Organo-metallic bonds

In a first approximation supra-Cp metal complexes can be prepared the same way as normal or other Cp-metal and organo-metal bonds in general. The methods used most often (see Appendix) are the metathesis reaction [Eq. (1)] followed in number by oxidative additions (Eq. (2)] and metallation/deprotonation reactions [Eq. (3)]. The latter is especially important for the cyclpentadienyl alkali metal compounds. A useful variation of reaction (3) is the formation of CpTl in an acid/base reaction from cyclopentadiene and thallium ethoxide [Eq. (3b)]. This represents a convenient route to cyclopentadienylthallium compounds, which are also valued (in place of Cp alkalis) as mild Cp-transfer reagents for the synthesis of difficultly isolable cyclopentadienyl derivatives (77). 

Protonation of a saturated carbon atom is possible only if an organo-metallic bond can be broken at the same time in an aliphatic electrophilic substitution (see Vol. 12, Chap. 2), viz. 

The possibility of observing organo-metallic bonding which may be present in the metal containing films is likely to be destroyed by exposure of the samples to the air. 

All that has been said in this section applies with equal force to the use of organo-lithium reagents in the synthesis of alcohols. Grignard reagents are one source of nucleophilic carbon organolithium reagents are another. Both have substantial carbanionic char acter in their- car bon-metal bonds and undergo the same kind of reaction with aldehydes and ketones. 

C. Eabom and R. W. Bott, Synthesis and reactions of the silicon-carbon bond, Organo-metallic Compounds of the Croup IV Elements, ed. A. G. MacDiarmid, Vol. 1, Part 1. Marcel Dekker, New York (1968). 

The different reactivities of the carbon—boron and carbon—zirconium bonds toward electrophiles are a consequence of the different bond polarities and the different electronegativities of boron and zirconium. Moreover, zirconium is a transition metal, while boron exhibits intriguing transition metal-like chemistry [55], It is thus reasonable to presume that the combined use of boron and zirconium in organic chemistry should be synergistic, affording products and chemistry not attainable with the individual organo-metallics alone. 

The X-ray crystal structures of the bisterphenyl derivatives are isomor-phous and essentially isostructural. They exist as V-shaped, discrete monomers with the closest M-M (M = Ge, Sn or Pb) contacts being 8.409(1), 8.392(3), and 8.388(1) A, respectively. The C-M-C bond angles are essentially invariant, having the values 114.2(2), 114.7(2), and 114.5(6)°, respectively. The angles are the widest reported for any cr-bonded MR2 organo-metallic derivative with monodentate ligands.104... 

Most organic chlorides, bromides and iodides react with certain metals to give compounds containing carbon-metal bonds. Such compounds are known as organo-metallic compounds. An... 

Structures of immobilized rhodium complexes on the sihca support have been proposed on the basis of the data obtained from C, P and Si MAS-NMR. NMR spectra of the rhodium-modified solid materials confirmed that trimethylsiloxide ligand was removed from the rhodium coordination sphere during the immobilization process. Formation of a new covalent bond between the rhodium organo-metallic moiety and the silica support occurs, probably with evolution of trimethylsilanol, which is rapidly converted into disiloxane (Me3Si)20. The presence of this molecule in the solution obtained after the silica surface modification process was confirmed by GCMS analysis. 

Alkanes can also be activated by oxidative addition of coordinatively unsaturated organo-metallic reagents. In the presence of carbon monoxide, C—C bond formation can ensue, e.g., the conversion of pentane to hexanal7. Note that this method, highly selective for primary sites, is complementary to the radical-based chemistry outlined above. 

---