Oxidative dehydrogenation of coordinated ethylenediamine in an iridium(III) triamine complex, [Ir(en)PyCl3]

The action of chlorine or bromine on [Ir(en)PyCl 3 ] (I) was studied. The interaction of I with bromine water results in the formation of a bromamine complex, [Ir(H 2 N-CH 2 -CH 2 -NHBr)PyCl3] (II). It was shown that oxidative dehydrogenation of I proceeds stepwise: first, a compound with one C=N bond in the chelate ring is formed, [Ir(HN=CH-CH 2 -NH 2 )PyCl 3 ] (III); then, the formation of the compound [Ir(HN=CH-CH=NH)PyCl 3 ] (IV) with two double bonds in the chelate ring takes place. Slow evaporation of the reaction solution leads to the formation of a compound with a C-OH fragment at the double bond in the chelate ring, [Ir(HN=C(OH)-CH=NH)PyCl 3 ] . H 2 O (V). The IR absorption spectra of I-V were studied. An X-ray diffraction study of III-V was carried out. The crystals of III are monoclinic, space group P2 1 /n, a = 11.382(2) A, b = 8.249(2) A, c = 12.470(2) A, β = 94.55(3)°, V = 1167.1(4) A 3 , Z = 4, R h k l = 0.045. The crystals of IV are orthorhombic, space group Pbca, a = 7.573(2) A, b = 12.174(2) A, c = 24.476(5) A, V = 2256.5(8) A 3 , Z = 8, R h k l = 0.032. The crystals of V are monoclinic, space group P21/n, a = 9.965(2) A, b = 9.212(2) A, c = 14.256(3) A, β = 107.29(3)°, V = 1249.5(5) A 3 , Z = 4, R h k l = 0.020. In the three structures, all hydrogen atoms were located and refined. In complexes III- V, the coordination polyhedron of iridium atoms is an octahedron (three chlorine atoms, the nitrogen atom of pyridine, and two nitrogen atoms of the bidentate organic ligand). In III, the bidentate ligand possesses one N=C bond; in IV and V, two N=C bonds. The nitrogen atom of pyridine and the presence of one (in III) or two double N=C bonds (conjugated in IV and V) influence the C-C bond in the bidentate ligand. In the bidentate ligand of V, the hydrogen atom bonded to the carbon atom is replaced by an OH group. A stable hydrogen bond between the oxygen atoms of the ligand and the water molecule is formed in the crystal. The environment of the water oxygen atom is tetrahedral and consists of two hydrogen atoms, the hydrogen atom of the OH group, and the lone pair.