102133-06-2Relevant academic research and scientific papers
Ruthenium complexes with diazadienes. 4. Arene diazadiene ruthenium(II) complexes [(η6-arene)(RN=CR′ - CR′=NR)Ru(L)]n+ (n = 1, L = Cl, I, alkyl; n = 2, L = MeCN, η2-C2H4) and arene diazadiene ruthenium(0)
Tom Dieck, Heindirk,Kollvitz, Wolfgang,Kleinw?chter, Ingo
, p. 1449 - 1457 (2008/10/08)
Diazadiene ligands (dad = RN=CR′-CR′=NR) substitute acetonitrile (L) in [(η6-C6H6)RuL2Cl]+ and give the orange or brown complexes [(η6-C6H6)Ru(dad)Cl]+ (2) which can be reduced quantitatively to the red complexes (η6-C6H6)Ru(dad) (5). These Ru(0) half-sandwich compounds undergo oxidative addition with alkyl iodides R″I, to give [(η6-C6H6)Ru(dad)(σ-R″)] +. Their rate of formation strongly depends on steric factors. A σ-ethyl complex (R″ = Et) reacts further with trityl tetrafluoroborate with hydride abstraction to give the [(η6-C6H6)(η2-C 2H4)Ru(dad)]2+ cation. A similar series of complexes is obtained with the asymmetrical arene 1,2-diethyl-4-methylbenzene, introducing a chiral arene ruthenium fragment. 1H NMR spectra are discussed with respect to symmetry, diastereotopy, and chirality as well as conformational barriers and related steric problems. The η6-arene and the dad ligands are close enough to each other so that the arene can determine the conformation of the dad N substituents; vice versa, larger N substituents contribute to the lability of the η6-arene. Cyclovoltammetric studies show the enhanced arene lability on oxidation of 2; the likewise irreversible reduction proceeds, in agreement with preparative reactions, with loss of Cl- and formation of the Ru(0) complexes 5. According to electron spectroscopic data dad ligands display their special properties more clearly in complexes of low formal oxidation state. The Ru → dad CT absorptions are not very characteristic in the Ru(II) complexes 2 as compared to (dad)RuII systems with stronger donor ligands. In the Ru(0) case the increase in absorption intensity, the absence of solvato-chromism, and the dependence on substituents indicate, together with electrochemical results, the increasing π → π* character of the main absorption band, which is related to strong ground-state backbonding. The bonding is discussed in comparison to other half-sandwich complexes.
