Substituent effect in para substituted Cr(CO)5-pyridine complexes

Systematic studies on the substituent effect in para substituted Cr(CO)(5)-pyridine complexes have been carried out on the basis of DFT quantum-chemical calculations. Ten simple and mostly common substituents were chosen in order to analyze possibly the largest spectrum of substituent effects. The following substituents were taken into consideration: NO, NO2, CN, CHO, F, H, CH3, OCH3, OH and NH2. Additionally, the Cr-N and Cr-C bonds were characterized on the basis of Atoms in Molecules topological analysis of electron density. It has been found that the substituents in position 4 of the pyridine ring influence the Cr-N bond of Cr(CO)(5)-Pyridine complex in a systematic manner, as a result of with, the pyridine moiety has a diversified ability of participating in the interaction with the Cr atom of Cr(CO)(5) moiety. It has also been found, that the electron withdrawing substituents additionally stabilize the Cr-N bond, whereas the electron donating ones weaken it. The substituent effect mainly affects the pi-component of the Cr-N bond. This effect proceeds in the whole Cr-pyridine-R moiety, and it is additionally reflected in the corresponding changes in metal-carbonyl bonds, particularly the trans Cr-CO bond. (c) 2007 Elsevier B.V. All rights reserved.