Cyaphide Generation at an Aluminium(I) Center: A Useful Precursor for Phosphorus-Containing Heterocycles

Abstract

The synthesis of an aluminium(III) cyaphido complex, accessed through the formal oxidative addition of PCOSiⁱPr₃ at an aluminium(I) metal center, is reported. Reaction of Al(^DippNacNac) (^DippNacNac = CH{C(CH₃)N(Dipp)}₂; Dipp = 2,6-di(iso-propyl)phenyl) with PCOSiⁱPr₃ affords the aluminium(III) complex Al(^DippNacNac)(OSiⁱPr₃)(CP) in moderate (42%) isolated yield. Formation of this compound is accompanied by the concomitant formation of two isomeric side-products: a four-membered metallacycle Al(^DippNacNac)[κ²-P(O)CSiⁱPr₃], and the phospha-aluminirene Al(^DippNacNac)(η²-PCOSiⁱPr₃). The reactivity of Al(^DippNacNac)(OSiⁱPr₃)(CP) is governed by the enhanced covalency of the Al–CP bond relative to magnesium(II) cyaphido complexes, and the steric protection offered to the cyaphide moiety by the ß-diketiminato and siloxide ligands. Despite the diminished reactivity of this compound when compared to more ionic complexes of the cyaphide ion, the C≡P triple bond takes part in [2+1], [2+3] and [2+4] cyclization reactions with Ni(COD)₂, organic azides, and 2,3-dimethyl-butadiene, respectively. These reactions can be used to access phosphorus-containing heterocycles that can be readily detached from the aluminium(III) platform using iodation and transmetallation strategies.