A series of Al(III) chloride [LAl-Cl]; Al(III) alkoxide [LAl-OR] 2 ; and Zn(II) [LZn] 2 complexes with Schiff base ligands were obtained. 1 H NMR and X-ray diffraction studies indicate that [LAl-Cl] complexes have C s symmetry and the Al center is penta-coordinated. The Al(III) alkoxide complex [L 5 Al-O i Pr] 2 is a dimer bridged by O i Pr − with the Al center in a distorted octahedral environment. Zn complexes [LZn] 2 are double helix dimers with tetra-coordinated Zn centers. The catalytic activity for the ring-opening polymerization of rac-lactide was evaluated. The best activity in this series is shown by the aluminium chloride complex with a flexible three-carbon bridge; more flexible four-carbon bridges lower the activity.

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The reaction of 1,2-Ethylendiamine-N,N -bis(1H-pyrrol-2-yl)methylene (L 1 H), 1,2-benzenediamine-N,N -bis(1Hpyrrol-2-yl)methylene (L 2 H) and 3,4-Dimethyl-1,2-benzenediamine-N,N -bis(1 H-pyrrol-2-yl)methylene (L 3 H) with one equivalent of AlR 2 R (R = alkyl, R = alkyl, Cl) in toluene afforded the monometallic complexes [LAlR ] (1-12). All the complexes were characterized by analytical and spectroscopic methods. Compounds 1, 3, 4, 6, 7, and 11 were characterized bya singlecrystal X-ray structural analyses. Due to the rigidity imposed by the ligand, 1, 3 and 4, with an ethylene "backbone" connecting the two nitrogens, adopt a severely distorted tbp geometry (av. = 0.68). On the other hand 6, 7 and 11, with a phenylene backbone, adopt an intermediate tbp-sqp geometry (av. = 0.43). The study of the X-ray crystal structures suggests that, like group 13 Salen complexes, flexible bridges between the two imine groups favor a tbp geometry while more rigid backbones, like phenylene rings, lead to an intermediate sqp and tbp geometry. Based on the geometrical parameter for previously reported aluminum complexes with Schiff base ligands and those presented herein, it is possible to propose that upon the coordination geometries of five coordinated aluminum complexes are less tbp distorted ( ≈ 1) the catalytic activity on ROP increases.

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Novel mononuclear metal complexes with the general formula {[(NC 4 H 3 ) 2 CH 2 -CNNC 6 H 2 (R 2 )]MMe 2 } (M=Ga, R=H (1); M=Al, R=Me (2)) and {[(OC 4 H 2 CH 3 ) 2 CH 2 -CNNC 6 H 4 ]MMe 3 } (M=Ga (3); M=Al (4)) results when benzimidazole derivatives ligands are mixed with trimethylaluminum and trimethylgallium. The X-ray crystal structures of 1 and 4 are described.The structural data revealed that 1 is a mononuclear gallium compound with the pendant pyrrol moiety coordinated to the metal center, while 4 is a mononuclear aluminum complex that does not show any kind of interaction between the pendant furan moiety and the aluminum center. F.A. Vengoechea-Gómez et al. / Synthesis and characterization of new types of aluminum and gallium complexesScheme 1. Bifunctional catalysts (ii-iii) and ligand (iv) previously reported.