NMR Spectroscopic and X-ray Crystallographic Study of Methylcobalt(III) Compounds with Saturated Amine Ligands

The 13C chemical shifts of methylcobalt(III) compounds with saturated amine ligands in cis positions to the methyl
group and a monodentate ligand, L = CN-, NH3, NO2-, N3-, H2O, or OH-, in the trans position are reported. The
amine ligands used, 1,2-ethanediamine (en), 1,3-propanediamine (tn), N,N‘-bis(2-aminoethyl)-1,3-propanediamine
(2,3,2-tet), N,N‘-bis(3-aminopropyl)-1,2-ethanediamine (3,2,3-tet), and 1,4,8,11-tetraazacyclotetradecane (cyclam),
all exert an apparent cis influence on the 13C resonance signal of the coordinated methyl group. In the trans-[Co(en)2(CH3)(L)]n+ series the 15N resonance frequency of the coordinated en has also been measured. The influence
of L on the en 15N chemical shifts is reverse the influence on the methyl 13C chemical shifts except in the case of
L = NO2-, which affects a further deshielding of the amine nitrogen nucleus. The methyl 1JCH coupling constants
in the trans-[Co(en)2(CH3)(L)]n+ series range from 128.09 Hz (L = CN-) to 134.11 Hz (L = H2O). The crystal
structures of trans-[Co(en)2(CH3)(ClZnCl3)], trans-[Co(3,2,3-tet)(CH3)(N3)]ClO4, trans,trans-[(CH3)(en)2Co(CN)Co(en)2(CH3)](PF6)3(CH3CN), and cis-[Co(en)2(CH3)(NH3)]ZnCl4 were determined from low-temperature X-ray diffraction
data.