The interconversion of dichlorobis(N -n -propylsalicylaldimine)zinc(II) and bis(N -n -propylsalicylaldiminato)zinc(II) Michele A. Torzilli, Shalton Colquhoun, Danielle Doucet, Robert H. Beer * Department of Chemistry, Fordham University, Bronx, NY 10458, USA Received 1 August 2001; accepted 3 December 2001 Abstract The interconversion of the zinc(II) complex of the neutral ligand adduct of N -n -propylsalicylaldimine Zn(L pr H) 2 Cl 2 and its salicylaldiminato counterpart Zn(L pr ) 2 is investigated. The compound Zn(L pr H) 2 Cl 2 is prepared by the reaction of anhydrous ZnCl 2 with 2 equiv. of N -n -propylsalicylaldimine (L pr H) in benzene. A crystallographic study of the distorted tetrahedral Zn(L pr H) 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(L pr H) 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(L pr H) 2 Cl 2 with Et 3 N or NaOH forms Zn(L pr ) 2 . The reverse reaction, protonation of Zn(L pr ) 2 with anhydrous HCl, produces Zn(L pr H) 2 Cl 2 . These reactions demonstrate the interrelationship between the zinc salicylaldimine adduct and its corresponding salicylaldiminato complex. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Schiff bases; Salicylaldimine adducts; Interconversion; X-ray crystal structures; Zinc complexes; Zwitterion 1. Introduction The salicylaldimine ligand forms the basis of an extensive class of chelating ligands that has enjoyed popular use in the coordination chemistry of transition and main group elements [1  /3]. The reaction of the neutral phenol-imine form of the salicylaldimine ligand with a suitable metal starting material in the presence of base is a simple and direct means of preparing metal salicylaldiminato complexes (Scheme 1). In these com- plexes, the deprotonated phenolate-imine form of the ligand acts as a bidentate monoanionic N/O donor. Despite the frequent use of this preparative method, comparatively few of the putative precursors or inter- mediates involved in this reaction prior to deprotona- tion of the ligand have been structurally characterized [1,2,4  /11] and, similarly, the precursors formed by the reverse reaction are not isolated typically [12,13]. We report here an example of the interconversion of a structurally characterized precursor and its correspond- ing deprotonated salicylaldiminato complex using the zinc(II) dichloride adduct of N -n -propylsalicylaldimine (L pr H). These reactions corroborate the role of neutral salicylaldimine adducts in the formation of salicylaldi- minato complexes. 2. Experimental 2.1. Materials and methods Reagents and solvents were used as received from commercial sources. The ligand N -n -propylsalicylaldi- mine (L pr H) and the protonated ligand (L pr H 2 )(CF 3 SO 3 ) were synthesized by generally accepted methods [1,14] and Zn(L pr ) 2 by modification of related literature procedures [15,16]. Infrared and electronic spectroscopic data were collected on a Mattson Satellite FTIR and Perkin  /Elmer Lambda 6 instrument, respec- tively. The 1 H NMR spectroscopic data were obtained on a Bruker AVANCE 300 NMR spectrometer at * Corresponding author. Tel.: 1-718-817-4430; fax: 1-718-817- 4432. E-mail address: beer@fordham.edu (R.H. Beer). Polyhedron 21 (2002) 697  /704 www.elsevier.com/locate/poly 0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII:S0277-5387(02)00839-2