Epoxide ring opening in a zinc(II) complex in water without any Lewis acid catalyst: Formation of only one diastereomer out of 23

Abstract The epoxide ring in 5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L) opens up in its reaction with 4-methylaniline and 4-methoxyaniline in water in equimolar proportion at room temperature without any Lewis acid catalyst to give a monohydrate of 6-(4-methyl-phenylamino)-5,6-dihydro-1,10-phenanthrolin-5-ol (L′·H 2 O) and 6-(4-methoxyphenyl-amino)-5,6-dihydro-1,10-phenanthrolin-5-ol (L″) respectively. Reaction time decreases from 72 to 14 h in boiling water. But the yields become less. Reaction of L with Zn(ClO 4 ) 2 ·6H 2 O in methanol in 3:1 molar ratio at room temperature affords white [ZnL 3 ](ClO 4 ) 2 ·H 2 O. The X-ray crystal structure of the acetonitrile solvate [ZnL 3 ](ClO 4 ) 2 ·MeCN has been determined which shows that the metal has a distorted octahedral N 6 coordination sphere. [ZnL 3 ](ClO 4 ) 2 ·2H 2 O reacts with 4-methylaniline and 4-methoxyaniline in boiling water in 1:3 molar proportion in the absence of any Lewis acid catalyst to produce [ZnL′ 3 ](ClO 4 ) 2 ·4H 2 O and [ZnL″ 3 ](ClO 4 ) 2 ·H 2 O, respectively in 1–4 h time in somewhat low yield. In the 1 H NMR spectra of [ZnL′ 3 ](ClO 4 ) 2 ·4H 2 O and [ZnL″ 3 ](ClO 4 ) 2 ·H 2 O, only one sharp methyl signal is observed implicating that only one diastereomer out of the 2 3 possibilities is formed. The same diastereomers are obtained when L′·H 2 O and L″ are reacted directly with Zn(ClO 4 ) 2 ·6H 2 O in tetrahydrofuran at room temperature in very good yields. Reactions of L′·H 2 O and L″ with Ru(phen) 2 Cl 2 ·2H 2 O (phen = 1,10-phenanthroline) in equimolar proportion in methanol–water mixture under refluxing condition lead to the isolation of two diastereomers of [Ru(phen) 2 L′](ClO 4 ) 2 ·2H 2 O and [Ru(phen) 2 L″](ClO 4 ) 2 ·2H 2 O.