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

A route to directly access mixed Al–Fe polyphosphide complexes was developed. The reactivity of pentaphosphaferrocene, [Cp*Fe(η⁵-P₅)] (Cp*=C₅Me₅), 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-ⁱPr₂C₆H₃NCMe]₂CH}⁻) 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.