A Stable Planar-Chiral <i>N</i>‑Heterocyclic Carbene with a 1,1′-Ferrocenediyl Backbone Alex R. Petrov Anatoli Derheim Jan Oetzel Michael Leibold Clemens Bruhn Stefan Scheerer Steffen Oßwald Rainer F. Winter Ulrich Siemeling 10.1021/acs.inorgchem.5b01064.s003 https://acs.figshare.com/articles/dataset/A_Stable_Planar_Chiral_i_N_i_Heterocyclic_Carbene_with_a_1_1_Ferrocenediyl_Backbone/2152801 This paper focuses on the stable, ferrocene-based <i>N</i>-heterocyclic carbene (NHC) <i>rac</i>-[Fe­{(η<sup>5</sup>-<i>t-</i>BuC<sub>5</sub>H<sub>3</sub>)­NpN}<sub>2</sub>C:] (<b>A′-Np</b>, Np = neopentyl), which is planar-chiral due to the two <i>tert</i>-butyl substituents in 3,3′-positions. <b>A′-Np</b> was synthesized in nine steps starting from 1,1′-di-<i>tert</i>-butylferrocene (<b>1</b>), the first step being its 3,3′-dilithiation to afford <i>rac</i>-[Fe­(η<sup>5</sup>-<i>t</i>-BuC<sub>5</sub>H<sub>3</sub>Li)<sub>2</sub>] (<i>rac</i>-fc′Li<sub>2</sub>, <b>2</b>). The structures of <i>rac</i>-fc′(SiMe<sub>3</sub>)<sub>2</sub> (<b>3</b>), <i>rac</i>-fc′Br<sub>2</sub> (<b>4</b>), <i>rac</i>-fc′(N<sub>3</sub>)<sub>2</sub> (<b>5</b>), and the immediate carbene precursor [<b>A′-Np</b>H]­BF<sub>4</sub> were determined by single-crystal X-ray diffraction (XRD). The chemical properties of <b>A′-Np</b> were found to be very similar to those of its <i>tert</i>-butyl-free congener <b>A-Np</b>, 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 <i>cis</i>-[RhCl­(<b>A′-Np</b>)­(CO)<sub>2</sub>], indicating the high donicity of <b>A′-Np</b> as a ligand. Consistent with its ambiphilic nature, <b>A′-Np</b> was found to react readily with carbon monoxide, affording the betainic enolate (<b>A′-Np</b>)<sub>2</sub>CO as four stereoisomers, viz. (<i>R</i><sub>p</sub><i>R</i><sub>p</sub>-<b>A′-Np</b>)C­(O<sup>–</sup>)­(<i>R</i><sub>p</sub><i>R</i><sub>p</sub>-<b>A′-Np</b><sup>+</sup>), (<i>S</i><sub>p</sub><i>S</i><sub>p</sub>-<b>A′-Np</b>)C­(O<sup>–</sup>)­(<i>S</i><sub>p</sub><i>S</i><sub>p</sub>-<b>A′-Np</b><sup>+</sup>), (<i>R</i><sub>p</sub><i>R</i><sub>p</sub>-<b>A′-Np</b>)C­(O<sup>–</sup>)­(<i>S</i><sub>p</sub><i>S</i><sub>p</sub>-<b>A′-Np</b><sup>+</sup>), and (<i>S</i><sub>p</sub><i>S</i><sub>p</sub>-<b>A′-Np</b>)C­(O<sup>–</sup>)­(<i>R</i><sub>p</sub><i>R</i><sub>p</sub>-<b>A′-Np</b><sup>+</sup>). The former two isomers were structurally characterized as a racemic compound by single-crystal XRD. <b>A′-Np</b> was found to react swiftly with dichloromethane, affording the addition product <b>A′-Np</b>H–CHCl<sub>2</sub> in a reaction that is unprecedented for diaminocarbenes. <b>A-Np</b>H–CHCl<sub>2</sub> was obtained analogously. Both compounds were structurally characterized by single-crystal XRD. An electrochemical investigation of <b>A′-Np</b> 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 <b>A-Np</b> were identified to be incorrect, since unnoticed hydrolysis of the NHC had taken place, affording <b>A-Np</b>(H<sub>2</sub>O). The hydrolysis products of <b>A-Np</b> and <b>A′-Np</b> were found to be reversibly oxidized at half-wave potentials of −0.418 and −0.437 V, respectively. 2015-07-06 00:00:00 hydrolysis products carbon monoxide THF IR data electrochemical data parameter value square wave voltammetry addition product HOMO energies chemical properties ambiphilic NHCs XRD betainic enolate electrochemical investigation carbene precursor racemic compound ambiphilic nature