Vibrational spectra, molecular structure and rotational isomerism in “staircase” carbonyl complexes of transition metals

Abstract

Abstract Fourier transform infrared (FT-IR) spectra have been studied of “staircase” cyclopentadienyl complexes containing two or three metal carbonyl fragments bound by the metal-carbon bond Cp(CO) 2 Fe-CpmMn(CO) 3 ( I ), Cp(CO) 2 Fe-CpmFe(CO) 2 CH 2 Ph ( II ), Cp(CO) 2 Fe-Cpm(CO) 2 Fe-CpmMn(CO) 3 ( III ), Cp(CO) 2 Mo-Cpm(CO) 2 Fe-CpmMn(CO) 3 ( IV ), Cp(CO) 3 W-Cpm(CO) 2 Fe-CpmMn(CO) 3 ( V ), Cp(CO) 2 Fe-Cpm(CO) 2 Fe-BmCr(CO) 3 ( VI ), Cr(CO) 3 Bm-CpmFe(CO) 2 CH 2 Ph ( VII ), where Cp = η 5 : η 5 -C 5 H 4 , Bm = η 1 : η 6 -C 6 H 5 , as well as model mononuclear complexes Cp(CO) 2 FeCH 2 Ph (VIII), CpMn(CO) 3 ( IX ), and ( η 6 -C 6 H 6 )Cr(CO) 3 ( X ). The spectra were interpreted on the basis of the local symmetry of each metal carbonyl center. The v CC positions are determined by the mutual electronic effects of each center. CpmM(CO) n groups are strong electron acceptors and cause an increase in the v CO of adjacent M(CO) n groups. Cp(CO) n M groups, being electron donors, lead to a decrease in the frequencies of neighbouring groups. Temperature dependent FT-IR spectra in pentane solutions and solid matrices were measured. Rotational isomers, formed due to rotation about the metal-carbon bond, were found in solutions and solid matrices. A molecular mechanics calculation for I proved the possibility of such rotation.