Extremely low barrier to rotation of dihydrogen in the complex IrClH[sub 2]([eta][sup 2]-H[sub 2])(P[sup i]Pr[sub 3])[sub 2]

Journal Article · Wed Nov 17 04:00:00 EST 1993 · Journal of the American Chemical Society; (United States)

DOI:https://doi.org/10.1021/ja00076a100· OSTI ID:7235486

Eckert, J ^[1]; Jensen, C M; Jones, G ^[2]; Clot, E; Eisenstein, O ^[3]

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1. Los Alamos National Lab., NM (United States)
2. Univ. of Hawaii, Honolulu, HI (United States)
3. Universite de Paris-Sud (France)

The isolation and characterization of the iridium nonclassical polyhydride complex IrClH[sub 2]([eta][sup 2]-H[sub 2])(P[sup i]Pr[sub 3])[sub 2] (1) was recently reported. An increased understanding of the nature of the dihydrogen-metal interaction in 1 should help in elucidating the fundamental process of activation of dihydrogen at iridium centers as well as the role of dihydrogen complexes in homogeneous catalysis. A considerable amount of insight into the dihydrogen-metal interaction has been obtained through studies of the barrier to rotation of the dihydrogen ligand by use of inelastic neutron scattering (INS) techniques. We have accordingly performed INS measurements of the rotational transitions of the dihydrogen ligand in 1 to determine the height of its rotational barrier. This barrier was also calculated by an ab initio method. Both the very low value of the observed rotational barrier and the very pronounced fourfold component in the shape of the barrier in 1 may be related to the very rapid dihydrogen-hydride exchange. On the basis of the solid-state NMR study as well as theoretical work on related compounds, we propose that a bis-dihydrogen form is the most likely intermediate in the observed pairwise dihydrogen-hydride exchange and that the unavailability of such an Ir(I) intermediate could account for the much higher barriers to dihydrogen-hydride exchange and dihydrogen rotation found for the monohydride dichloro analogue. If the equilibrium orientation of this intermediate has the H-H axes aligned with P-Ir-P, a rotation through 90[degrees] is required of each dihydrogen ligand which corresponds to the location of the secondary set of potential minima. 13 refs., 1 fig., 1 tab.

• OSTI ID: 7235486
• Journal Information: Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 115:23; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
400201* -- Chemical & Physicochemical Properties
BARYONS
COHERENT SCATTERING
COMPLEXES
DIFFRACTION
ELEMENTARY PARTICLES
ELEMENTS
ENERGY LEVELS
EXCITED STATES
FERMIONS
HADRONS
HYDROGEN
IRIDIUM COMPLEXES
LIGANDS
MAGNETIC RESONANCE
NEUTRONS
NONMETALS
NUCLEAR MAGNETIC RESONANCE
NUCLEONS
RESONANCE
ROTATIONAL STATES
SCATTERING
TRANSITION ELEMENT COMPLEXES
X-RAY DIFFRACTION