Metal- and Ligand-Supported Reduction of the {Fe2S2} Cluster as a Path to Formation of Molecular Group 13 Element Complexes {Fe2S2M} (M = Al, Ga)

Abstract

The first examples of molecular cluster complexes with the Fe2S2(CO)6 moiety covalently bound to the group 13 elements Al and Ga have been synthesized and characterized. The complexes [(Cp*M)Fe2(μ3-S)2(CO)6] with M = Al (1), Ga (2) have been synthesized by the reduction of [Fe2S2(CO)6] by the corresponding M(I) complexes [AlCp*]4 and [GaCp]. Analogously, upon reduction of [Fe2S2(CO)6] by a Ga(II) complex, [(dpp-Bian)Ga]2 (dpp-Bian = 1,2-bis{(2,6-diisopropylphenyl)imino}acenaphthene), the compound [((dpp-Bian)Ga)Fe2(μ3-S)2(CO)6] (3) is formed. The M atoms in 1 and 2 are coordinated by the two S atoms; thus, the fragment Fe2S2(CO)6 is considered to be dianionic. The Cp* moiety is bound differently to the Al (η5) and Ga (η2) atoms, which can be rationalized on the basis of DFT calculations showing different orbital structures for the analogous compounds. In compound 3 the Ga atom is coordinated by the two S atoms as well; therefore, the fragment Fe2S2(CO)6 is considered to be dianionic, while the Bian ligand is radical anionic, as confirmed by the structure, EPR spectra, and DFT. The redox-active Bian ligand thus takes part in the reduction of the Fe2S2 cluster and changes its formal charge (−2 → −1), along with the Ga center (+2 → +3). Analogously to 3, the Al complex [((dpp-Bian)Al)Fe2(μ3-S)2(CO)6] (4) is formed in solution and detected by EPR, but it is not stable enough to be crystallized. In contrast to the case for 1 and 2, the calculated molecular and electronic structures of 3 and 4 are similar.