Electron-deficient metal fragment

Apart from electron-deficient metal fragments, free metal atoms as well as metal ions can insert into C-H and C-C bonds. In 1980, Billups et al. demonstrated that photoexcited Fe atoms in a methane matrix reacted to provide HFeCHg. Ozin and McCaffrey subsequently studied this reaction in greater detail and found that the reaction is reversible at different wavelengths [Eq. 

Benzoquinone is widely recognized as a useful oxidant in organic and inorganic chemistry [79,80]. It often reacts with transition metals by coordination of the electron-deficient alkene fragment to the metal center, forming... 

The existence of the agostic bond C-II " M has been firmly established by X-ray and neutron diffraction methods. The symbolic representation C-H M indicates formal donor interaction of a C-H bond with an electron-deficient metal atom M. As in all 3c-2e bridging systems involving only three valence orbitals, the bonded C-II M fragment is bent. The agostic bond will be further discussed in Section 11.5.3. 

Further developments are likely as the chemistry of the compounds described above is explored. Moreover, entirely new dimensions may be added. For example, the synthesis of tungsten-alkylidyne complexes with carba-borane ligands with cage structures smaller than the icosahedral C2B9 fragment should result in the isolation of new electronically unsaturated metal cluster and electron-deficient molecules of types as yet unknown. 

The 1,2- and 1,7-isomers are susceptible to degradation with strong base, which removes one boron atom from each of the cages. In the 1,2-isomers either the 3- or 6-boron atom is removed while for the 1,7-isomers either the 2- or 3-boron atom is removed. The boron atoms capable of extraction in each isomer are adjacent to both heteroatoms. These boron atoms are the most electron-deficient and the most susceptible to nucleophilic base attack. The 11-atom fragments are not normally isolated as the ollide ions themselves but in a protonated form (i.e., 1,2-B9C2H12-). The extra protons are easily removed with base prior to metal complexation. The ollide ions discussed in this section may well exist as open-face icosahedral fragments (Fig. 2). This point has not been definitely determined yet and an alternative... 

An interesting tautomerism is possible for compounds of type 19 (or 18). As shown in Eq. (1), the lone pair of electrons could be moved onto the metal fragments, resulting in breakage of the M-M bond, creating a planar EM3 unit (40). This creates an electron-deficient E center, but such molecules have precedent in [E Fe(CO)4 3]2 (E = Sn, Pb). Such intermediates could well be stabilized by partial multiple bonding as for the other ini-dene compounds. 

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