Conformational analysis of coordination compounds. XIV. Proton, carbon-13, cobalt-59 and platinum-195 n.m.r. spectra of six-membered diamine chelaterings

Abstract

The conformations adopted by six-membered diamine chelate rings in complexes of the types [Co(NH₃),L]³⁺, [Co(CN)₄L]^-, [Pt(bpy)L]²⁺, [Pt(NH₃)₂L]²⁺ and [CoL₃]³⁺ have been studied by n.m.r. techniques. The ligands (L) used in the study were meso- and (+)-pentane-2,4-diamine, butane-1,3-diamine, propane-1,3-diamine and 2-methylpentane-2,4-diamine. It has been found that for most complexes of meso-pentane-2,4-diamineth e diequatorial chair conformation predominates, although for the bipyridineplatinum(II) complex it is unclear whether the skew-boat conformation is significantly populated or the chair structure is unusually distorted. For (+)-pentane-2,4-diamine chelates, which normally adopt the skew-boat conformation in octahedral complexes, the chair conformation with an axial and an equatorial methyl group has a mole fraction of 0.5 and 0.7 for the bipyridine- and diammine-platinum(II) complexes, respectively. In tetraammine(butane-1,3- diamine)cobalt(III) the chelate ring is in the chair conformation with the methyl equatorial.