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*=C5Me5), with two different low-valent aluminum compounds was investigated. The steric and electronic environment around the [AlI] centre are found to be crucial for the formation of the resulting Al–Fe polyphosphides. Reaction with the sterically demanding [Dipp-BDIAlI] (Dipp-BDI={[2,6-iPr2C6H3NCMe]2CH}−) resulted in the first Al-based neutral triple-decker type polyphosphide complex. For [(Cp*AlI)4], an unprecedented regioselective insertion of three [Cp*AlIII]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.