David Specklin

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.

Mononuclear and dinuclear complexes of manganese(III) and Iron(III) supported by 2-salicyloylhydrazono-1,3-dithiane ligand: synthesis, characterization and magnetic properties

The coordination chemistry of 2-salicyloylhydrazono-1,3-dithiane (H2L) was studied with manganese and iron ions. The following complexes have been isolated as crystalline materials, and their crystal structures have been determined by single crystal X-Ray crystallography: MnIII(acac)(HL)2 (1) (acac = acetylacetonate), MnIII(HL)3·CH2Cl2 (2), FeIII(HL)3·2CHCl3 (3), FeII(H2L)2Cl2·2CH3OH (4), FeIII2(μ-OMe)2(HL)4·0.5CH3OH (5), FeIII2(μ-O) (HL)4·3CH2Cl2 (6). All attempts to synthesize the dinuclear μ-methoxo complex [MnIII2(μ-OMe)2(HL)4] have so far failed, even when the procedure used in the case of 2-salicyloylhydrazono-1,3-dithiolane (H2L′) ligand, which worked very efficiently, was employed. The new iron dinuclear μ-methoxo complex (5) presented in this study shows antiferromagnetic intramolecular coupling (J = −21.1 cm−1), which is in agreement with the theoretical study proposed previously for its manganese analogue.

Accessing Two-Coordinate ZnII Organocations by NHC Coordination: Synthesis, Structure, and Use as π-Lewis Acids in Alkene, Alkyne, and CO2 Hydrosilylation

Discrete two-coordinate ZnII organocations of the type (NHC)Zn-R+ are reported, thanks to NHC stabilization. In preliminary reactivity studies, such entities, which are direct cationic analogues of long-known ZnR2 species, act as effective and tunable π-Lewis acid catalysts in alkene, alkyne, and CO2 hydrosilylation.

Bifunctional Squaramides as Organocatalysts for Lactide Polymerization: Catalytic Performance and Comparison with Monofunctional Analogues

Amine‐functionalized squaramides 1 and 2 were prepared and shown to be suitable polymerization organocatalysts for the controlled ring‐opening polymerization (ROP) of l‐lactide (l‐LA) in the presence of an alcohol source such as BnOH (which acts as an initiator) to afford chain‐length‐controlled and narrow‐dispersion poly(l‐lactide) (PLLA) under mild reaction conditions. The ROP experimental and polymer analysis data are consistent with the action of 1 and 2 as bifunctional hydrogen‐bonding (HB) catalysts that are able to activate both the lactide monomer and initiator BnOH thanks to their dual HB acceptor and donor properties. As a comparison, aminosquaramide 3, a direct analogue of 1 but a weaker HB donor because of the absence of electron‐withdrawing NH substituents, displays little lactide ROP activity, which highlights the key role of monomer activation through HB in the present systems. Unlike aminosquaramides 1 and 2, related monofunctional squaramides 4 and 5 are inactive in l‐LA ROP in the presence of BnOH, but the addition of NEt3, as an external HB acceptor, allows the ROP to proceed with the production of well‐defined PLLA. A cooperative dual activation with an activated monomer/activated chain‐end mechanism is most likely operative in the lactide ROP mediated by 1 and 2 in the presence of BnOH.