SELECTIVE METAL-ASSISTED OXIDATIVE CLEAVAGE OF A C-N BOND - SYNTHESISAND CHARACTERIZATION OF THE MONONUCLEAR IRON(III) [FE(BPG)CL-2] COMPLEX AND ITS 2 [FE(BPA)CL-3] AND [FE(BPE)CL-3] DERIVATIVES

A new example of a site-selective metal-assisted oxidative cleavage of a C-N bond is reported. This phenomenon occurs in the nitrogen-center ed tetradentate tripodal BPG ligand (BPG = (bis(2-pyridylmethyl)amino) acetate), which combines one carboxylate and two pyridines as pendant groups, when coordinated to iron(III). The corresponding iron(III) [Fe (BPG)Cl-2] complex (1) is transformed to the iron(III) [Fe(BPA)Cl-3] c omplex (2) with the tridentate BPA ligand (BPA = bis(2-pyridylmethyl)a mine) retaining only two pyridine pendant groups, while the initial BP G carboxylate group is transformed to glyoxylic acid. The [Fe(BPA)Cl-3 ] complex (2) has been fully characterized as well as another, [Fe(BPE )Cl-3] (3), formed with the tridentate BPE ligand (BPE = methyl (bis(2 -pyridylmethyl)amino)acetate) which, in addition to two pyridines, pre sents an eater group. The crystal structures of these two complexes ha ve been resolved. The asymmetric unit of complex 2 has been characteri zed by two mononuclear neutral molecules linked by two hydrogen bonds. (Crystal data for 2: orthorhombic, Pna2(1), a = 15.603(8) Angstrom, b = 8.485(4) Angstrom, c = 22.752(11) Angstrom, alpha = beta = gamma = 90 degrees, V = 3012(3) Angstrom(3), Z = 8,R = 0.0582 [2813 reflection s with I > 2 sigma(I)], and R-w = 0.1430.) Complex 3 is symmetric with the iron center, the amine nitrogen, one choride and the three atoms of the carboxylate group in special positions in the mirror plane. (Cr ystal data for 3: orthorhombic, Pmn2(1), a = 10.418(4) Angstrom, b = 1 2.952(5) Angstrom, c = 7.353(3) Angstrom, alpha = beta = gamma = 90 de grees, V = 992.2(7) Angstrom(3), Z = 2, R = 0.0500 [513 reflections wi th I > 2 sigma(I)], and R-w = 0.1231.) Redox potentials corroborate th e structural features (E degrees = -38 mV for 1, -19 mV for 2, and +14 5 mV for 3 vs SCE in acetonitrile). Preliminary studies of the [Fe(BPG )Cl-2] complex have shown that it reacts in its reduced form with diox ygen.