Synthesis and Electrochemical Properties of cis- and trans-[Mo₂(O₂C-Fc)₂(DArF)₂] (O₂C-Fc = Ferrocenecarboxylate; DArF = N,N′-Diarylformamidinate)

Abstract

The reaction of cis-[Mo2(O2C-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 [Mo2(O2C-Fc)2(DArF)2]. Even though the trans-[Mo2(O2C-Fc)2(DArF)2] isomers were originally expected to be the sole products, the corresponding cis-[Mo2(O2C-Fc)2(DArF)2] complexes were isolated as well via crystallization and verified unambiguously by X-ray crystallography. All novel complexes, namely, cis-[Mo2(O2C-Fc)2(DPhF)2] (cis-2a), cis-[Mo2(O2C-Fc)2(DTfmpF)2] (cis-2b), and trans-[Mo2(O2C-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 [Mo2](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-[Mo2(O2C-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 CH2Cl2 as solvent. Furthermore, the second oxidation of the Mo2-handle [Mo2](5+)/[Mo2](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.

Filling a Gap: Electrochemical Property Comparison of the Completed Compound Series [Mo2(DArF)n(O2C-Fc)4–n] (DArF = N,N′-Diarylformamidinate; O2C-Fc = Ferrocenecarboxylate)

“…On the other hand, the major species obtained from the reaction of cis-1 and 3 equiv of DAniF − is the previously published trans-[Mo 2 (DAniF) 2 (O 2 C-Fc) 2 ]. 15 Interestingly, the mono-substituted complex [Mo 2 (DAniF)(O 2 C-Fc) 3 ] (2b) can be isolated as a side product. It has been structurally characterized via NMR spectroscopy (Figure S11 in the Supporting Information) and X-ray crystallography (Figure 3).…”

“…Syntheses. As shown in Scheme 1, the reaction conditions are similar to those published recently by our group, 15 with DArF − ligands prepared independently via reacting the corresponding formamidine (HDArF) with sodium methoxide in CH 3 CN. The obtained base is then injected into the solution, containing precursor cis-1.…”

“…In theory, six configurations of Mo 2 complexes coordinated by two different bridging ligands are feasible (Figure 1). There are numerous examples of the Tetra, 41 Bis, 15,16,19,40 and Non 43,48 (o-DMophF = N,N′-bis(2-methoxyphenyl)formamidinate) 54 has been reported to date.…”

“…It has been established that ligand basicity is largely proportional to the electronic donating ability of a given ligand, thus decreasing in the order DArF − ≈ Fc−CO 2 − > CH 3 CN. 15 In order to shed more light on the ambiguous ligand basicity when DArF − and Fc−CO 15,41,48 series, are reported in this work. This series of complexes are promising candidates for the synthesis of molecular wires due to the differing redox activities of the otherwise closely related compounds.…”

Redox Potential Tuning of Dimolybdenum Systems through Systematic Substitution by Guanidinate Ligands

“…The UV–vis spectra of compounds 1 – 3 show two absorption peaks: one near the UV region (∼300 nm) and one in the visible region (∼450 nm). The low-energy transition in the region of 400–600 nm, assigned to Mo 2 δ → Mo 2 δ*, has been well established in the literature for quadruply bonded paddlewheel dimolybdenum compounds. ,, The energy of this transition relies on the nature of the ancillary ligands . The absorption spectra of 1 – 3 are shown in Figure .…”