Trapping of a Ruthenium−Butatrienylidene Intermediate by Tertiary Amines. 2-Ammoniobutenynyl Complexes

Abstract

2-Ammoniobutenynyl Ru-complexes trans-[Cl(dppm) 2 Ru-CtC-C(NR 2 R′)dCH 2 ] + PF 6 -(3ag) have been prepared in a one-pot procedure from cis-[RuCl 2 (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) 2 RudCdCdCdCH 2 ] + as the reactive intermediate. Amine complexes cis-[Ru(dppm) 2 Cl(NR 2 R′)] + are frequently formed as side products and the 4-dimethylaminopyridine derivative cis-[Ru(dppm) 2 Cl(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 NEt 3 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 C 3 bridge. EPR spectroscopic investigations of the oxidized forms of the NEt 3 and PhCH 2 NMe 2 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 CtC stretch.

Experimental and Theoretical Studies of Charge Delocalization in Biruthenium–Alkynyl Complexes Bridged by Thiophenes

“…The free electron that is localized on an organometallic rutheniumA C H T U N G T R E N N U N G (III) center usually exhibits a Dg value of between 0.3 and 0.6. [29] [24,35] which further supports the previous analysis of the experimental data and the DFT calculations.…”

Synthesis and study of olefin metathesis catalysts supported by redox-switchable diaminocarbene[3]ferrocenophanes

“…71 X-band EPR spectra of 18 after treatment with DDQ in CH 2 Cl 2 were recorded at 110 K ( Fig. 9C; see also Fig.…”

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

“…A likely related reaction has been employed in the conversion of alkynyl fragments connected to the apical carbon of Co 3 C clusters of general form [Co 3 (μ 3 -CCϵCR)-(CO) 7 (dppm)] into acyl groups and CO. Thus, the reaction of [Co 3 (μ 3 -CCϵCR)(CO) 7 [151] The cyclic voltammograms of these cationic ammonium complexes are, generally, typified by a pseudo-reversible oxidation couple in addition to two closely spaced, chemically irreversible reduction processes. Observations from EPR and UV/Vis/ NIR/IR spectroelectrochemical experiments are consistent with a Ru II /Ru III redox process defining the oxidation couple, in contrast to the ligand-centred oxidation behaviour of most ruthenium alkynyl complexes (see above), although readily understandable on account of the electron-withdrawing character of the ammonium substituent.…”