Metal carbonyl compounds

The sonochemistry of solutes dissolved in organic Hquids also remains largely unexplored. The sonochemistry of metal carbonyl compounds is an exception (57). Detailed studies of these systems led to important mechanistic understandings of the nature of sonochemistry. A variety of unusual reactivity patterns have been observed during ultrasonic irradiation, including multiple ligand dissociation, novel metal cluster formation, and the initiation of homogeneous catalysis at low ambient temperature (57). 

Some catalysts are ha2ardous materials, or they react to form ha2ardous substances. For example, catalysts used for hydrogenation of carbon monoxide form volatile metal carbonyl compounds such as nickel carbonyl, which are highly toxic. Many catalysts contain heavy metals and other ha2ardous components, and environmentally safe disposal has become an increasing concern and expense. 

Chlorodifluoromethyl Ketone Metal Carbonyl Compound Yield of Aldol (%)... 

Vibrational spectra of transition metal carbonyl compounds. L. M. Haines and M. H. B. Stiddard, Adv, Inorg. Chem. Radiochem., 1969,12, 53-133 (340). 

Substitution reactions of metal carbonyl compounds. D. A. Brown, Inorg. Chim. Acta, Rev., 1967, 1,35-47 (76). 

Azolides are also capable to acylate anionic metal carbonyl compounds. For instance, disodium tetracarbonylferrate as well as the corresponding ruthenium and osmium compounds can be formylated with formylimidazole in the presence of boric acid methyl ester ... 

Fig. 7.2 indicates the electron distribution of HO of carbon monoxide which largely localizes at the carbon atom 79>. This orbital resembles a lone-pair AO on the carbon atom and leads to the expectation that the carbon atom would behave as the electron-donating centre. As a matter of fact, the CO molecule coordinates with a metal cation by M—C—O type linkage (M represents a metal cation) in various metal carbonyl compounds. It is of interest to remark that the total electron population of the CO molecule has been shown by recent reliable calculation 80> to be rich on the oxygen atom in place of the carbon atom. 

Metal carbonyl compounds are other suitable precursors for the synthesis of NPs by thermal decomposition. The main advantage is the formation of CO that is expelled from the IL phase due to its poor solubility. However, high temperatures are commonly used to decompose such precursors. Metal NPs of Cr(0), Mo(0), and W(0) were prepared by thermal or photolytic decomposition of their respective monometallic carbonyl compounds [M(CO)6] dispersed in ILs [52]. Similarly, the precursors [Fe2(CO)9], [Ru3(CO)i2], and [Os3(CO)12] were employed in order to obtain stable metal NPs (1.5-2.5 nm) in BMI.BF4 [53]. The same procedure was extended to the preparation of lr(0), Rh(0), and Co(0) NPs in ILs [54]. 

Of course, even in low temperature solutions, unstable compounds may not be very long-lived. Modern fast-scanning FT-IR interferometers can produce high signal-to-noise spectra in a single scan. This means that metal carbonyl compounds with half-lives as short as 2 seconds can be easily detected using an unmodified interferometer (28,29). With improved interferometers, we anticipate that such studies will soon be extended to compounds with lifetimes —100 mseconds. However, detection of shorter lived species, such as reaction intermediates, requires much faster and more sensitive techniques. 

Selective Photochemistry. It is well known that for many substituted metal carbonyl compounds in solution, photochemical loss of either CO or the substituent L can be promoted depending... 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

The determination of this quantity, which is of interest in many different types of metal carbonyl compound, is a contentious matter and relatively few measurements... 

The dominant photochemical reaction of metal carbonyl compounds is loss of carbon monoxide, which is usually followed by substitution of another ligand to replace the expelled carbon monoxide. 

Carbon monoxide and low valent transition metals are known to give various quite well described complexes. However, due to the strong coordination to CO, these metal carbonyl compounds are not very reactive towards carbon-halogen bonds. Thus the carbonylation of organic halides remains a difficult reaction since the presence of CO leads to the deactivation of the catalytic system. Various attempts to overcome this drawback have however been reported. 

Thus it has been shown that some metal-carbonyl compounds can be activated by electrochemical reduction generating reactive anionic species. Without going into details, it is worth pointing out that the synthesis of aldehydes can be obtained by electrolyzing a stoichiometric mixture of alkyl halides and ironpentacarbonyls (Eq. 17) [124, 125] ... 

Despite the apparent generality of this Wittig-type process, it must be noted that the reactions of Ph3P=C=PPh3 with transition-metal carbonyl compounds do not always result in the formation of phosphonioacetylide moieties. Thus, replacement of, instead of addition to (see Scheme 24), the CO group has been observed in some... 

A,A-disubstituted derivatives 1-5. Amination of Group 1, 2, 11 and 12 organometallic compounds and a-metallated carbonyl compounds with these reagents takes place by a direct introduction of the R1R2N+ group to carbanions and enolates and for completion the reactions require only hydrolytic work-up (Scheme 3). 

The use of 0-acylhydroxylamine-type reagents for amination of a-metallated carbonyl compounds is limited. The use of 0-mesitoylhydroxylamine 2j or 0-(3,5-dinitromesitoyl) hydroxylamine 2k in the amination of the enolate derived from 3-methylbutanoic acid was unsuccessful ". 

There are a few reports on the amination of a-metallated carbonyl compounds with 0-(arenesulfonyl)hydroxylamine-type reagents. However, in recent years there has been substantial progress in Af-(alkoxycarbonyl) 0-(arenesulfonyl)hydroxylamine [alkyl N-(arenesulfonyloxy)carbamate]-type reagents for the amination of enolates and eniminates. 

A-Metal derivatives of A-(aUtoxycarbonyl) 0-(arenesulfonyl)hydroxylamines, [alkyl A-metal A-(arenesulfonyloxy)carbamates] 3i-o have been used in the amination of a-metallated carbonyl compounds to give A-Boc [N(COOBu-f)] or A-Alloc [N(COOCH2 CH=CH)] protected a-aminocarbonyl compounds. 

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