Frustrated β-chloride elimination. Selective arene alkylation by α-chloronorbornene catalyzed by electrophilic metallocenium ion pairs

Aswini K. Dash, Tryg R. Jensen, Charlotte L. Stern, Tobin J. Marks

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Single-site polymerization catalysts generated in situ via activation of Cp*MMe3 (Cp* = C5Me5; M = Ti, Zr), (CGC)MMe2 (CGC = C5Me4SiMe2NBu t; M = Ti, Zr), and Cp2ZrMe2 with Ph 3C+B(C6F5)4- catalyze alkylation of aromatic molecules (benzene, toluene) with α-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C6H 5 (1a), C6H4-CH3 (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-d n-norbornane-7-d1 (aryl-dn = C 6D5 (1a-d6), C6D4CD 3 (1b-d8)) are obtained via catalytic arylation of α-chloronorbornene in either benzene-d6 or toluene-d 8. Isolated ion-pair complexes such as (CGC)ZrMe(toluene) +B(C6F5)4- and Cp*2ThMe+B(C6F5) 4- also catalyze the reaction of α-chloronorbornene in toluene-d8 to give 1b-d8 in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h-1 (for the Cp*TiMe 3/Ph3C+B(C6F5) 4--catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by 1H, 2H, 13C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using 1H- 1H COSY, 1H-13C HMBC, and 1H- 1H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle.

Original languageEnglish
Pages (from-to)12528-12540
Number of pages13
JournalJournal of the American Chemical Society
Volume126
Issue number39
DOIs
Publication statusPublished - Oct 6 2004

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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