Lewis Acid Stabilized Methylidene And Oxoscandium Complexes

摘要

Tebbe's reagent, Cp_2Ti[μ_2-CH_2)(μ_2-Cl)Al(CH_3)_2], can be categorized as a quintessential organometallic reagent due to its role in catalytic olefin metathesis and stoichiometric methylidene group-transfer processes. It has been instrumental in the design of more efficient catalysts as well as the synthesis of natural products and commodity chemicals and materials. The preparation of Tebbe's reagent involves treatment of Cp_2TiCl_2 with 2 equiv of Al(CH_3)_3, resulting in the elimination of CH_4 and AlCl(CH_3)_2. Likewise, the analogue Cp_2Ti[μ_2-CH_2)(μ_2-CH_3)Al(CH_3)_2] is prepared by addition of Al(CH_3)_3 to Cp_2Ti(CH_3)_2. Although originally speculated by Tebbe, the role of A](CH_3)_3 along the deprotonation step has been addressed by Grubbs (Ti) and Schrock (Ta). Surprisingly, for over 30 years the report of a scandium (or lanthanide) methylidene complex analogous to Tebbe's reagent has not been realized. In fact, scandium alkylidene complexes are unknown to date, while their lanthanide relatives have been scarcely documented. We were curious as to whether Al(CH_3)_3 could stabilize a highly polarized Sc=CH_2 ligand as it does in the case of Ti. Here, we describe the preparation of such a ligand, its isolation, and use as a Bronsted base or as a group 3 Wittig reagent.