Carbon monoxide, reaction with metal atoms

The bonding between carbon monoxide and transition-metal atoms is particularly important because transition metals, whether deposited on soHd supports or present as discrete complexes, are required as catalysts for the reaction between carbon monoxide and most organic molecules. A metal—carbon ( -bond forms by overlapping of metal orbitals with orbitals on carbon. Multiple-bond character between the metal and carbon occurs through formation of a metal-to-CO TT-bond by overlap of metal-i -TT orbitals with empty antibonding orbitals of carbon monoxide (Fig. 1). 

Of these reactions in which CO coordinates with the oxidized form of metals, the most important is the reaction with the iron atom in the hemoglobin of the blood, leading to carbon monoxide poisoning. This iron atom is part of a ring structure similar to that in chlorophyll (Chap. 6), and it ordinarily takes part in the metabolic process by reversibly forming a Fe—0—0— compound with the oxygen of the air. If carbon monoxide... 

Carbon monoxide reacts with unsaturated compounds (or components which are able to form unsaturated compounds) and a nucleophilic compound containing a mobile H-atom in the presence of certain metal carbonyls to yield carboxylic acid derivatives. This reaction is called carbonylation or, if acetylenes or olefins are reacted with carbon monoxide and water, sometimes is named hydrocarboxylation. 

With an atomic number of 28 nickel has the electron conflguration [Ar]4s 3c (ten valence electrons) The 18 electron rule is satisfied by adding to these ten the eight elec Irons from four carbon monoxide ligands A useful point to remember about the 18 electron rule when we discuss some reactions of transition metal complexes is that if the number is less than 18 the metal is considered coordinatively unsaturated and can accept additional ligands... 

Oxo Synthesis. Ad of the synthesis gas reactions discussed to this point are heterogeneous catalytic reactions. The oxo process (qv) is an example of an industriady important class of reactions cataly2ed by homogeneous metal complexes. In the oxo reaction, carbon monoxide and hydrogen add to an olefin to produce an aldehyde with one more carbon atom than the original olefin, eg, for propjiene ... 

If the reaction temperature is raised to 430 K and the carbon monoxide pressure to 3 atm, coordination of the metal atom in the rearranged product occurs via the phosphorus site, as in 159 (M = Cr, Mo, W) [84JOM(263)55]. Along with this product (M = W) at 420 K, formation of the dimer of 5-phenyl-3,4-dimethyl-2//-phosphole, 160 (the a complex), is possible as a consequence of [4 - - 2] cycloaddition reactions. Chromium hexacarbonyl in turn forms phospholido-bridged TiyP)-coordinatedcomplex 161. At 420 K in excess 2,3-dimethylbutadiene, a transformation 162 163 takes place (82JA4484). 

Even if it is assumed that the reaction is ionic, Occam s Razor would lead to the conclusion that the system is too complex and that the effort to keep it ionic is too great. It is difficult to undersand why step 8c is slow and why a simple uncharged complex would not be equally reasonable. We prefer a mechanism in which the carbon monoxide molecule is adsorbed parallel to the surface and in which the oxygen orbitals as well as the carbon orbitals of C=0 bond electrons interact with the metal. It seems reasonable that hydrogenolysis occurs exclusively only because the oxygen is held in some way while the two bonds are broken and it finally desorbs as water. The most attractive picture would be (a) adsorption of CO and H2 with both atoms on the surface... 

With respect to the thermodynamic stability of metal clusters, there is a plethora of results which support the spherical Jellium model for the alkalis as well as for other metals, like copper. This appears to be the case for cluster reactivity, at least for etching reactions, where electronic structure dominates reactivity and minor anomalies are attributable to geometric influence. These cases, however, illustrate a situation where significant addition or diminution of valence electron density occurs via loss or gain of metal atoms. A small molecule, like carbon monoxide,... 

For over 15 years we have conducted research utilizing metal atoms in low temperature spectroscopic and synthetic studies at Rice University.8 Our synthetic work was started in the late 1960s with the work of Krishnan, on lithium atom reactions with carbon monoxide, extended by Meier- in his studies of lithium atom reactions with water and ammonia and expanded over the next several years to include metal atom interactions with HF, H2O, H3N, H4C, and their hundreds of organic analogs—RF, R2O, ROH, R3N,. . . H3N, R4C, R3CH, etc. A most exciting aspect of... 

It is generally assumed that the Lewis acid in 3 decreases the charge on the metal, i.e., increases its electrophilicity. The removal of charge from the nickel allows additional electron donors to coordinate to the nickel atom, and reaction with, for example, 2 moles of carbon monoxide or 1 mole of 1,5-cyclooctadiene (COD) gives the insoluble, catalytically inactive and presumably ionic complexes 7 and 8. In contrast, 7r-allyl-nickel halides (1) add only 1 mole of carbon monoxide while they do not react with COD (52). 

Thus, the reaction of (Th[(CH3>5C5]2 2 2 (JJL) with the organoactinide dihaptoacyls was investigated to learn whether the inserted carbon monoxide was susceptible to any unusual modes of hydride reduction. In particular, analogues to the well-known insertion of carbenes into metal and metalloid hydride bonds (59,60) would offer a means to functionalize the acyl carbon atom. 

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