β-Elimination and insertion of CNR in transient pentamethylcyclopentadienyl-imido-tantalum dialkyl complexes. X-ray structure of [TaCp*{N(2,6-Me2C6H3)}(CH2=CH2)(PMe3)]

Abstract

The transient dialkyl complexes [TaCp*R2(NAr)] (Cp*=C5Me5; R=Et, n-Pr; Ar=2,6-Me2C6H3), obtained by alkylation of [TaCp*Cl2(NAr)] with two equiv. of RMgCl in diethylether at low temperature, react with one equiv. of PMe3 to give [TaCp*(NAr)(CH2CHR)(PMe3)] (R=H1, Me2) after β-elimination and reductive elimination of alkane. When the same alkylation is carried out and then one equiv. of CN(2,6-Me2C6H3) is added after heating to room temperature, the alkyl iminoacyl insertion products [TaCp*R{η2-CR=N(Ar)}(NAr)] (R=Et3, n-Pr4) are obtained. However when alkylation with one equiv. of MgClR (R=Et, n-Pr, i-Pr) is carried out at ambient temperature after the addition of CN(2,6-Me2C6H3), the chloro iminoacyl complexes [TaCp*Cl{η2-CR=NAr)}(NAr)] (R=Et 5, n-Pr 6, i-Pr 7) are isolated. The structure of [TaCp*(NAr)(CH2=CH2) (PMe3)] (1) has been determined by X-ray diffraction methods.