Characterization of manganese sandwich complexes by 55Mn NMR spectroscopy

Article abstract of DOI:10.1016/0022-328X(94)05052-D

55Mn NMR data are reported for manganese sandwich complexes of the type <(η⁵-C5H5)Mn(η⁶-C6H6)> (1), <(η⁵- C5H5)Mn(η⁶-C6H5-R')> iPr (3), ^tBu (4), Ph (5), SiMe3 (6a), GeMe3 (6b), SnMe3 (6c), PbMe3 (6d), SMe (6e)>, <(η⁵-C5H4-R)Mn(η⁶-C6H6)> , <(η⁵-C5H4-R)Mn(η⁶-C6H5-R')> , <(η⁵-C5R5)Mn(η⁶-C7H8)> and <(η⁵-C5R5)Mn(η⁶-C8H10)> .The chemical shifts δ55Mn cover a range of ca. 350 ppm for complexes 1 to 12 (δ55Mn ca. -180 to ca. +170 relative to ^- aq), whereas further 55Mn deshielding up to ca. 1000 ppm is observed for complexes 14 to 17.Any relationship between the formal oxidation number of Mn and 55Mn magnetic shielding has to be discarded.The large range of the δ55Mn data for sandwich complexes indicates that 55Mn magnetic shielding depends on the electronic structure of the frontier orbitals which is significantly affected by the ring substituents.Chemical shifts δ53Cr (relative to ^2- aq) for 6-C6H6)2> (-1206) and <(η⁶-C6H6)Cr(CO)3> (-1580) have been determined for comparison.Keywords: Manganese sandwich complexes; 55Mn NMR; 53Cr NMR