INTRAZEOLITE METAL-CARBONYL TOPOTAXY - A COMPREHENSIVE STRUCTURAL AND SPECTROSCOPIC STUDY OF INTRAZEOLITE GROUP-VI METAL HEXACARBONYLS AND SUBCARBONYLS


ÖZKAR S. , OZIN G., MOLLER K., BEIN T.

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol.112, no.26, pp.9575-9586, 1990 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 112 Issue: 26
  • Publication Date: 1990
  • Doi Number: 10.1021/ja00182a016
  • Title of Journal : JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
  • Page Numbers: pp.9575-9586

Abstract

This paper focuses attention on the intrazeolite anchoring, thermal decarbonylation, ligand exchange, and addition chemistry of M(CO)6-M'56Y, where M = Cr, Mo, W; M' = H, Li, Na, K, Rb, Cs. The key points to emerge from this study include the following. (i) M(CO)6-M'56Y samples have the hexacarbonylmetal(O) molecule associated with two alpha-cage extraframework cations (or Bronsted protons), via the oxygen end of two trans bonded carbonyls with a saturation loading of 2M(CO)6/alpha-cage. (ii) M(CO)6-M'56Y samples have the hexacarbonylmetal(O) guest confined to the internal surface of the zeolite with a homogeneous distribution throughout the zeolite crystals. (iii) A Mo and Rb EXAFS structure analysis of 8{Mo(CO)6}-Rb56Y shows that the alpha-cage encapsulated Mo(CO)6 guest maintains its structural integrity, with some evidence for anchoring via extraframework Rb+ cations. (iv) A rapid C-13O intrazeolite ligand exchange occurs M(12CO)6-M '56Y to yield M(12CO)m(13CO)6-m-M'56Y, the extent of which depends on the 13CO loading. (v) M(CO)3-M'56Y can be cleanly generated via the mild vacuum thermal decarbonylation of M(CO)6-M56Y, the tricarbonyl stoichiometry of which is unequivocally established from its observed and calculated diagnostic M(12CO)n(13CO)3-n-M'56Y vibrational isotope pattern and from EXAFS structural data. (vi) Intrazeolite ractions of M(CO)3-M'56Y with large and small arenes, trienes, and phosphines cleanly yield the respective intrazeolite six-coordinate complexes (shown to be identical with the products of direct impregnation of the latter complexes), thereby supporting the tricarbonylmetal(0) assignment as well as pinpointing the location of the M(CO)3-M'56Y tricarbonylmetal(0) fragment on the internal surface of the zeolite. (vii) Cation effects in the mid/far-IR, EXAFS data, and optical reflectance spectra indicate that the supercage-confined M(CO)3-M'56Y moiety is anchored to an oxygen framework site rather than to an extrawork cation site via the metal or oxygens of the carbonyls. (viii) The tricarbonyl fragments show C(s) and C3-upsilon symmetry depending on the choice of M and M' which can be rationalized in terms of a second-order Jahn-Teller effect. (ix) EXAFS data for the mild thermal decomposition of Mo(CO)3-Rb56Y demonstrates the formation of molybdenum atoms statistically distributed in the zeolite lattice.