Diphosphines based on an inherently chiral calix[4]arene scaffold: synthesis and use in enantioselective catalysis

Abstract

C(O)NHCMe(Ph)H, 10) have been synthesised. The enantiomerically pure calixarenes 7, 8 and 10 having an AABC substitution pattern are inherently chiral. Reaction of the latter three diphosphines with [Pd(2-Me-allyl)(THF) 2 ]BF 4 (THF = tetrahydrofuran) afforded the chelate complexes [Pd(2-Me-allyl)(diphosphine)]BF 4 11-13, respectively, while reaction with [Rh(NBD)(THF) 2 ]BF 4 (NBD = norbornadiene) resulted in quantitative formation of the complexes [Rh(NBD)(diphosphine)]BF 4 14-16, respectively. As a result of allyl rotation, the palladium complexes 11-13 exist in solution as two interconverting species. These complexes efficiently catalyse the alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate, the turnovers being ca. 30 h Ϫ1 . Enantioselectivity was shown to depend on the size difference between the B and C substituents. Thus, while virtually no induction was observed with the chiral calixarene 10 bearing two identical substituents, ee's of 45% and 67% respectively were observed with 12 and 11, which have a more marked dissymmetry. Similar trends were observed in the catalytic hydrogenation of dimethyl itaconate with the rhodium complexes 14-16, leading to ee's of 48%, 25% and 0%, respectively. Related chiral calixarenes in which the two phosphine arms occupy proximal instead of distal phenolic positions were found to be considerably less effective in catalysis of both allylic alkylation and hydrogenation.

Tuning the Stoichiometry of Lanthanide Complexes with Calixarenes: Bimetallic Complexes with a Calix[6]arene Bearing Ether‐Amide Pendant Arms

“…Since the latter mechanism has been observed with O-substituted p-tert-butylcalix [6]arenes, [26] it is reasonable to assume that the lack of substitution on the phenol groups allows for rapid aromatic-through-the-annulus rotation and, hence, the apparent high symmetry observed is the result of fast interconversion between the different conformers. 4 indeed showed the compound adopting a cone conformation in solution, in which the four complexing arms are held together in closed proximity, thereby providing a suitable octadentate coordination site for lanthanide cations. [14] The X-ray crystal structure of the lutetium complex further showed that a water molecule was encapsulated in the cavity formed by the four dioxo-ethylene bridges (OϪC1ϪC2ϪO), with H-bonding interactions between this water molecule and the oxygen atoms.…”

“…The ether-amide substituent was designed so that it can act as a bidentate ligand forming a five-membered cycle upon coordination of its ether and amide functions to trivalent lanthanide ions Ln III . We have shown that A 4 bL 4 acts as an inorganic-organic receptor, encapsulating both a lanthanide ion and a solvent molecule. In addition, the crystal structure of the Lu III 1:1 complex shows the coordination cavity predisposed to further accommodate one water molecule hydrogen-bonded to the oxygen atoms of the phenol units, which rigidifies the induced cavity, and binds the metal ion.…”

“…[1,2] They are currently being used in the design of chemical sensors, [3] catalysts, [4] and selective ligands for the complexation of d [5] and f [6,7] metal ions, as well as for the self-assembly, through π-stacking, H-bonding or coordination interactions, of elaborate supramolecular structures. [8,9] As a consequence, many studies have aimed no bound water molecules, and the other one with two ligated water molecules.…”

Synthesis of the First Chiral, Functionalised‐Bridged Resorcinarenes in Asymmetric Catalysis: Evidence for Intracavity Asymmetric Catalysis

“…Matt has shown that a lower-rim, inherently chiral calixarene scaffold can be used in allylic alkylation (palladium) and hydrogenation (rhodium), though low ees were obtained. [4] Others have shown that cooperative effects may potentially be provided by supramolecular interactions involving the concave bowl. [5] However, a comprehensive picture has yet to emerge regarding application of directing effects in the bowl towards designing superior asymmetric catalysts for carrying out reactions rather than purely for recognition phenomenon.…”

Site-selective hexa-hetero-functionalization of α-cyclodextrin an archetypical C6-symmetric concave cycle

“…For instance a tridifferentiated C 4 resorcinarene, with three different groups, was synthesized en route to superbowl containers 28 . Tridifferentiated calix(4)arenes were also synthesized as racemic mixtures because of their inherent asymmetry [29][30][31] . In the realm of molecules of higher symmetry, C 6 calix(6)arenes with three 32,33 or even four 34 functionalities (tetradifferentiated) have also been described albeit inherently as racemic mixtures.…”