Borane complexes carbon-hydrogen

Arene ruthenium and osmium complexes play an increasingly important role in organometallic chemistry. They appear to be good starting materials for access to reactive arene metal hydrides or 16-electron metal(O) intermediates that have been used recently for carbon-hydrogen bond activation. Various methods of access to cyclopentadienyl, borane, and carborane arene ruthenium and osmium complexes have been reported. 

They are cleaved by refluxing in ethanol, methanolic sodium carbonate, TFA," or ammonium chloride. The aminoborane was found to be stable to LDA and KHMDS. Pd-C was found to be very effective for the cleavage of an intermediate borane complex during the synthesis of the sensitive FR-66979. The hydrogen liberated during this decomposition will cleave benzylamines. ... 

Barton and his students [24] and, more recently, by other groups [25], The second transformation in Scheme 12 illustrates the conversion of a tartrate-derived thio-carbonate into a malate using hypophosphorous acid [26]. Phosphine-borane complexes have also been proposed as convenient hydrogen atom donors for the deoxygenation [27],... 

Lower dialkyl sulfides are often employed as valuable solvents. Most organic sulfides with low molecular mass have intense unpleasant odors. Cotmnercial dimethyl sulfide contains highly malodorous impurities such as carbon disulfide, carbonyl sulfide, methyl thiol, dimethyidisulfide, hydrogen sulfide and other sidfurous compounds at low levels. Dialkyl sulfide borane complexes of high purity are used to produce low odor dialkyl sulfides by enantioselective reduction. ... 

The dominant factors reversing the conventional ds-hydroboration to the trans-hydroboration are the use of alkyne in excess of catecholborane or pinacolborane and the presence of more than 1 equiv. of EtsN. The P-hydrogen in the ris-product unexpectedly does not derive from the borane reagents because a deuterium label at the terminal carbon selectively migrates to the P-carbon (Scheme 1-5). A vinylidene complex (17) [45] generated by the oxidative addition of the terminal C-H bond to the catalyst is proposed as a key intermediate of the formal trans-hydroboration. 

The domain of hydrides and complex hydrides is reduction of carbonyl functions (in aldehydes, ketones, acids and acid derivatives). With the exception of boranes, which add across carbon-carbon multiple bonds and afford, after hydrolysis, hydrogenated products, isolated carbon-carbon double bonds resist reduction with hydrides and complex hydrides. However, a conjugated double bond may be reduced by some hydrides, as well as a triple bond to the double bond (p. 44). Reductions of other functions vary with the hydride reagents. Examples of applications of hydrides are shown in Procedures 14-24 (pp. 207-210). 

Unsaturated epoxides are reduced preferentially at the double bonds by catalytic hydrogenation. The rate of hydrogenolysis of the epoxides is much lower than that of the addition of hydrogen across the carbon-carbon double bond. In a, -unsaturated epoxides borane attacks the conjugated double bond at -carbon in a cis direction with respect to the epoxide ring and gives allylic alcohols [660], Similar complex reduction of epoxides occurs in a-keto epoxides (p. 126). 

Hydroboration-oxidation of alkenes preparation of alcohols Addition of water to alkenes by hydroboration-oxidation gives alcohols via anti-Markovnikov addition. This addition is opposite to the acid-catalysed addition of water. Hydrohoration is regioselective and syn stereospecific. In the addition reaction, borane bonds to the less substituted carbon, and hydrogen to the more substituted carbon of the double bond. For example, propene reacts with borane and THF complex, followed by oxidation with basic hydrogen peroxide (H2O2), to yield propanol. 

Phosphine complexes. Maintenance of a tetrahedral state of the phosphorus atom in such complexes and enhancement of acidity of the hydrogen atoms attached to an adjacent carbon enable the enantioselective deprotonation by the s-BuLi/(-)-sparteine complex. Oxidative coupling of the lithio derivatives and removal of the borane units accomplish the synthesis of Cj-symmetric P-chiral diphosphines. 

The results of ab initio calculations for the addition of borane to ethene depend on the level of the calculation. " For the reaction of borane with propene in the gas phase, Houk and co-workers identified a n complex and two transition states, one for attachment of the boron atom to the carbon bearing two hydrogen atoms and one for attachment of the boron atom to the methyl-substituted carbon atom. As in the case of ethene, the n complex formed from propene was found to be lower in energy than the reactants. The transition state for attachment of the boron atom to the CH2 position was found to be 3.7 kcal/mol lower in energy than the alternative transition state, and the difference in energy was attributed to a combination of electronic and steric factors. ... 

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