While many [NiFe]-hydrogenase model complexes have been synthesized, only the Ni(II)Fe(II)(μ-H) state, known as Ni-R, has been accurately modeled. We present here a model system that is the first example of complexes akin to the Ni(II)Fe(II) and Ni(I)Fe(II) states of [NiFe]-hydrogenase, known as Ni-SIa and Ni-L respectively. The triple-decker sandwich compound [Cp3Ni2]BF4 (Cp−=cyclopetadienide) reacts with Fe(pdt)(dppe)(CO)2 to yield the heterobimetallic compound [CpNi(pdt)Fe(dppe)CO]BF4 ([1]BF4) with concomitant elimination of nickelocene (Figure 1). Compound [1]BF4 is reduced upon treatment with cobaltocene to yield the neutral, mixed-valent complex CpNi(pdt)Fe(dppe)CO (1). EPR spectroscopic studies of 1 reveal strong coupling to the cyclopentadienyl protons and weak coupling to the phosphorus center, indicating 1 is a nickel(I) paramagnet. Additionally, Mössbauer spectroscopy suggests the iron centers in [1]BF4 and 1 are best described as low-spin iron(II). Compound 1 reacts with stoichiometric acid to generate [1]+ and 0.5 equiv. of H2, indicating that this model system is formally a proton reduction catalyst (Figure 2).

Model compounds of [NiFe]-hydrogenase in the Ni-SIa and Ni-L states

249th National Meeting (2015)

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