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Different Modes of Reactivity of Cp*W(NO)(alkyl)(η3-allyl) Complexes with Cyclic Amines: The Influence of the Allyl Ligands

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posted on 14.04.2008, 00:00 by Jenkins Y. K. Tsang, Miriam S. A. Buschhaus, Chikako Fujita-Takayama, Brian O. Patrick, Peter Legzdins
Metathesis reactions between Cp*W(NO)(CH2EMe3)Cl (E = C or Si) and a variety of bis(allyl)magnesium reagents lead to the formation of 18e Cp*W(NO)(alkyl)(η3-allyl) complexes. The compounds Cp*W(NO)(CH2CMe3)(η3-CH2CHCMe2) (1), Cp*W(NO)(CH2CMe3)(η3-CH2CMeCH2) (2), Cp*W(NO)(CH2CMe3)(η3-CH2CHCHMe) (3), Cp*W(NO)(CH2CMe3)(η3-CH2CHCHPh) (4), Cp*W(NO)(CH2SiMe3)(η3-CH2CHCHMe) (5), and Cp*W(NO)(CH2CMe3)(η3-CH2CHCH2) (6) have thus been synthesized in moderate yields. The solid-state molecular structures of 3, 4, 5, and 6 feature σ−π distorted allyl ligands in the endo conformation. Complex 1 effects the concurrent N−H and α-C−H activations of pyrrolidine and piperidine under ambient conditions and forms the alkyl amido complexes Cp*W(NO)(CH2CMe3)(NC4H7-2-CMe2CHCH2) (7) and Cp*W(NO)(CH2CMe3)(NC5H9-2-CMe2CHCH2) (8), respectively. Complexes 25 react with pyrrolidine in a similar manner, but the reaction of 3 to produce Cp*W(NO)(CH2CMe3)(NC4H7-2-CH2CMeCH2) (10) is not as clean since 3 is thermally unstable at 20 °C. Unfortunately, the concurrent N−H and α-C−H activation transformation encompasses only a very limited range of substrates, namely cyclic amines. Complex 6, which contains an unsubstituted allyl ligand, exhibits a unique mode of reactivity with pyrrolidine and piperidine, incorporating 2 equiv of the amines and forming Cp*W(NO)(NC4H8)(CHMeCH2NC4H8) (13) and Cp*W(NO)(NC5H10)(CHMeCH2NC5H10) (14), respectively. Plausible mechanisms are suggested to account for the different modes of reactivity of the Cp*W(NO)(alkyl)(η3-allyl) compounds with the cyclic amines. All new complexes have been characterized by conventional spectroscopic methods, and representative compounds have also been subjected to single-crystal X-ray crystallographic analyses.