Transformations in Transition-Metal Carbonyls Containing Arsenic: Exploring the Chemistry of [Et4N]2[HAs{Fe(CO)4}3] in the Search for Single-Source Precursors for Advanced Metal Pnictide Materials
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posted on 2016-02-04, 00:00 authored by Desmond
E. Schipper, Benjamin E. Young, Kenton H. WhitmireThe chemistry of [Et4N]2[HAs{Fe(CO)4}3] ([Et4N]2[I]) has
been explored with the goal of preparing heterometallic compounds
for use as single-source precursors to metal pnictide phases. Reaction
of AgPF6 with [Et4N]2[I] in THF produces [Et4N][HAs{Fe2(CO)6(μ-CO)(μ-H)}{Fe(CO)4}] in 12% yield, but the
yield is improved to 71% if the reaction is carried out with added
[Et4N][HFe(CO)4]. The structure possesses rare
As–H and {Fe2(CO)6(μ-CO)(μ-H)}
fragments. The addition of [CPh3][BF4] to [Et4N]2[I] in THF gives [Et4N][Fe3(CO)9(μ-CO){μ3-AsFe(CO)4}] in 45% yield. This compound is also obtained
as a minor product from oxidation of [Et4N]2[I] with 1 equiv of AgPF6, AsCl3, SbCl3, or BiCl3 in THF. The cluster consists
of an Fe3As tetrahedron with an isolated Fe(CO)4 unit bound to the arsenic in a spiked-tetrahedral arrangement. Refluxing
[Et4N]2[I] with 1 equiv of AgPF6 in THF produces [Et4N][(μ-H)2Fe3(CO)9){μ3-AsFe(CO)4}]. This cluster is similar to [Et4N][Fe3(CO)9(μ-CO){μ3-AsFe(CO)4}] with the bridging CO being replaced by two bridging hydride ligands.
Treatment of [Et4N]2[I] with 1
equiv of Mn(CO)5Br in THF gives the spirocyclic compound
[Et4N][{FeMn(CO)8}(μ4-As){Fe2(CO)6(μ-CO)(μ-H)}] in 52% yield. Refluxing
this cluster in the presence of triethylamine and an additional 1.8
equiv of Mn(CO)5Br gives [Et4N][Fe3(CO)9(μ-CO){μ3-AsMn(CO)4Br-cis}] in low yield. Alternatively, treating [Et4N][{FeMn(CO)8}(μ4-As){Fe2(CO)6(μ-CO)(μ-H)}] with triflic acid or an
oxidant ([Ox] = Cu+, Ag+, Cu2+, CPh3+) in dichloromethane produces the two neutral
compounds (μ-H)2Fe3(CO)9{μ3-AsMn(CO)5} and {FeMn(CO)8}(μ4-As){Fe2(CO)8} in trace amounts and
high yield, respectively. The former could be removed by treatment
with base in nonpolar solvents. Neutral {FeMn(CO)8}(μ4-As){Fe2(CO)8} can then be isolated
by filtration and evaporation in 74% yield. An improved synthesis
of the known [Fe3(CO)9(μ-CO){μ3-PFe(CO)4}]− as its tetraethylammonium
salt is also included. All compounds were characterized by spectroscopy,
by ESI-mass spectrometry, and by single-crystal X-ray diffraction.
