Synthesis and properties of (η2-C,X) chelate arylcarbene complexes [Fe(C5Me5)(L){η2-C(OMe)C6H 4-o-X}][OTf] (L = CO, PMe3; X = OMe, Cl)

Géraldine Poignant, Sylvain Nlate, Véronique Guerchais, Andrew J. Edwards, Paul R. Raithby

Research output: Contribution to journalArticlepeer-review

Abstract

The methoxycarbene complexes [Fe(C5Me5)(CO)2{=C(OMe)C6H 4-o-X}][OTf] (2a, X = OMe; 2b, X = Cl) are good precursors of the corresponding (η2-C,X) chelate carbene complexes [Fe(C5Me5)(CO){η2-C(OMe)C6H 4-o-X}][OTf] (OTf = CF3SO3) (5a,b). The η2-chloro derivative 5b has been characterized by X-ray diffraction, confirming the formation of a five-membered ring metallacycle. All the new carbene complexes, including the nonheteroatom-stabilized carbene complex [Fe(C5Me5)(CO)2{=C(H)C6H 4-O-OMe}][OTf] (4a), have been fully characterized by 1H and 13C NMR spectrocopy. The lability of the chelating o-substituent is chemically demonstrated by the formation of the corresponding neutral iodo carbene complexes [Fe(C5Me5)(CO)(I){η1-C(OMe)C 6H4-o-X}] (6a,b), the competitive O-demethylation process being thus inhibited. Selective ligand exchange reactions of 5a,b afford various substituted complexes such as [Fe(C5Me5)(CO)n(PMe3){η x-C(OMe)C6H4-o-OMe}][OTf] (11, n = 1, x = 1; 12, n = 0 x = 2); the mono- and bis(acetonitrile) complexes [Fe(C5Me5)(L)(CH3CN){η1 C(OMe)C6H4-o-Cl}][OTf] (14, L = CH3CN; 15, L = CO) have been also synthesized. The reactivity of 5a toward NaBH4 is highly dependent on the solvent. Specific hydride addition occurs in 9:1 THF-MeOH to give the expected complex [Fe(C5Me5)(CO){η2-CH(OMe)C 6H4-o-OMe}] (9) as a single diastereoisomer, while reduction in pure THF affords the organoborohydride complex [Fe(C5Me5)(CO){η2-H2BHCH 2C6H4-o-OMe}] (10). The latter reaction involves a formal insertion of BH3 into a Fe-C bond, promoted by the potential vacant coordination site. The carbene ligand is easily displaced and recovered as free carbonylcontaining organic substrates (aldehyde or ester) from both types of carbene complexes upon bubbling of O2.

Original languageEnglish
Pages (from-to)124-132
Number of pages9
JournalOrganometallics
Volume16
Issue number1
DOIs
Publication statusPublished - 7 Jan 1997

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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