RESUMO
The reaction of [(C(5)Me(5))Ir(Solvent)(3)][BF(4)](2) (1) with (2,5-dimethoxy-4,6-dimethyl-1,3-xylylene)-15 crown-4 (2) affords the metalated crown-ether complex [(eta(5)-C(5)Me(5))Ir(eta(6)-C(18)H(28)O(6))][BF(4)](2) (3) in 88% yield. Complex 3 undergoes a facile Me-O bond cleavage to give the related semiquinone form of the metalated crown-ether [(eta(5)-C(5)Me(5))Ir(eta(5)-C(17)H(25)O(6))][BF(4)] (4). A single-crystal X-ray structure determination of complex 4 is reported. Complex 4 crystallizes in the monoclinic space group P2(1)/m with a = 8.187(5) Å, b = 17.193(4) Å, and c = 10.900(3) Å, alpha = 90 degrees, beta = 109.68(1) degrees, gamma = 90 degrees, and Z = 2. The structure provides us with valuable information about the nature of the eta(5)-semiquinone form of the metalated crown-ether and reveals that, surprisingly, the Me-O unit close to the crown chain is the one that undergoes hydrolysis. A rationale consistent with the experimental results is advanced.
RESUMO
Four new saponins were isolated from the alcoholic extract of the bark of Cylicodiscus gabunensis by means of flash chromatography. They were characterized on the basis of spectral and chemical data as 3-O-beta-[alpha-L-arabinopyranosyl (1----2),alpha-L-arabinopyranosyl(1----3),beta-D-glucopyranosyl(1- ---)] maslinic acid-28-[beta-D-glucopyranosyl(1----6),beta-D-glucopyranosyl(1----2),alp ha-L- rhamnopyranosyl(1----)] ester; 3-O-beta-[alpha-L-arabinopyranosyl(1----2),alpha-L-arabinopyran osyl (1----3),beta-D-glucopyranosyl(1----)]maslinic acid-28-[beta-D-glucopyranosyl(1----2),alpha-L-rhamnopyranosyl(1----)] ester, 3-O-beta-[alpha-L-arabinopyranosyl(1----2),alpha-L-arabinopyran osyl (1----3),beta-D-glucopyranosyl(1----)]maslinic acid and 3-O-beta(alpha-L-arabinopyranosyl(1----3),beta-D-glucopyranosyl (1----)] cylicodiscic acid.
