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rdf:type
lifeskim:mentions
pubmed:issue
35
pubmed:dateCreated
2002-8-28
pubmed:abstractText
We show that imidazolium salts do not always give normal or even aromatic carbenes on metalation, and the chemistry of these ligands can be much more complicated than previously thought. N,N'-disubstituted imidazolium salts of type [(2-py)(CH(2))(n)(C(3)H(3)N(2))R]BF(4) react with IrH(5)(PPh(3))(2) to give N,C-chelated products (n = 0, 1; 2-py = 2-pyridyl; C(3)H(3)N(2) = imidazolium; R = mesityl, n-butyl, i-propyl, methyl). Depending on the circumstances, three types of kinetic products can be formed: in one, the imidazole metalation site is the normal C2 as expected; in another, the metalation occurs at the abnormal C4 site; and in the third, C4 metalation is accompanied by hydrogenation of the imidazolium ring. The bonding mode is confirmed by structural studies, and spectroscopic criteria can also distinguish the cases. Initial hydrogen transfer can take place from the metal to the carbene to give the imidazolium ring hydrogenation product, as shown by isotope labeling; this hydrogen transfer proves reversible on reflux when the abnormal aromatic carbene is obtained as final product. Care may therefore be needed in the future in verifying the structure(s) formed in cases where a catalyst is generated in situ from imidazolium salt and metal precursor.
pubmed:language
eng
pubmed:journal
pubmed:status
PubMed-not-MEDLINE
pubmed:month
Sep
pubmed:issn
0002-7863
pubmed:author
pubmed:issnType
Print
pubmed:day
4
pubmed:volume
124
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
10473-81
pubmed:dateRevised
2003-11-3
pubmed:year
2002
pubmed:articleTitle
Abnormal ligand binding and reversible ring hydrogenation in the reaction of imidazolium salts with IrH(5)(PPh(3))(2).
pubmed:affiliation
Department of Chemistry, 225 Prospect Street, Yale University, New Haven, Connecticut 06520-8107, USA.
pubmed:publicationType
Journal Article