Expanded Mercaptocalixarenes: A New Kind of Macrocyclic Ligands for Stabilization of Polynuclear Thiolate Clusters.

The syntheses and properties of expanded 4-tert-butyl-mercaptocalix[4]arenes, in which the methylene linkers are replaced by -CH2 NRCH2 - or -CH2 NRCH2 - and -CH2 NRCH2 CH2 CH2 NRCH2 - units, are described. The new macrocycles were obtained in a step-wise manner, utilizing fully protected, i. e. S-alkylated, derivatives of the oxidation-sensitive thiophenols in the cyclisation steps. Reductive cleavage of the macrobicyclic or macrotricyclic intermediates (6, 7, 11) afforded the free thiophenols (H4 8, H4 9, and H4 12) in preparative yields as their hydrochloride salts. The protected proligands can exist in two conformations, resembling the "cone" and "1,3-alternate" conformations found for the parent calix[4]arenes. The free macrocycles do not show conformational isomerism, but are readily oxidized forming intramolecular disulfide linkages. Preliminary complexation experiments show that these expanded mercaptocalixarenes can serve as supporting ligands for tetranuclear thiolato clusters.

Kinetic control in the chiral recognition of three-bladed propellers.

The ion pair of the stereolabile C(3)-symmetric, i(+)o proton complex [1H](+) of diaza-macropentacycle 1 and the configurationally stable Delta-TRISPHAT ([Delta-3](-)) anion exists in the form of two diastereomers, namely, [Delta-(1.H)][Delta-3] and [Lambda-(1.H)][Delta-3], the ratio of which, in terms of diastereomeric excess (de) decreases in the order [D(8)]THF (28%)>CD(2)Cl(2) (22%)>CDCl(3) (20%)>[D(8)]toluene (16%)>C(6)D(6) (7%)>[D(6)]acetone (0%) at thermodynamic equilibrium. Except in the case of [D(6)]acetone, the latter is reached after a period of time that increases from 1 h ([D(8)]THF) to 24 h (CDCl(3)). Moreover, the initial value of the de of [1.H][Delta-3] in CDCl(3), before the thermodynamic equilibrium is reached, depends on the solvent in which the sample has been previously equilibrated (sample "history"). This property has been used to show that the crystals of [1.H][Delta-3] formed by slow evaporation of CH(2)Cl(2)/CH(3)OH mixtures had 100% de, which indicates that [1.H][Delta-3] has enjoyed a crystallization-induced asymmetric transformation. Structural studies in solution (NMR spectroscopy) and in the gas phase by calculations at the semiempirical PM6 level of theory suggest that the optically active anion is docked on the i(+) (endo) external side of the proton complex such that one of the aromatic rings of [Delta-3](-) is inserted into a groove of [1.H](+), a second aromatic ring being placed astride the outside i(+) pocket. Solvent polarity controls the thermodynamics of inversion of the [1.H](+) propeller. However, both polarity and basicity control its kinetics. Therefore, the rate-limiting steps correspond to the ion-pair separation/recombination and [1.H](+)/1 deprotonation/protonation processes, rather than the inversion of [1H](+), the latter being likely to take place in the deprotonated form (1).

The proton complex of a diaza-macropentacycle: structure, slow formation, and chirality induction by ion pairing with the optically active 1,1'-binaphthyl-2,2'-diyl phosphate anion.

The protonation of a sterically crowded [N2S6] macropentacycle (1) with 1 equiv of CF3SO3H in CDCl3 is slow and gives the singly (oo(+) [1 x H](+)) and doubly (o(+)o(+) [1 x 2H](2+)) protonated forms as kinetic products, the i(+)o form of [1 x H](+) being the thermodynamic product. i(+)o [1 x H](+) is C3 helically chiral in the solid state and in solution. The barrier to racemization (DeltaG(double dagger)) of the [1 x H](+) propeller is >71 kJ mol(-1). The ammonium proton is encapsulated in the tetrahedral coordination sphere provided by the endo (i) nitrogen bridgehead atom and the three proximal thioether sulfurs, which makes [1 x H](+) a proton complex. Use of the optically active acid (R)-(-)- or (S)-(+)-1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BNPH) in chloroform allowed us to induce a significant diastereomeric excess (24% de), which produced a detectable ICD. The de was decreased in acetone-d6 (10%), suggesting that the sense of chirality of [1 x H](+) is controlled by ion-pair interactions. Detailed NMR studies allowed us to locate the chiral anion on the endo side of [1 x H](+), in the cavity lined by endo t-Bu groups, and to establish that the rate of anion exchange in [1 x H][(S,R)-(+/-)-BNP] was higher than the rate of propeller inversion of [1 x H](+).

The in, out asymmetric pseudo-triple helical form of a D3h diaza-macropentacycle.

A sterically encumbered [N(2)S(6)] macropentacycle (5) related to diazamacrobicycles and cryptands has been synthesized in 53% yield by the [1+1] condensation reaction between functionalized macrocyclic and macrotricyclic precursors. A macrononacycle (18) resulting from the corresponding [2+2] condensation was isolated in 7% yield from the reaction mixture. Both compounds showed broad features in their room-temperature (1)H NMR spectra, but their maximal average symmetry (D(3h) and D(2h), respectively) was achieved at high temperature (380 K). At low temperature (200 K, CD(2)Cl(2) solution), the macropentacycle is "frozen" to a single asymmetric (C1) conformation on the (1)H NMR time scale, which has also the molecular structure observed in the solid state by X-ray crystallography: pseudo-triple helical ( not equalC(3)) shape, io (in, out) form resulting from the endo/exo configuration at the nitrogen bridgehead atoms, and similar orientations of the tosyl substituents. The solution dynamics of the molecule can be described by coupled bridgehead nitrogen inversion, triple helix symmetrization, and reversal of triple helix handedness, with DeltaGc = 54.2 kJ mol(-1) in CD(2)Cl(2) at 300 K. Adoption of the io form by macropentacycle 5 in the crystal and in solution at low-temperature most probably results from the steric crowding and strain introduced by the [15]ane-N(2)S(2) macrocyclic bridging subunits.

Simultaneous freezing of chirality and in-out conformation of a macropentacyclic cryptand by protonation.

Compound 1, a cryptand-derived macropentacycle, is a flexible molecule that encompasses many conformations (symmetrical, unsymmetrical, and chiral ones) depending on the observation temperature (VT 1H NMR). Selective monoprotonation of this molecule leads to a totally unsymmetrical, rigidly chiral species in solution (1H NMR). Helical chirality and in-out conformation of monoprotonated 1 are observed in the solid state by X-ray diffraction analysis, as well as the proton location. The latter is bound to the endo bridgehead nitrogen atom and involved in hydrogen-bonding interactions with the three closest sulfurs. Significant induction of chirality is triggered by reaction of 1 with the optically active (R)-(-)-1,1'-binaphthyl-2,2'-diylphosphoric acid. It proceeds with a maximum 24% diastereomeric excess, as shown by the splitting, in the 62:38 intensity ratio, of several 1H NMR signals. These correspond to the two indistinguishable diastereomeric ion pairs: (Lambda-[1-H])((R)-(-)-BNP) and (Delta-[1-H])((R)-(-)-BNP).