Ab initio metadynamics simulations of oxygen/ligand interactions in organoaluminum clusters
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Car-Parrinello molecular dynamics combined with a metadynamics algorithm is used to study the initial interaction of O 2 with the low-valence organoaluminum clusters Al 4 Cp 4 (Cp = C 5 H 5 )and Al 4 Cp ∗ 4 (Cp ∗ = C5[CH3]5). Prior to reaction with the aluminum core, simulations suggest that the oxygen undergoes a hindered crossing of the steric barrier presented by the outer ligand monolayer. Acombinationoftwocollectivevariablesbasedonaluminum/oxygendistanceandlateraloxygen displacement was found to produce distinct reactant, product, and transition states for this process. In the methylated cluster with Cp ∗ ligands, a broad transition state of 45 kJ/mol was observed due to direct steric interactions with the ligand groups and considerable oxygen reorientation. In the non-methylated cluster the ligands distort away from the oxidizer, resulting in a barrier of roughly 34 kJ/mol with minimal O 2 reorientation. A study of the oxygen/cluster system fixed in a triplet multiplicity suggests that the spin state does not affect the initial steric interaction with the ligands. The metadynamics approach appears to be a promising means of analyzing the initial steps of such oxidation reactions for ligand-protected clusters.
The article of record as published may be found at http://dx.doi.org/10.1063/1.4897256
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