Hydrocarbons, with Organometallic derivatives

Three basic methods have been used for the preparation of organodihaloboranes, RBX2 (1) the direct interaction of hydrocarbons with haloboranes, (2) the reaction of organometallic derivatives with haloboranes, and (3) the halogenation of organoboranes. One of the most convenient laboratory procedures involves the reaction of tetraorganotin derivatives with trihaloboranes, BX3.1-8 This reaction works particularly well for the preparation of alkyldihaloboranes as outlined below. 

Hydrocarbons with suitably acidic (allylic, benzylic, propargylic, acetylenic) hydrogens can be transformed to organometallic derivatives, which then can react with alkylating agents to yield alkylated products. 

Azulene (Figure 7.48) is an intriguing variant wherein the cyclohep-tatrienyl unit is fused with a five-membered ring. The organometallic chemistry of this hydrocarbon and related derivatives is less intensely studied but includes the 18VE derivatives shown, obtained from reactions with simple binary carbonyls. 

This remarkable reaetion is relevant first because the process did not require an expensive and toxic metal catalyst and second because an aromatic hydrocarbon ArH (mesitylene in the reported example) was directly used as the nucleophile, in contrast to what happens with thermal reactions, where a nucleophilic organometallic derivative Ar M is used, as in the Stille (M = SnR3), Kumada (M = MgX) and Suzuki [M = 11(011)2] reactions. 

Spectra-structure correlation charts showing the probable positions of the characteristic absorption frequencies of some 1000 aliphatic, aromatic, and heterocyclic compounds [ ], together with various classes of aliphatic and organometallic derivatives in the 15-to 35-/1 region, are shown in Figs. 3 and 4. Some of the important classes of compounds studied and summarized in these correlation charts are alkanes, alkenes, cyclopropanes, cyclopentanes, cyclohexanes, substituted benzenes, polynuclear hydrocarbons, heterocyclics. 

The site of reaction on an unsaturated organometallic molecule is not restricted to the most probable position of the metallic atom or cation or to a position corresponding to any one resonance structure of the anion. This has been discussed in a previous section with reference to the special case of reaction with a proton. Although the multiple reactivity is particularly noticeable in the case of derivatives of carbonyl compounds, it is not entirely lacking even in the case of the derivatives of unsaturated hydrocarbons. Triphenylmethyl sodium reacts with triphenylsilyl chloride to give not only the substance related to hexaphenylethane but also a substance related to Chichi-babin s hydrocarbon.401 It will be recalled that both the triphenyl-carbonium ion and triphenylmethyl radical did the same sort of thing. 

We are not aware of any industrial application that uses metal activation of C-H bonds to obtain functionalised molecules. We have included this topic, because it is potentially of great importance by providing a short-cut for the conversion of hydrocarbons to its functionalised derivatives. Two extreme cases will be discussed, reactions with electron-rich metal complexes and reactions with electrophilic metal complexes. As always in organometallic chemistry there are cases in between that utilise both bonding interactions. 

Organometallic Titaniam(iv) Compounds.—Charge-transfer interactions between TiC and aromatic hydrocarbons and fluorocarbons have been characterized by spectrophotometric studies. " The other work described here will mainly be concerned with selected aspects of the chemistry of Ti -alkyl and -cyclopentadienyl derivatives. 

Some organometallic compounds are prepared best by the reaction of a strong base or an alkyl metal derivative with an acidic hydrocarbon, such as an alkyne ... 

Metallaboranes mirror the metal hydrocarbyl complexes of organometallic chemistry and offer the promise of a similar rich chemistry.1 Indeed there are a number of strictly isoelectronic borane and hydrocarbon complexes in which a C atom is formally replaced with a B or BH moiety.2 Comparison of the structure and properties of these compound pairs highlights interesting similarities and differences between the organic and inorganic derivatives.3... 

Organo-Zn, -Cd and -Hg derivatives can be prepared from other compounds by proton-metal exchange with acidic hydrocarbons by olefin insertion and by metal-metal exchange with other organometallics. In all cases alkyl groups are substituted by other... 

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