Complexed to Metal Atoms

Harman and co-workers738 reported the synthesis of arenium cations stabilized by Os complexation (for example, 415) via protonation with triflic acid of [Os(NH3)5(Ar)](OTf)2 complexes (Ar = benzene, toluene, xylenes, naphthalene, anthracene). 

There are also several carbocations that have an a-Jt-complexed organometallic system. Cation 416 was easily prepared as the hexachloroantimonate salt739 [Eq. (3.117)]. 

EQUILIBRATING (DEGENERATE) AND HIGHER (FIVE OR SIX) COORDINATE (NONCLASSICAL) CARBOCATIONS 

As recognized in the pioneering work of Meerwein, Ingold, and Whitmore,10 12 18 19 744 trivalent alkyl cations (C H2 +i+) play important roles in the acid-catalyzed transformations of hydrocarbons as well as various electrophilic and Friedel-Crafts-type reactions. Trivalent alkyl cations can directly be formed by the ionization of lone-pair (nonbonded electron pair) containing precursors (w-bases) such as alkyl halides, alcohols, thiols, and so on, or by protonation of singlet carbenes or olefins. 

Protonated alkanes (C H2 , 3 ) also play a significant role in alkane reactions. Saturated hydrocarbons can be protonated to alkonium ions, of which the methonium ion CH5+, 422 [Eq. (3.119)] is the parent, and formation of these pentacoordinate carbocations involves two-electron three-center (2e—ic) bonds. The dotted lines in the structure symbolize the bonding orbitals of the three-center bonds [Eq. (3.119)] their point of junction does not represent an additional atom. 

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