Pyridine-2,6-bis(thioether) (SNS) Complexes of Ruthenium as Catalysts for Transfer Hydrogenation

Michael J. Page, Jörg Wagler, Barbara A. Messerle

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Coordination of the pincer ligand 2,6-bis(tert-butylthiomethyl)pyridine (SNS tBu) to Ru(PPh 3) 3Cl 2 and Ru(MeCN) 4Cl 2 led to the isolation of the complexes Ru(SNS tBu)Cl 2(PPh 3) (1) and Ru(SNS tBu)Cl 2(MeCN) (4), respectively. Substitution of one chloride ligand from 1 and 4 with acetonitrile proved facile via salt metathesis with NaBPh 4 to yield [Ru(SNS tBu)Cl(MeCN)(PPh 3)]BPh 4 (2) and [Ru(SNS tBu)Cl(MeCN) 2]BPh 4 (5). Reaction of 1 with an excess of AgBF 4 in acetonitrile afforded the dicationic complex [Ru(SNS tBu)(MeCN) 2(PPh 3)](BF 4) 2 (3); however reaction of 4 under analogous conditions afforded the unusual silver-bridged dimer [Ru(SNS tBu)(MeCN) 2Cl] 2[μ-Ag(MeCN) 2] 2(BF 4) 4 (6), which retained the second chloride ligand on ruthenium. The less sterically encumbered compounds 5 and 6 were shown to have fluxional conformational arrangements associated with an inversion of the tetrahedrally hybridized thioether centers. Compounds 1-4 were also investigated as catalysts for the transfer hydrogenation of acetophenone. Steric congestion within these complexes was found to negatively impact on catalyst activity, with the less sterically encumbered complexes yielding the highest activity. In the case of 4 an extremely high turnover frequency of ca. 87?000 h -1 was achieved for this reaction.

Original languageEnglish
Pages (from-to)3790-3798
Number of pages9
JournalOrganometallics
Volume29
Issue number17
DOIs
Publication statusPublished - 13 Sep 2010
Externally publishedYes

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