No abstract

Although alkyl complexes of [Fe4S4] clusters have been invoked as intermediates in a number of enzymatic reactions, obtaining a detailed understanding of their reactivity patterns and electronic structures has been difficult owing to their transient nature. To address this challenge, we herein report the synthesis and characterization of a 3:1 site-differentiated [Fe4S4]2+–alkyl cluster. Whereas [Fe4S4]2+ clusters typically exhibit pairwise delocalized electronic structures in which each Fe has a formal valence of 2.5+, Mössbauer spectroscopic and computational studies suggest that the highly electron-releasing alkyl group partially localizes the charge distribution within the cubane, an effect that has not been previously observed in tetrahedrally coordinated [Fe4S4] clusters.

Phosphatetrahedranes ( t BuCP) 2 and ( t BuC) 3 P were recently reported and represent the first tetrahedranes containing a mixed carbon/phosphorus core. Herein, we report that tetrahydrofuran (THF) solutions of the parent triphosphatetrahedrane HCP 3 may be generated in 31% yield (NMR internal standard yield) by combining [Na(THF) 3 ][P 3 Nb(ODipp) 3 ] (Dipp = 2,6diisopropylphenyl), INb(ODipp) 3 (THF), and bromodichloromethane in thawing THF. While HCP 3 was found to be stable in dilute THF solutions for extended periods of time, the concentration of the solution at −40 °C led to the formation of a black precipitate, which has been tentatively assigned as a polymerized form of HCP 3 . HCP 3 reacts readily with (dppe)Fe(Cp*)Cl (dppe = 1,2-bis(diphenylphosphino)ethane, Cp*= η 5 -C 5 Me 5 ) in the presence of Na[BPh 4 ] to form a purple cationic iron complex of triphosphatetrahedrane (50% yield), which was structurally characterized in a single-crystal X-ray diffraction experiment. Additionally, we present a series of homodesmotic equations analyzed via quantum chemical calculations that suggest triphosphatetrahedrane is the least strained of the mixed C/P phosphatetrahedranes.