TerPh (2), respectively. Compounds 1 and 2 further undergo reduction with KC8 to produce Tip─Sb═LSi─LSi═Sb─Tip (3) and TerPh─Sb═LSi─LSi═Sb─TerPh (4). The solid-state structures and DFT studies show that all compounds have σ-type lone pairs at each Sb atom. It forms a strong pseudo-π-bond with Si. The pseudo-π-bond is formed by the hyperconjugative donation of the π-type lone pair at Sb to the Si-N σ* MO. The quantum mechanical studies indicate that compounds 3 and 4 has delocalized pseudo-π-MOs arising from hyperconjugative interactions. Hence, 1 and 2 can be considered as isoelectronic to imine, while 3 and 4 are isoelectronic to ethane-1,2-diimine. The proton affinity studies indicate that the pseudo-π-bond resulting from the hyperconjugative interaction is more reactive than the σ-type lone pair.

A Neutral Borylene and its Conversion to a Radical by Selective Hydrogen Transfer.

A successful selective reduction of X2B-Tip (Tip = 1,3,5-iPr3-C6H2, X = I, Br) with KC8 and Mg metal, respectively, in the presence of a hybrid ligand (C6H4(PPh2)LSi) leads to a stable low-valent five-membered ring as a boryl radical [C6H4(PPh2)LSiBTip][Br] (1) and neutral borylene [C6H4(PPh2)LSiBTip] (2). Compound 2 reacts with 1,4-cyclohexadiene, resulting in hydrogen abstraction to afford the radical [C6H4(PPh2)LSiB(H)Tip] (3). Quantum chemical studies reveal that compound 1 is a B-centered radical, and compound 2 is a phosphane and silylene stabilized neutral borylene in a trigonal planar environment, whereas compound 3 is an amidinate-centered radical. Although compounds 1 and 2 are stabilized by hyperconjugation and π-conjugation, they display high H-abstraction energy and basicity, respectively.

Linear and Bent Cp*2 Si: Reversible Phase Transition of a Key Molecule.

The solid-state structure of decamethylsilicocene Cp*2 Si with a bent and a linear molecule in the same unit cell was so far considered an exception in relation to the structures of its all-bent heavier analogues Cp*2 E with E=Ge, Sn, Pb. Here, we present the solution to this conundrum by reporting a low-temperature phase, where all three symmetrically independent molecules are present in a bent formation. This reversible enantiotropic phase transition occurs in the temperature range between 80 K and 130 K and provides a rationale for the unexpected linear molecule based in entropy beyond hand-waving explanations such as electronic reasons or packing effects.

Alkali Metal Based Triimidosulfite Cages as Versatile Precursors for Single-Molecule Magnets.

Based on the potassium [{S(tBuN)2 (tBuNH)}2 K3 (tmeda)-K3 {(HNtBu)(NtBu)2 S}2 ] (1) and sodium precursors [S(tBuN)3 (thf)3 -Na3 SNa3 (thf)3 (NtBu)3 S] (2), [S(tBuN)3 (thf)3 Na3 {(HNtBu)(NtBu)2 S}] (3) and [(tmeda)3 S-{Na3 (NtBu)3 S}2 ] (4) the syntheses and magnetic properties of three mixed metal triimidosulfite based alkali-lanthanide-metal-cages [(tBuNH)Dy{K(0.5tmeda)}2 {(NtBu)3 S}2 ]n (5) and [ClLn{Na(thf)}2 {(NtBu)3 S}2 ] with Ln=Dy (6), Er (7) are reported. The corresponding potassium (1) and sodium (2-4) based cages are characterized through XRD and NMR experiments. Preventing lithium chloride co-complexation led to a significant increase of SMM performance to previously reported sulfur-nitrogen ligands. The subsequent DyIII -complexes 5 and 6 display slow relaxation of magnetization at zero field, with relaxation barriers U=77.0 cm-1 for 5, 512.9 and 316.3 cm-1 for 6, respectively. Significantly, the latter complex 6 also exhibits a butterfly-shaped hysteresis up to 7 K.

A Carbene-Stabilized Boryl-Phosphinidene.

Herein, the synthesis and characterization of the carbene-stabilized boryl phosphinidenes 1-3 are reported. Compounds 1-3 are obtained by reacting Me-cAAC=PK (Me2 -cAAC=dimethyl cyclic(alkyl)(amino)carbene) and dihaloaryl borane in toluene. All three compounds were characterized by X-ray crystallography. Quantum mechanical studies indicated that these compounds have two lone pairs on the P center viz., an σ-type lone pair and a "hidden" π-type lone pair. Hence, these compounds can act as double Lewis bases, and the basicity of the π-type lone pair is higher than the σ-type lone pair.

A Sodium Sodate as Precursor for Lanthanide Bis(4-R-benzoxazol-2-yl)methanide Single-Molecule Magnets.

From the sodium sodate precursor [(Na(thf)6][Na{(4-Me-NCOC6H3)2CH}2] (1) three isostructural dinuclear lanthanide complexes [(µ-Cl)LnIII{(4-MeNCOC6H3)2CH}2]2 with Ln = Gd (2), Dy (3), and Er (4) based on the N,N'-chelating monoanionic bis(4-methylbenzoxazol-2-yl)methanide ligand (titled "Mebox") were synthesized and characterized by X-ray diffraction and magnetic measurements. The sodium precursor 1 was analyzed via X-ray diffraction and diffusion-ordered NMR spectroscopy experiments (DOSY-NMR) in order to investigate its aggregation in solution and the solid state. The sodium analog [(thf)3Na(NCOC6H4)2CH] (1') based on the bis(benzoxazol-2-yl)-methanide ligand (titled "box") was prepared and analyzed for comparison reasons. From the lanthanide derivatives 2-4, the DyIII complex 3 displays slow relaxation of magnetization at zero field, with a relaxation barrier of U = 315.7 cm-1. The coupling strength between the two lanthanide centers was estimated with the GdIII equivalent 2, giving a weak antiferromagnetic coupling of J = -0.035 cm-1.

Si-H···Se Chalcogen-Hydride Bond Quantified by Diffraction and Topological Analyses.

The Si-H···Se contact in 1-mesitylselanyl-8-(dimethylsilyl)naphthalene (1), which exhibits the spatial arrangement of a δ-agostic interaction from geometric considerations, was investigated. Is this just enforced by close 1,8-proximity or is this a favorable interaction? Charge density studies are best suited to investigate the exact origin of the interaction and to quantify the properties. Hence, they are most elucidating. High-resolution X-ray diffraction data of 1 were collected, and a multipole refinement followed by a topological analysis using Bader's quantum theory of atoms in molecules was employed. The resulting bond properties were set in relation to high-level computational parameters. The comparison to Si-H···[M] agostics, hydride bonding, chalcogen bonds, and charge-inverted hydrogen bonds qualified the Si-H···Se noncovalent interaction to be best classified as a chalcogen-hydride bond.

Insertion Reaction of Me3SiN3 with Bis(germylene).

Herein, we describe the redox reaction of bis(germylene) PhC(NtBu)2Ge-Ge(NtBu)2CPh with different equivalents of Me3SiN3 affording two distinct products. The reaction of Me3SiN3 with bis-germylene in a 1:1 molar ratio results in compound 1 at -78 °C; however, treatment of bis-germylene with a 2.1 equiv of Me3SiN3 at room temperature results in compound 2. The formation of 1 and 2 can be rationalized by two successive 3 + 1 cycloadditions of Me3SiN3 with the germanium center of bis(germylene) and N2 elimination. All of the compounds are well-characterized by various spectroscopic techniques and single-crystal X-ray structural analyses. Density functional theory (DFT) calculations suggest that compound 2 has a dicoordinated nitrogen atom, which is stabilized by hyperconjugative interactions, resulting in pseudo-germylimine moiety. However, the dicoordinated nitrogen atom shows high basicity as indicated by proton affinity values. These are rare examples of isolated products that show insertion as well as simultaneous redox properties of bis(germylene).

Isolation and Properties of the Long Elusive Deep Blue Soluble [K3 {(Nt Bu)3 S}2 ]. Cage Radical.

The reaction of potassium metal with sulfurtriimide S(Nt Bu)3 (II) gives the long elusive deep blue cage radical [K3 {(Nt Bu)3 S}2 ]. (1_K) that crystallizes at -35 °C from toluene solution. The subsequent physical characterization via X-ray structure analysis, UV/Vis-, and EPR spectroscopy from solution reveals the existence of one unpaired electron delocalized within the whole cage, i.e. coupling with the six nitrogen atoms, as well as the three potassium atoms caped by the two SN3 ligands. The present X-ray structure analysis further supports previous assumptions made on the parent compound 1_Li obtained from [Li4 {(Nt Bu)3 S}2 ] (I) and finally elucidates the structural arrangement of the SN3 caps and alkali metals in such radical cage species.