NDLI: Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Demonceau, Albert Delaude, Lionel Borguet, Yannick Zaragoza, Guillermo
Description	Author Affiliation: Borguet Y ( Laboratory of Organometallic Chemistry and Homogeneous Catalysis, Institut de Chimie (B6a), Université de Liège, Sart-Tilman par 4000, Liège, Belgium. l.delaude@ulg.ac.be.)
Abstract	Deprotonation of 1,3-di(2-tolyl)benzimidazolium tetrafluoroborate with a strong base afforded 1,3-di(2-tolyl)benzimidazol-2-ylidene (BTol), which dimerized progressively into the corresponding dibenzotetraazafulvalene. The complexes [RhCl(COD)(BTol)] (COD is 1,5-cyclooctadiene) and $cis-[RhCl(CO)_{2}(BTol)]$ were synthesized to probe the steric and electronic parameters of BTol. Comparison of the percentage of buried volume $(\%V_{Bur})$ and of the Tolman electronic parameter (TEP) of BTol with those determined previously for 1,3-dimesitylbenzimidazol-2-ylidene (BMes) revealed that the two N-heterocyclic carbenes displayed similar electron donicities, yet the 2-tolyl substituents took a slightly greater share of the rhodium coordination sphere than the mesityl groups, due to a more pronounced tilt. The anti,anti conformation adopted by BTol in the molecular structure of [RhCl(COD)(BTol)] ensured nonetheless a remarkably unhindered access to the metal center, as evidenced by steric maps. Second-generation ruthenium–benzylidene and isopropoxybenzylidene complexes featuring the BTol ligand were obtained via phosphine exchange from the first generation Grubbs and Hoveyda–Grubbs catalysts, respectively. The atropisomerism of the 2-tolyl substituents within $[RuCl_{2}(=CHPh)(PCy_{3})(BTol)]$ was investigated by using variable temperature NMR spectroscopy, and the molecular structures of all four possible rotamers of $[RuCl_{2}(=CH-o-O^{i}PrC_{6}H_{4})(BTol)]$ were determined by X-ray crystallography. Both complexes were highly active at promoting the ring-closing metathesis (RCM) of model α,ω-dienes. The replacement of BMes with BTol was particularly beneficial to achieve the ring-closure of tetrasubstituted cycloalkenes. More specifically, the stable isopropoxybenzylidene chelate enabled an almost quantitative RCM of two challenging substrates, viz., diethyl 2,2-bis(2-methylallyl)malonate and N,N-bis(2-methylallyl)tosylamide, within a few hours at 60 °C.
ISSN	14779226
Issue Number	21
Journal	Dalton Trans.
Volume Number	44
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2015-06-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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