Sample application: complex organometallic reaction
First-principle molecular dynamics is used to simulate the migratory insertion of carbon-monoxide (CO) into zirconium-carbon bonds anchored to a calix[4]arene moiety.
The problem: Migratory insertions of CO and alkyl-isocyanides into meta-alkyl bonds are observed for most of the early d-block metals, leading to the formation of a new carbon-carbon bond. [An alkyl is a univalent (or free) radical containing only carbon and hydrogen atoms arranged in a chain. Calix[4]arene contains the CH3 metyl group].
The migratory CO insertion can be studied assuming the coordination of CO to the zirconium center (Image 2 in the figure on the left) and then by calculating the time evolution of the carbon-carbon distance in CH3-CO, the metal-carbon one in Zr-CH3 and the metal-oxygen one in Zr-O.
Results:
· A new CH3-CO carbon-carbon bond is formed as indicated by the decrease in the CH3-CO distance.
· The CH3 group detaches from the metal center upon CO insertion.· The structure transforms spontaneously into the non-molecular, CO4 tetrahedra-based solid
(Fig. b), when the temperature is raised to 1000 K and the pressure slowly increased up to 100 GPa,
· A Zr-O bond establishes (see image 4 in the above picture) after the initial formation of a transient species (image 3 in the above picture).
Tools:
Car-Parrinello code, available within Quantum Espresso package for first-principle molecular dynamics.
References:
· R. Car and M. Parrinello, Unified Approach for Molecular Dynamics and Density-Functional Theory: Phys. Rev. Lett. 55 (1985) 2471.
· S. Fantacci, F. de Angelis, A. Sgamellotti, and N. Re: Dynamical Density Functional Study of the Multistep CO Insertion into Zirconium-Carbon Bonds Anchored to a Calix[4]arene Moiety, Organometallics, 20 (2001) 4031.