Synthesis, Molecular Structure, and Electrochemistry of 1‐Ferrocenyl‐1,2‐dicarba‐closo‐dodecaboranes

Abstract

Bis(dimethylsulfido)decaborane, 6,9‐(Me2S)2‐arachno‐B10H12, reacts smoothly with ferrocenyl alkynes FcC≡CR [1a–h; Fc = ferrocenyl, R = H (1a), CH3 (1b), Ph (1c), 4‐MeO2CC6H4 (1d), Fc (1e), C≡CFc (1f), C(O)CH3 (1g), and CO2CH2CH3 (1h)] to afford the corresponding 1‐ferrocenyl‐1,2‐dicarba‐closo‐dodecaboranes 2a–h in good yields. Ester 2h was further reduced to the respective hydroxymethyl derivative, 1‐Fc‐2‐CH2OH‐1,2‐closo‐C2B10H10 (3). The reaction of 6,9‐(Me2S)2‐B10H12 with FcC≡CSiMe3 proceeded in a different manner to produce (among other products) an SMe2 adduct of an opened decaborane substituted with a 2‐ferrocenyl‐2‐(trimethylsilyl)ethen‐1‐yl group (4). This compound probably results through hydroboration of the starting alkyne and migration of the SiMe3 group. All prepared compounds were characterized by spectroscopic methods (1H, 13C, and 11B NMR spectroscopy, IR spectroscopy, and mass spectrometry), and their molecular structures were determined by single‐crystal X‐ray diffraction analysis. In addition, the compounds were studied by cyclic and differential pulse voltammetry on a platinum disc electrode to reveal simple ferrocenyl‐centered oxidations for the singly ferrocenylated carboranes and two consecutive oxidation waves for compounds 2e and 2f, which possess two ferrocenyl substituents.

Boron Clusters with a Ferrocenylalkynyl Group Bonded to Boron: Synthesis, Characterization, and Electrochemical Trends

“…In contrast, dicarba‐ closo ‐dodecaboranes are known to be electron‐withdrawing substituents when the substituent is bonded to one of the cluster carbon atoms 5c. This agrees well with the relatively high redox potential reported for [1‐Fc‐2‐FcC≡C‐ closo ‐1, 2‐C 2 B 10 H 10 ] 20. Even if the substituent is attached to a boron atom in close proximity to one or both of the C cluster atoms in 1, 2‐ and 1, 7‐dicarba‐ closo ‐dodecaboranes the cages are electron‐withdrawing substituents as evident from the respective Hammett constants 6a,26…”

“…For [1‐Fc‐2‐FcC≡C‐ closo ‐1, 2‐C 2 B 10 H 10 ], which was described in the literature, the redox potentials of the ferrocenyl unit that is directly bonded to one of the C cluster atoms and the ferrocenylalknyl moiety that is attached to the second C cluster atom are very similar and so the waves partially overlap. Therefore, no E 1/2 for the individual redox processes was given but only E pa = 0.330 V and E pc = 0.175 V for both events in 1, 2‐dichloroethane 20. Although a different solvent was used for the study, the values indicate a significantly higher redox potential for the ferrocenylalkynyl unit in [1‐Fc‐2‐FcC≡C‐ closo ‐1, 2‐C 2 B 10 H 10 ] compared to [9‐FcC≡C‐ closo ‐1, 2‐C 2 B 10 H 11 ] ( 5 ).…”

“…So far, only three other ferrocenylalkynyl derivatives of boron clusters have been described in the literature. The ferrocenylalkynyl group of [1‐Cp‐2‐Ph‐6‐FcC≡C‐ closo ‐1, 2,3, 4‐ M C 3 B 7 H 8 ] ( M = Fe,18 Ru19) is bonded to a boron atom, whereas in [1‐Fc‐2‐FcC≡C‐ closo ‐1, 2‐C 2 B 10 H 10 ] the group is attached to one of the cluster carbon atoms 20. The structural properties of the derivatives were studied by single‐crystal X‐ray diffraction and by DFT calculations.…”

Synthesis of a Neutral Mixed‐Valence Diferrocenyl Carborane for Molecular Quantum‐Dot Cellular Automata Applications

“…The molecular structures of the six carboranes were confirmed and compared by single‐crystal X‐ray diffraction analysis (Figure 2 and Supporting Information) 12. 13 The FeC bond lengths in Fc 2 C 2 B 10 ( 1 a ), FcC 2 B 10 ( 1 b ), Fc 2 C 2 B 9 − ( 2 a ), and Fc 2 C 2 B 9 − ( 2 b ) fall in the narrow range 2.036(4)–2.056(2) Å, consistent with Fe II centers in ferrocenes 14.…”

o-Carborane, Ferrocene, and Phthalocyanine Triad for High-Mobility Organic Field-Effect Transistors

“…In addition, compound 2 was characterized by a single-crystal X-ray diffraction analysis (Table S1). The molecular structure of compound 2 is shown in Figure 1 24 The C−C bond length of 1,2 disubstituted o-carboranes shows large variations depending on electronic and steric effects of substituents; in 2 the observed C−C bond length of o-carborane cage is 1.74 Å. 25 The dihedral angle between the cyclopentadienyl ring and the As shown in Figure 2, the complexes 5, 6, and 7 have similar 1 H NMR spectra.…”