New Chloro, μ-Oxo, and Alkyl Derivatives of Dioxomolybdenum(VI) and -Tungsten(VI) Complexes Chelated with N₂O Tridentate Ligands:  Synthesis and Catalytic Activities toward Olefin Epoxidation

Abstract

A new series of cis-dioxomolybdenum(VI) complexes MoO(2)(L(n))Cl (n = 1-5) were prepared by the reaction of MoO(2)Cl(2)(DME) (DME = 1,2-dimethoxyethane) with 2-N-(2-pyridylmethyl)aminophenol (HL(1)) or its N-alkyl derivatives (HL(n)) (n = 2-5) in the presence of triethylamine. The new mu-oxo dimolybdenum compounds [MoO(2)(L(n))](2)O (n = 1, 4, 5, 7) were also prepared by treating the corresponding ligand HL(n) with MoO(2)(acac)(2) (acac = acetylacetonate) in warm methanolic solutions or (NH(4))(6)[Mo(7)O(24)].4H(2)O in the presence of dilute HCl. Treatment of MoO(2)(L(1))Cl or [MoO(2)(L(1))](2)O with the Grignard reagent Me(3)SiCH(2)MgCl gave the alkyl compound MoO(2)(L(1))(CH(2)SiMe(3)), which represents the first example of dioxomolybdenum(VI) alkyl complex supported by a N(2)O-type ancillary ligand. The analogous chloro and mu-oxo tungsten derivatives WO(2)(L(n))Cl (n = 6, 7) and [WO(2)(L(n))](2)O (n = 1, 4, 6, 7) were prepared by the reaction of WO(2)Cl(2)(DME) with HL(n) in the presence of triethylamine. Similar to their molybdenum analogues, the tungsten alkyl complexes WO(2)(L(n))(R) (n = 6, 7; R = Me, Et, CH(2)SiMe(3), C(6)H(4)(t)Bu-4) were synthesized by treating WO(2)(L(n))Cl or [WO(2)(L(n))](2)O (n = 6, 7) with the appropriate Grignard reagents. The catalytic properties of selected dioxo-Mo(VI) and -W(VI) chloro and mu-oxo complexes toward epoxidation of styrene by tert-butyl hydroperoxide (TBHP) were also investigated.

Intramolecular oxidation of the ligand 4-methyl-2-N-(2-pyridylmethyl)aminophenol (Hpyramol) upon coordination with iron(II) chloride and manganese(II) perchlorate

“…1). This Hpyramol ligand was reported in 2002 by Wong et al [12] as tungstate and molybdate complexes for the catalysed-epoxidation of styrene. Nevertheless, no crystal structure with this ligand could be found in the Cambridge Structural Databse (January 2004 update) [13].…”

“…The ligand Hpyramol (3) was prepared by reductive amination starting from 2-amino-4-methylphenol (1) and picolinaldehyde (2), according to the experimental procedure reported by Wong et al [12] with slight modifications (see Fig. 2).…”

“…The present paper describes the preparation and characterisation of two new potential oxidation catalysts, namely [FeCl 2 (pyrimol)(MeOH)](MeOH) and Mn(ClO 4 )-(pyrimol)(Hpyrimol)] 2 , obtained from 4-methyl-2-N -(2-pyridylmethyl)aminophenol (Hpyramol) [12] which was oxidized to 4-methyl-2-N -(2-pyridylmethylene)aminophenol (Hpyrimol) upon coordination with the metal salts ( Fig. 1).…”

cis-Dioxomolybdenum(VI) Complexes Containing Chiral Ligands: Synthesis and Catalytic Application in Olefin Epoxidation

“…Although a number of X-ray diffraction studies have been reported concerning the bidentated coordination of pyridine and quinoline derivatives [31], only three bimetallic dioxomolybdenum(VI) complexes have been described containing anionic tridentated ligands [32][33][34]. Therefore, complex 1 represents the first X-ray characterization for a monometallic molybdenum complex bearing a N,N',O-tridentated ligand [35,33]. The Mo-Cl bond are relatively long (2.52 Å) because of the strong trans influence of the oxo ligand; the expected range of Mo-Cl bond distances in cis-dioxo Mo(VI) complexes are 2.36-2.41 Å [36,37].…”

High oxidation state organomolybdenum and organotungsten chemistry in protic environments

“…[43] (M = Mo, W). Derivatives where the alkyl-or aryl-oxido scaffold is supported by additional Lewis bases (mostly N-donor ligands) are also known, such as [MO 2 (CH 3 ) 2 L 2 ] (M = Mo, W; L 2 = N-based chelating ligand such as a bipyridine [44][45][46][47][48] or a 1,4-diazadiene [44,49]), WO(CH 3 ) 4 (bipy) [46], and (XL 2 )MO 2 R (M = Mo, W; XL 2 = 3 -HB(3,5-Me 2 pz) 3 [50,51], 2-N-(2-pyridylmethyl)aminophenolato [52]). Compounds containing both alkyl and cyclopentadienyl derivatives, e.g.…”