A Stable Neutral Compound with an Aluminum–Aluminum Double Bond

Homodinuclear multiple-bonded neutral Al compounds, aluminum analogues of alkenes, have been a notoriously difficult synthetic target over the past several decades. Herein, we report the isolation of a stable neutral compound featuring an AlAl double bond stabilized by N-heterocyclic carbenes. X-ray crystallographic and spectroscopic analyses demonstrate that the dialuminum entity possesses <i>trans</i>-planar geometry and an Al–Al bond length of 2.3943(16) Å, which is the shortest distance reported for a molecular dialuminum species. This new species reacts with ethylene and phenyl acetylene to give the [2+2] cycloaddition products. The structure and bonding were also investigated by detailed density functional theory calculations. These results clearly demonstrate the presence of an AlAl double bond in this molecule

A Stable Neutral Compound with an Aluminum–Aluminum Double Bond

Homodinuclear multiple-bonded neutral Al compounds, aluminum analogues of alkenes, have been a notoriously difficult synthetic target over the past several decades. Herein, we report the isolation of a stable neutral compound featuring an AlAl double bond stabilized by N-heterocyclic carbenes. X-ray crystallographic and spectroscopic analyses demonstrate that the dialuminum entity possesses <i>trans</i>-planar geometry and an Al–Al bond length of 2.3943(16) Å, which is the shortest distance reported for a molecular dialuminum species. This new species reacts with ethylene and phenyl acetylene to give the [2+2] cycloaddition products. The structure and bonding were also investigated by detailed density functional theory calculations. These results clearly demonstrate the presence of an AlAl double bond in this molecule

Structural Characterization and Photochemical Properties of Mono- and Bimetallic Cu-Mabiq Complexes

We present a series of monometallic ([Cu­(Mabiq)­OTf] (<b>1</b>) and [Cu­(Mabiq)] (<b>2</b>)) and bimetallic copper-Mabiq complexes ([Cu₂­(Mabiq)­(PPh₃)₂­(OTf)₂] (<b>3</b>) and [Cu₂­(Mabiq)­(PPh₃)₂]­PF₆ (<b>4</b>)). The latter compounds contain an additional Cu^I center that binds in a tetrahedral fashion to the external bipyrimidine nitrogens of the macrocyclic ligand. Compounds <b>3</b> and <b>4</b> represent the first examples of bimetallic transition metal Mabiq complexes, stable both in solution and in the solid state. The structural and electronic properties of compounds <b>1</b>–<b>4</b> were analyzed by means of X-ray crystallography, cyclic voltammetry, and spectroscopic methods. One-electron reduced <b>2</b> and <b>4</b> consist of a Cu^II ion coordinated by a Mabiq ligand radical, [Cu^II­(Mabiq^•)]. Thus, both bimetallic compounds are mixed-valent with respect to the copper oxidation states. Complexes <b>2</b> and <b>4</b> can be generated photochemically, upon irradiation of <b>1</b> or <b>3</b> with visible light in the presence of a sacrificial electron donor

Silicon and Oxygen’s Bond of Affection: An Acyclic Three-Coordinate Silanone and Its Transformation to an Iminosiloxysilylene

A long-term dream comes true: An acyclic, neutrally charged silanone at last! Here, we report on the first examples of isolable acyclic, neutral, three-coordinate silanones <b>2</b> with indefinite stability as solids and lifetimes in solution of up to 2 days. The electronic properties of the SiO bond were investigated via DFT calculations and revealed the π-donating <i>N</i>-heterocyclic imino (NHI) and σ-donating silyl groups as key factors for their enhanced stability. Besides initial reactivity studies of <b>2</b> toward CO₂ and methanol, different isomerization pathways depending on the silyl substitution pattern were found. For <b>2a</b> (R = TMS), a 1,3-silyl shift gave an intermediary disilene, which was trapped as unique NHC-disilene adduct <b>6</b>. For the more stable silanone <b>2b</b> (R = <i>t</i>-Bu), a selective transformation to the first reported room temperature stable, acyclic, two-coordinate <i>N</i>,<i>O</i>-silylene <b>7</b> exhibiting a fascinating siloxy ligand was observed. Both compounds were fully characterized experimentally and their bonding features were analyzed by theoretical calculations

Synthesis of Lewis Acidic, Aromatic Aminotroponiminate Zinc Complexes for the Ring-Opening Polymerization of Cyclic Esters

Three novel aminotroponiminate (ATI) zinc complexes <b>I</b>–<b>III</b> (<b>I</b> = [(Ph₂)­ATI]­Zn–N­(SiMe₃)₂, <b>II</b> = [(C₆H₃-2,6-C₂H₅/Ph)­ATI]­Zn–N­(SiMe₃)₂, and <b>III</b> = [(C₆H₃-2,6-CH­(CH₃)₂/Ph)­ATI]­Zn–N­(SiMe₃)₂) were synthesized and tested in the ring-opening polymerization of the lactones β-<i>rac</i>-butyrolactone (BBL) and <i>rac</i>-lactide (LA). The ligands, with two of them literature unknown, were readily obtained via a three-step synthesis from tropolone. Forming a five-membered metallacycle with zinc, the complexes were further structurally examined via single-crystal X-ray analysis and compared with that of the established, 6-ringed β-diiminate (BDI) complex <b>IV</b> ([CH­(CMeNPh)₂]­Zn–N­(SiMe₃)₂). The influence of the varying metallacycle ring size on the polymerization was evaluated. <i>In situ</i> IR measurements indicate a higher catalytic activity of the novel ATI complexes <b>I</b>–<b>III</b> for BBL compared with the BDI system <b>IV</b>. The activity and degree of control were further improved by an <i>in situ</i> generated alkoxy initiating group generated after the addition of 2-propanol. An enhanced initiator efficiency allowed the synthesis of polymers with controlled molecular weights and narrow polydispersities. Furthermore, <b>II</b> and <b>III</b> exhibited a high activity in the ring-opening polymerization of <i>rac</i>-LA. Hereby, reaction time and initiator efficiency could also be optimized at a higher temperature or by the addition of 2-propanol

High-Melting, Elastic Polypropylene: A One-Pot, One-Catalyst Strategy toward Propylene-Based Thermoplastic Elastomers

This contribution provides the simple one-pot, one-catalyst synthesis of high-melting (<i>T</i>_m ∼ 140 °C), high-molecular-weight, elastic polypropylene (^<i>e</i>PP) offering an excellent reversible deformation behavior. The produced propylene-based thermoplastic elastomers contain of ^<i>i</i>PP–^<i>a</i>PP block structures embedded in an amorphous polypropylene matrix which is enabled by the variable stereoselective behavior of ethylene-bridged fluorenylindenyl (EBFI) <i>ansa</i>-metallocene complexes. For the tailored synthesis of these high-melting ^<i>e</i>PPs the intricate interplay of various mechanisms, which collectively define the stereoregularity of the produced polypropylenes, was examined, and a decisive impact of different chelate ring conformers was elucidated. In this connection, the accurate adjustment of conformational interconversion with respect to the chain propagation and termination rate facilitated a directed switching between iso- and unselective polypropylene sequences in the catalytic production of highly temperature-stable, elastic polypropylene

Lone pair···π interactions on the stabilization of intra and intermolecular arrangements of coordination compounds with 2-methyl imidazole and benzimidazole derivatives

<p>Spectroscopic and single crystal X-ray diffraction studies of coordination compounds of Co^II, Ni^II, Zn^II, and Pd^II with phenylsulfonyl imidazole and benzimidazole derivatives (2-mfsiz, 2-mfsbz) were performed. The relevance of non-covalent interactions on the stabilization of intra and intermolecular arrangements in the ligands and their coordination compounds was investigated. The imidazole 2-mfsiz ligand presents two enantiomeric conformers, where the ethylphenylsulfone moiety stabilizes intermolecular lone pair···π (S–O···π_(phe)) and H···π contacts, while its tetrahedral coordination compounds, [M(2-mfsiz)₂X₂] (M²⁺ = Co, Ni, Zn; X = Cl, Br) showed intramolecular lone pair···π interactions (S–O···π_(iz)). On the other hand, compounds [Cu₂(2-mfsiz)₂(µ₂-AcO)₄] and <i>trans-</i>[Pd(2-mfsiz)₂Cl₂] do not present lone pair···π interactions due to the metal ion geometry (square base pyramidal or square planar), which leads to formation of π_(iz)···π_(phe) interactions. For the benzimidazole ligand 2-mfsbz, an intramolecular, H_(phe)···π_(bz) contact was observed, remaining in its tetrahedral and octahedral coordination compounds, [M(2-mfsbz)₂X₂] (M²⁺ = Co, Zn; X = Cl, Br, NO₃). This interaction limits the free rotation of the ethylphenylsulfone moiety for stabilization of an intermolecular lone pair···π interaction (S–O···π_(iz)). The dimeric [Zn₂(2-mfsiz)₂(µ²-AcO)₄] compound has a π_(bz)···π_(phe) contact. Theoretical calculations confirmed the non-covalent interactions in the ligands and their coordination compounds.</p