om0c00435_si_001.pdf (1.12 MB)
Synthesis of Tungsten(VI) Imido Alkylidene Bispyrrolide Complexes via the Isocyanate Route
journal contribution
posted on 2020-08-14, 20:44 authored by Janis
V. Musso, Mathis J. Benedikter, Paul Gebel, Iris Elser, Wolfgang Frey, Michael R. BuchmeiserA general route to
tungsten(VI) imido alkylidene bispyrrolide complexes
via the extrusion of CO2 from the reaction of one equivalent
of an aryl isocyanate with WOCl4 to form the corresponding
imido complexes is reported. The otherwise required 2-fold excess
of an aniline derivative in this reaction sequence is circumvented
in the reaction of W(O)Cl4 with Ar-NCO (Ar = 2,6-Me2-C6H3, 2,6-iPr2-C6H3, 2,6-Cl2-C6H3, 3,5-Me2-C6H3) to W(NAr)Cl4. In the subsequent steps, the scope of
the synthesis of tungsten(VI) (NAr) alkylidene complexes
via the isocyanate route, which was so far limited to Ar = 2,6-Me2-C6H3 and 2,6-iPr2-C6H3, was extended to Ar = 2,6-Cl2-C6H3 and 3,5-Me2-C6H3. From those tungsten alkylidene complexes, the use of inexpensive
and readily available reagents facilitates the synthesis of tungsten(VI)
bispyrrolide complexes of the type W(NAr)(CHCMe2Ph)(Pyr)2(DME) and W(NAr)(CHCMe2Ph)(Me2Pyr)2 (Ar = 2,6-Me2-C6H3, 2,6-iPr2-C6H3, 2,6-Cl2-C6H3, 3,5-Me2-C6H3; Pyr = pyrrolide,
Me2Pyr = 2,5-dimethylpyrrolide), also avoiding the use
of triflic acid. Thereby, both competitive yields with regard to previously
published routes and high atom economy and thus cost-effectiveness
are achieved. In addition, the peculiarities in the alkylation of
complexes of the type W(NAr)(OtBu)2Cl2(THF) have been investigated and factors leading
to undesired overalkylation are outlined.
