Issue 26, 2015

16-Electron pentadienyl- and cyclopentadienyl-ruthenium half-sandwich complexes with bis(imidazol-2-imine) ligands and their use in catalytic transfer hydrogenation

Abstract

Bis(η5-2,4-dimethylpentadienyl)ruthenium(II), [(η5-C7H11)2Ru] (1, “open ruthenocene”), which has become accessible in high yield and large quantities via an isoprene-derived diallyl ruthenium(IV) complex, can be converted into the protonated open ruthenocene 2 by treatment with HBF4 and subsequently into the protonated half-open ruthenocene 3 by reaction with cyclopentadiene. The electronic structure of 3 was studied by DFT methods, revealing that the CH-agostic complex [(η5-C5H5)Ru{(1-4η)-C7H122-C5,H5}]BF4 (A) represents the global minimum, which is 3.7 kcal mol−1 lower in energy than the hydride complex [(η5-C5H5)RuH(η5-C7H11)]BF4 (B). 2 and 3 were treated with the ligands N,N′-bis(1,3,4,5-tetramethylimidazolin-2-ylidene)-1,2-ethanediamine (BLMe) and N,N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,2-ethanediamine (BLiPr) to afford the cationic 16-electron pentadienyl and cyclopentadienyl complexes [(η5-C7H11)Ru(BLR)]BF4 (4a, R = Me; 4b, R = iPr) and [(η5-C5H5)Ru(BLR)]BF4 (5a, R = Me; 5b, R = iPr). All complexes catalyse the transfer hydrogenation of acetophenone in isopropanol, and the most active complex 4a in this reaction was employed for the hydrogenation of a broader range of aliphatic and aromatic ketones.

Graphical abstract: 16-Electron pentadienyl- and cyclopentadienyl-ruthenium half-sandwich complexes with bis(imidazol-2-imine) ligands and their use in catalytic transfer hydrogenation

Supplementary files

Article information

Article type
Paper
Submitted
18 Mar 2015
Accepted
02 Apr 2015
First published
07 Apr 2015
This article is Open Access
Creative Commons BY-NC license

Dalton Trans., 2015,44, 11717-11724

Author version available

16-Electron pentadienyl- and cyclopentadienyl-ruthenium half-sandwich complexes with bis(imidazol-2-imine) ligands and their use in catalytic transfer hydrogenation

T. Glöge, K. Jess, T. Bannenberg, P. G. Jones, N. Langenscheidt-Dabringhausen, A. Salzer and M. Tamm, Dalton Trans., 2015, 44, 11717 DOI: 10.1039/C5DT01080B

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