Rhodium stretching frequency

For rhodium complexes the IR stretch frequency of ram-RhClL2(CO) has been used [14],... 

This implies that the three frequencies in the hydrido complex are a combination of two CO stretching frequencies and one rhodium hydrido stretching frequency. 

The complexes in Table I have been assigned an end-on geometry on the basis of spectroscopic data, chemical behavior, and, in the case of a macrocyclic rhodium complex, X-ray crystallographic data (53). The 0-0 stretching frequencies and 0-0 bond lengths are useful indicators of the electronic structure of coordinated dioxygen (54-59),... 

In addition, the effect of para-substitution of the aryl group in triphenyl phosphine was studied. Substitution influences the IR frequencies of the complexes RhH(P(C6H4R)3)2(CO)2, as shown in Table 6.6. Both hydride-metal and C-O stretching frequencies show a regular increase with %-value. The lower electron density on the metal leads to a decrease in back-donation from rhodium to the carbonyl ligand and hence higher frequencies for the CO stretches are... 

TABLE I Infrared Carbonyl Stretching Frequencies for Cyclopentadienyl Manganese and Rhodium Complexes"... 

Chlorocarbonylbis(triphenylphosphine)rhodium and chlorocarbonylbis(triphenylarsine)rhodium form bright yellow crystalline solids which are readily soluble in chloroform and dichloromethane, moderately soluble in benzene and carbon tetrachloride, and sparingly soluble in ether and aliphatic hydrocarbons. The phosphine complex (m.p. 195 to 197°) and the arsine complex (m.p. 242 to 244°) are reported to have carbonyl stretching frequencies (using KBr disks) at 1960 and 1963 cm., respectively. ... 

Scheme 3 is supported by the isolation from the reaction mixture of a yellow rhodium complex that does not exhibit carbonyl stretching frequencies in the infrared. This compound, originally postulated to be RhC CAr)... 

Figure 1 quite clearly demonstrates that the bimetallic complexes generated from the dicationic precursor 5r have considerably lower electron densities on the rhodium atoms, as indicated by the 100 cm higher vco stretching frequencies, relative to the electron-rich neutral bimetallic hydrido-carbonyl species formed from the reaction of 8r with H2/CO. 

Erkey studied the hydroformylation of 1 -octene in scCOi using several different fluoralkyl and fluoralkoxy functionalized aryl phosphines [29]. They found an increasing activity of the rhodium catalyst with decreasing basicity ofthe phosphine ([3,5-(CF3)jC sHs] 3P > [4-CF3QH4]3P and [3-CFj QH4]3P > [4-CF30CgH4]3P). The basicity was measured by the carbonyl stretching frequencies ofthe complexes. 

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