Synthesis and spectroscopic studies of homo- and heteroleptic N-arylsalicylaldimin- ates of titanium(IV), zirconium(IV) and chromium(III) Shashank Mishra   and Anirudh Singh* Department of Chemistry, University of Rajasthan, Jaipur 302 004, India   Present address: Department of Chemistry, Institute of Basic Sciences, Bundelkhand University, Jhansi 284 218, India Received 22 May 2003; accepted 28 July 2003 Abstract Homo- and heteroleptic N-arylsalicylaldiminate derivatives of Ti IV and Zr IV of the type, MX 4)x (OC 6 H 4 CH@NAr) x (X ¼ OPr i , x ¼ 2,3; X ¼ Cl, x ¼ 1,2,3,4; Ar ¼ C 6 H 3 Me 2 -2,6, C 6 H 3 Et 2 -2,6) have been prepared by reactions in the desired molar ratios of: (i) Ti(OPr i ) 4 /Zr(OPr i ) 4 Æ Pr i OH with N-arylsalicylaldimines in benzene, and (ii) MCl 4 (M ¼ Ti, Zr) with Me 3 SiOC 6 H 4 CH@NAr or HOC 6 H 4 CH@NAr in the presence of Et 3 N as a base or the potassium salt of N-arylsalicylaldimines in benzene. The three homoleptic derivatives of Cr III , Cr(OC 6 H 4 CH@NAr) 3 (Ar ¼ C 6 H 2 Me 3 -2,4,6, C 6 H 3 Et 2 -2,6, C 6 H 3 Pr i 2 -2,6) have also been prepared by salt-elimination. All of these new derivatives have been characterized by elemental analyses, spectroscopic [i.r., 1 H and 13 C-n.m.r. (Ti and Zr complexes), and electronic (for Cr complexes)] studies, as well as molecular weight measurements. Introduction During the last three decades, there have been interest- ing developments in the chemistry of titanium(IV) and zirconium(IV) derivatives of Schiff bases [1–5], reflecting the role of the metal ion size in influencing coordination states. For example, tetrakis(N-ethylsalicylaldiminate) derivatives of titanium(IV) [1] and zirconium(IV) [2] are six- and eight-coordinate, respectively. Furthermore, bis derivatives of titanium(IV) of the type, [Ti(OC 10 H 6 CH@ NCH 2 CHRO) 2 ] (R ¼ H, Me), are monomeric with six- coordinate titanium, whereas analogous derivatives of zirconium(IV) have been found to be dimeric with a seven-coordinate zirconium atom [3]. Compared to group metals, only a small number of chromium(III) complexes of Schiff bases are known [6–8], with the central chromium ion having an octahedral geometry. It is also interesting to note that derivatives of the type, (acac) 2 MX 2 (M ¼ Ti, Zr, Sn, etc.;X ¼ an anionic ligand such as Cl ) , OR ) , OAr ) , etc.) exhibit cis and trans isomeric forms, the predominence of which is influenced by both the nature of the chelating as well as monod- entate anionic ligands [9–12]. In view of the above, it was considered worthwhile to investigate derivatives of titanium(IV), zirconium(IV) and chromium(III) derived from N-arylsalicylaldimines such as HOC 6 H 4 CH@NC 6 H 3 Me 2 -2,6; HOC 6 H 4 CH@ NC 6 H 2 Me 3 -2,4,6; HOC 6 H 4 CH@NC 6 H 3 Et 2 -2,6 and HOC 6 H 4 CH@NC 6 H 3 Pr i 2 -2,6, which not only provide considerable steric bulk around the metal centre but are also expected to enhance the solubility of the resulting products. Experimental Rigorous precautions were taken to exclude moisture from the glassware used for the reactions. The (BDH) solvents and reagents were dried by refluxing over the appropriate drying agents (given in parentheses): ben- zene, toluene, n-hexane (Na/benzophenone), CCl 4 - (P 2 O 5 ), Et 3 N(KOH), and distilled prior to use. Ti(OPr i ) 4 [13] and Zr(OPr i ) 4 Æ Pr i OH [14] were prepared by the literature procedures. The new N-arylsalicylaldimines were prepared as described in our recent publication [15]. Me 3 SiOC 6 H 4 CH@NAr were prepared according to the method described in literature [16]. Titanium and zirconium were determined as metal dioxides (MO 2 ), whereas chromium was determined as lead chromate [17]. Chlorine was determined by Volhard’s method [17] and isopropanol in the azeotrope was estimated by the oxidimetric method [18]. 1 H (89.55 MHz, CDCl 3 ) and 13 C-(22.49 MHz, CCl 4 ) n.m.r. spectra were recorded on a JEOL FX-90Q spectrometer using TMS as an internal reference. I.r. spectra (4000–200 cm )1 ) were recorded as Nujol mulls using CsI optics on a Nicolet Magna-550 spectrophotometer. Electronic spectra of Cr III deriva- tives were recorded on a Cary-50 Bio spectrophotometer in C 6 H 6 solution using a 5 mm quartz cell. Molecular weights were determined ebullioscopically in benzene using a Gallenkamp ebulliometer. Synthesis of new complexes Ti(OPr i ) 2 (OC 6 H 4 CH@NC 6 H 3 Et 2 -2,6) 2 (1) A benzene solution (70 cm 3 ) containing Ti(OPr i ) 4 (2.28 g, 8.04 mmol) and HOC 6 H 4 CH@NC 6 H 3 Et 2 -2,6 * Author for correspondence Transition Metal Chemistry 29: 164–169, 2004. 164 Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands.