α-Halogenoacetanilides as hydrogen-bonding organocatalysts that activate carbonyl bonds: fluorine versus chlorine and bromine.

α-Halogenoacetanilides (X=F, Cl, Br) were examined as H-bonding organocatalysts designed for the double activation of CO bonds through NH and CH donor groups. Depending on the halide substituents, the double H-bond involved a nonconventional CH⋅⋅⋅O interaction with either a HCXn (n=1-2, X=Cl, Br) or a HCAr bond (X=F), as shown in the solid-state crystal structures and by molecular modeling. In addition, the catalytic properties of α-halogenoacetanilides were evaluated in the ring-opening polymerization of lactide, in the presence of a tertiary amine as cocatalyst.

Allosteric effects in binuclear homo- and heterometallic triple-stranded lanthanide podates.

This work illustrates a simple approach for deciphering and exploiting the various free energy contributions to the global complexation process leading to the binuclear triple-stranded podates [Ln(2)(L9)](6+) (Ln is a trivalent lanthanide). Despite the larger microscopic affinities exhibited by the binding sites for small Ln(3+), the stability constants measured for [Ln(2)(L9)](6+) decrease along the lanthanide series; a phenomenon which can be ascribed to the severe enthalpic penalty accompanying the intramolecular cyclization around small Ln(III), combined with increasing anticooperative allosteric interligand interactions. Altogether, the microscopic thermodynamic characteristics predict β(1,1,1)(La,Lu,L9)/β(1,1,1)(Lu,La,L9) = 145 for the ratio of the formation constants of the target heterobimetallic [LaLu(L9)](6+) and [LuLa(L9)](6+) microspecies, a value in line with the quantitative preparation (>90%) of [LaLu(L9)](6+) at millimolar concentrations.

(Thio)Amidoindoles and (thio)amidobenzimidazoles: an investigation of their hydrogen-bonding and organocatalytic properties in the ring-opening polymerization of lactide.

The mechanism of the ring-opening polymerization (ROP) of lactide catalyzed by two partner hydrogen-bonding organocatalysts was explored. New amidoindoles 4 a,c, thioamidoindoles 4 b,d, amidobenzimidazoles 5 a,c, and thioamidobenzimidazoles 5 b,c were synthesized and used as activators of the monomer. In the solid state and in solution, compounds 4 and 5 showed a propensity for self-association, which was evaluated.

Ring-opening polymerization of L-lactide efficiently triggered by an amido-indole. X-ray structure of a complex between L-lactide and the hydrogen-bonding organocatalyst.

N-(3,5-Bis(trifluoromethyl)phenyl)-1H-indole-2-carboxamide 1e is an efficient hydrogen-bonding organocatalyst for the ring-opening polymerization of l-lactide. This new catalytic species does control the dispersity (1.08) and molecular weight (3460 g/mol vs 3064 in theory) of the poly(l-lactides) prepared in 2 h.

Effective concentration as a tool for quantitatively addressing preorganization in multicomponent assemblies: application to the selective complexation of lanthanide cations.

The beneficial entropic effect, which may be expected from the connection of three tridentate binding units to a strain-free covalent tripod for complexing nine-coordinate cations (Mz+ = Ca2+, La3+, Eu3+, Lu3+), is quantitatively analyzed by using a simple thermodynamic additive model. The switch from pure intermolecular binding processes, characterizing the formation of the triple-helical complexes [M(L2)3]z+, to a combination of inter- and intramolecular complexation events in [M(L8)]z+ shows that the ideal structural fit observed in [M(L8)]z+ indeed masks large energetic constraints. This limitation is evidenced by the faint effective concentrations, ceff, which control the intramolecular ring-closing reactions operating in [M(L8)]z+.

Isolation and characterization of the first circular single-stranded polymetallic lanthanide-containing helicate.

A thorough examination of the disassembly of bimetallic triple-stranded lanthanide helicates [Ln2(Li)3]6+ (stoichiometry S = m/n = 2/3 = 0.67, global complexity GC = m + n = 2 + 3 = 5) in excess of metals shows the competitive formation of standard linear bimetallic complexes [Ln2(Li)2]6+ (S= 1.0, GC = 4), and circular trimetallic single-stranded helicates [Ln3(Li)3]9+ (S= 1.

A novel extended covalent tripod for assembling nine-coordinate lanthanide(III) podates: a delicate balance between flexibility and rigidity.

The introduction of long semirigid spacers between the capping carbon atom of the tripod and the unsymmetrical tridentate binding units provides the novel, extended covalent podand tris-[2-[2-(6-diethylcarbamoylpyridin-2-yl)-1-ethyl-1H-benzoimidazol-5-yl-methoxy]ethyl]methane (L(15)). Reaction of L(15) with lanthanide(III) in acetonitrile produces stable podates [Ln(L(15))](3+) (Ln=La-Lu) in which three tridentate binding units are facially organized. These wrap around the nine-coordinate pseudo-tricapped trigonal-prismatic metal ions.