Early carbonyl metalate derivative

It is only since the early 1980s that significant progress has been made with aldol reactions. This chapter introduces some of the most important developments on the addition of metallic enolates and the more important of the related allylic metal derivatives to carbonyl compounds. These processes are depicted as paths A and B in Scheme 3-1. 

The active nitrene intermediate should insert into a saturated C-H bond [8], excluding also that reaction 27 proceeds via the corresponding N-(2-aminobenzoyl)amidc. Nucleophilic nitrene complexes are known to react with the carbonyl group of aldehydes and ketones to yield the corresponding imines and a metal-oxo complex [91], However, the driving force of this reaction is the oxophilicity of early transition metals used in [91], whereas the catalyst used in this work are derivatives of the late-transition metals. Oxo derivatives of these metals in the low oxidation state are ver> rare. The mechanism followed by this reaction requires further investigation in order to be clarified. 

The Wittig-type olefination of carbonyl compounds is one of the characteristic reactions of carbene complexes. High-valent carbene complexes of early transition metals show ylide-like reactivity to vards carbonyl compounds. In 1976, Schrock first demonstrated that niobium and tantalum neopentylidene complexes 1 and 2, the typical nucleophilic Schrock-type carbene complexes, olefinate various carbonyl compounds including carboxylic acid derivatives [4]. 

The early workers in coordination chemistry were more interested in the theory of bonding and structure than in any practical usefulness which the compounds might have. In more recent times, however, applications have developed. Perhaps the most important of these is in catalysis, especially for hydrogenation and the activation of carbon-hydrogen bonds. Metal carbonyls and their derivatives have played a large part in this application, as well as in carbonylation reactions such as the recently developed process for converting methanol to acetic acid 42... 

In the case of rhodium, however, it was demonstrated early that in the synthesis of [Rh6C(CO)l5]2 the encapsulated carbon atom originated as chloroform, which had reacted with the rhodium carbonyl anion [Rh7(CO)l6]3- (59). In the cobalt analog, [Co6C(CO)l5]2-, the carbon atom is derived indirectly from carbon tetrachloride [via Co3(CO)9CCl] (60) Both these syntheses are performed under mild conditions, and there are apparently no examples of carbidocarbonyl clusters of cobalt or rhodium prepared directly from the metal carbonyls under pyrolysis conditions. 

Consequently, in the early work with hydridosilicon derivatives, diethyl ether was normally used in the case of very volatile products, dimethyl ether offered some practical advantages. It was tacitly assumed that a polar solvent was essential in order to dissolve, at least partly, the transition-metal carbonyl derivative. More recently, however, it has become clear that alkanes, although nonpolar, provide a very suitable reaction medium, and can be used in cases where ethers, for example, are inimical to the products (8, 32, 306, 310). The hydrocarbon, besides acting as a diluent for the silicon halide, seems to assist the separation of alkali halide from the surface of the reacting transition-metal carbonyl salt. 

As indicated above, the antiknock effect is shown by many compounds. Outstanding among these are the organometallic compounds of many metals. Effective derivatives of many metals include alkyl compounds, aryls, carbonyls, nitrosyls, phosphines, cyclopentadienyls, and many mixed compounds. The aromatic amines are also good antiknock agents, but far less effective than the organometallic compounds. The reason why commercialization efforts were concentrated on tetraethyllead early in the history of antiknock investigations is evident from Table 1, which is a composite of early data 6 8,216). 

Nitrile derivatives of the metal carbonyls have been discussed together with other nitrogen donor molecules in a number of contexts. Much of the early work has been reviewed by Manuel 337) in his article on Lewis base-metal carbonyl complexes in Volume 3 of this series, and by Stroh-meier 436) in his review of photochemical substitution reactions. In general, nitriles are weaker Lewis donors than phosphorus and nitrogen bases 436), but compared to carbon monoxide, better electron donors but poorer acceptors 427). Force constants and assignments for a series of complexes [(MeCN)jjM(CO)g J (M = Cr, Mo, W) were studied 165, 228, 296) and... 

Early in the development of the chemistry of the metal carbonyls and their derivatives, Cotton et al. (42) concluded that the number of infrared-active carbonyl stretching vibrations of a complex is determined by the idealized local symmetry of the terminal carbonyl groups. Although exceptions to this generalization are to be found (50, 60, 117, 134), its utility is now widespread (5, 17, 60, 116, 119). A consequence of this generalization is that the isomeric form of a complex may be determined... 

---