10.1021/om9903240.s001
Rainer F. Winter
Rainer F.
Winter
F. M. Hornung
F. M.
Hornung
Trapping of a Ruthenium−Butatrienylidene
Intermediate by Tertiary Amines. 2-Ammoniobutenynyl
Complexes<sup>†</sup>
American Chemical Society
1999
Ru
EPR spectroscopic investigations
reactive
butadiyne
Cl
square wave voltammetry
tran
NEt 3
PF
complexes 3
oxidation
Complexe
ci
Ammoniobutenynyl
3 f point
PhCH 2 NMe 2
UV
amine
C 3 bridge
Amine
IR
1999-09-01 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Trapping_of_a_Ruthenium_Butatrienylidene_Intermediate_by_Tertiary_Amines_2-Ammoniobutenynyl_Complexes_sup_sup_/3785031
2-Ammoniobutenynyl Ru-complexes <i>trans-</i>[Cl(dppm)<sub>2</sub>Ru−C<b>⋮</b>C−C(NR<sub>2</sub>R‘)CH<sub>2</sub>]<sup>+</sup>PF<sub>6</sub><sup>-</sup> (<b>3a</b>−<b>g</b>) have been prepared in a one-pot procedure from <i>cis-</i>[RuCl<sub>2</sub>(dppm)<sub>2</sub>], excess butadiyne,
and various tertairy amines, whereas 4-(dimethylamino)pyridine binds to the unsaturated
carbon ligand via the pyridine nitrogen to give <b>3h</b>. These results may be rationalized by
envoking the butatrienylidene complex <i>trans-</i>[Cl(dppm)<sub>2</sub>RuCCCCH<sub>2</sub>]<sup>+</sup> as the reactive
intermediate. Amine complexes <i>cis</i>-[Ru(dppm)<sub>2</sub>Cl(NR<sub>2</sub>R‘)]<sup>+</sup> are frequently formed as side
products and the 4-dimethylaminopyridine derivative <i>cis-</i>[Ru(dppm)<sub>2</sub>Cl(4-DMAP)]<sup>+</sup> was
obtained in high yield in the absence of butadiyne but under otherwise identical reaction
conditions. Complexes <b>3</b> have been characterized by various spectroscopic and electrochemical
techniques including cyclic and square wave voltammetry and, in the case of the NEt<sub>3</sub>
derivative <b>3a</b>, also by X-ray crystallography. Most complexes <b>3</b> undergo a fully reversible
one-electron oxidation at half-wave potentials that depend on the amine substituent. This
provides evidence for delocalization over the conjugated C<sub>3</sub> bridge. EPR spectroscopic
investigations of the oxidized forms of the NEt<sub>3</sub> and PhCH<sub>2</sub>NMe<sub>2</sub> derived complexes <b>3a</b> and
<b>3f</b> point to Ru-centered radical dications. The irreversible reduction of complexes <b>3</b> occurs
in two closely spaced, poorly defined waves and ultimately releases the respective free amine,
which itself is reactive toward the Ru(III) oxidation product. Following the oxidation of <b>3a
</b>and <b>3f</b> by UV/vis and IR spectroelectrochemistry revealed a blue shift of the prominent
absorption band and a bleaching of the C<b>⋮</b>C stretch.