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A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1′-Ferrocenediyl Backbone

A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1′-Ferrocenediyl Backbone

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PETROV, Alex R., Anatoli DERHEIM, Jan OETZEL, Michael LEIBOLD, Clemens BRUHN, Stefan SCHEERER, Steffen OSSWALD, Rainer F. WINTER, Ulrich SIEMELING, 2015. A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1′-Ferrocenediyl Backbone. In: Inorganic Chemistry. 54(13), pp. 6657-6670. ISSN 0020-1669. eISSN 1520-510X. Available under: doi: 10.1021/acs.inorgchem.5b01064

@article{Petrov2015Stabl-31871, title={A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1′-Ferrocenediyl Backbone}, year={2015}, doi={10.1021/acs.inorgchem.5b01064}, number={13}, volume={54}, issn={0020-1669}, journal={Inorganic Chemistry}, pages={6657--6670}, author={Petrov, Alex R. and Derheim, Anatoli and Oetzel, Jan and Leibold, Michael and Bruhn, Clemens and Scheerer, Stefan and Oßwald, Steffen and Winter, Rainer F. and Siemeling, Ulrich} }

Siemeling, Ulrich Winter, Rainer F. Derheim, Anatoli Scheerer, Stefan 2015 Oßwald, Steffen Petrov, Alex R. eng Petrov, Alex R. Winter, Rainer F. Oßwald, Steffen Scheerer, Stefan Derheim, Anatoli Bruhn, Clemens Oetzel, Jan Leibold, Michael A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1′-Ferrocenediyl Backbone Siemeling, Ulrich 2015-09-30T09:49:15Z Oetzel, Jan This paper focuses on the stable, ferrocene-based N-heterocyclic carbene (NHC) rac-[Fe{(η(<sup>5</sup>)-t-BuC<sub>5</sub>H3)NpN}<sub>2</sub>C:] (A'-Np, Np = neopentyl), which is planar-chiral due to the two tert-butyl substituents in 3,3'-positions. A'-Np was synthesized in nine steps starting from 1,1'-di-tert-butylferrocene (1), the first step being its 3,3'-dilithiation to afford rac-[Fe(η(<sup>5</sup>)-t-BuC<sub>5</sub>H<sub>3</sub>Li)<sub>2</sub>] (rac-fc'Li<sub>2</sub>, 2). The structures of rac-fc'(SiMe<sub>3</sub>)<sub>2</sub> (3), rac-fc'Br<sub>2</sub> (4), rac-fc'(N<sub>3</sub>)<sub>2</sub> (5), and the immediate carbene precursor [A'-NpH]BF<sub>4</sub> were determined by single-crystal X-ray diffraction (XRD). The chemical properties of A'-Np were found to be very similar to those of its tert-butyl-free congener A-Np, both being ambiphilic NHCs with rather high calculated HOMO energies (ca. -4.0 eV) and low singlet-triplet gaps (ca. 35 kcal/mol). A Tolman electronic parameter value of 2050 cm<sup>-1</sup> was derived from IR data of cis-[RhCl(A'-Np)(CO)<sub>2</sub>], indicating the high donicity of A'-Np as a ligand. Consistent with its ambiphilic nature, A'-Np was found to react readily with carbon monoxide, affording the betainic enolate (A'-Np)<sub>2</sub>CO as four stereoisomers, viz. (R<sub>p</sub>R<sub>p</sub>-A'-Np)═C(O(-))(R<sub>p</sub>R<sub>p</sub>-A'-Np<sup>+</sup>), (S<sub>p</sub>S<sub>p</sub>-A'-Np)═C(O<sup>-</sup>)(S<sub>p</sub>S<sub>p</sub>-A'-Np<sup>+</sup>), (R<sub>p</sub>R<sub>p</sub>-A'-Np)═C(O<sup>-</sup>)(S<sub>p</sub>S<sub>p</sub>-A'-Np<sup>+</sup>), and (S<sub>p</sub>S<sub>p</sub>-A'-Np)═C(O<sup>-</sup>)(R<sub>p</sub>R<sub>p</sub>-A'-Np<sup>+</sup>). The former two isomers were structurally characterized as a racemic compound by single-crystal XRD. A'-Np was found to react swiftly with dichloromethane, affording the addition product A'-NpH-CHCl<sub>2</sub> in a reaction that is unprecedented for diaminocarbenes. A-NpH-CHCl<sub>2</sub> was obtained analogously. Both compounds were structurally characterized by single-crystal XRD. An electrochemical investigation of A'-Np by cyclic and square wave voltammetry revealed a reversible oxidation of the carbene at a half-wave potential of -0.310 vs ferrocene/ferrocenium (THF/NBu<sub>4</sub>PF<sub>6</sub>). The electrochemical data previously published for A-Np were identified to be incorrect, since unnoticed hydrolysis of the NHC had taken place, affording A-Np(H<sub>2</sub>O). The hydrolysis products of A-Np and A'-Np were found to be reversibly oxidized at half-wave potentials of -0.418 and -0.437 V, respectively. Leibold, Michael Bruhn, Clemens 2015-09-30T09:49:15Z

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