THE INFRARED-SPECTRA OF BASE-FREE DIOXYGEN ADDUCTS OF RUTHENIUM(II) AND OSMIUM(II) PORPHYRINS

The IR spectrum of Ru(TPP) cocondensed with O-16(2) at approximately 30 K exhibits two O-O stretching bands at 1167 and 1114 cm-1 which are shifted to 1101 and 1057 cm-1, respectively, by O-16(2)/O-18(2) substitution. The former at 1167 (1101 cm-1 is assigned to the end-on type dioxygen adduct, Ru(TPP)O2 whereas the latter at 1114 (1057) cm-1 is attributed to the O2-bridging adduct, [Ru(TPP)]2O2. The IR spectrum of Os(TPP) cocondensed with O-16(2) under similar conditions exhibits only one O-O stretching band at 1090 cm-1 which is shifted to 1030 cm-1 by O-16(2)/O-18(2) substitution. This band is also attributed to the bridging dioxygen adduct [Os(TPP)]2O2. These assignments are made baised on the trends in frequencies and intensities of the O-O stretching bands in the Fe, Ru and Os series and the results of warm-up experiments on the IR spectrum of the Ru(TPP)-O2 system.