Coordination Behavior of a P4‐Butterfly Complex towards Transition Metal Lewis Acids: Preservation versus Rearrangement

The reactivity of the P4 butterfly complex [{Cp’’’Fe(CO)2}2(μ,η1:1‐P4)] (1, Cp’’’=η5‐C5H2tBu3) towards divalent Co, Ni and Zn salts is investigated. The reaction with the bromide salts leads to [{Cp’’’Fe(CO)2}2(μ3,η2:1:1‐P4){MBr2}] (M=Co (2Co), Ni (2Ni), Zn (2Zn)) in which the P4 butterfly scaffold is preserved. The use of the weakly ligated Co complex [Co(NCCH3)6][SbF6]2, results in the formation of [{(Cp’’’Fe(CO)2)2(μ3,η4:1:1‐P4)}2Co][SbF6]3 (3), which represents the second example of a homoleptic‐like octaphospha‐metalla‐sandwich complex. The formation of the threefold positively charged complex 3 occurs via redox processes, which among others also enables the formation of [{Cp’’’Fe(CO)2}4(μ5,η4:1:1:1:1‐P8){Co(CO)2}][SbF6] (4), bearing a rare octaphosphabicyclo[3.3.0]octane unit as a ligand. On the other hand, the reaction with [Zn(NCCH3)4][PF6]2 yields the spiro complex [{(Cp’’’Fe(CO)2)2(μ3,η2:1:1‐P4)}2Zn][PF6]2 (5) under preservation of the initial structural motif. Highly flexible: By coordination to Lewis acids the P4 butterfly complex can preserve the initial P4 butterfly scaffold and act as a 4σ e− donor. However, in the presence of weakly ligated d6 metals, the P4 unit tends to rearrange. This leads to a rare octaphospha‐cobalt‐sandwich complex in which the P4 units have isomerized into aromatic cyclo‐P4[Fe]2 units ([Fe]=Cp’’’Fe(CO)2). Additionally, also a dimerization to an all‐phosphorus derivative of bicylo[3.3.0]octane is observed.