Structural studies on encapsulation of tetrahedral and octahedral anions by a protonated octaaminocryptand cage

• I. Ravikumar,
• P. S. Lakshminarayanan,
• E. Suresh and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2009, 5, No. 41, doi:10.3762/bjoc.5.41

• encapsulation of one perchlorate, hydrogen sulfate and hexafluorosilicate, respectively inside the cage of L1 in their protonated states. Further, detailed structural analysis on complex 1 reveals that the hexaprotonated L1 encapsulates a perchlorate via two N–H···O and five O–H···O hydrogen bonds from

• C–H···F hydrogen bonds with [H8L1]8+. In the cases of complexes 2 and 3, the cryptand L1 in octaprotonated state shows monotopic encapsulation of the guest and the final conformation of these receptors is spherical in nature compared to the elongated shape of hexaprotonated state of L1 in complex 1

• incorporated in a suitable ligand topology make them attractive receptors for anions [1][2][3][4]. Azamacropolycycles L1 and L2 (Figure 1) have shown encapsulation of different anions in their protonated states [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. For example, azamacropolycycle L1 (Figure 1

An exceptional P-H phosphonite: Biphenyl- 2,2'-bisfenchylchlorophosphite and derived ligands (BIFOPs) in enantioselective copper- catalyzed 1,4-additions

• T. Kop-Weiershausen,
• J. Lex,
• J.-M. Neudörfl and
• B. Goldfuss

Beilstein J. Org. Chem. 2005, 1, No. 6, doi:10.1186/1860-5397-1-6

• , exhibit slightly different degrees of pyramidality, as it is measured by angle sums (planarity) from 300° to 309° (Table 2, Scheme 4). The degree of encapsulation of the phosphorus atoms by the fenchane units is measured by the distance (d) of the phosphorus atoms to the center of the biaryl axes (C1-C1

• ', Scheme 4). The tightest encapsulation and fenchane embedding of phosphorus atoms is apparent for the halophosphites BIFOP-Cl (1, 2.471 Å) and BIFOP-Br (2, 2.476 Å, Table 2), explaining their unusual low reactivity (Table 1). Cu-catalyzed, enantioselecitve 1,4-additions of diethylzinc to 2-cyclohexene-1