New heptacoordinate tungsten(II) complexes with α-diimine ligands in the catalytic oxidation of multifunctional olefins


New tungsten(II) and molybdenum(II) heptacoordinate complexes [MX2(CO)3(LY)] (MXLy: M = W, Mo; X = Br, I; LY = C5H4NCY = N(CH2)2CH3 with Y = H (L1), Me (L2), Ph (L3)) were synthesized and characterized by spectroscopic techniques and elemental analysis. The two tungsten complexes WXL1 (X = Br, I) were also structurally characterized by single crystal X-ray diffraction. The metal coordination environment is in both a distorted capped octahedron. The complexes with L1 and L2 ligands were grafted in MCM-41, after functionalization of the ligands with a Si(OEt)3 group. The new materials were characterized by elemental analysis, N2 adsorption isotherms, 29Si MAS and 13C MAS NMR. The tungsten(II) complexes and materials were the first examples of this type reported. All complexes and materials were tested as homogeneous and heterogeneous catalysts in the oxidation of multifunctional olefins (cis-hex-3-en-1-ol, trans-hex-3-en-1-ol, geraniol, S-limonene, and 1-octene), with tert-butyl hydroperoxide (TBHP) as oxidant. The molybdenum(II) catalyst precursors are in general very active, reaching 99% conversion and 100% selectivity in the epoxidation of trans-hex-3-en-1-ol. Their performance is comparable with that of the [Mo(?3-C3H5)X(CO)2(LY)] complexes, but it increases with immobilization. On the other hand, most of the W(II) complexes display an activity similar or inferior to that of the Mo(II) analogues and it decreases after they are supported in MCM-41. DFT calculations show that tungsten complexes and iodide ligands are more easily oxidized from M(II) to M(VI) than molybdenum ones, while the energies of relevant species in the catalytic cycle are very similar for all complexes, making the theoretical rationalization of experimental catalytic data difficult.




Chemistry, Inorganic & Nuclear


Vasconcellos-Dias, M; Nunes, CD; Felix, V; Brandao, P; Calhorda, MJ

nossos autores


We thank the Fundacao para a Ciencia e a Tecnologia (FCT), Portugal, for financial support to Centro de Quimica e Bioquimica (UID/MULTI/00612/2019), Centro de Quimica Estrutural (UIDB/00100/2020 and UIDP/00100/2020), and BioISI -Biosystems & Integrative Sciences Institute UIDB/04046/2020 and UIDP/04046/2020). M. Vasconcellos-Dias thanks FCT for a PhD grant (SFRH/BD/37690/2007). The crystallographic studies were supported by CICECO-Aveiro Institute of Materials (UIDB/50011/2020 & UIDP/50011/2020), financed by National Funds through the FCT/MEC, and co-financed by QREN-FEDER through COMPETE under the PT2020 Partnership Agreement. We acknowledge M. S. Saraiva and P. Ferreira for help with some catalytic reactions and solid-state NMR, respectively.

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