Structure and Dynamics of a Dihydrogen/Hydride Ansa Molybdenocene Complex

Pons, Vincent; Conway, Stephen L. J.; Green, Malcolm L. H.; Green, Jennifer C.; Herbert, Benjamin J. and Heinekey, D. Michael (2004). Structure and Dynamics of a Dihydrogen/Hydride Ansa Molybdenocene Complex. Inorganic Chemistry, 43(11) pp. 3475–3483.

DOI: https://doi.org/10.1021/ic0496875

Abstract

In contrast to [Cp2MoH3]+, which is a thermally stable trihydride complex, the ansa-bridged analogue [(η-C5H4)2CMe2MoH(H2)]+ (1) is a thermally labile dihydrogen/hydride complex. Partial deuteration of the hydride ligands allows observation of JH-D = 11.9 Hz in 1-d1 and 9.9 Hz in 1-d2 (245 K), indicative of a dihydrogen/hydride structure. There is a slight preference for deuterium to concentrate in the dihydrogen ligand. A rapid dynamic process interchanges the hydride and dihydrogen moieties in complex 1. Low temperature 1H NMR spectra of 1 give a single hydride resonance, which broadens at very low temperature due to rapid dipole−dipole relaxation (T1 = 23 ms (750 MHz, 175 K) for the hydride resonance in 1). Low temperature 1H NMR spectra of 1-d2 allow the observation of decoalescence at 180 K into two resonances. The bound dihydrogen ligand exhibits hindered rotation with ΔG150 = 7.4 kcal/mol, but H atom exchange is still rapid at all accessible temperatures (down to 130 K). Density functional calculations confirm the dihydrogen/hydride structure as the ground state for the molecule and give estimates for the energy of two hydrogen exchange processes in good agreement with experiment. The presence of the C ansa bridge is shown to decrease the ability of the metallocene fragment to donate to the hydrogens, thus stabilizing the (η2-H2) unit and modulating the barrier to H2 rotation.

Viewing alternatives

Metrics

Public Attention

Altmetrics from Altmetric

Number of Citations

Citations from Dimensions
No digital document available to download for this item

Item Actions

Export

About

Recommendations