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.