Regioselective Insertion of Aluminum(I) in the cyclo‐P(5) Ring of Pentaphosphaferrocene

A route to directly access mixed Al–Fe polyphosphide complexes was developed. The reactivity of pentaphosphaferrocene, [Cp*Fe(η (5)‐P(5))] (Cp*=C(5)Me(5)), 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)Pr(2)C(6)H(3)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‐P(5) ring of [Cp*Fe(η(5)‐P(5))] 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.