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

Handle URI:
http://hdl.handle.net/10754/599545
Title:
Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins
Authors:
Borguet, Yannick; Zaragoza, Guillermo; Demonceau, Albert; Delaude, Lionel
Abstract:
© The Royal Society of Chemistry. 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 (%VBur) 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 [RuCl2(=CHPh)(PCy3)(BTol)] was investigated by using variable temperature NMR spectroscopy, and the molecular structures of all four possible rotamers of [RuCl2(=CH-o-O<sup>i</sup>PrC6H4)(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.
Citation:
Borguet Y, Zaragoza G, Demonceau A, Delaude L (2015) Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins. Dalton Trans 44: 9744–9755. Available: http://dx.doi.org/10.1039/c5dt00433k.
Publisher:
Royal Society of Chemistry (RSC)
Journal:
Dalton Trans.
Issue Date:
2015
DOI:
10.1039/c5dt00433k
PubMed ID:
25734488
Type:
Article
ISSN:
1477-9226; 1477-9234
Sponsors:
The financial support of the “Fonds de la Recherche Scientifique–FNRS”, Brussels, through grant J.0058.13 is gratefully acknowledged. The authors would like to thank Prof. Luigi Cavallo and Dr Laura Falivene, KAUST, Saudi Arabia, for generating the steric maps depicted in Fig. 5 and S4.
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Full metadata record

DC FieldValue Language
dc.contributor.authorBorguet, Yannicken
dc.contributor.authorZaragoza, Guillermoen
dc.contributor.authorDemonceau, Alberten
dc.contributor.authorDelaude, Lionelen
dc.date.accessioned2016-02-28T05:53:07Zen
dc.date.available2016-02-28T05:53:07Zen
dc.date.issued2015en
dc.identifier.citationBorguet Y, Zaragoza G, Demonceau A, Delaude L (2015) Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins. Dalton Trans 44: 9744–9755. Available: http://dx.doi.org/10.1039/c5dt00433k.en
dc.identifier.issn1477-9226en
dc.identifier.issn1477-9234en
dc.identifier.pmid25734488en
dc.identifier.doi10.1039/c5dt00433ken
dc.identifier.urihttp://hdl.handle.net/10754/599545en
dc.description.abstract© The Royal Society of Chemistry. 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 (%VBur) 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 [RuCl2(=CHPh)(PCy3)(BTol)] was investigated by using variable temperature NMR spectroscopy, and the molecular structures of all four possible rotamers of [RuCl2(=CH-o-O<sup>i</sup>PrC6H4)(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.en
dc.description.sponsorshipThe financial support of the “Fonds de la Recherche Scientifique–FNRS”, Brussels, through grant J.0058.13 is gratefully acknowledged. The authors would like to thank Prof. Luigi Cavallo and Dr Laura Falivene, KAUST, Saudi Arabia, for generating the steric maps depicted in Fig. 5 and S4.en
dc.publisherRoyal Society of Chemistry (RSC)en
dc.titleRuthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefinsen
dc.typeArticleen
dc.identifier.journalDalton Trans.en
dc.contributor.institutionUniversite de Liege, Liege, Belgiumen
dc.contributor.institutionUniversidad de Santiago de Compostela, Santiago de Compostela, Spainen

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