Understanding Synthetic Peculiarities of Cationic Molybdenum(VI) Imido Alkylidene N‐Heterocyclic Carbene Complexes

Abstract

We report on novel synthetic approaches to molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes including the first NHC alkylidene complexes featuring pentafluorophenyl-substituted imido ligands, highly basic 6-Mes (6-Mes = 1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene) NHC ligands and the preparation of the first representatives of cationic 14-electron Mo imido alkylidene NHC catalysts bearing sterically demanding anionic terphenoxide ligands. Also, the Mo imido alkylidene and alkylidyne NHC bisalkoxide complexes [Mo(NR)(CHCMe 2 Ph)(NHC)(OR′) 2 ], [Mo(NH-C 6 F 5 )-(CCMe 2 Ph)(aIMes){OCMe(CF 3 ) 2 } 2 ] (aIMes = 1,3-dimesitylimidazol-5-ylidene, an abnormally C 5 -bound imidazolylidene) and [Mo(NH-2-CF 3 -C 6 H 4 )(CCMe 2 Ph)(6-Mes){OCMe(CF 3 ) 2 } 2 ] are presented. Anionic Mo amido alkylidyne complexes have been [a]

Origin and Use of Hydroxyl Group Tolerance in Cationic Molybdenum Imido Alkylidene N‐Heterocyclic Carbene Catalysts

“…Indeed, the imido alkylidene motif is remarkably stable considering the fact that it is generated via protonation of a bisimido species, often with excess acid or alcohols . Amido alkylidyne complexes, however, seem to be close in energy and form reversibly from imido alkylidenes by formal proton transfer . Data published by Schrock et al.…”

“… Synthesis of cationic monocarboxylate species 11 – 15 from bistriflates 9 a – d via mixed monotriflate/monocarboxylate complex 10 or in situ generation of cationic monotriflate species and subsequent salt metathesis. Synthesis of cationic monocarboxylate complexes 17 a , b from dichloride NHC alkylidenes 16 a , b . Ad=adamantyl.…”

“…This results in a maximum distance between the NHC and the protic groups as compared to cis coordination, which in turn makes protonation of the NHC less probable. Recently, we reported on oxo‐bridged dimers that formed in the reaction of a Mo‐imido alkylidene NHC complex containing a basic aryloxide with water . Moreover, it was shown that protonation of Mo( N ‐Ad)(CHCMe 2 Ph)(NHC)(pyrrolide)(aryloxide) selectively eliminates pyrrole .…”

“…Synthesis of cationic monocarboxylate complexes 17 a,b from dichloride NHC alkylidenes 16 a,b. [16] Ad = adamantyl.…”

“…Recently, we reported on oxo-bridged dimers that formed in the reaction of a Mo-imido alkylidene NHC complex containing a basic aryloxide with water. [16] Moreover, it was shown that protonation of Mo(N-Ad)(CHCMe 2 Ph)-(NHC)(pyrrolide)(aryloxide) selectively eliminates pyrrole. [21] Also, other examples in which pyrrole was eliminated from metal imido alkylidene NHC bispyrrolide complexes or cationic metal imido alkylidene NHC monopyrrolide complexes were reported.…”