Alkyl hydride adducts

Although insertion of metals into C-H bonds of alkanes, alkenes, and aromatics has been known for a long time, the direct intermolecular insertion of a metal fragment into a C-H bond of an alkane to provide a stable alkyl hydride adduct was achieved only in 1982. The intermediate 16-electron, electron-deficient transition metal fragment (or metals such as Ir, Rh, Ru, etc.) was generated photochemically by the decomposition of the appropriate metal dihydride or metal carbonyl. 

Bergman and Janowicz showed " - that photolysis of [Cp (PMe3)IrH2] in a variety of alkane solvents gave the corresponding alkyl hydride adducts with elimination of H2 [Eq. (6.88)]. These adducts were also found to eliminate alkanes thermally at 110°C and exchange with other alkanes. 

Thus lithium alanate forms stable 1 2, 1 3, and 1 4 adducts with triethylalane (127). The 1 2 adduct is crystalline (m.p. +29°C) the other compounds are liquids. On the other hand, if lithium alanate and triethylalane are mixed in 1 1 molecular proportions an alkyl-hydride exchange is the main result and a crystalline product of approximate composition Li[(C2H6)AlH3] is obtained (127). 

Donor Adducts. These are again similar to borane adducts, the stability order being B > A1 > Ga and also similar to adducts of the halides and alkyls where the stability order is halides > alkyls > hydrides. The most studied adducts are the trialkvlamine alanes (alane =-AIH3). Trimethylamine-gives both 1 1 and 1 2 adducts but the latter are stable only in the presence of an excess of amine ... 

The data on the synthesis of azabicyclo[3.3.1]nonanes fused with azoles have recently been published [102-104]. The first step of the reaction is the formation of hydride adducts 125 by action of NaBHa (Scheme 61). These adducts undergo the Mannich condensation with formaldehyde and alkyl amines to give 3-R-l,5-dinitroa-zabicyclo[3.3.1]nonanes 126, fused with azole fragments across the C(7)-C(8) bond. 

Prochiral olefins such as the (Z)-a-acetamidocinnamic acid derivatives, MAC and EAC, bind to the rhodium-DIPAMP catalyst to form the diastereomeric olefin complexes A and A shown in Scheme 15.18. Oxidative addition of dihydrogen to each of the diastereom-ers forms diastereomeric hydride complexes B and B, each of which imdergoes migratory insertion to form alkyl hydride complexes C and C. These complexes then undergo reductive elimination to form the amino acid ester products. The stereochemistry of the organic products can be predicted for the two parallel paths, assuming that the addition of occms to the face of the olefin coordinated to Rh. The N-acetyl-(R)-phenylalanine ester would be produced from the olefin adduct A and the (S)-product from A. ... 

As we have seen, oxidative addition is the inverse of reductive elimination and vice versa. In principle, each reaction is reversible, but in practice the reactions tend to go in the oxidative or reductive direction only. The position of equilibrium in any particular case is governed by the overall thermodynamics this in turn depends on the relative stabilities of the two oxidation states and the balance of the A—B versus the M—A and M—B bond strengths. Alkyl hydride complexes commonly eliminate alkane, but only rarely do alkanes oxidatively add to a metal. Conversely, alkyl halides commonly add to metal complexes, but the adducts rarely reductively eliminate the alkyl halide. Third-row elements, which tend to have stronger metal-ligand bonds, tend to give more stable adducts. Occasionally, an equilibrium is established in which both the forward and back reactions are observed. 

In some cases similar structures are discussed for corresponding lithium organic compounds. But from a preparative point of view the lead hydride adducts cannot be compared to these metal organic adducts because the former give on hydrolysis the hydrated reactants, the latter the alkylated... 

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

Alkyl mercuric hydrides are generated in situ by reduction of an alkyl mercuric salt with sodium borohydridc (Scheme 3.91). Their use as radical traps was first reported by Hill and Whitesides491 and developed for the study of radical-olefin reactions by Giese,489490 Tirrell492 and coworkers. Careful choice of reagents and conditions provides excellent yields of adducts of nucleophilic radicals (e.g. -hexyl, cyclohexyl, /-butyl, alkoxyalkyl) to electron-deficient monomers (e.g. acrylics). 

Silyl(pinacol)borane (88) also adds to terminal alkenes in the presence of a coordinate unsaturated platinum complex (Scheme 1-31) [132]. The reaction selectively provides 1,2-adducts (97) for vinylarenes, but aliphatic alkenes are accompanied by some 1,1-adducts (98). The formation of two products can be rationalized by the mechanism proceeding through the insertion of alkene into the B-Pt bond giving 99 or 100. The reductive elimination of 97 occurs very smoothly, but a fast P-hydride elimination from the secondary alkyl-platinum species (100) leads to isomerization to the terminal carbon. 

Nickel(O) reacts with the olefin to form a nickel(0)-olefin complex, which can also coordinate the alkyl aluminum compound via a multicenter bond between the nickel, the aluminum and the a carbon atom of the trialkylaluminum. In a concerted reaction the aluminum and the hydride are transferred to the olefin. In this mechanistic hypothesis the nickel thus mostly serves as a template to bring the olefin and the aluminum compound into close proximity. No free Al-H or Ni-H species is ever formed in the course of the reaction. The adduct of an amine-stabihzed dimethylaluminum hydride and (cyclododecatriene)nickel, whose structure was determined by X-ray crystallography, was considered to serve as a model for this type of mechanism since it shows the hydride bridging the aluminum and alkene-coordinated nickel center [31]. 

A thio-substituted, quaternary ammonium salt can be synthesized by the Michael addition of an alkyl thiol to acrylamide in the presence of benzyl trimethyl ammonium hydroxide as a catalyst [793-795]. The reaction leads to the crystallization of the adducts in essentially quantitative yield. Reduction of the amides by lithium aluminum hydride in tetrahydrofuran solution produces the desired amines, which are converted to desired halide by reaction of the methyl iodide with the amines. The inhibitor is useful in controlling corrosion such as that caused by CO2 and H2S. 

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