RESUMO
Controlled-potential electrochemical oxidation of cis-[Ru(ROCS2)2(PPh3)2] (R = Et, iPr) yielded corresponding Ru(III) complexes, and the crystal structures of cis-[Ru(ROCS2)2(PPh3)2] and trans-[Ru(ROCS2)2(PPh3)2](PF6) were determined. Both pairs of complexes exhibited almost identical coordination structures. The Ru-P distances in trans-[Ru(III)(ROCS2)2(PPh3)2](PF6) [2.436(3)-2.443(3) A] were significantly longer than those in cis-[Ru(II)(ROCS2)2(PPh3)2] [2.306(1)-2.315(2) A]: the smaller ionic radius of Ru(III) than that of Ru(II) stabilizes the trans conformation for the Ru(III) complex due to the steric requirement of bulky phosphine ligands while mutual trans influence by the phosphine ligands induces significant elongation of the Ru(III)-P bonds. Cyclic voltammograms of the cis-[Ru(ROCS2)2(PPh3)2] and trans-[Ru(ROCS2)2(PPh3)2]+ complexes in dichloromethane solution exhibited typical dual redox signals corresponding to the cis-[Ru(ROCS2)2(PPh3)2](+/0) (ca. +0.15 and +0.10 V vs ferrocenium/ferrocene couple for R = Et and iPr, respectively) and to trans-[Ru(ROCS2)2(PPh3)2](+/0) (-0.05 and -0.15 V vs ferrocenium/ferrocene for R = Et and iPr, respectively) couples. Analyses on the basis of the Nicholson and Shain's method revealed that the thermal disappearance rate of transient trans-[Ru(ROCS2)2(PPh3)2] was dependent on the concentration of PPh3 in the bulk: the rate constant for the intramolecular isomerization reaction of trans-[Ru(iPrOCS2)2(PPh3)2] was determined as 0.338 +/- 0.004 s(-1) at 298.3 K (deltaH* = 41.8 +/- 1.5 kJ mol(-1) and deltaS* = -114 +/- 7 J mol(-1) K(-1)), while the dissociation rate constant of coordinated PPh3 from the trans-[Ru(iPrOCS2)2(PPh3)2] species was estimated as 0.113 +/- 0.008 s(-1) at 298.3 K (deltaH* = 97.6 +/- 0.8 kJ mol(-1) and deltaS* = 64 +/- 3 J mol(-1) K(-1)), by monitoring the EC reaction (electrode reaction followed by chemical processes) at different concentrations of PPh3 in the bulk. It was found that the trans to cis isomerization reaction takes place via the partial dissociation of iPrOCS2(-) from Ru(II), contrary to the previous claim that it takes place by the twist mechanism.
RESUMO
The physical properties of N-[1-(4-methoxyphenyl)-1-methylethyl]-3-oxo-4-aza-5a-androst-1-ene-17beta-carboxamide (CS-891), a novel and orally effective testosterone 5-reductase inhibitor, were investigated by differential scanning calorimetry, powder X-ray diffraction at elevated temperature and single crystal X-ray crystallography. CS-891 was revealed to exist as two enantiotropic forms, a low-temperature stable form (Form A) and a high-temperature stable form (Form B) which reversibly transforms to Form A at around 58 degrees C. The effect of grinding temperature on the transition of CS-891 between the amorphous and the crystalline state during grinding of the eantiotropes was examined. Form A transformed into an amorphous form during the grinding process while the product temperature was kept below the transition temperature. On the other hand, when the product temperature during grinding reached above the transition temperature, Form A transformed into an amorphous form and some of the amorphous form converted back to Form B. Form B crystallized from the amorphous form was physically stable even at below the transition temperature. The amorphous form in equilibrium with Form B exhibited remarkable physical stability in comparison with the amorphous form obtained by continued grinding below the transition temperature.
