Molybdenum(VI) dioxo complexes with tridentate phenolate ligands.
A series of new molybdenum(VI) dioxo complexes of the type [MoO(2)ClL(X)] with potentially monoanionic phenolate ligands L(X) (L = 4,6-di-tert-butyl-2-{[(X)methylamino]methyl}-phenolate; L(OMe), where X = 2'-methoxyethyl; L(SEt), where X = 2'-ethylthioethyl; L(NEt2), where X = 2'-diethylaminoethyl; and L(NMe2), where X = 2'-dimethylaminoethyl) have been synthesized as models for molybdoenzymes. All molybdenum complexes were readily accessible by employing the eta(2)-coordinate pyrazolate complex [MoO(2)Cl(eta(2)-t-Bu(2)pz)]. The nitrogen ligand can easily be exchanged by the monoanionic phenolate ligands L(X) in toluene at room temperature, leading to monosubstituted complexes 1-4 as yellow to red powders in good yields. Suitable single crystals for X-ray diffraction analysis of complexes 2 and 3 were obtained from a concentrated benzene solution. Both complexes reveal a six-coordinate molybdenum atom in a distorted octahedral surrounding, with a tridentate fac coordination of the ligand. Additionally, the complexes were characterized by elemental analysis; IR, UV/vis, and NMR spectroscopy; and mass spectrometry. For complexes 1 and 2, only one isomer can be detected in solution, whereas complexes 3 and 4 reveal the formation of two isomers in a 1:1 ratio for 3 and in a 1:3 ratio for 4. Optimized geometries and relative free energies of all possible isomers have been established by DFT calculations, indicating two isomers in solutions of 3 and 4 to be two types of facially coordinated complexes. Furthermore, this is supported by gauge-independent atomic orbital calculations of the (1)H NMR shifts with a high correlation of experimental and calculated shifts for the fac compounds. Oxygen atom transfer reactions of 1 to PMe(3) quickly form monooxo molybdenum compound cis,mer-[MoOCl(2)(PMe(3))(3)].
Institut für Chemie, Bereich Anorganische Chemie, Karl-Franzens-Universität Graz, Schubertstrasse 1, 8010 Graz, Austria.
Martina E
ME
Judmaier
Andreas
A
Wallner
Gregor N
GN
Stipicic
Karl
K
Kirchner
Judith
J
Baumgartner
Ferdinand
F
Belaj
Nadia C
NC
Mösch-Zanetti
D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D010636:Phenols / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory
D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D008982:Molybdenum; D010100:Oxygen