Metal carbonyls addition

Synthesis of Heteronuclear and Polynuclear Metal Carbonyls. Heteronuclear metal carbonyls are usually synthesized either by metathesis (27) or addition (28,40). 

Garbonylation of Olefins. The carbonylation of olefins is a process of immense industrial importance. The process includes hydroformylation and hydrosdylation of an olefin. The hydroformylation reaction, or oxo process (qv), leads to the formation of aldehydes (qv) from olefins, carbon monoxide, hydrogen, and a transition-metal carbonyl. The hydro sdylation reaction involves addition of a sdane to an olefin (126,127). One of the most important processes in the carbonylation of olefins uses Co2(CO)g or its derivatives with phosphoms ligands as a catalyst. Propionaldehyde (128) and butyraldehyde (qv) (129) are synthesized industrially according to the following equation ... 

Exposure to metal carbonyls can present a serious health threat. Nickel carbonyl is considered to be one of the most poisonous inorganic compounds. However, the toxicological information available on metal carbonyls is restricted to the mote common, commercially important compounds such as Ni(CO)4 and Ee(CO). Other metal carbonyls are considered potentially dangerous, especially ia the gaseous state, by analogy to nickel and iron carbonyls. Data concerning toxicological studies on a few common metal carbonyls are Hsted ia Table 6 (185). Additional toxicity data are OSHA personal exposure limits (PEL) for Ee(CO) this is 8 h at 0.1 ppm, whereas for the much more toxic Ni(CO)4 it is 8 h at 0.001 ppm, with a toxic concentration TCLq low (of 7 mg/m ) for human inhalation. 

The carbonyl addition reactions of benzylmetals, compared to the allylic counterparts, have found few applications in stereoselective synthesis, apparently for the following reasons The carbonyl addition of alkali metal salts (M = Li, Na, K, Cs) of benzyl anions, with few exceptions, usually proceeds with low levels of simple diastereoselectivity affording mixtures of syn- or <7 / -diastereomers (see Section 1.3.2.3.1.). 

Thus, the allyllithium, -sodium or -potassium derivatives are the ones which are most easily generated (Section D.1.3.3.3.1.1.), but they are of limited value in stereoselective carbonyl addition reactions. Usually these reagents need to be tuned" in their reactivity by metal exchange prior to application in order to achieve high selectivities. 

I.3.3.3.I.2. Stereoselective Carbonyl Addition Reactions of Allyl Alkali Metals... 

Finally, intermediate cationic allyl complexes of palladium15,16 and ruthenium17, produced from allylic esters by the action of substoichiometric amounts of the metal catalyst, have been electronically inverted by reduction to become nucleophilic anion equivalents, which are capable of carbonyl addition. 

The transition metal catalysed addition of a hydridosilane to a multiply-bonded system is known as hydrosilylation (1). Under such conditions, alkynes undergo clear cis-addition, so providing one of the most direct routes to vinylsilanes (Chapter 3). Hydridosilanes also add to the carbonyl group of saturated aldehydes and ketones, to produce alkyl silyl ethers. Fot example, under suitable conditions, 4-t-butylcyclohexanone (2) can be reduced with a high degree of stereoselectivity. 

The metal carbonyls Ni(CO)4, Fe(CO)s, and Cr(CO)6 are observed to be diamagnetic. This follows from the theoretical discussion if it is assumed that an electron-pair bond is formed with each carbonyl for the nine eigenfunctions available (3d64s4p3) are completely filled by the n bonds and 2(9 — n) additional electrons attached to the metal atom (n = 4, 5, 6). The theory also explains the observed composition of these unusual sub-... 

In the metal-carbonyl catalysed hydrocarboxylation of alkynes ( Reppe reaction ) nearly exclusive cia-addition of H—COOH is found (Ohashi et al., 1952). 

With respect to CO complexes, the luminescence spectra of a series of Group VI metal carbonyls and substituted carbonyls were obtained in frozen gas matrices at 12K. In addition, the IR spectra of HCo(CO>4 and HCo(CO)3 (proposed as an intermediate in hydroformylation) were observed in an argon matrix. ... 

Double-bond isomerization can also take place in other ways. Nucleophilic allylic rearrangements were discussed in Chapter 10 (p. 421). Electrocyclic and sigmatropic rearrangements are treated at 18-27-18-35. Double-bond migrations have also been accomplished photochemically, and by means of metallic ion (most often complex ions containing Pt, Rh, or Ru) or metal carbonyl catalysts. In the latter case there are at least two possible mechanisms. One of these, which requires external hydrogen, is called the nwtal hydride addition-elimination mechanism ... 

In addition, hydrogen bonding was still observed at 3,583 cm (Fig.l A). IR peaks in VC.O region (Fig.l B) shifted to lower frequency after adsorption due to precursor-support interaction and differed from that of cluster solution implying that precursor was not intact after adsorption on support but still in the form of metal carbonyl species. 

We have reviewed experiments on two classes of systems, namely small metal particles and atoms on oxide surfaces, and Ziegler-Natta model catalysts. We have shown that metal carbonyls prepared in situ by reaction of deposited metal atoms with CO from the gas phase are suitable probes for the environment of the adsorbed metal atoms and thus for the properties of the nucleation site. In addition, examples of the distinct chemical and physical properties of low coordinated metal atoms as compared to regular metal adsorption sites were demonstrated. For the Ziegler-Natta model catalysts it was demonstrated how combination of different surface science methods can help to gain insight into a variety of microscopic properties of surface sites involved in the polymerization reaction. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

The lanthanides are congeners of the Group IIIA metals scandium and yttrium, with the +3 oxidation state usually being the most stable. These ions are strong oxyphilic Lewis acids and catalyze carbonyl addition reactions by a number of nucleophiles. Recent years have seen the development of synthetic procedures involving lanthanide metals, especially cerium.195 In the synthetic context, organocerium... 

Heteronuclear compounds containing gold(I) and other metal atoms which present Au -M interactions are well represented in the area of metal carbonyl clusters. The addition of a AuPR3+ or Au2(/u-P-P)2+ fragment to a metal cluster results in the formation of Au—M bonds often with retention of the cluster framework. Several reviews have been reported recently,3153-3155 and so it will not be treated here. Some representative examples are found in Figure 26. 

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