IR carbonyls

Adduct formation by IrCl(CO)(PPh3)2 and similar compounds results in a shift in the IR carbonyl stretching frequency (Table 2.8). 

Synergistic studies were carried out on mixed metal carbonyl and mixtures of metal carbonyl complexes by Pakkanen and coworkers.94 95 A largely applied research approach, results are reported below in Table 23 for Fe-Ru and Fe Os carbonyl catalysts. Also tested (not shown) were Fc -Co and Fe-Rh carbonyl catalysts, Ru-Co and Ru Rh carbonyl catalysts, and Co-Rh, Co-Ir, and Rh Ir carbonyl catalysts. Typical conditions T = 100 °C Pco = 0.42-0.60 atm pyridine = 2.0-4.0 ml H20 = 0.36 ml. Note that dppe = Ph2PCH2CH2PPh2. The data shown in Table 23 are representative of the TON for their catalysts. 

The chemistry of Ir carbonyl clusters on the surface of MgO clearly mimics that occurring in basic solution [58] or on the silica surface added with alkali carbonates... 

TABLE 2. IR carbonyl wavenumber shifts" and equilibrium constants for the reactions of sec-BuIi with substituted phenyl sec-butyl ketones in cyclohexane at 25°C ... 

Fortunately, the mid-IR stretches of the terminal carbonyls of simple carbonyl iodide complexes of Rh and Ir occur in the region 1950 to 2150 cm Their extinction coefficients are sufficiently strong that even in aqueous AcOH, which would not be a solvent of choice for mid-IR spectroscopy, at concentrations in the range of 100s of ppm w/w, the simple Rh or Ir carbonyl iodides can be detected by FTIR with a modest acquisition time. Indeed much of the original IR work to study both Rh and Ir catalysed carbonylation by workers at Monsanto [11, 25] and by Schrod et al. [26] appears to have been carried out using continuous wavelength machines. 

Spectroscopic Studies of the Model Reaction Steps of the Ir Carbonylation Cycle 209 5.6... 

Strohmeier showed that the IR carbonyl frequencies of metal complexes could be used as a measure of the electronic properties of the ligands [8]. Tolman introduced a systematic approach to describe electronic and steric ligand effects [9]. The electronic parameter / is based on the difference in the IR frequencies of Ni(CO)3L and the reference compound Ni(CO)3(P Bu3), similar to the method introduced by Strohmeier. For phosphorus ligands the cone angle 6 is defined as the apex angle of a cylindrical cone, centered at 2.28 A from the center of the P atom, which touches the outermost atoms of the model. 

TABLE 2. IR carbonyl absorption frequencies (CHCI3) and selected NMR chemical shifts (CDCI3) for A-alkoxy-A-chloroamides (R CON(Cl)OR ) and precursor hydroxamic esters... 

The IR carbonyl stretch frequencies for a number of simple A,A-dialkoxyamides, -ureas and -carbamates are presented in Table 11 and reflect an increase of between 20 and 30 cm relative to the hydroxamic esters from which they were derived. In confirmation of theoretical studies, N—C(0) double-bond character is considerably less than in the hydroxamic esters, although the carbonyl stretch frequencies are not as... 

TABLE 11. IR carbonyl absorption frequencies for A,iV-dialkoxyamides ureas and carbamates (R ON(OR )COR ) and their precursor hydroxamic esters (R ONHCOR )... 

In 1997, Chakrabarty et al. reported the isolation of 9-carbethoxy-3-methylcarba-zole (5) and 9-formyl-3-methylcarbazole (6) from the roots of M. koenigii (17). These metabolites are the first 9-formyl and 9-carbethoxy carbazole derivatives obtained from plant sources. 9-Formyl-3-methylcarbazole (6) showed weak cytotoxicity against both mouse melanoma B16 and adriamycin-resistant P388 mouse leukemia cell lines. The structural assignment of these two alkaloids was based on the IR- and H-NMR spectra which were lacking any signal of an NH group. Additional structural support for 9-carbethoxy-3-methylcarbazole (5) was provided by the similarity of the UV absorption spectrum with that of a synthetic sample, obtained by reaction of 3-methylcarbazole with ethyl chloroformate in the presence of base. Further structural support for 9-formyl-3-methylcarbazole (6) was derived from a comparison of the UV spectrum and the IR carbonyl absorption (1696 cm ) with those of an authentic sample of 9-formyl-3-methylcarbazole (1700 cm ), prepared by the treatment of 3-methylcarbazole (2) with 98% formic acid (17) (Scheme 2.3). 

Although the valence bond description of pyran-2-one could include a zwitterionic contribution involving the carbonyl group, thus making the ring aromatic, there is little evidence to support this. For example, the IR carbonyl frequency (1740 cm ) is typical of an unsaturated lactone, and the chemical shifts of the ring protons in the H NMR spectrum indicate that there is no ring current. 

The addition of AT-sulfinylanilines to aldehydes supposedly gives 3-aryl-l,2,3-oxathiazetidines identified from nitrogen analysis, lack of an IR carbonyl stretch, the presence of an oxygen-sulfur band at 1160-1260 cm-1, and by the fact they eliminate sulfur dioxide upon heating (71JOU966). 

Matrix isolation studies usually permit spectroscopic observation of the species M(CO), M(CO)2,. M(CO) , the coordinatively saturated molecule. In some early studies, species thought to be simple unsaturated carbonyls were in fact carbonyls of metal clusters Mx(CO) a very low concentration of metal in the matrix (e.g., I mol in 104 mol noble gas) has to be used to prevent clustering. All the partially coordinated carbonyls are only matrix species, that is, they only exist when completely isolated from other molecules of their own kind or from CO. The coordinately saturated carbonyls are of more interest in the context of this review. The following new molecules have been reported Au(CO)2 (84a) Ag(CO)3, Cu2(CO)6 (46, 87) Pd(CO)4 (22), Pt(CO)4 (69) Rh2(CO)g, Ir2(CO)g (37) M(CO)6[M = Pr, Nd, Gd, Ho, Yb (100), Ta (24), U (117)]. The Cu, Pd, Pt, Rh, and Ir carbonyls can be obtained by condensing the metal vapors with pure CO at 40 K and then pumping off excess CO to leave a film of the carbonyl. The Cu, Pd, and Pt carbonyls decompose under vacuum temperatures above -100°C, and the Rh and Ir carbonyls dimerize with loss of CO to give M4(CO)12 above -60°C. The gold and silver carbonyls are not stable outside matrix isolation conditions. Unfortunately, the literature is presently unclear about the stability of the Ta and lanthanide hexacarbonyls outside a matrix. 

Figure 12 IR carbonyl frequencies for some pyran-2-ones...

The EHT MO calculated bond orders and IR carbonyl frequencies for pyran-4-one and chromone are given in Table 10. 

From measurements of the IR carbonyl frequencies, it was inferred that the 4-hydroxy-pyran-2-one (230) and the 2-hydroxypyran-4-one (231) exist as such in the solid state. In ethanol solution, however, (231) gives the tautomer (232) (59JA2427). 

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