Lydia Karmazin

Normal-to-Abnormal NHC Rearrangement of Al(III) , Ga(III) , and In(III) Trialkyl Complexes: Scope, Mechanism, Reactivity Studies, and H2 Activation.

The present contribution reports experimental and theoretical mechanistic investigations on a normal-to-abnormal (C2-to-C4-bonded) NHC rearrangement processes occurring with bulky group 13 metal NHC adducts, including the scope of such a reactivity for Al compounds. The sterically congested adducts (nItBu)MMe3 (nItBu=1,3-di-tert-butylimidazol-2-ylidene; M=Al, Ga, In; 1 a-c) readily rearrange to quantitatively afford the corresponding C4-bonded complexes (aItBu)MMe3 (4 a-c), a reaction that may be promoted by THF. Thorough experimental data and DFT calculations were performed on the nNHC-to-aNHC process converting the Al-nNHC (1 a) to its aNHC analogue 4 a. A nItBu/aItBu isomerization is proposed to account for the formation of the thermodynamic product 4 a through reaction of transient aItBu with THF-AlMe3 . The reaction of benzophenone with (nItBu)AlMe3 afforded the zwitterionic species (aItBu)(CPh2 -O-AlMe3 ) (6), reflecting the unusual reactivity that such bulky adducts may display. Interestingly, the nItBu/Al(iBu)3 Lewis pair behaves like a frustrated Lewis pair (FLP) since it readily reacts with H2 under mild conditions. This may open the way to future reactivity developments involving commonly used trialkylaluminum precursors.

A Ca2+‐, Mg2+‐, and Zn2+‐Based Dendritic Contractile Nanodevice with Two pH‐Dependent Motional Functions

A contractile dendritic motional device is reported where metal ions with biological importance--Ca(2+) (the main regulatory and signaling species of the natural muscles), Mg(2+), and Zn(2+)--initiate two kinds of motional functions. The first motional function is the metal-ion-induced contraction of a linear strand into a Z-shaped dinuclear complex, and the second one is the change of the height of Z-shaped complexes via transmetalation. By means of the pH-dependent counterligand tren, the two motional features of the machine can depend on alternate additions of acid and base. An optical response is associated with the conversion of the linear form (which is yellow) into the metalated Z-shaped one (which is red).

Crystal structure of 1,1′-{(pentane-1,5-di­yl)bis[(aza­niumylyl­idene)methanylyl­idene]}bis(naphthalen-2-olate)

The whole molecule of the title Schiff base is generated by twofold rotational symmetry. It crystallizes as a bis-zwitterion, and there are two intramolecular N—H⋯O hydrogen bonds present. In the crystal, molecules are linked by pairs of C—H⋯O hydrogen bonds forming ribbons propagating along [001].

Heterogeneous microwave-assisted Ullmann type methodology for synthesis of rigid-core ionic liquid crystals

We present an efficient Ullmann-type synthesis methodology enabling the preparation of imidazolium compounds with an extended aromatic core in three steps. This procedure begins with a microwave-assisted, heterogeneously catalysed cross-coupling reaction in the presence of Cu(II)-doped NaY zeolite to obtain imidazole-aromatic derivatives directly in good yield. The innovation is that this reaction does not require solvent, ligand or an inert atmosphere. Subsequently, these derivatives have been alkylated with bromoalkanes and the bromide of the imidazolium products exchanged for [BF4]− or [PF6]− anions. We have studied the influence of the methyl group (inductive effect) on the aromatic unit during the coupling reaction as well as its impact on different arrangements in the crystalline state. We have been able to extend this synthesis to ionic liquid crystal compounds which display lamellar self-organization (smectic A). The mesomorphic behavior and phase transition temperatures were investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS).

Tuning crystallochromism in diketopyrrolopyrrole-co-thieno[3,2-b]thiophene derivatives by the architecture of their alkyl side chains

Two diketopyrrolopyrrole-co-thieno[3,2-b]thiophene derivatives substituted with either branched ethylhexyl (TTDPP-EH) or linear hexyl side chains (TTDPP-C6) have been synthesized. The impact of the side chain architecture on the structure and optical properties has been evaluated. TTDPP molecules crystallize in triclinic unit cells observed in both single crystals and in thin films. The most striking difference between the two compounds is the packing of the molecules. For TTDPP-EH, pairs of molecules overlap only at their thienothiophene (TT) ring tips leading to a weak excitonic coupling of the J-type character. In contrast, TTDPP-C6 molecules stack in a 1D columnar structure with extended molecular overlapping. A transverse displacement of the molecules along their molecular axis allows a partial overlap of electron-rich TT and electron-poor DPP units. This leads to a stronger excitonic coupling with apparent coexistence of H- and J-like absorption features. Interestingly, both single crystals and oriented thin films change color with light polarization. This sensitivity to light polarization is related to the presence of two different excitonic couplings within TTDPP-C6.

Entrapment of THF-stabilized Iridacyclic Ir(III)-“Silylenes” from Double H-Si Bond Activation and H2 Elimination

The reaction of H3 SiR (R=Ph, nBu) with cationic η5 -C5 Me5 - (Cp*) and benzo[h]quinolinyl-based iridacycle [1 b]+ gives rise to new [(IrH)→SiRH2 ]+ adducts. In the presence of THF these adducts readily undergo elimination of H2 gas at subambient temperature to form THF-stabilized metallacyclic IrIII silylene complexes, which were characterized in situ by NMR spectroscopy, trapped in minute amounts by reactive crystallization, and structurally characterized by XRD. Theoretical investigations (static DFT-D reaction-energy profiling, ETS-NOCV) support the promoting role of THF in the H2 elimination step and the consolidation of the Ir-to-Si interaction in the spontaneous (ΔG<0) formation of Ir silylenes in the presence of THF. Mechanistic insights indicate that the Ir silylene species arising from the [1 b]+ /phenylsilane system are relevant catalytic species in the hydrodefluorination of fluoroalkanes.

CCDC 1569735: Experimental Crystal Structure Determination

Related Article: Fethi Elaieb, David Semeril, Claude Bauder, Dominique Matt, Corinne Bailly, Lydia Karmazin|2018|Polyhedron|139|172|doi:10.1016/j.poly.2017.10.020

CCDC 1569736: Experimental Crystal Structure Determination

Related Article: Fethi Elaieb, David Semeril, Claude Bauder, Dominique Matt, Corinne Bailly, Lydia Karmazin|2018|Polyhedron|139|172|doi:10.1016/j.poly.2017.10.020