Complexes alcohol

Much rarer than the inclusion of phenols is complex formation between alcohols and pyridinomacrocycles. In some combinations (selected macro-cycles and alcohols) complexes could be isolated (Weber and Vogtle, 1980). TTie hydrogen bond formation between pyridines and alcohols is the basis for an application, the additions of alcohols to ketenes catalysed by concave pyridines [13] (Liining et al., 1991b Schyja, 1995). 

Cyclopentadienone iron alcohol complexes like 37 were generated from the reactions of [2,5-(SiMe3)2-3,4-(CH2)4(ri -C4COH)]Fe(CO)2H (36) and aromatic aldehydes [47]. This process can be used for the iron-catalyzed hydrogenation of aldehydes (Fig. 18 and Fe-H Complexes in Catalysis ). 

Casey CP, Guan H (2009) Cyclopentadienone iron alcohol complexes synthesis, reactivity, and implications for the mechanism of iron-catalyzed hydrogenation of aldehydes. J Am Chem Soc 131 2499-2507... 

For a liver alcohol dehydrogenase (LADH) model an NS2O coordination sphere is required. The chelating aldehydes are ideal for the formation of this donor set when combined with bis(pentafluoro-thiophenolato)zinc. Structural data on the complexes with one equivalent of 6-methylpyridine-2-carbaldehyde, 6-methoxypyridine-2-carbaldehyde, 2-(dimethylamino)benzal-dehyde) demonstrate that the coordination sphere for LADH has been reproduced to a close approximation and the corresponding alcohol complexes have also been characterized.354 Other thiophenols have been used to form such complexes but have not been structurally characterized.304... 

The cationic tantalum dihydride Cp2(CO)Ta(H)2]+ reacts at room temperature with acetone to generate the alcohol complex [Cp2(C0)Ta(H01Pr)]+, which was isolated and characterized [45]. The mechanism appears to involve protonation of the ketone by the dihydride, followed by hydride transfer from the neutral hydride. The OH of the coordinated alcohol in the cationic tantalum alcohol complex can be deprotonated to produce the tantalum alkoxide complex [Cp2(C0)Ta(01Pr)]. Attempts to make the reaction catalytic by carrying out the reaction under H2 at 60 °C were unsuccessful. The strong bond between oxygen and an early transition metal such as Ta appears to preclude catalytic reactivity in this example. 

The cationic tungsten dihydride [Cp(CO)2(PMe3)W(H)2]+ hydrogenates the C=0 bond of propionaldehyde within minutes at 22 °C, leading to the formation of cis and truns isomers of Cp(CO)3W(l IO"Pr) Oif (Eq. (28)) [42]. The cis isomer of the alcohol complex released the free alcohol faster than the trans isomer. A similar stoichiometric ionic hydrogenation of acetone was also observed using [Cp(CO)2(PMe3)W(H)2]+. 

The proposed mechanism for this H/D exchange is shown in Scheme 7.9. The formation of the alkoxide complex likely proceeds by displacement of the water ligand by the alcohol, forming an unobserved alcohol complex that transfers D+ to the OD ligand, producing an OD2 ligand. 

Rhodium diphosphine catalysts can be easily prepared from [Rh(nbd)Cl]2 and a chiral diphosphine, and are suitable for the hydrogenation of imines and N-acyl hydrazones. However, with most imine substrates they exhibit lower activities than the analogous Ir catalysts. The most selective diphosphine ligand is bdppsuif, which is not easily available. Rh-duphos is very selective for the hydrogenation of N-acyl hydrazones and with TOFs up to 1000 h-1 would be active enough for a technical application. Rh-josiphos complexes are the catalysts of choice for the hydrogenation of phosphinyl imines. Recently developed (penta-methylcyclopentyl) Rh-tosylated diamine or amino alcohol complexes are active for the transfer hydrogenation for a variety of C = N functions, and can be an attractive alternative for specific applications. 

With the aid of BF3 OEt2, methoxyborolane (R,R)-114 reacts with (.E)- or (Z)-crotylpotassium to provide (is,R,R)-115 and (Z,R,R)-115, respectively. After adding the aldehyde to a solution of crotyl-borolane in THF at —78°C for 4 hours, 2-aminoethanol is added. The solution is warmed to room temperature, and oxidative cleavage at this point gives the homoallylic alcohols with high stereoselectivity. The borolane moiety can be recovered by precipitating it as an amino alcohol complex and can be reused without any loss of enantiomeric purity. As shown in Scheme 3-43, the (.E)- and (Z)-crotyl compounds lead to anti- and -products 116, respectively. The diastereoselectivity is about 20 1, and the ee for most cases is over 95% (Table 3-11). 

In 1963, an asymmetric synthesis of chloroallenes was reported by the SNi reaction of propargyl alcohols with thionyl chloride [34]. Since then, rearrangement of pro-pargylic precursors has been one of the most useful methodologies for the synthesis of allenes [35]. Treatment of 84, obtained by asymmetric reduction with LiAlH4-Dar-von alcohol complex, with thionyl bromide gave 86 as the major product via 85 (Scheme 4.21) [36],... 

An enantioenriched propargylic phosphate was converted to a racemic allene under the foregoing reaction conditions (Eq. 9.152) [124]. It is proposed that the racemization pathway involves equilibration of the allenyl enantiomers via a propargylic intermediate (Scheme 9.37). Both the allenylpalladium precursor and the allenylsamarium reagent could racemize by this pathway. When a chiral alcohol was used as the proton source, the reaction gave rise to enantiomerically enriched allenes (Table 9.61) A samarium alcohol complex is thought to direct the protonolysis (Scheme 9.38). 

The dynamic NMR technique allows investigations on the rate of exchange between 3-substituted quinuclidinium ions and water. The rate of dissociation of amine/water (or amine/alcohol) complexes is determined71 by the free energy contribution from the pKa-dependent hydrogen bond breaking, and from dispersion forces between acceptor and donor which may be at the most 40% of the activation energy of the dissociation of the complex. Similar importance may be attributed to a term for the formation of a cavity prior to the dissociation of the complexes. 

ATH with Ruthenium Complexes of Amino Alcohol Complexes Linked to the Primary Face of P-Cyclodextrin 48... 

Fig. 22. Reduction of 63 with various ruthenium amino alcohol complexes attached to the primary face of p-CD yield and ee of the resulting alcohol is given below the ruthenium ligand.

The EAN of iron in this complex is 34, but it may be a solvated ion. Treatment of the salt with water gives 2-butanone, which was presumed to have been formed via nucleophilic attack on the cation to give a TT-allyl alcohol complex. This complex was then assumed to rearrange via the tricarbonyl hydride to an enol complex, which collapses to the ketone ... 

Iron and acetic or dilute hydrochloric acid can be safely used for the reduction of nitro group to an amino group in nitro esters. The problem arises when a nitro ester is to be reduced to a nitro alcohol. Nitro groups are not inert toward the best reagents for the reduction of esters to alcohols, complex hydrides. However the rate of reduction of a nitro group by lithium... 

Figure 7 Block diagram of the integrated natural gas to alcohols complex.

Class (3) reactions include proton-transfer reactions of solvent holes in cyclohexane and methylcyclohexane [71,74,75]. The corresponding rate constants are 10-30% of the fastest class (1) reactions. Class (4) reactions include proton-transfer reactions in trans-decalin and cis-trans decalin mixtures [77]. Proton transfer from the decalin hole to aliphatic alcohol results in the formation of a C-centered decalyl radical. The proton affinity of this radical is comparable to that of a single alcohol molecule. However, it is less than the proton affinity of an alcohol dimer. Consequently, a complex of the radical cation and alcohol monomer is relatively stable toward proton transfer when such a complex encounters a second alcohol molecule, the radical cation rapidly deprotonates. Metastable complexes with natural lifetimes between 24 nsec (2-propanol) and 90 nsec (tert-butanol) were observed in liquid cis- and tra 5-decalins at 25°C [77]. The rate of the complexation is one-half of that for class (1) reactions the overall decay rate is limited by slow proton transfer in the 1 1 complex. The rate constant of unimolecular decay is (5-10) x 10 sec for primary alcohols, bimolecular decay via proton transfer to the alcohol dimer prevails. Only for secondary and ternary alcohols is the equilibrium reached sufficiently slowly that it can be observed at 25 °C on a time scale of > 10 nsec. There is a striking similarity between the formation of alcohol complexes with the solvent holes (in decalins) and solvent anions (in sc CO2). 

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