Hideshi Iki

Selective functionalization of calix[4]arenes via tricarbonylchromium complexes

Abstract Tricarbonylchromium complexes of 25,26,27,28-tetrapropoxycalix[4]arene conformers (14Pr) were synthesized. Since the benzene ring is activated through complexation with Cr(CO)3, the functional groups (e.g. [sbnd]D, [sbnd]CH3, and [sbnd]CHO) could be selectively introduced into the Cr(CO)3-complexed benzene ring. The substitution reaction occurred mainly at the p-position. The para selectivity was attributed to the steric crowding being relatively lower than that around the meta and benzyl position. This view was supported by the X-ray crystallographic study of 1,3-alternate-14Pr·(CO)3. This is a novel and general methodology for selective introduction of functional groups into calix[n]arenes.

X-ray crystallographic studies of a Mn(II)-bridged biscalix[4]arene with a large inner cavity

Abstract A complex isolated from a mixture of tetrasodium 5,11,17,23-tetra-sulfonatocalix[4]arene-25,26,27,28-tetrol and Mn(II) has been analyzed by X-ray crystallography. The crystal packing diagram featured a clay-like bilayer structure as reported previously for the analogous crystals. Interestingly, Mn(II) ions present in the hydrophilic layer cross-link two hydrophobic layers through coordination to the sulfonato groups. Because of this complex formation the repeat unit of the layer (12.1 A) is shorter than those for analogous systems (13.7 –15.0 A). The structure features a Mn(II)-bridged biscalix[4]arene with a large inner cavity. X-Ray crystallographic and ESR spectral data show that Mn(II) ions adopt a distorted octahedral coordination geometry with two sulfonato groups occupying the cis coordination. This is a novel coordination mode for a metal-bridged biscalix[4]arene in the solid state.

Thiadiphosphetane disulfide as a metal extractant which shows high Ag+ selectivity

It was shown that cis-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,2,4-thiadiphosphetane 2,4-disulfide (1) acts as an excellent Ag+-selective extractant. Two-phase solvent-extraction and spectral examination with 1H and 31P NMR established that 1 forms a 1:1 complex with Ag+ using the P(=S)-S-P(=S) linkage designed in the rigid four-membered ring.

X-Ray Crystallographic Studies of Tricarbonylchromium Complexes of Calix[4]arene Conformers: On an Unusual Conformation which Appears in Cone Conformers

The structures of three arene-tricarbonylchromium complexes prepared from cone and 1,3-alternate-25, 26,27,28-tetrapropoxycalix[4]arene(1) and Cr(CO)6 were determined by single crystal X-ray studies. Crystal data for 1,3-alternate-1·Cr(CO)3 are space groupP21/a,a=19.496(3)A,b=11.118(2)A,c=19.121(2)A, β=109.95°(1) andV=3895A3. The structure was refined toRw=0.068. Crystal data for cone-1·Cr(CO)3 are space groupP21/a,a=21.457(4)A,b=12.184(1)A,c=14.816(2)A, β=91.61°(1) andV=3872A3. The structure was refined toRw=0.077. Crystal data for cone-1·2Cr(CO)3 are space groupP21/a,a=18.019(3)A,b=41.347(4)A,c=11.743(2)A, β=97.39°(1) andV=8676A3. The single crystal included two similar but slightly different structures but the data were successfully refined toRw=0.092. The structure of 1,3-alternate-1·Cr(CO)3 differs only slightly from that of the regular 1,3-alternate calix[4]arene. In contrast, cone-1·Cr(CO)3 and cone-1·2Cr(CO)3 show an unusual conformation with a pair of faced gablelike roofs, which is considerbly distorted from the regular cone calix[4]arene. The origin of this distortion is discussed in combination with the spectral studies.

Syntheses and spectral characterizations of tricarbonylchromium complexes of calix[4]arenes

The 1:1 arene–tricarbonylchromium complexes were synthesized for the first time from four conformational isomers of 25,26,27,28-tetra propoxycaIix [4]arene (14Pr) and Cr(CO)6. The 1:2, 1:3 and 1:4 complexes of cone-14Pr were also synthesized by increasing the ratio of Cr(CO)6 against cone-14Pr. The 1:2 complex was a mixture of two compounds, which were identified as distal and proximal isomers of cone-14Pr·2Cr(CO)3. The relative stability of the 1:1 complex was estimated via its oxidation by CuCl2. The pseudo-first-order rate constants appeared to be in the order of 1,3-alternate-14Pr > 1,2-alternate-14Pr > cone-14Pr > 2,6-dimethylanisole. The results indicate that the 14Pr·Cr(CO)3 complexes are less stable than the corresponding monomeric complex. The 1:1 complexes with partial-cone-14Pr and 1,2-alternate-14Pr were demonstrated to be a pair of racemates by 1H NMR spectroscopy using a chiral shift reagent (Pirkles reagent).

Synthesis and spectral characterization of tricarbonylchromium complexes of calix[4]arene conformers

Arene–tricarbonylchromium complexes were synthesized for the first time from cone, 1,2-alternate and 1,3-alternate conformers of 25,26,27,28-tetrapropoxycalix[4]arene.