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A new fluorescence macrocyclic receptor based on the Zn(II) complex of a C 2 -terpyridine and a crown ether has been developed for molecular recognition of zwitterionic amino acids in water/DMF solution with remarkable selectivity towards l -aspartate ( K = 4.5 × 10 4 M −1 ) and l -cysteine ( K = 2.5 × 10 4 M −1 ).

New chiral C1-symmetric bidentate ligands, which possess two different nitrogen heterocycles, 1,3-thiazolyl, 1-methylimidazolyl or pyrazinyl and one pyridyl group, were prepared by Krohnke condensation in 36–59% overall yield. Stable Pd(II)-allyl and Cu(II) chloride complexes formed by some of the ligands were obtained in 60–65% yields. X-ray crystal structure analysis of a copper(II) complex having 1-methylimidazolyl group indicated that it is a μ-chloro bridge dimer. The Pd(II)-allyl complexes were found to be active catalysts in the asymmetric allylic substitution of 1,3-diphenylprop-2-enyl acetate. The best result observed was 85% e.e. and 99% isolated yield. In addition, the in situ generated Cu(OTf)2 complexes were found to be active catalysts in cyclopropanation of styrene with ethyl diazoacetate.

Chiral bidentate ligands 1-3, which contain a combination of thiazolyl and pyridyl donors units, were prepared. The syntheses are facile and being based on Krohnke condensation of a pinene derivative to form the pyridine ring. Modification at the 8-position of the tetrahydroquinoline ring can be carried out by alkylation reaction with 2a and 3a but not 1a. The structure of a copper(II) perchlo- rate complex of 1a was characterized with X-ray crystallography, which reveals the binding of the pyridyl-thiazole as a N-N donors at the copper center. The copper(I) thiazolyl-pyridine complexes prepared in situ are active catalysts in the enantioselective allylic oxidation of cyclohexene using tert-butyl perbenzoate as the oxidant. The isolated yields of the allylic benzoate were up to 98%, and enantioselec- tivity was up to 62% e.e. � 2005 Elsevier B.V. All rights reserved.

Iodo-(5,10,15,20-tetrakis(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl)porphyrinatorhodium(III), designated as [Rh(P*)(I)], was prepared and its catalytic activity in the asymmetric cyclopropanation of alkenes with ethyl diazoacetate (EDA) was examined. High catalyst turnovers (TON >103) and moderate enantioselectivities (up to 68% ee) were observed. However, the obtained trans/cis ratios are low. Competition experiments revealed that electron-donating substituents on styrene accelerate the cyclopropanations. The log(kX/kH) versus σ+ plot for substituted styrenes exhibits a good linearity with a small negative ρ+ value (−0.14). [Rh(P*)(I)] is also active in the intramolecular cyclopropanation of allyl diazoacetates. A comparison between rhodium and ruthenium porphyrin complexes was made.

Extensive investigations of asymmetric intermolecular cyclopropanation of terminal alkenes with diazoacetates catalyzed by ruthenium porphyrin [Ru(P*)(CO)(EtOH)] (1, H2P = 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene-9-yl]porphyrin) and the application of catalyst 1 to asymmetric intramolecular cyclopropanation of allylic or homoallylic diazoacetates are described. The intermolecular cyclopropanation of styrene and its derivatives with ethyl diazoacetate afforded the corresponding cyclopropyl esters in up to 98% ee with high trans/cis ratios of up to 36 and extremely high catalyst turnovers of up to 1.1 x 10(4). Examination of the effects of temperature, diazoacetate, solvent, and substituent in the intermolecular cyclopropanation reveals that (i) both enantioselectivity and trans selectivity increase with decreasing temperature, (ii) sterically encumbered diazoacetates N2CHCO2R, such as R = Bu(t), and donor solvents, such as diethyl ether and tetrahydrofuran, are beneficial to the trans selectivity, and (iii) electron-donating para substituents on styrene accelerate the cyclopropanations, with the log(k(X)/k(H)) vs sigma(+) plot for para-substituted styrenes p-X-C6H4CH=CH2 (X = MeO, Me, Cl, CF3) exhibiting good linearity with a small negative rho(+) value of -0.44 +/- 0.09. In the case of intramolecular cyclopropanation, complex 1 promoted the decomposition of a series of allylic diazoacetates to form the cyclopropyl lactones in up to 85% ee, contributing the first efficient metalloporphyrin catalyst for an asymmetric intramolecular cyclopropanation. Both the inter- and intramolecular cyclopropanations were proposed to proceed via a reactive chiral ruthenium carbene intermediate. The enantioselectivities in these processes were rationalized on the basis of the X-ray crystal structures of closely related stable chiral carbene complexes [Ru(P*)(CPh2)] (2) and [Ru(P*)(C(Ph)CO2CH2CH=CH2)] (3) obtained from reactions of complex 1 with N2CPh2 and N2C(Ph)CO2CH2CH=CH2, respectively.

Transport characteristics of single crystal bismuth films on Si(111)-7 × 7 are found to be metallic or insulating at temperatures below or above TC, respectively. The transition temperature TC decreases as the film thickness increases. By combining thickness dependence of the films resistivity, we find the insulating behaviour results from the states inside film, while the metallic behaviour originates from the interface states. We show that quantum size effect in a Bi film, such as the semimetal-to-semiconductor transition, is only observable at a temperature higher than TC.

Re(I) tricarbonyl bipyridine and terpyridine complexes catalyse stereospecific cyclopropanation of alkenes; high selectivity of cyclopropane vs coupling and an ee of 73% and 62% for cis- and trans-cyclopropanes of styrene respectively were achieved with the [Re(L)(CO)(3)(MeCN)]OTf complex (L = chiral C(2)-symmetric terpyridine ligand).