First-Row Transition Metal Complexes of the Hexadentate Macrocycle 1,4,7-Tris(5-tert-buty1-2-hydroxybenzyl)-1,4,7-triazacyclononane (LH₃). Crystal Structures of [LTi^IV]BPh₄, [LCr^III], [LFe^III], and [(LH)₂Fe^III₂](ClO₄)₂·2H₂O

The new hexadentate macrocycle containing three phenolate pendant arms has been prepared from 1,4,7-triazacyclononane and 3 equiv of 2-bromomethyl-4-tert-butylphenyl acetate: Tripotassium l,4,7-tris(5-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononanate (K₃L; C₃₉H₅₄N₃O₃K₃). The reaction of trivalent first-row transition metals with the trianion affords monomeric pseudooctahedral complexes, of which the following have been characterized: LV^III (2); LCr^III (5); LMn^III (6); LFe^III (8); LCo^III (9). Monocationic complexes containing a tetravalent metal ion have also been prepared: [LTi^IV]PF₆; [LV^IV](ClO₄) (3); [LMn^IV]BPh₄ (7). [LV^V](ClO₄)₂ (4) has been synthesized by oxidation of 2 or by reaction of NH₄VO₃ and K₃L in acidic CH₃CN solution. In acidic methanolic solutions of 5, 8, and 9 dimeric species were obtained as crystalline solids: [(LH)₂M^III₂](ClO₄)2·2H₂O (M = Cr^III (10), Fe^III (11), Co^III (12)). The crystal structures of [LTi^IV]BPh₄, 5, 8, and 11 have been determined by X-ray crystallography: [LTi]BPh₄, orthorhombic, space group P2₁2₁2₁, a = 10.856(6) Å, b = 19.33(2) Å, c = 26.49(2) Å, Z = 4; 5, trigonal, space group R3, a = 23.547(3) Å, c = 6.521(1) Å, Z = 3; 8, trigonal, space group R3, a = 23.64(2) Å, c = 6.599(7) Å, Z = 3; 11, monoclinic, space group P2₁/n, a = 16.48(1) Å, b = 13.78(1) Å, c = 17.84(1) Å, β = 93.72(6)^°; Z = 2. Electronic spectral data, magnetic properties, and the electrochemistry of the new complexes are reported. The d_π-p_π bonding of the phenolate-metal M-O bonds is analyzed as a function of the dⁿ electronic configuration of the respective metal ion.