Cyaphide generation at an aluminium(i) center: a useful precursor for phosphorus-containing heterocycles

The synthesis of an aluminium(iii) cyaphido complex, accessed through the formal oxidative addition of PCOSi ⁱ Pr₃ 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 PCOSi ⁱ Pr₃ affords the aluminium(iii) complex Al(^DippNacNac)(OSi ⁱ Pr₃)(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)[κ ²-P(O)CSi ⁱ Pr₃], and the phospha-aluminirene Al(^DippNacNac)(η ²-PCOSi ⁱ Pr₃). The reactivity of Al(^DippNacNac)(OSi ⁱ Pr₃)(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 β-diketiminato and siloxide ligands. Despite the diminished reactivity of this compound when compared to more ionic complexes of the cyaphide ion, the C[triple bond, length as m-dash]P triple bond partakes 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.