C-H bond activation of coordinated pyridine: ortho-pyridyl-ditechnetiumhydridocarbonyl metal cyclus. Crystal structure and dynamic behavior in solution.
The reaction of pyridine with ditechnetium decacarbonyl [Tc2(CO)10] (1) leads to a novel ortho-pyridyl-ditechnetium hydrido complex, [Tc2(mu-H)(mu-NC5H4)(NC5H5)2(CO)6] (2) and its precursor [Tc2(mu-CO)2(NC5H5)2(CO)6] (3). At ambient temperature 1 was found to react slowly with pyridine to afford the substitution product 3 after 120 h. However, heating the reaction mixture to reflux exclusively leads to the pyridine-ortho-metalated complex 2 in only 30 min. Similarly, complex 3 can be converted completely into 2 upon heating in pyridine for 30 min. Both compounds 2 and 3 were characterized by NMR spectroscopy and X-ray analysis. Both compounds 2 and 3 show a complex dynamic behavior in solution that was investigated by one-dimensional and two-dimensional NMR spectroscopy. Both compounds 2 and 3 show isomerization in solution according to the relative position of the non-bridging pyridine ligands. For 2 the existence of three isomers was shown at equilibrium conditions, 2a (56%) with trans-diaxial, 2b (38%) with cis-diaxial, and 2c (6%) with axial-equatorial arrangement of the non-bridging pyridines. For 3 an equilibrium was detected between two isomers, 3a (67%) with a cis-diaxial and 3b (33%) with a trans-diaxial arrangement of the pyridines.
Zuhayra
Maaz
M
Klinik fur Nuklearmedizin, Universitatsklinikum Schleswig Holstein, Campus Kiel, Arnold-Heller-Strasse 9, D-24105 Kiel, Germany. mzuhayra@nuc-med.uni-kiel.de
Lützen
Ulf
U
Lützen
Arne
A
Papp
Laszlo
L
Henze
Eberhard
E
Friedrichs
Gernot
G
Oberdorfer
Franz
F