Toward Alkane Functionalization Effected with Cp*W(NO)(alkyl)(eta(3-)allyl) Complexes
|Title||Toward Alkane Functionalization Effected with Cp*W(NO)(alkyl)(eta(3-)allyl) Complexes|
|Publication Type||Journal Article|
|Year of Publication||2009|
|Authors||Semproni SP, Graham PM, Buschhaus MS, Patrick BO, Legzdins P|
|Type of Article||Article|
|Keywords||ALLYL LIGANDS, CHEMISTRY, H BOND ACTIVATION, MOLYBDENUM, REACTIVITY|
Cp*W(NO)(n-alkyl)(eta(3)-allyl) complexes result from the selective activations of the terminal C-H bonds of alkanes. Consequently, the reactions of prototypical members of this family of complexes with a range of electrophilers and nucleophiles have been explored with a view to developing methods for functionalizing the newly formed alkyl ligands. The two principal complexes investigated in this regard have been Cp*W(NO)CH2SiMe3)(eta(3)-CH2CHCHMe) (1) and Cp*W(NO)(CH2C6H5)-(eta(3)-CH2CHCHMe) (2). In has been found that treatment of 1 and 2 with the oxidant I-2 at - 60 degrees C produces Cp*W(NO)I-2 and terminallly functionalized ICH2SiMe3 and ICH2C6H5, respectively. Oxidation of 1 by H2O2 also results in the loss of the allyl ligand and production of known oxo peroxo complex Cp*W(O)(eta(2)-O-2)(CH2SiMe3). Treatment of 1 and 2 with electrophiles affords the products resulting from addition of the electrophile to the electron-rich terminus of the sigma(-)pi distorted allyl ligands in the reactants. Thus, reagents of the type E-X (E = triphenylcarbenium, H. catecholborane; X = Cl, BF4) liberate CH3CH = CHCH2E and form the organometallic products Cp*W(NO)(X)(CH2SiMe3) and cp*W(NO)(X)(CH2C6H5), respectively. Exposure of the tungsten alkyl allyl complexes to isocyanide reagents leads to the formation of complexes insertion of isocyanide into the tungsten-allyl linkages. For instance, reaction of 1 with 2,6-xylylisocyanide produces Cp*w-(NO)(CH2SiMe3)(eta(2)-CH3CH2CHCHC = NC6H3Me2) (4b). A similar reaction of 2 with 2.6-xylylisocyanide affords both unconjugated and conjugated isocyanide insertion products, while treatment of 2 with n-butylisocyanide produces primarily the conjugated product. Finally. exposure of these tungsten alkyl allyl complexes to 1000 psi of CO gas generally results in the desired migratory insertion of the CO into the metal-alkyl linkages to form acyl compounds. Hence, 1 is first converted into Cp*W(NO)-(C(O)CH2SiMe3)(eta 3-CH2CHCHMe), which then subsequently transforms into isolable Cp*W(NO)-(C(O)CH3)(eta 3-CH2CHCHMe) (7). Interestingly, 2 does not react with CO under these experimental conditions. Nevertheless, the generality of this mode of reactivity is established by the fact that similar treatment of four other Cp*(W)(NO)(CH2CMe3)(eta(3)-allyl) complexes with CO gas at elevated pressures does afford the corresponding acyl products (8-11). All new organometallic complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of several compounds have been established by X-ray crystallographic analyses.