SOMC-Designed Silica Supported Tungsten Oxo Imidazolin-2-iminato Methyl Precatalyst for Olefin Metathesis Reactions

Abstract

Synthesis, structure, and olefin metathesis activity of a surface complex [(≡Si-O-)W(═O)(CH)-ImN] (4) (Im = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) supported on silica by a surface organometallic chemistry (SOMC) approach are reported. The reaction of N-silylated 2-iminoimidazoline with tungsten(VI) oxytetrachloride generated the tungsten oxo imidazolin-2-iminato chloride complex [ImNW(═O)Cl] (2). This was grafted on partially dehydroxylated silica pretreated at 700 °C (SiO) to afford a well-defined monopodal surface complex [(≡Si-O-)W(═O)Cl-ImN] (3). 3 underwent alkylation by ZnMe to produce [(≡Si-O-)W(═O)(CH)-ImN] (4). The alkylated surface complex was thoroughly characterized by solid-state NMR, elemental microanalysis, Raman, FT-IR spectroscopies, and XAS analysis. 4 proved to be an active precatalyst for self-metathesis of terminal olefins such as propylene and 1-hexene.

Effect of Lewis Acids on the Catalyst Activity for Alkene Metathesis, Z-/E- Selectivity and Stability of Tungsten Oxo Alkylidenes

“…Catalyst heterogenization prevented bimolecular deactivation and, as a consequence, the resulting complexes show very high catalytic activities and stabilities overperforming the imido analogues particularly when reacting with internal olefins. These high activities and stabilities are also reported for silica grafted tungsten oxo alkyl complexes that act as alkylidene precursors (21 in Scheme 2) [49][50][51].…”

Density Functional Theory Study of the Reaction between d0 Tungsten Alkylidyne Complexes and H2O: Addition versus Hydrolysis

“…The activation free-energy differences among the three substrates are within 3 kcal/mol for both pathways, suggesting that the intrinsic electronic effects are not very significant. Instead, steric effects may play a more important role in controlling the reaction pathway, a finding that may suggest new precursor designs. ,,, For instance, replacing an alkyl group with an aryl group may substantially change the steric effect and lead to a new product distribution.…”

“…Instead, steric effects may play a more important role in controlling the reaction pathway, a finding that may suggest new precursor designs. 52,53,80,81 For instance, replacing an alkyl group with an aryl group may substantially change the steric effect and lead to a new product distribution.…”

Recent Advances of Imidazolin-2-iminato in Transition Metal Chemistry

“…[100][101][102][103][104] Tamm and co-workers contributed to this field by reporting first tungsten and molybdenum alkylidyne complexes bearing strongly electrondonating imidazolin-2-iminato ligands in combination with electron-withdrawing fluorinated alkoxides. [105][106] The reactions between the trialkoxides alkylidyne precursors 39 with lithium salt of imidazolin-2-imides at room temperature conveniently afforded the metal complexes 40 [107] The reaction between tungsten(VI) oxytetrachloride and 1 equivalent of N-silylated 2-iminoimidazoline in dichloromethane under the refluxing condition afforded the rapid precipitation of complex Im Dipp NWOCl3 (41) as orange crystalline solid in high yield (84%) (Scheme 23).…”