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 π-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.