Vibrational spectroscopy studies of Co 2(CO) 6(PPh 3) 2/Al 2O 3 interacting with CO, H 2 and C 3H 6

Abstract

Five wt.% of bis(triphenylphosphine)dicobalt hexacarbonyl supported on γ-alumina (BDSA)was prepared by grinding Co 2(CO) 6(PPh 3) 2 and γ-alumina together in a glove box. Raman and photoacoustic (PAS) bands of BDSA at room temperature in the range of wave numbers between 950 and 1600 cm −1 indicated an interaction of the phenyl groups in Co 2(CO) 6(PPh 3) 2 with hydroxyl groups on the surface of γ-alumina. A new Raman band appeared at 1797 cm −1 and was assigned to a carbonyl species hydrogen-bonded to hydroxyl groups on the surface of γ-alumina. At elevated temperature under vacuum, this hydrogen-bonded species disappeared and the appearance of a partially decarbonylated species was identified by Raman spectroscopy. The BDSA was equilibrated with CO, H 2 and C 3H 6 at room temperature, at 85 °C and at 170 °C. At 170 °C, the Raman and diffuse reflectance spectra of BDSA are both quite different from those of BDSA below 110 °C. Hydro-formylation occurred at 170 °C and ambient pressure to produce aldehydes. The cobalt carbonyl species supported on γ-alumina at 170 °C was no longer a dicobalt species; it had been converted into a tetrameric cobalt cluster. Similar results were observed under homogeneous reaction conditions.