Adducts of Ferrocenylboranes and Pyridine Bases: Generation of Charge-Transfer Complexes and Reversible Coordination Polymers

Binding Cooperativity of Two Different Lewis Acid Groups at the Edge of Ferrocene

“…A significantly lower average energy barrier for the two isomers of 4 of Δ${G{{\,{\ne}\hfill \atop 298\hfill}}}$ = 54.9±0.4 kJ mol −1 relative to those of 5 with Δ${G{{\,{\ne}\hfill \atop 298\hfill}}}$ = 70.3±0.1 kJ mol −1 was deduced from the corresponding Eyring plots (Figure 5, Table 3). 30, 31 These results are consistent with the seminal work by Brown and co‐workers, who showed that the binding strength of organoborane adducts with substituted pyridine derivatives strongly depends on both electronic and steric factors 32. A comparison with thermodynamic data for the monofunctional ferrocenylborane [FcB(Ph)Me] and the respective complexes [FcB(Ph)Me]⋅Py and [FcB(Ph)Me]⋅DMAP is instructive: The barrier of rotation about the CpB bond for [FcB(Ph)Me] was found to be comparatively low (Δ${G{{\,{\ne}\hfill \atop {\rm rot}\hfill}}}$ was estimated to be <40 kJ mol −1 ; cf.…”

Examination of the Pyridine Binding to the Bifunctional Lewis Acid B,B′-Diphenyldiboradiferrocene

“…Several bands are observed in the region typical of B−N stretching vibrations (ca. 1150 to 1050 cm −1 ) at 1103, 1072, 1048, 1032 cm −1 for trans - 5b and at 1105, 1078, 1034 cm −1 for trans - 5c ; similar modes are also found for the mono-adducts 4b at 1105, 1072, 1046 cm −1 and 4c at 1104, 1081, 1050, 1032 cm −1 . However, the free acid 3 also shows a number of bands in this region (1107, 1082, 1041 cm −1 ).…”

“…More definite evidence of nucleophile binding is provided from inspection of the region for the CC/CN ligand stretching modes around 1450 to 1650 cm −1 , where the free acid 3 shows only very weak IR modes. Intense bands are found for trans - 5c at 1629 and 1542 cm −1 and for 4c at 1632 and 1543 cm −1 , which are similar to those reported for FcBMe 2 (DMAP) (1636, 1544 cm −1 ) and strongly shifted to higher energy in comparison to the free ligand vibrations (1603, 1537, 1519 cm −1 ). The spectra of trans - 5b and 4b feature prominent bands at 1628, 1504 cm −1 and 1627, 1503 cm −1 , respectively, which are similar to those for FcBMe 2 (picoline) (1628, 1507 cm −1 ).…”

Synthesis and Structure of a Ferrocenylboron Dication

“…Compared to the tetracoordinated boronium monocation [FcBMe(2,2′-bipy)] + (bipy ) 2,2′-bipyridine) reported by Wagner et al, 12a the ferrocene-based oxidation of the boron dication 4 is shifted by about 260 mV to higher potentials. This is in accordance with the observed trend of increasing oxidation potentials for the Fe II /Fe III redox process in going from a monoanionic species [Fc 2 BMe 2 ] -(-430 mV) 13 to a neutral compound [FcBMe 2 (NC 5 H 4 -4-Me)] (-330 mV) 14 and to a monocationic compound [FcBMe 2 (NC 5 H 4 -4-C 5 H 4 NC 3 H 7 )] + (-250 mV). 14 However, the type of borane substituent also has a great impact on the oxidation potentials, as can be inferred from the strongly differing potentials of the monocationic compounds [FcBMe 2 (NC 5 H 4 -4-C 5 H 4 NC 3 H 7 )] + (-250 mV) and [FcBMe(2,2′-bipy)] + (-20 mV).…”