Carbonylation molecules

Nickel, rhodium, palladium, platinum, and Raney cobalt (43) have all been used successfully in reductive alkylations. Platinum is the most used by far (J6). With small carbonyl molecules, such as acetone, palladium is about as effective as platinum, but as the molecular weight increases, platinum is apt to be more effective (SO). 

Fig. 11. Possible planar arrangements of poly(tetrahydropyran-2,6-diylimino-carbonyl) molecules provided all hydrogen bonds are ideally regularly formed between the chains58)...

The unsymmetric n face of carbonyl groups is postulated to be attributable to orbital interactions between a o-fragment and a tt-fragment. Interactions between two 7t fragments in a carbonyl molecule can also lead to an unsymmetrical orbital phase environment [3]. 

There was no evidence for production of (n C5H5)Co(C0) in Ar matrices, presumably because of very ready recombination with CO in the matrix cage. Whether a matrix isolated carbonyl molecule can eject CO without automatic reconbination probably requires the photochemical path to lead to a ground state fragment in which the empty coordination site is oriented away from the photo-ejected CO - see the Cr(C0)5 photochemical scheme (Figure 3).]... 

We compared our results in Pt catalysts with that of Pt-carbonyl molecules (12), which are often used as models of the Pt catalytic surface. The data for [Pt3g(C0)44]2 was obtained from a sample prepared by Dahl and Murphy at the University of Wisconsin. The data for the remaining three molecules was obtained from Brown et al. (12). As can be seen in Table I, we found that the position of the surface Pt resonance in our catalysts is very close to those in various Pt carbonyls. (The variations among the positions shown in Table I are small compared to typical variations among Pt compounds. See Figure 6.) Thus,... 

Table I. Position of NMR peaks in Pt catalysts and various Pt-carbonyl molecules...

Hydrogen abstraction can also occur from within the excited carbonyl molecule, with the reaction occurring preferentially to give a 1,4-biradical where the unpaired electrons are four atoms apart ... 

Since one molecule of B gives three carbonyl molecules, it must be a diene and not an alkyne. 

Carbonyl reactions may be understood in terms of two basic processes addition of a nucleophile to the carbonyl carbon (Equation 8.1) and removal of a proton from the carbon adjacent to the carbonyl group (Equation 8.2). In the first process the carbonyl molecule is acting as a Lewis acid, and in the second... 

Only the unprotonated amine with the free electron pair on nitrogen participated in the reaction (6). The dependence of the height of the more positive wave on the logarithm of the amine concentration is shown in Fig. lb the slope corresponds to a reaction of one carbonyl molecule with one amine. From the ratio of the wave-heights of the first and second waves, it is possible to calculate values of the overall equilibrium constant Ks = K 2K3HOH-], provided that the effect of protonation of the amine and of the Schiff base expressed by equations (4 a) and (4 b) is taken into account. 

Tlie use of aqueous NaOH results in the isolation of a 0-hydroxy ketone provided the alcohol is not a substituted benzyl alcohol. The alcohol can be heated with add or I3 to yield the o -unsaturated carbonyl molecule. In cases wliere the initially formed alcohol is a derivative of benzyl alcohol, a molecule of H,C is lost spontaneously. 

This reaction is concerned with the condensation or aldehydes and ketones of different structure. This reaction works best if one of the carbonyl molecules contains no G-hydrogcns. 

Finally, Richardson and his students have recently reported a study of excited state energy distribution between dissimilar carbonyl molecules produced from 1,2-dioxetanes [15] (Richardson et al., 1979). The location of the excitation energy on one or the other of the carbonyl products, as determined by trapping with olefins, appears to approach a Boltzmann-like distribution determined by the carbonyl triplet energies. 

Fig. 4. K-edge XANES calculated for the model carbonyl molecule X(CO)6 for various angles of rotation, 0, of the oxygen shell. From Pendry (233).

Since this concept is a relatively familiar one, let us simply provide a few examples that are pertinent to metal atom cluster chemistry and organometallic chemistry. Some of them derive directly from the isoelectronic relationships already noted in connection with simple metal carbonyl molecules. 

Table 14-1. Kinetic parameters (in 10 s ) obtained for the photoreduction of quinone and carbonyl molecules (XCO) in micellar (RH) solutions at room temperature with an X-band PYDESR method (Ro 334mT) [17-19].

The shielding tensors for O and " C in the CO molecule are anisotropic with zero asymmetry, reflecting the axial symmetry of the molecule. The isotropic shift of C with respect to TMS is 185 ppm, and the anisotropy in the solid is 406 ppm. Upon linear coordination in transition metal carbonyl molecules, these values typically change by tens of ppm 103). In the few bridge-coordinated compounds for which data are available the isotropic shifts are around 230 ppm and the anisotropies 175 ppm. (No data for solid-state platinum carbonyls have been reported, but there is no reason to believe that they are an exception.) In the CO molecule, the isotropic shift of O is 350 ppm with respect to H2O, and the anisotropy is 675 ppm. Again, these values change by a few tens of ppm in solid molecular metal carbonyls with linear coordination 104). 

Nucleophilic addition to the carbonyl Molecules with symmetry Synthesis In action ch25... 

Nucleophilic substitution at carbonyl molecules cyclic compounds ch33... 

A mechanism consistent with these observations is presented in Figure 8. Excited state aromatic carbonyl molecules having N,n triplet states are known to abstract hydrogen from alcohols, ethers and other substrates. In contrast, n.n excited states (i.e., perylene and anthracene) are not observed to participate in this reaction. The addition of THF to perylene and anthracene resulted in only slight increases in polymerization rates and product yields. ( 5)... 

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