Agostic interaction

The word agostic was introduced by Malcom Green and Maurice Brookhart into the field of the Chimie Organométallique to describe a weak flexible interaction between a Métal of transition and a CH bond related to a carbon atom which is held close to central metal by the means of an interaction π or σ.

The word comes from the Greek for " to hold close to soi". This interaction resembles of close with the state of transition from an oxidizing addition or a réductive elimination. The agostic interactions are best shown in Cristallographie but can be deduced from the presence of a peak NMR ¹H which is shifted towards the strong fields compared with that of an aryl or normal alkane, approaching this that a ligand hydride. The constant of J_CH coupling is generally lowered to 70-100 Hz instead of the 125 Hz normally awaited for a carbon-hydrogen connection sp ³. The energy of the interaction is estimated at approximately 10-15 kcal/mole (40-60 kJ/mol) starting from experimental results of studies of numerical chemistry. This interaction is thus slightly stronger than the majority of the hydrogen bonds.

The bonds agostic play sometimes a role in the catalytic reactions while increasing rigidity states of transition. For example, in a Catalysis Ziegler-Natta, the metal center, strongly électrophile, has agostic interactions with the polymer chain in formation.

The term agostic was wide in an unsuitable way in order to include other flexible interactions in three centers like the complexation of H₂ on tungsten illustrated by W (CO) ₃ (PPrⁱ₃) ₂H₂.

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