Alkanes organometallics + acids

It has been reported that neat samples of several phenylboranes exhibit well resolved resonances for boron-bonded carbon atoms at ambient temperature in contrast to solutions of the same compounds. n.m.r. has been used in structural and configurational analyses of organometallic derivatives of alkane-nitronic acids. ... 

Alkenes frequently have two kinds of C—H bonds, vinyl and allyl, that are generally more acidic than the C—H bonds of saturated alkanes. Quantitative measures of acidity are related to the chemistry of the corresponding carbanions and carbanion salts or organometallic compounds. Several methods have been used for the study of anions in the gas phase1. For many acids it is possible to measure equilibrium constants for equilibria of the type in equation 1. From such equilibrium constants with compounds RH of independently known gas-phase acidity, it has been possible to determine the acidities of a wide range of compounds2. 

Organometallics are generally strong nucleophiles and bases. They react with weak acids, e.g. water, alcohol, carboxylic acid and amine, to become protonated and yield hydrocarbons. Thus, small amounts of water or moisture can destroy organometallic compounds. For example, ethylmag-nesium bromide or ethyllithium reacts with water to form ethane. This is a convenient way to reduce an alkyl halide to an alkane via Grignard and organolithium synthesis. 

The heterolytic activation of H2 in the above system is particularly interesting in that it may be applicable to reactions in which ionic hydrogenation of hindered substrates from a metal catalyst and H2 is desired. In 1989, Bullock reported the first examples of ionic hydrogenation wherein a mixture of an organometallic hydride such as CpMoH(CO)3 and a strong acid like HO3SCF3 reduces sterically hindered olefins to alkanes via protonation to carbocations followed by hydride transfer from the metal hydride [Eq. (10)] (49). 

The secondary reduction of the terminal radical by Sml2 generates samarium alkyl species which are suitable for classical organometallic reactions, e.g. protonation, acylation, reactions with carbon dioxide, disulfides, diselenides, or the Eschenmoser salt. A broad variety of products is available (hydroxy-substituted alkanes, esters, carboxylic acids, thioethers, selenoethers, tertiary amines) by use of the double-redox four-step (reduction-radical reaction-reduction-anion reaction) route (Scheme 20) [73]. 

This has allowed us to identify, for the first time in solution at room temperature, organometallic noble gas complexes which are formed following irradiation of metal carbonyls in supercritical noble gas solution. We have found that these complexes are surprisingly stable and have reactivity comparable to organometallic alkane complexes. In addition, we have studied the co-ordination of COj to metal centres in supercritical CO2 (scCOj) and shown that v(C-O) bands provide a very sensitive probe for the oxidation state of the metal centre. We found evidence, albeit circumstantial, for the formation and reactivity of ri -O bound metal COj complexes in solution at or above room temperature and found these highly reactive COj complexes have similar reactivity to the analogous Xe complexes [11-12]. We have also used TRIR to examine the reactivity of CpMofCO), radicals in scCOj and found evidence for an interaction, possibly Lewis Acid/Base, between CpMo(CO), and scCO [13]. 

Organomagnesium and organolithium compounds are such strong bases that they will react immediately with any acid that is present in the reaction mixture—even with very weak acids such as water and alcohols. When this happens, the organometallic compound is converted into an alkane. If D2O is used instead of H2O, a deuterated compound will be obtained. 

C-H o-bond activation of hydrocarbons by transition metal complexes is of considerable importance in modern organometallic chemistry and catalytic chemistry by transition-metal complexes [1], because a functional group can be introduced into alkanes and aromatic compounds through C-H o-bond activation. For instance, Fujiwara and Moritani previously reported synthesis of styrene derivatives from benzene and alkene via C-H o-bond activation of benzene by palladium(ll) acetate [2]. Recently, Periana and his collaborators succeeded to activate the C-H o-bond of methane by the platinum(ll) complex in sulfuric acid to synthesize methanol [3], Both are good examples of the reaction including the C-H o-bond activation. 

---