Half-sandwich imido complexes of niobium bearing alkyne, benzyne and benzylidene ligands: relatives of the zirconocene family

Abstract

Reactions of [Nb(C₅H₅)(NC₆H₃Prⁱ₂-2,6)Cl₂] 1a and [Nb(C₅Me₅)(NC₆H₃Prⁱ₂-2,6)Cl₂] 1b with 1 and 2 equivalents of benzylpotassium respectively gave the niobium benzyl derivatives [Nb(C₅H₅)(NC₆H₃Prⁱ₂-2,6)Cl(CH₂Ph)] 2 and [Nb(C₅Me₅)(NC₆H₃Prⁱ₂-2,6)(CH₂Ph)₂] 3. Treatment of 3 with trimethylphosphine afforded the benzylidene complex [Nb(C₅Me₅)(NC₆H₃Prⁱ₂-2,6)(PMe₃)(CHPh)] 4. Complex 1a reacted with phenylmagnesium chloride in the presence of PMe₃ to give [Nb(C₅H₅)(NC₆H₃Prⁱ₂-2,6)Ph₂(PMe₃)] 5 which upon heating at 70 °C in heptane, converts to the η²-benzyne complex [Nb(C₅H₅)(NC₆H₃Prⁱ₂-2,6)(η²-C₆H₄)(PMe₃)] 6. The niobium(III) complexes [Nb(C₅H₅)(NC₆H₄Bu^t-2)(PMe₃)₂] 8a and [Nb(C₅Me₅)(NC₆H₃Prⁱ₂-2,6)(PMe₃)₂] 8b were obtained upon magnesium reduction of 1a and 1b respectively in the presence of an excess of PMe₃. They were converted into [Nb(C₅H₅)(NC₆H₄Bu^t-2)(η²-R¹CCR²)(PMe₃) (R¹ = R² = Ph 9a; R¹ = Ph, R² = H 9b) and [Nb(C₅Me₅)(NC₆H₃Prⁱ₂-2,6)(η²-PhCCPh)(PMe₃)] 9c upon treatment with the appropriate alkyne. The molecular structures of the 2-tert-butylimido complexes [Nb(C₅H₅)(NC₆H₄Bu^t-2)Cl₂] 7 and 9a have been determined.