A Molecular Mechanics Model of Ligand Effects. 4. Binding of Amines to Cr(CO)5: ER Values for Amines

Moon Gun Choi, Theodore L. Brown

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Molecular mechanics methods have been applied to compute the energy-minimized structures of a series of 27 alkylamines and their complexes with Cr(CO)5. The MMP2 force field was employed, using the comprehensive computational program BIOGRAF. The computed structures of Cr(CO)5(L) (L = piperidine or quinuclidine) are in good agreement with the structural parameters determined by X-ray diffraction studies. In general, substantial changes in the lowest energy conformations are observed in the complexes as compared with the free ligands. The energy-minimized structures are employed to calculate a new measure of ligand steric effect, the ligand repulsive energy, ER, obtained by computing the van der Waals repulsive force acting between the ligand and Cr(CO)5 fragments along the Cr-N axis, at the equilibrium Cr-N distance, re. The repulsive force is scaled by re to obtain ER: ER = re[dEVdw(repulsive)/dr(Cr-N)]. The amine ER values correlate well with cone angle for amines (rcorr = 0.94). The amine ER values are compared with those of phosphines. The advantages of ER as a measure of ligand steric effect are also described.

Original languageEnglish
Pages (from-to)1548-1553
Number of pages6
JournalInorganic Chemistry
Issue number9
Publication statusPublished - 1993

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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