Formation of η2 C-H agostic rhodium arene complexes and their relevance to electrophilic bond activation

Arkadi Vigalok, Olivier Uzan, Linda J W Shimon, Yehoshoa Ben-David, Jan M L Martin, David Milstein

Research output: Contribution to journalArticle

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Abstract

Reaction of the ligand 1,3-bis((di-tert-butylphosphino)methyl)benzene (1a) with the [RhCO]+ fragment in THF resulted in clean formation of the crystallographically characterized his-chelated complex 2a which contains an η2 agostic Rh C-H bond. Both the NMR data and the X-ray crystal structure show strong interaction between the metal center and the agostic C-H bond, which results in high acidity of the agostic proton. Reaction of 2a with a weak organic base (NEt3 or collidine) affords the known cyclometalated complex 3. Reaction of the new ligand 1,3-bis((di-tert- butylphosphino)methyl)-4,5,6-trimethoxybenzene (1b) with the [RhCO]+ fragment in THF gives the analogous to 2a agostic complex 2b. Analysis of the NMR data and the reactivity of both 2a and 2b showed that there is very little, if any, contribution of a metal arenium structure. This interpretation is supported by B3LYP/LANL2DZ density functional calculations on model compounds. Thus, deprotonation of η2 aromatic C-H agostic complexes can be proposed as an alternative route to electrophilic metalation of aromatic compounds.

Original languageEnglish
Pages (from-to)12539-12544
Number of pages6
JournalJournal of the American Chemical Society
Volume120
Issue number48
DOIs
Publication statusPublished - Dec 9 1998

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Rhodium
Metals
Chemical activation
Ligands
Nuclear magnetic resonance
Deprotonation
Aromatic compounds
Toluene
Acidity
Density functional theory
Protons
Benzene
Crystal structure
X-Rays
X rays
gamma-collidine

ASJC Scopus subject areas

  • Chemistry(all)

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Formation of η2 C-H agostic rhodium arene complexes and their relevance to electrophilic bond activation. / Vigalok, Arkadi; Uzan, Olivier; Shimon, Linda J W; Ben-David, Yehoshoa; Martin, Jan M L; Milstein, David.

In: Journal of the American Chemical Society, Vol. 120, No. 48, 09.12.1998, p. 12539-12544.

Research output: Contribution to journalArticle

Vigalok, Arkadi ; Uzan, Olivier ; Shimon, Linda J W ; Ben-David, Yehoshoa ; Martin, Jan M L ; Milstein, David. / Formation of η2 C-H agostic rhodium arene complexes and their relevance to electrophilic bond activation. In: Journal of the American Chemical Society. 1998 ; Vol. 120, No. 48. pp. 12539-12544.
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AB - Reaction of the ligand 1,3-bis((di-tert-butylphosphino)methyl)benzene (1a) with the [RhCO]+ fragment in THF resulted in clean formation of the crystallographically characterized his-chelated complex 2a which contains an η2 agostic Rh C-H bond. Both the NMR data and the X-ray crystal structure show strong interaction between the metal center and the agostic C-H bond, which results in high acidity of the agostic proton. Reaction of 2a with a weak organic base (NEt3 or collidine) affords the known cyclometalated complex 3. Reaction of the new ligand 1,3-bis((di-tert- butylphosphino)methyl)-4,5,6-trimethoxybenzene (1b) with the [RhCO]+ fragment in THF gives the analogous to 2a agostic complex 2b. Analysis of the NMR data and the reactivity of both 2a and 2b showed that there is very little, if any, contribution of a metal arenium structure. This interpretation is supported by B3LYP/LANL2DZ density functional calculations on model compounds. Thus, deprotonation of η2 aromatic C-H agostic complexes can be proposed as an alternative route to electrophilic metalation of aromatic compounds.

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