Monoxide, coordinated, reactions

Having greater resemblance to natural fatty acids are the products of the coordination-catalyzed hydrocarboxylation of olefins with water and carbon monoxide (Reppe reaction) [58] ... 

Since 1985, several thousands of publications have appeared on complexes that are active as catalysts in the addition of carbon monoxide in reactions such as carbonylation of alcohols, hydroformylation, isocyanate formation, polyketone formation, etc. It will therefore be impossible within the scope of this chapter to review all these reports. In many instances we will refer to recent review articles and discuss only the results of the last few years. Second, we will focus on those reports that have made use explicitly of coordination complexes, rather than in situ prepared catalysts. Work not containing identified complexes but related to publications discussing well-defined complexes is often mentioned by their reference only. Metal salts used as precursors on inorganic supports are often less well defined and most reports on these will not be mentioned. 

M(tj-CsH5)2 fragment with 7r-acceptor and -donor ligands and have emphasized the orbital interactions with conformational consequences, e.g., for carbene and olefin ligands. They have also discussed insertion reactions of olefins and carbon monoxide coordinated to this metal fragment 134). 

From the standpoint of the present review, we will focus on compounds in which unusual and potentially reactive features of CO coordination are revealed, and on certain classes of reactions in which the conversion of CO to other chemical entities is achieved. For the purposes of determining what a reactive mode of CO coordination is and in what way the CO ligand can be activated, it is first instructive to briefly review the primary modes of carbon monoxide coordination. These are illustrated as Lewis structures... 

Both Marko and Aldridge postulate tricarbonyl intermediates to account for the inverse dependence of rate on carbon monoxide pressure. Reaction of such intermediates with molecular hydrogen as in Eq. (61) is discussed in the section on coordinatively unsaturated intermediates. 

The interaction of carbon monoxide with palladium salts produces under rela tively mild (but rigorously anhydrous) conditions such species as [Pd(CO)Cl2 ] 2, [Pdj CU(CO)j and probably, under higlier carbon monoxide pressure, species such as Pd(CO)2 CI3. Only under severe conditions are reduced species such as [Pd(CO)Xlrt X = Br. Cl formed, but since the catalytic reaction is carried out under a relatively mild carbon monoxide pressure, it is rather improbable that such reduced species are present in considerable amounts. For a general discus sion of the mechanism, however, the characteri .ation of the exact nature of the palladium(Il) carbonyl complexes formed m sint is irrelevant, ( nerally speaking, carbon monoxide coordination to a Pd(U) ion will produce a facile nucleophilic attack on CO by the alcohol. The question of whether such an attack is produced by free alcohol or by a palladium bonded alkoxy group, is worth examination. 

An associative mechanism for carbonylation of iodobis(triphenylphosphine)aryl-platinum(II) complexes has been suggested. The carbon monoxide insertion reaction of PtI(Me)(CO)(PPh3), promoted by tertiary arsines or by SbPha, involves the intermediacy of the three-coordinate intermediate PtI(COMe)(PPh3). The nature of the intermediates in the carbonylation of trans-PtX(PhXPR3)2 was investigated and found to involve formation of a five-coordinate complex ". ... 

Carbon monoxide insertion into the copper-alkyl bond is indirectly shown by reaction of CO with dibutylcuprate(I), an anionic dialkyl derivative of dicoordinated copper(I). The product of the reaction, dibutylketone, may be rationalized by assuming carbon monoxide coordination to the anionic copper complex, followed by alkyl migration to the unstable anionic complex Cu[C(0)Bu](Bu) , with subsequent reductive elimination to the observed organic product. 

Although the reaction pathway is not known in detail, these results support an attack of an alcohol molecule on carbon monoxide coordinated to a cupric species in solution bearing chloride (and possibly hydroxo) ligands, for the generation of the alkoxy carbonyl intermediate (see equation 5). The hydroxo ligands buffer the system acidity. 

When Pd(II) is used as catalyst, the reaction can be initiated by an (alkoxycar-bonyl)paUadium species deriving from attack of the nucleophilic function of the substrate on carbon monoxide coordinated to palladium. This species then inserts the unsaturated... 

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... 

Reaction of diphenyl-2-thienylphosphine with Ru3(CO)l2 gives the tiVp) ti Ti C) coordinated species, 144, along with cluster 145 where two ligand molecules participate in coordination, one via the phosphorus atom and the C=C bond of the heteroring, and the other via the phosphorus atom only. P-Coordination in the products of such an interaction is known [95JOM(488)85]. Complex 144, the main product, interacts with carbon monoxide to yield the P-coordinated cluster, 146,... 

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). 

The reaction of an alkyne 1 and an alkene 2 in the presence of dicobaltoctacar-bonyl to yield a cyclopentenone 3 is referred to as the Pauson-Khand reaction Formally it is a [2 + 2 + 1 ]-cycloaddition reaction. The dicobaltoctacarbonyl acts as coordinating agent as well as a source of carbon monoxide. 

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