om9903240_si_001.pdf (428.11 kB)
Trapping of a Ruthenium−Butatrienylidene Intermediate by Tertiary Amines. 2-Ammoniobutenynyl Complexes†
journal contribution
posted on 1999-09-01, 00:00 authored by Rainer F. Winter, F. M. Hornung2-Ammoniobutenynyl Ru-complexes trans-[Cl(dppm)2Ru−C⋮C−C(NR2R‘)CH2]+PF6- (3a−g) have been prepared in a one-pot procedure from cis-[RuCl2(dppm)2], excess butadiyne,
and various tertairy amines, whereas 4-(dimethylamino)pyridine binds to the unsaturated
carbon ligand via the pyridine nitrogen to give 3h. These results may be rationalized by
envoking the butatrienylidene complex trans-[Cl(dppm)2RuCCCCH2]+ as the reactive
intermediate. Amine complexes cis-[Ru(dppm)2Cl(NR2R‘)]+ are frequently formed as side
products and the 4-dimethylaminopyridine derivative cis-[Ru(dppm)2Cl(4-DMAP)]+ was
obtained in high yield in the absence of butadiyne but under otherwise identical reaction
conditions. Complexes 3 have been characterized by various spectroscopic and electrochemical
techniques including cyclic and square wave voltammetry and, in the case of the NEt3
derivative 3a, also by X-ray crystallography. Most complexes 3 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 C3 bridge. EPR spectroscopic
investigations of the oxidized forms of the NEt3 and PhCH2NMe2 derived complexes 3a and
3f point to Ru-centered radical dications. The irreversible reduction of complexes 3 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 3a
and 3f by UV/vis and IR spectroelectrochemistry revealed a blue shift of the prominent
absorption band and a bleaching of the C⋮C stretch.