HEXADENTATE N3O3 AMINE PHENOL LIGANDS FOR GROUP-13 METAL-IONS - EVIDENCE FOR INTRASTRAND AND INTERSTRAND HYDROGEN-BONDS IN POLYDENTATE TRIPODAL AMINE PHENOLS

Several N3O3 amine phenols (H-3L1 = 1,2,3-tris((2-hydrox benzyl)amino)propane; H-3L2 = 1,2,3-tris((5-chloro-2-hydroxybenzyl)amino)propane; H-3L3 = 1,2,3-tris((2-hydroxy-5-methoxybenzyl)amino)propane; H-3L4 = 1,2,3-tris((3,5-dichloro-2-hydroxybenzyl)amino)propane) were 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 tap (tap = 1,2,3-triaminopropane) with 3 equiv of either salicylaldehyde or ring-substituted salicylaldehydes. Neutral binary metal complexes, [M(L)] (M = Al, L = L2, IA; M - Ga, In, L = L1-L4), 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 structure of [Ga(L3)].2CH3OH was determined by X-ray methods. Crystals of [Ga(L3)].2CH3OH are monoclinic, of space group P2(1)/n, with a = 13.115(3) angstrom, b = 15.674(2) angstrom, c = 14.439(2) angstrom, beta = 100.62(1)-degrees, and Z = 4. The structure of [Ga(L3)].2CH3OH was solved by the Patterson method and was refined by full-matrix least-squares procedures to R = 0.028 for 4529 reflections with I greater-than-or-equal-to 3sigma(I). In [Ga(L3)].2CH3OH, the Ga atom is coordinated by six (N3O3) donor atoms in a slightly distorted octahedral coordination geometry. The cavity of the tap-based N3O3 amine phenol ligand matches well the size of Ga3+. Variable-temperature H-1 NMR spectral data revealed rigid solution structures for all the aluminum, gallium, and indium complexes, with no evidence for fluxional behavior; the complexes remained very rigid at solution temperatures higher than 120-degrees-C. Reaction of H-3L1 with acetone produces a new amine phenol H3L' containing a 2,2-dimethylimidazolidine ring. The molecular structure of H3L' was determined by X-ray methods. Crystals of H3L' are triclinic, P1BAR, with a = 10.8209(8) angstrom, b = 12.436(1) angstrom, c = 9.1556(8) angstrom, alpha = 92.561(9)-degrees, beta = 101.028(6)-degrees, gamma = 84.506(8)-degrees, and Z = 2. The structure of H3L' was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.036 for 2825 reflections with I greater-than-or-equal-to 3sigma(I). The H3L' structural data revealed strong intrastrand (O-H --- N) and very weak interstrand (N-H --- N) H-bonds, which contribute, at least in part, to the highly preorganized ligand framework of polydentate tripodal amine phenols.