10.1021/ja311966h.s002 Thomas L. Gianetti Thomas L. Gianetti Grégory Nocton Grégory Nocton Stefan G. Minasian Stefan G. Minasian Neil C. Tomson Neil C. Tomson A. L. David Kilcoyne A. L. David Kilcoyne Stosh A. Kozimor Stosh A. Kozimor David K. Shuh David K. Shuh Tolek Tyliszczak Tolek Tyliszczak Robert G. Bergman Robert G. Bergman John Arnold John Arnold Diniobium Inverted Sandwich Complexes with μ‑η<sup>6</sup>:η<sup>6</sup>‑Arene Ligands: Synthesis, Kinetics of Formation, and Electronic Structure American Chemical Society 2013 electron density sandwich complexes 2 b antibonding π system Electronic StructureMonometallic niobium arene complexes 1 H NMR spectroscopy diamagnetic molecules XANES BDI ligands UV 7 b Diniobium Inverted Sandwich Complexes arene ligands arene 1 H NMR chemical shifts monoprotonated cationic dissociative mechanism Nb atoms JCH sp 3 hybridization oxidation state arene carbons 2013-02-27 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Diniobium_Inverted_Sandwich_Complexes_with__sup_6_sup_sup_6_sup_Arene_Ligands_Synthesis_Kinetics_of_Formation_and_Electronic_Structure/2439898 Monometallic niobium arene complexes [Nb­(BDI)­(N<sup><i>t</i></sup>Bu)­(R-C<sub>6</sub>H<sub>5</sub>)] (<b>2a</b>: R = H and <b>2b</b>: R = Me, BDI = <i>N</i>,<i>N</i>′-diisopropylbenzene-β-diketiminate) were synthesized and found to undergo slow conversion into the diniobium inverted arene sandwich complexes [[(BDI)­Nb­(N<sup><i>t</i></sup>Bu)]<sub>2</sub>(μ-RC<sub>6</sub>H<sub>5</sub>)] (<b>7a</b>: R = H and <b>7b</b>: R = Me) in solution. The kinetics of this reaction were followed by <sup>1</sup>H NMR spectroscopy and are in agreement with a dissociative mechanism. Compounds <b>7a</b>-<b>b</b> showed a lack of reactivity toward small molecules, even at elevated temperatures, which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H­(OEt<sub>2</sub>)]­[B­(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], resulting in the monoprotonated cationic inverted sandwich complex <b>8</b> [[(BDI<sup>#</sup>)­Nb­(N<sup><i>t</i></sup>Bu)]­[(BDI)­Nb­(N<sup><i>t</i></sup>Bu)]­(μ-C<sub>6</sub>H<sub>5</sub>)]­[B­(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] and the dicationic complex <b>9</b> [[(BDI<sup>#</sup>)­Nb­(N<sup><i>t</i></sup>Bu)]<sub>2</sub>(μ-RC<sub>6</sub>H<sub>5</sub>)]­[B­(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]<sub>2</sub> (BDI<sup>#</sup> = (ArNC­(Me))<sub>2</sub>CH<sub>2</sub>). NMR, UV–vis, and X-ray absorption near-edge structure (XANES) spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb–arene interactions. The X-ray crystal structures, UV–vis spectra, arene <sup>1</sup>H NMR chemical shifts, and large <i>J</i><sub>CH</sub> coupling constants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding π system of the arene ligands. However, Nb L<sub>3,2</sub>-edge XANES spectra and the lack of sp<sup>3</sup> hybridization of the arene carbons indicate that the Nb → arene donation is not accompanied by an increase in Nb formal oxidation state and suggests that 4d<sup>2</sup> electronic configurations are appropriate to describe the Nb atoms in all four complexes.