H/D exchange on silica-grafted tantalum(V) imido amido [(≡SiO) <inf>2</inf>Ta<inf>(V)</inf>(NH)(NH<inf>2</inf>)] synthesized from either ammonia or dinitrogen: IR and DFT evidence for heterolytic splitting of D <inf>2</inf>

Priscilla Avenier, Xavier Solans-Monfort, Laurent Veyre, Filippo Renili, Jean Marie Basset, Odile Eisenstein, Mostafa Taoufik, Elsje Alessandra Quadrelli

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11 Citations (Scopus)

Abstract

Abstract The silica-grafted Ta(V) imido amido complex [(≡SiO)2Ta(NH)(NH2)], 2, obtained from the reaction of either ammonia or dinitrogen plus hydrogen with the silicagrafted hydrides [(≡SiO)(III)H], 1a, and [(≡SiO)2- Ta (V)H3], 1b, undergoes H/D exchange with D2. In situ IR spectroscopy shows that the fully labelled compound [(≡SiO) 2Ta(ND)(ND2)], 2-d, can be obtained by moderate heating (60 °C, 3 h) under D2 atmosphere (550 torr, 300 eq. with respect to Ta), and that the exchange is reversible. The observed stretching and bending frequencies of 2-d are in agreement with the expected isotopic shift upon H/D replacement with respect to literature values reported for 2 and have been corroborated by the independent synthesis of 2-d by reaction of deuterated 1a and 1b with N2 and D2. Density functional theory (DFT) calculations, performed using a periodic or a cluster model, explored the structures and energetics of all minima involved in the reaction with H 2 and showed that among the explored pathways the energetically preferred mechanisms for H2 reaction with [{(μ-O)[(HO) 2SiO]2}Ta(V)(NH) (NH2)], 2q, is the heterolytic cleavage of either the imido Ta=N or the amido Ta-N bonds, to yield respectively [{(μ-O)[(HO)2SiO]2}TaH(NH 2)2], 3q (Δ= -9.5 kcal mol-1 and ΔG298K = +2.6 kcal mol-1 with respect to 2q) and [{(μ-O)[(HO)2SiO]2}Ta(NH) (NH3)], 4q (Δ = -6.0 kcal mol-1 and ΔG298K = +7.9 kcal mol -1 with respect to 2q). All activation barriers are moderate (between 17.7 and 30.2 kcal mol-1) in agreement with the observed mild heating conditions necessary for the reaction to occur. © Springer Science+Business Media, LLC 2009.
Original languageEnglish
Pages (from-to)1482-1491
JournalTopics in Catalysis
Volume52
DOIs
Publication statusPublished - 1 Oct 2009

Keywords

  • Ammonia
  • Dihydrogen
  • Dinitrogen
  • H/D exchange
  • Heterolytic splitting
  • Imido amido
  • Tantalum (V)

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