The interconversion of dichlorobis(N-n-propylsalicylaldimine)zinc(II) and bis(N-n-propylsalicylaldiminato)zinc(II)

The interconversion of the zinc(II) complex of the neutral ligand adduct of N-n-propylsalicylaldimine Zn((LH)-H-pr)(2)Cl-2 and its salicylaldiminato counterpart Zn(L-pr)(2) is investigated. The compound Zn((LH)-H-pr)(2)Cl-2 is prepared by the reaction of anhydrous ZnCl2 with 2 equiv. of N-n-propylsalicylaldimine ((LH)-H-pr) in benzene. A crystallographic study of the distorted tetrahedral Zn((LH)-H-pr)(2)Cl-2 adduct reveals that the oxygen atom of the ligand is deprotonated and bound to the zinc atom while the nitrogen is protonated and non-coordinating. An infrared spectrum of Zn((LH)-H-pr)(2)Cl-2 exhibits a C=N stretch at a higher energy (1658 cm(-1)) than the free ligand (1632 cm(-1)) consistent with the presence of the iminium. moiety. In contrast, the deprotonated ligand of the crystallographically characterized salicylaldiminato complex Zn(L-pr)(2) coordinates to zinc in its prototypical bidentate monoanionic coordination mode. Deprotonation of Zn((LH)-H-pr)(2)Cl-2 with Et3N or NaOH forms Zn(L-pr)(2). The reverse reaction, protonation of Zn(L-pr)(2) with anhydrous HCl, produces Zn((LH)-H-pr)(2)Cl-2. These reactions demonstrate the interrelationship between the zinc salicylaldimine adduct and its corresponding salicylaldiminato complex. (C) 2002 Elsevier Science Ltd. All rights reserved.