Organometallic compounds classification

C.E. Holloway and M. Melnik, Tin Organometallic Compounds Classification and Analysis of Crystallographic and Structural Data. Part I. Monomeric Derivatives (2000).53 C.E. Holloway and M. Melnik, Part II. Dimeric derivatives. (2000).54 C.E. Holloway and M. Melnik. Part III. Oligomeric derivatives (2000).55 C.E. Holloway and M. Melnik, Heterometallic tin compounds Classification and Analysis of Crystallographic and Structural Data Part I. Dimeric Derivatives (2001).56... 

The classification of metals, their salts, and organometallic compounds, based on the Principle of Hard-Soft Acids and Bases (HSAB) of Pearson [112,116,156-158], is discussed in detail in Sec. 1.2.2. 

Figure 2.4 Classification of cr-organometallic compounds. (From Ref. 184k. Reproduced with permission.)...

The U.N. classification scheme defines water-reactive substances as substances which are liable to become spontaneously flammable or to give off flammable gases in dangerous quantities by interaction with water. Water-reactive substances include, among others, alkaline metals (Na, K, Li, etc.), hydrogenates, and organometallic compounds. 

The more comprehensive definitions have grown to include metalloids and even what were considered only a few decades ago to be nonmetals. Furthermore, some are of the opinion that the so-called metals need not always be attached formally to carbon in order to have compounds with organometallic characteristics. An extreme case is the concept that carbon itself may partake of the characteristics of a metal and on such a classification simple compounds such as ethane or benzene are in and of themselves, organometallic compounds. 

The substitution reactions of organometallic compounds, in which heterolytic attack at the carbon is usually by electrophiles, are not susceptible to the simple mechanistic classification (SnI, Sn2, and S i) which is so useful in discussing nucleophilic reactions of organo-nonmetallic compounds. The situation is complicated by the propensity of the metal to increase its coordination number, and a spectrum of mechanisms has to be considered in which electrophilic attack at carbon is accompanied by or preceded by nucleophilic attack at the metal. 

In real organometallic compounds this classification, based on the assumption of electronically well defined regions in the molecules ( localized molecular orbitals), is generally not very useful. In the class of cyclometal-lated complexes, however, it has been shown that this scheme can be applied often successfully, despite the strongly covalent character of the M-C bonds present. 

Some other contributions of organometallic compounds to fundamental research are (a) the detection of free alkyl radicals by the pyrolysis of lead alkyls (b) the classification of hydrocarbon acidity via organoalkali compounds (c) the study of Lewis acid-base interactions with Group III alkyls (d) the development of the concept of electron-deficient compounds by the study of metal alkyls (e) the discovery of stereospecific olefin polymerization and (f) the investigation of nucleophilic additions to unsaturated organic compounds via reactive metal alkyls. 

The Covalent Bond Classification (CBC) Method is an insightful approach specifically designed for covalent molecules and is particularly applicable to organometallic compounds. The conceptual core of the CBC method is to classify each ligand as a neutral species on the basis of its orbital interactions with the metal. This classification requires considering three fundamental interactions, represented by the symbols L, X, and Z... 

Classification Organometallic compounds Empirical C2HeMg02 Formula (CH30)2Mg... 

---