The Reactivity of the P4-Butterfly Ligand [{Cp'''Fe(CO)2}2(µ,η1:1-P4)] Towards Transition Metal Complexes: Coordination versus Rearrangement

Abstract The reaction of the P4 butterfly compound [{Cp'''Fe(CO)2}2(μ,η1:1-P4)] (1, Cp''' = C5H2tBu3) towards various transition metal complexes is investigated. On the one hand, the reaction of 1 with [(PPh3)Au(tht)][PF6] (tht = tetrahydrothiophene) and [M(CO)4(nbd)] (M = Cr, Mo, W; nbd = norbornadiene) yields chelating complexes of the type [{Cp'''Fe(CO)2}2(µ3,η1:1:1:1-P4){Au(PPh3)}] (2d) and [{Cp'''Fe(CO)2}2(µ3,η1:1:1:1-P4){M(CO)4}] (2a-c, M = Cr, Mo, W), respectively, bearing intact P4 butterfly ligands with exceedingly small bite angles (ca. 65°). The reaction of 1 with Ag[PF6] even afforded the spiro complex [{(Cp'''Fe(CO)2)2(µ3,η1:1:1:1-P4)}2Ag][PF6] (3), in which the silver cation is coordinated in a distorted tetrahedral fashion by two P4 butterfly motifs. On the other hand, the reaction of 1 with the carbonyl containing Lewis acids Fe2(CO)9 or Co2(CO)8 leads to rearrangement yielding [{Cp'''Fe(CO)2}2{Co(CO)3}2(μ4,η2:2:1:1-P4)] (4), incorporating a folded cyclo-P4 scaffold, and [{Cp'''Fe(CO)2}2(µ4,η1:1:1:3-P4CO){Fe(CO)4}{Fe(CO)3}] (5), displaying a tetraphosphole structural motif obtained after carbonyl insertion, respectively. The products are comprehensively characterized by different spectroscopic methods as well as single crystal X-ray diffraction analysis and theoretical calculations.