TY - JOUR
T1 - Molybdenum(VI) cis-dioxo complexes bearing (poly)pyrazolylmethane and -borate ligands
T2 - Syntheses, characterization and catalytic applications
AU - Santos, A. M.
AU - Kühn, F. E.
AU - Bruus-Jensen, K.
AU - Lucas, I.
AU - Romão, C. C.
AU - Herdtweck, E.
PY - 2001
Y1 - 2001
N2 - Reaction of MoO2Cl2(THF)2 with mono- (L1) and bi-dentate (L2) pyrazole type ligands leads to octahedral complexes of formula MoO2Cl2(L1)2 and MoO2Cl2(L2) (1, L1 = 3,5-Me2pz; 2, L2 = Me2C(pz)2). The structure of 2 has been determined crystallographically. Reaction of MoO2X2(THF)2 (X = (Cl or Br) with tridentate ligands (L3, e.g. tris(pyrazolyl)methane or tris(pyrazolyl)borate, leads to the replacement of both co-ordinated solvent molecules and one of the chloride ligands to give [MoO2X(L3)]X (3, X = Cl, L3 = HC(pz)3; 4, X = Br, L3 = HC(pz)3; 5, X = Cl, L3 = HC(3,5-Me2pz)3) and MoO2Cl{((pz)3BH}) 6. Depending on the donor ability and the steric bulk of the ligand, rapid rotation is observed at room temperature in some cases. At lower temperatures the structures are less fluxional. Nevertheless, bidentate and tridentate pyrazolyl ligands produce distinctly different chemical shifts in the 95Mo NMR spectra. The turnover frequencies of the described complexes in olefin epoxidation, with t-butyl hydroperoxide as oxidizing agent, are in the range of 150-460 [mol/(mol catalyst h)]. This activity is in the middle of the range observed for MoO2X2L2 complexes with N-donor ligands.
AB - Reaction of MoO2Cl2(THF)2 with mono- (L1) and bi-dentate (L2) pyrazole type ligands leads to octahedral complexes of formula MoO2Cl2(L1)2 and MoO2Cl2(L2) (1, L1 = 3,5-Me2pz; 2, L2 = Me2C(pz)2). The structure of 2 has been determined crystallographically. Reaction of MoO2X2(THF)2 (X = (Cl or Br) with tridentate ligands (L3, e.g. tris(pyrazolyl)methane or tris(pyrazolyl)borate, leads to the replacement of both co-ordinated solvent molecules and one of the chloride ligands to give [MoO2X(L3)]X (3, X = Cl, L3 = HC(pz)3; 4, X = Br, L3 = HC(pz)3; 5, X = Cl, L3 = HC(3,5-Me2pz)3) and MoO2Cl{((pz)3BH}) 6. Depending on the donor ability and the steric bulk of the ligand, rapid rotation is observed at room temperature in some cases. At lower temperatures the structures are less fluxional. Nevertheless, bidentate and tridentate pyrazolyl ligands produce distinctly different chemical shifts in the 95Mo NMR spectra. The turnover frequencies of the described complexes in olefin epoxidation, with t-butyl hydroperoxide as oxidizing agent, are in the range of 150-460 [mol/(mol catalyst h)]. This activity is in the middle of the range observed for MoO2X2L2 complexes with N-donor ligands.
UR - http://www.scopus.com/inward/record.url?scp=0034743870&partnerID=8YFLogxK
U2 - 10.1039/b009202i
DO - 10.1039/b009202i
M3 - Article
AN - SCOPUS:0034743870
SN - 1470-479X
SP - 1332
EP - 1337
JO - Journal of the Chemical Society. Dalton Transactions
JF - Journal of the Chemical Society. Dalton Transactions
IS - 8
ER -