Regioselective Insertion of Aluminum(I) in the cyclo-P5 Ring of Pentaphosphaferrocene

Abstract

A route to directly access mixed Al-Fe polyphosphide complexes was developed. The reactivity of pentaphosphaferrocene, [Cp*Fe(η⁵ -P₅ )] (Cp*=C₅ Me₅ ), with two different low-valent aluminum compounds was investigated. The steric and electronic environment around the [Al^I ] centre are found to be crucial for the formation of the resulting Al-Fe polyphosphides. Reaction with the sterically demanding [Dipp-BDIAl^I ] (Dipp-BDI={[2,6-ⁱ Pr₂ C₆ H₃ NCMe]₂ CH}^- ) resulted in the first Al-based neutral triple-decker type polyphosphide complex. For [(Cp*Al^I )₄ ], an unprecedented regioselective insertion of three [Cp*Al^III ]²⁺ moieties into two adjacent P-P bonds of the cyclo-P₅ ring of [Cp*Fe(η⁵ -P₅ )] was observed. The regioselectivity of the insertion reaction could be rationalized by isolating an analogue of the reaction intermediate stabilized by a strong σ-donor carbene.

Keywords: aluminum; ferrocene; polyphosphides; regioselectivity; triple-decker.