75506-18-2Relevant academic research and scientific papers
Rhodium carbonyl cluster chemistry under high pressure of carbon monoxide and hydrogen. 3. Synthesis, characterization, and reactivity of HRh(CO)4
Vidal, José L.,Walker
, p. 249 - 254 (1981)
The fragmentation of Rh4(CO)12 in dodecane solutions under 1241-1379 atm of carbon monoxide at 5-12°C has been established by high-pressure infrared spectroscopy to give Rh2(CO)8. Noticeable spectral changes are caused by the introduction of small amounts of hydrogen (1542 atm, CO:H2 = 4.5:1). Fourier subtraction of the spectra of these two species left bands at 2070 (m), 2039 (vs), and 2008 (w) cm-1. By analogy to the spectra previously observed for HIr(CO)4 and HCo(CO)4 this pattern is assigned to HRh(CO)4, a species that has eluded previous attempts of detection. The reaction of [M(CO)4]- (M = Co, Rh, Ir) with protonic acids in tetraglyme-toluene under high pressure of carbon monoxide resulted in the formation of HM(CO)4 (M = Co, Rh, Ir), with the reaction having been readily detected in the case of iridium with phosphoric acid (Ir:P = 0.38:4.12), while a stronger acid such as sulfuric acid was required for cobalt (Co:S = 0.95:29.9) and rhodium (Rh:S = 0.90:29.4) for the detection of a similar reaction. These results suggest that the proton affinity of these ions varies as [Ir(CO)4]- > [Co(CO)4]- > [Rh(CO)4]-. The differences in the acid strength of the corresponding conjugate acids, HM(CO)4 (M = Co, Rh, Ir), was determined under high pressures of CO-H2 by reaction with amines of different basicities such as N-methylmorpholine (pK(water, 25°C) = 7.4) and N,N-dimethylaniline (pK(water, 25°C) = 4.8) after formation of the tetracarbonylmetal hydrides, in situ. HIr(CO)4 is not deprotonated in a detectable fashion by N-methylmorpholine (Ir:N = 1:10), while HCo(CO)4 is deprotonated by this amine (Co:N = 2.4:1.0) but not by N,N-dimethylaniline (Co:N = 2.4:3.0). By contrast HRh(CO)4 readily undergoes deprotonation with this amine (Rh:N, = 2.7:1.0). These results correspond to the following trend in Br?nsted acidity: HRh(CO)4 > HCo(CO)4 > HIr(CO)4.
