Oxo-molybdenum and oxo-tungsten complexes of Schiff bases relevant to molybdoenzymes.
A series of octahedral dioxomolybdenum(VI) complexes of the type [MoO(2)L(2)] {L = 4-Ar-pent-2-en-ol; L(i-Pr2Ph) with Ar = 2,6-diisopropylphenyl (1); L(Me2Ph) with Ar = 2,6-dimethylphenyl (2), L(MePh) with Ar = 2-methylphenyl (3) and with Ar = phenyl (4)} and dioxotungsten(VI) compounds [WO(2)L(2)] {L(i-Pr2Ph) (5); L(Me2Ph) (6) and L(MePh) (7)} with Schiff bases have been synthesized as models for oxotransferases. Spectroscopic characterization in solution shows with the sterically encumbered ligands L(i-Pr2)Ph and L(Me2)Ph isomerically pure products whereas the ligand with only one substituent in ortho position at the aromatic ring L(MePh) revealed a dynamic mixture of three isomers as confirmed by variable temperature NMR spectroscopy. Single crystal X-ray diffraction analyses of compounds 1, 2, and 4 and showed them to be in the N,N-trans conformation consistent with the larger steric demand at nitrogen. Oxygen atom transfer (OAT) properties towards trimethylphosphine were investigated leading to the isolation of two mononuclear molybdenum(IV) compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) as confirmed by spectroscopic and crystallographic means. The kinetics of OAT between complex [MoO(2)(L(Me2Ph))(2)] (2) and PMe(3) was investigated by UV/Vis spectroscopy under pseudo-first-order conditions revealing single-step reactions with Eyring values of DeltaH(double dagger) = +60.79 kJ mol(-1) and DeltaS(double dagger) = -112 J mol(-1) K(-1) and a first-order dependence of phosphine consistent with a slow nucleophilic attack of the phosphine showing the octahedral geometries of this system to be unfavorable for OAT. Compound 1 showed no OAT reactivity towards PMe(3) emphasizing the influence of sterical properties. Furthermore, the reactivity of the reduced compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) towards molecular oxygen was investigated leading, in the case of 8, to the substitution of PMe(3) by O(2) under formation of the peroxo compound [MoO(O(2))(L(Me2Ph))(2)] (10). In contrast, the analogous reaction employing 9 led to oxidation forming the dioxo compound [MoO(2)(L(MePh))(2)] (3).
Lyashenko
Ganna
G
Institut für Chemie, Bereich Anorganische Chemie, Karl-Franzens-Universität Graz, Schubertstrasse 1, 8010, Graz, Austria.
Saischek
Gerald
G
Judmaier
Martina E
ME
Volpe
Manuel
M
Baumgartner
Judith
J
Belaj
Ferdinand
F
Jancik
Vojtech
V
Herbst-Irmer
Regine
R
Mösch-Zanetti
Nadia C
NC
D018360:Crystallography, X-Ray; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry*; D012545:Schiff Bases / Q000737:chemistry; D013237:Stereoisomerism; D014414:Tungsten / Q000737:chemistry*
D008024:Ligands; D009942:Organometallic Compounds; D012545:Schiff Bases; D008982:Molybdenum; D010088:Oxidoreductases; C100768:dimethylsulfide - acceptor oxidoreductase; D010100:Oxygen; D014414:Tungsten