Carbonyls metal interactions

Carbonyldlimidazolc, 78 Carbonyl-metal interactions, 74 Carbosiloxadienes, 452 Carboxy-ester interchange melt polyesterification, 113 Carboxy-ester interchange reactions, 62, 64, 69, 74... 

Bimetallic Complexes. There are two types of bimetaUic organometaUic thorium complexes those with, and those without, metal—metal interactions. Examples of species containing metal—metal bonds are complexes with Ee or Ru carbonyl fragments. Cp ThX(CpRu(CO)2), where X = Cl or 1, and Cp7Th(CpM(CO)2), where M = Ee or Ru, have both been prepared by interaction of CP2TI1X2 or Cp ThCl [62156-90-5] respectively, with the anionic metal carbonyl fragment. These complexes contain very polar metal—metal bonds that can be cleaved by alcohols. 

First, solvent molecules, referred to as S in the catalyst precursor, are displaced by the olefinic substrate to form a chelated Rh complex in which the olefinic bond and the amide carbonyl oxygen interact with the Rh(I) center (rate constant k ). Hydrogen then oxidatively adds to the metal, forming the Rh(III) dihydride intermediate (rate constant kj). This is the rate-limiting step under normal conditions. One hydride on the metal is then transferred to the coordinated olefinic bond to form a five-membered chelated alkyl-Rh(III) intermediate (rate constant k3). Finally, reductive elimination of the product from the complex (rate constant k4) completes the catalytic cycle. 

The energy factored force field for carbonyls contains interaction parameters as well as stretching parameters. Such parameters are invariably required to be positive, for CO groups attached to the same metal, by the experimental finding that symmetric combinations of the individual CO vibrations occur at higher frequencies than similar antisymmetric combinations. 

Interactions of metal ions with peptide carbonyl oxygen atoms have been surveyed by Chakrabarti (1990a). Of the 71 metal—carbonyl oxygen interactions studied, nine were with metals other than Ca. Only refined protein structures were included in the Chakrabarti survey, but structures at both lower and high resolution were accepted. Despite the differences in the proteins sampled, we have obtained values for the geometry... 

Fig. 9. Scatterplot of peptide carbonyl-metal ion interactions from the Brookhaven Protein Data Bank, with unidentate and bidentate examples indicated by circles and x s, respectively. [Reprinted with permission from Chakrabarti, P. (1990). Biochemistry 29 651-658. Copyright 1990 American Chemical Society.]...

Carboxypeptidase A was the first zinc enzyme to yield a three-dimensional structure to the X-ray crystallographic method, and the structure of an enzyme-pseudosubstrate complex provided a model for a precatalytic zinc-carbonyl interaction (Lipscomb etai, 1968). Comparative studies have been performed between carboxypeptidase A and thermolysin based on the results of X-ray crystallographic experiments (Argosetai, 1978 Kesterand Matthews, 1977 Monzingoand Matthews, 1984 Matthews, 1988 Christianson and Lipscomb, 1988b). Models of peptide-metal interaction have recently been utilized in studies of metal ion participation in hydrolysis (see e.g., Schepartz and Breslow, 1987). In these examples a dipole-ion interaction is achieved by virtue of a chelate interaction involving the labile carbonyl and some other Lewis base (e.g.. 

Knowing all these facts, especially the difficult access to fluorophosphines and the poor donating abilities of phosphorus trifluoride (5, 6), we decided to use another approach, which readily led to a number of coordination compounds with fluorophosphine ligands—namely, the fluorination of chlorophosphines already coordinated to the transition metal, where the 3s electrons of phosphorus are blocked by the complex formation. There was no reaction between elemental nickel and phosphorus trifluoride, even under extreme conditions, whereas the exchange of carbon monoxide in nickel carbonyl upon interaction with phosphorus trifluoride proceeded very slowly and even after 100 hours interaction did not lead to a well defined product (5,6). 

We have shown that A) interstitial hydride formation is observed only with partial occupation of the available holes, B) occupation of the interstitial position in isolated polyhedra is not observed, and C) occupation of all the holes in a close-packed lattice cancels metal-metal interactions. Therefore, it seems that interstitial hydrogen can be tolerated only in a fraction of the total number of holes, and with the weakening of metal-metal interactions. This behavior indicates strong competition between metal-metal and metal-hydrogen bonds, which is unique for hydrogen because interstitial carbon can stabilize some unusual arrangements in carbonyl carbide clusters (29, 30). 

The nature of the complexes of tellurophene and its benzo analogs depends on the type of metal carbonyl. Thus, interaction of tellurophene with (MeCN)3Cr(CO)3 yields the -complex [2 E = Te M = Cr(CO)3], whereas the reaction with Fe3(CO)12 is a complicated transformation [96JCS(D) 1545]. A similar reaction is observed for dibenzotellurophene. 

Highly enantioselective hydrogenation of functionalized ketones has been achieved with chiral phosphine-Rh(I) and -Ru(II) complexes [1,162], The presence of a functional group close to the carbonyl moiety efficiently accelerates the reaction and also controls the stereochemical outcome. The heteroatom-metal interaction is supposed to effectively stabilize one of the diastereomeric-transition states and/or key intermediates in the hydrogenation. 

Measured total sulfide levels confirm the major features of the hypotheses of Elliott and coworkers (8-11). in that sulfide seems to exist in remote oxic waters at concentrations approaching nanomolar, sufficient for meaningful metal interactions. The amplitude of the diurnal variation is too strong, however, for carbonyl sulfide hydrolysis to be the primary input, or for direct oxidation by O2 to be the sole sink, and alternate cycling processes are indicated. 

The salts of carbonyl metalates arc generally soluble only in polar solvents, in which absorptions are broader due to the dipole interactions of the solvent. The spectra are also often considerably dependent on the particular cation and solvent, due to the formation of ion pairs. The largest differences have been observed on going from alkali salts to salts of the large tetra-substituted ammonium and phosphonium cations the latter generally provide simpler spectra that indicate minor formation of ion pairs. A similar trend is observed in going from less polar (e.g., THF) to more polar solvents (e.g., CH3CN). 

On this basis, formally at least, the series 1-3 contain metal-metal triple bonds. As we shall see, the nature of the metal-metal bonding is quite different from that of carbon-carbon bonding in ethyne. Similarly, it is useful to regard the metal-metal bond order in the series 4-6 as double. However, the nature of the M=M bond is quite different from the C=C bond in ethene. The carbonyls are semi-bridging or bridging in 1-6 and are extensively involved in the metal-metal interactions. This has resulted in some differences of opinion as to whether one should really regard the metal-metal bonds as multiple. 

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