Synthesis and Electrochemical Properties of cis- and trans-[Mo?(o?C-Fc)2(DArF)2] (o?C-Fc = Ferrocenecarboxylate; DArF = N,N′-Diarylformamidinate)

By Cai, Xu-Min; Zimmermann, Teresa K.; Pothig, Alexander & Kuhn, Fritz E.
Published in Inorganic Chemistry NULL 2015

Abstract

The reaction of cis-[Mo?(o?C-Fc)2(NCCH3)4][BF4]2 (cis-1) with three electronically different N,N′-diarylformamidinate (DArF) ligands [DArF = N,N′-diphenylformamidinate (DPhF), N,N′-di(p-trifluoromethylphenyl)formamidinate (DTfmpF), and N,N′-di(p-anisyl)formamidinate (DAniF)] results in products of the general composition [Mo?(o?C-Fc)2(DArF)2]. Even though the trans-[Mo?(o?C-Fc)2(DArF)2] isomers were originally expected to be the sole products, the corresponding cis-[Mo?(o?C-Fc)2(DArF)2] complexes were isolated as well via crystallization and verified unambiguously by X-ray crystallography. All novel complexes, namely, cis-[Mo?(o?C-Fc)2(DPhF)2] (cis-2a), cis-[Mo?(o?C-Fc)2(DTfmpF)2] (cis-2b), and trans-[Mo?(o?C-Fc)2(DAniF)2] (trans-2c), were studied regarding their electrochemical properties with respect to electrolyte, solvent, and ligand. The electron-donating ligand DArF- enables the oxidation of the [Mo?]4+ unit prior to that of Fc, while the oxidation sequence is reversed when acetonitrile or diphosphine ligands are coordinated instead of formamidinate. In the case of trans-[Mo?(o?C-Fc)2(DAniF)2], interactions were found between the two redox-active ferrocenecarboxylate ligands, with a clear ΔE1/2 value originating from the peak-to-peak separation in DPV of around 100 mV with CH?Cl2 as solvent. Furthermore, the second oxidation of the Mo?-handle [Mo?]5+/[Mo?]6+ was exclusively observed with DAniF- as the ligand. Similar absorption patterns in UV-vis spectra were found within the series 2a-2c, corresponding to similar structural and electronic features of the complexes.

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