Synthesis of [(DPPNCH₂CH₂)₃N]^3- molybdenum complexes (DPP = 3,5-(2,5-Diisopropylpyrrolyl)₂C ₆H₃) and studies relevant to catalytic reduction of dinitrogen

Author(s)

Michael R. Reithofer, Richard R. Schrock, Peter Müller

Abstract

Molybdenum complexes that contain a new TREN-based ligand [(3,5-(2,5-diisopropyl-pyrrolyl)₂C₆H₃NCH ₂CH₂)₃N]^3- ([DPPN₃N] ^3-) that are relevant to the catalytic reduction of dinitrogen have been prepared. They are [Bu₄N]{[DPPN₃N]MoN₂}, [DPPN₃N]MoN₂, [DPPN₃N]MoN=NH, {[DPPN ₃N]MoN=NH₂}[BAr^f₄], [DPPN ₃N]Mo≡N, {[DPPN₃N]Mo≡NH}[BAr^f ₄], and {[DPPN₃N]MoNH₃}[BAr^f ₄]. NMR and IR data for [Bu₄N]{[DPPN₃N]MoN ₂} and [DPPN₃N]MoN₂ are close to those reported for the analogous [HIPTN₃N]^3- compounds (HIPT = hexaisopropylterphenyl), which suggests that the degree of reduction of dinitrogen is virtually identical in the two systems. However, X-ray studies and several exchange studies support the conclusion that the apical pocket is less protected in [DPPN₃N]Mo complexes than in [HIPTN₃N]Mo complexes. For example, ¹⁵N/¹⁴N exchange studies showed that exchange in [DPPN₃N]MoN₂ is relatively facile (t _1/2 a 1 h at 1 atm) and depends upon dinitrogen pressure, in contrast to the exchange in [HIPTN₃N]MoN₂. Several of the [DPPN₃N]Mo complexes, e.g., the [DPPN₃N]MoN₂ and [DPPN₃N]MoNH₃ species, are also less stable in solution than the analogous "parent" [HIPTN₃N]Mo complexes. Four attempted catalytic reductions of dinitrogen with [DPPN₃N]MoN yielded 2.53 ± 0.35 equiv of total ammonia. These studies reveal more than any other just how sensitive a successful catalytic reduction is to small changes in the triamidoamine supporting ligand.

Organisation(s)

External organisation(s)

Massachusetts Institute of Technology

Journal

Journal of the American Chemical Society

Volume

132

Pages

8349-8358

No. of pages

10

ISSN

0002-7863

DOI

https://doi.org/10.1021/ja1008213

Publication date

06-2010

Peer reviewed

Yes

Austrian Fields of Science 2012

104015 Organic chemistry, 104003 Inorganic chemistry

ASJC Scopus subject areas

Catalysis, General Chemistry, Biochemistry, Colloid and Surface Chemistry

Portal url

https://ucrisportal.univie.ac.at/en/publications/4b8d1e9b-5725-4a3c-81dd-35551385ce72