Alkali metals carbonyl compound reduction

Sometimes mercury derivatives formed in the preparation of alkali metal carbonyls by reduction with sodium amalgam are potential contaminants in metal carbonyl derivatives prepared from the resulting sodium compounds. Moreover, in large-scale preparations the quantity of mercury required for the dilute amalgams can be very large and thus inconvenient. It is possible to avoid the presence of mercury in reductions of metal carbonyls such as Mn2(CO)io and Co2(CO)g by the use of lithium wire in tetrahydrofuran 38). 

LiAlH4 as this avoids protonation of the enolate and the production of any over-reduction products. Cholest-4-en-3-one may be reduced to cholestanone (5a 5/8,1 19) with alkali-metal carbonyl chromates. The studies on intramolecular hydride shifts on hydroxy-ketones and -aldehydes have been extended. " The hydride shifts were examined in a number of y- and 5-hydroxy-carbonyI compounds by heating the substrates with alkaline alumina containing D2O. Exchange of protons on the carbon a to both oxygen functions signals the intramolecular hydride shift typically, the hemiacetals (95) and (96) each incorporate up to six deuterium atoms. The general conclusion, in common with literature precedent, is that, whereas 1,5-shifts are common, 1,4-shifts are rare. 

Carbonyl compounds of metallocene and half-metallocene are highly stable. Metallocene carbonyl complexes, (ri -C5R5)2M(CO)2 (M = Ti, Zr, Hf R = H, Me) have been characterized by IR spectra and X-ray analysis [173]. Anionic complexes [(t -C5R5)M(C0)4] (M = Ti, Zr, Hf R = H, Me) (55) were prepared by alkali metal naph-thalenide reduction of (r -C5R5)MCl3 followed by carbonylation [174,175]. 

Polynuclear anionic metal carbonyl compounds are usually prepared by reduction reactions of metal carbonyls M(CO) with such reducing agents as the alkali metals, NaBH4 in ethers, hydrocarbons, liquid ammonia, and similar solvents [see, for example, reactions (2.54), (2.55), (2.84), (2.89), (2.95>-(2.102), and (2.108)-(2.113)]. In alkali medium the metal carbonyls may be reduced by certain solvents (e.g., alcohols) or by the CO ligand itself, and in the presence of Lewis bases the carbonyls disproportionate to give anionic clusters. The mixed metal clusters containing platinum and rhodium are formed by reduction reactions of chloro complexes... 

Reduction with metal deuteride complexes (section Ill-A) is undoubtedly the most convenient way to convert carbonyl compounds into the corresponding deuterated alcohols. For stereochemical reasons, however, it is sometimes necessary to resort to reductions with alkali metals in O-deuterated alcohols, or in liquid deuterioammonia-O-deuterioalcohol mixtures. 

Carbonyl platinum dichloride has a distinctly basic character. It dissolves in excess of hydrochloric acid to a lemon-yellow solution, due, perhaps, to the formation of a soluble hydrochloride, PtCl2.CO.HCl. This solution is a powerful reducing agent, effecting the reduction of silver, gdld, and mercury from their salts.1 The monocarbonyl unites with soluble metallic chlorides, such as those of the alkali metals, to yield yellow, crystalline double salts. These, however, are so readily soluble and so easily decomposed that their satisfactory isolation has proved difficult. With the chlorides of certain organic bases, however, well-defined compounds have been obtained.4... 

McMurry developed a reduction procedure that is used for alkenation of carbonyl compounds in the presence of low-valent titanium (LVT) reagent. The reagent (thought to be a mixture of Ti(0) and Ti(II) species) is formed by the reduction of TiCU or TiCb with a suitable reducing agent (Zn-Cu alloy, LiAlH4 or alkali metal are the most commonly used). 

The state of the art of reductions with metal hydrides a decade ago was the subject of comprehensive reviews. A detailed survey of reductions of carbonyl compounds with alkali and alkaline earth metal hydrides, borane and derivatives, alane and derivatives, metal borohydrides, metal aluminohydrides, silanes, stannanes and transition metal hydrides was compiled. The properties, preparation and applications of each reagent were discussed together with methods for their determination, handling techniques... 

It must be emphasized that reduction of carbonyl compounds by dissolving metals, either in the presence or absence of an added proton donor is a kinetically controlled process. This was tacitly stated in 1972," and has been repeated or implied in more recent reviews of this topic. A recent study of the reduction of several bicyclo[2.2.1]heptanones using alkali metal-NH3-NH4Cl systems emphasizes that these reductions are kinetically controlled. ... 

Reduction of carbonyl compounds.l0 Aldehydes and ketones are reduced to the corresponding alcohols by alkali metals (Li, Na, K) in HMPT in the presence of a protic cosolvent such as /-butanol. 

Neutral Ti(CO)6 is an extremely unstable compound which decomposed even below -220 °C, as shown by matrix isolation spectroscopy [165]. The much more stable phosphine derivatives Ti(CO)3(dmpe)2, Ti(CO)5(dmpe), Ti(CO)5(PMe3)2, Ti(CO)4(PMe3)3 have been isolated [166-168]. In contrast, the dianionic salt [Ti(CO)6] (53) is thermally much more stable and decomposes only above 200 C. Complex 53 was obtained by reductive carbonylation of Ti(CO)3(dmpe)2 by alkali metal naphthalenides in the presence of cryptand [169]. Carbonylation of 79 also produces 53 [170]. The naph-thalenide-assisted reductive carbonylation of the zirconium tetrachloride afforded the zirconium analog [Zr(CO)6] (54) [171], which was also derived by carbonylation of the tris(diene) dianion 45 [150]. One anion [R3Sn] effectively stabilizes Ti(CO)e as an air stable monoanionic salt, [R3SnTi(CO)J [172]. 

It has been successfully used in reducing47 aliphatic aldehydes and aromatic ketones, and also in the pinacolization48 of aromatic aldehydes and ketones. Under similar conditions41 aliphatic ketones show very low reactivity toward reduction to give the corresponding secondary alcohols. The reduction of the various carbonyl compounds is suggested47 to proceed as follows (the dimer model of alkali metal ketyls may well apply to radical anions of oxophilic samarium) ... 

In the case of glass, however, no great variations in behaviour between different types are expected because of their very similar structure and surface composition. Chemical vapour deposition reactions had already been tried by the last century, for instance in the refinement and deposition of silicon by reduction of SiF4 and SiCU with alkali metals [71] and in the refining of Ni using Ni-carbonyl in the Mond process [72,73]. The major impact of chemical vapour deposition on thin-film technology took place, starting some 60 years ago, when refractory compounds such as metal carbides, nitrides, silicides, borides and oxides as well as mixed phases of... 

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