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A New ONO3‑ Trianionic Pincer-Type Ligand for Generating Highly Nucleophilic Metal–Carbon Multiple Bonds

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journal contribution
posted on 11.07.2012, 00:00 by Matthew E. O’Reilly, Ion Ghiviriga, Khalil A. Abboud, Adam S. Veige
Appending an amine to a CC double bond drastically increases the nucleophilicity of the β-carbon atom of the alkene to form an enamine. In this report, we present the synthesis and characterization of a novel CF3–ONO3‑ trianionic pincer-type ligand, rationally designed to mimic enamines within a metal coordination sphere. Presented is a synthetic strategy to create enhanced nucleophilic tungsten–alkylidene and −alkylidyne complexes. Specifically, we present the synthesis and characterization of the new CF3–ONO3‑ trianionic pincer tungsten–alkylidene [CF3–ONO]­WCH­(Et)­(OtBu) (2) and −alkylidyne {MePPh3}­{[CF3–ONO]­WC­(Et)­(OtBu)} (3) complexes. Characterization involves a combination of multinuclear NMR spectroscopy, combustion analysis, DFT computations, and single crystal X-ray analysis for complexes 2 and 3. Exhibiting unique nucleophilic reactivity, 3 reacts with MeOTf to yield [CF3–ONO]­WC­(Me)­(Et)­(OtBu) (4), but the bulkier Me3SiOTf silylates the tert-butoxide, which subsequently undergoes isobutylene expulsion to form [CF3–ONO]­WCH­(Et)­(OSiMe3) (5). A DFT calculation performed on a model complex of 3, namely, [CF3–ONO]­WC­(Et)­(OtBu) (3′), reveals the amide participates in an enamine-type bonding combination. For complex 2, the Lewis acids MeOTf, Me3SiOTf, and B­(C6F5)3 catalyze isobutylene expulsion to yield the tungsten–oxo complex [CF3–ONO]­W­(O)­(nPr) (6).