Carbon monoxide transition metal bonding

Fig. 1. (a) Formation of a ( -bond between a transition metal and carbon monoxide, (b) Metal-to-carbon monoxide TT-bond formation. 

Insertion reactions with carbon monoxide or sulfur dioxide are well known for compounds with carbon-transition-metal bonds, e.g.,... 

Formation of Carbon-Transition and Inner Transition Metal Bond 5.8.2.12. from Carbon Monoxide 5.8.2.12.1. by Direct Reaction of the Metals... 

The mechanism of hydrosilylation on a transition metal catalyst involves an intermediate with a carbon-transition metal bond. Carbon monoxide, if present, inserts into the carbon-metal bond to give an... 

The adsorption of carbon monoxide on metal surfaces can be qualitatively understood using a model originally formulated by Blyholder [45]. A simplified molecular orbital picture of the interaction of CO with a transition metal surface is given in Figure 6. The CO frontier orbitals 5a and 2n interact with the localized d metal states by splitting into bonding and antibonding hybridized metal-... 

Keywords Catalytic, C-H bond, Transition metal, Bond formation, Olefin, Carbon monoxide... 

An interesting cyclization reaction was reported that involved the reaction of dienes, diynes, or ene-ynes with transition metals to form cyclopentenone derivatives in the presence of carbon monoxide.363 in a simple example, ene-yne 444 was heated with dicobalt octacarbonyl and CO to give a 68% yield of 445.364 jjjj transformation has become an important synthetic tool known as the Pauson-Khand reaction.365 jhe mechanism probably involves insertion of the alkene (or alkyne) into the transition metal bond, which is why it is presented in this section. Formally, it is a [2+2+l]-cycloaddition, but the accepted mechanism is the one proposed by Magnus,364 and shown in Figure 13.8.366 n has been stated that further study is required to... 

The insertion of carbon monoxide into metal aryloxide bonds appears to be restricted to later transition metal complexes. The initial products of these reactions are aryloxy-carbonyls, which may be stable or undergo further reaction. Three examples of this type of reaction are shown in Eqs (6.66)-(6.68). ... 

When the carbon monoxide Inserts into all active transition-metal bonds during the selected contact time between carbon monoxide and active centres, t, and where multiple insertions do not take place, and where only one polymer chain grows from each transltlon-metal atom, the active centre concentration, C, in mol... 

We consider first some experimental observations. In general, the initial heats of adsorption on metals tend to follow a common pattern, similar for such common adsorbates as hydrogen, nitrogen, ammonia, carbon monoxide, and ethylene. The usual order of decreasing Q values is Ta > W > Cr > Fe > Ni > Rh > Cu > Au a traditional illustration may be found in Refs. 81, 84, and 165. It appears, first, that transition metals are the most active ones in chemisorption and, second, that the activity correlates with the percent of d character in the metallic bond. What appears to be involved is the ability of a metal to use d orbitals in forming an adsorption bond. An old but still illustrative example is shown in Fig. XVIII-17, for the case of ethylene hydrogenation. 

The saturation coverage during chemisorption on a clean transition-metal surface is controlled by the fonnation of a chemical bond at a specific site [5] and not necessarily by the area of the molecule. In addition, in this case, the heat of chemisorption of the first monolayer is substantially higher than for the second and subsequent layers where adsorption is via weaker van der Waals interactions. Chemisorption is often usefLil for measuring the area of a specific component of a multi-component surface, for example, the area of small metal particles adsorbed onto a high-surface-area support [6], but not for measuring the total area of the sample. Surface areas measured using this method are specific to the molecule that chemisorbs on the surface. Carbon monoxide titration is therefore often used to define the number of sites available on a supported metal catalyst. In order to measure the total surface area, adsorbates must be selected that interact relatively weakly with the substrate so that the area occupied by each adsorbent is dominated by intennolecular interactions and the area occupied by each molecule is approximately defined by van der Waals radii. This... 

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