HIGHLY FLEXIBLE CHELATING LIGANDS FOR GROUP 13 METALS - DESIGN AND SYNTHESIS OF HEXADENTATE (N3O3) TRIPODAL AMINE PHENOL LIGAND COMPLEXES OF ALUMINUM, GALLIUM, AND INDIUM

New, potentially hexadentate (N3O3) amine phenol ligands (H3IIa = 1,1,1-tris(((2'-hydroxybenzyl)amino)methyl)ethane; H3IIb = 1,1,1-tris(((5'-chloro-2'-hydroxybenzyl)amino)methyl)ethane; H3IIC = 1,1,1-tris(((5'-bromo-2'-hydroxybenzyl)amino)methyl)ethane; H3IId = 1,1,1-tris(((3',5'-dichloro-2'-hydroxybenzyl)amino)methyl)ethane) have been prepared and characterized by various spectroscopic methods (IR, FAB-MS, NMR). The N3O3 amine phenols are KBH4 reduction products of the corresponding Schiff bases derived from the condensation reactions of 1,1,1-tris(2-aminomethyl)ethane (tame) with 3 equiv of either salicylaldehyde or ring-substituted salicylaldehydes. Neutral binary metal complexes, [M(L)] (M = Al, Ga, In; L = IIa, IIb, IIc, IId) were obtained from the reactions of Al3+, Ga3+, or In3+ With N3O3 amine phenols in the presence of 3 equiv of a base (acetate or hydroxide). The molecular structures of {[AI(IIc)]4[Na(H2O)]2)(ClO4)2.6.2H2O, [Ga(IIa)].4.4H2O, and [In(IIa)].4.6H2O were determined by X-ray methods. Crystals of {[Al(IIc)]4[Na(H2O)]2}(ClO4)2.6.2H2O are orthorhombic, Pbcn, a = 27.226 (2) angstrom, b = 15.687 (4) angstrom, c = 30.013 (3) angstrom, and Z = 4, and those of [Ga(IIa)].4.4H2O and [In(IIa)].4.6H2O are isomorphous, crystallizing in the monoclinic space group C2/c, a = 32.105 (9) angstrom [32.654 (2) angstrom], b = 10.559 (2) angstrom [10.744 (2) angstrom], c = 19.626 (5) angstrom [19.429 (2) angstrom], beta = 118.43(1)-degrees [117.842(4)-degrees], and Z = 8 (bracketed values refer to the In complex). The structures were solved by the Patterson method and were refined by full-matrix least-squares procedures to R = 0.049, 0.039, and 0.038 for 5668, 4028, and 4625 reflections with I greater-than-or-equal-to 3sigma(I) for the Al, Ga, and In complexes, respectively. In these three complexes, the metal atoms (Al, Ga, and In) are all coordinated by six (N3O3) donor atoms in distorted octahedral coordination geometries. As the metal ion becomes larger, the amine phenol ligand accommodates the coordinated metal ion in a subtle fashion, such that there are no significant identifiable bond angle increases, suggesting that the ligand backbone is extremely flexible. Variable-temperature H-1 NMR spectral data revealed rigid solution structures for all aluminum, gallium, and indium complexes, with no evidence for fluxional behavior; the complexes remained very rigid at solution temperatures higher than 150-degrees-C.