화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.134, No.27, 11185-11195, 2012
A New ONO3- Trianionic Pincer-Type Ligand for Generating Highly Nucleophilic Metal-Carbon Multiple Bonds
Appending an amine to a C=C double bond drastically increases the nucleophilicity of the beta-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-allcylidene [CF3-ONO]W=CH(Et)((OBu)-Bu-t) (2) and -alkylidyne {MePPh3}{[CF3-ONO]W C(Et)((OBu)-Bu-t)} (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)((OBu)-Bu-t) (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)((OBu)-Bu-t) (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)(Pr-n) (6).