Hydride addition, acetylene

Reactions of dialkylaluminnm hydrides with acetylenes give addition products ... 

The addition reaction of alkyl and/or phenyl substituted silicon hydrides to acetylenes has limitations mainly due to the hydrogen donation step (cf. Scheme 5.1). Reaction (5.17) shows that the replacement of Ph by MesSi group in silanes made the reaction easier, the effect being cumulative. Indeed, the reaction time decreased from 88 h for PhsSiH to 3h for (TMS)3SiH [39], together with the amelioration of yields, and a slightly better cis stereoselectivity. 

Fig. 20. 4-31G transition states for hydride addition to acetylene and ethylene41 ... 

Species such as 74 and 75 could be intermediates in the trans addition of cobalt hydride to acetylene. 

An important feature of the LH form of the hydride is that it contains a Co111 bearing a very open coordination site for reaction with nucleophiles. There are several publications on the unusual reaction of naked cobalt111 in porphyrins with acetylenes and olefins.25611 J-258 This could also explain the trans addition of the hydrides to acetylenes. A charge-transfer intermediate in the reaction of the LH isomer with an acetylene or alkene could explain the difference in behavior of substituted versus unsubstituted olefins. If the above explanation is correct, then it would require essential equality between the energies of the Co—H and L—H complexes. Parameters such as solvent properties could shift the equilibrium concentrations of the two isomers of the hydrides, leading to apparently different results in the same reaction and explain poor reproducibility in stereoselectivities.232,233... 

Addition of arsenic hydrides to acetylenes has also been investigated to a limited extent. Dimethylarsine reacts violently with hexafluorobut-2-yne giving the expected butene derivative. The product is predominantly the... 

Typically, the anode consists of small particles of hydride-building alloy held together by a binder and conductive additive (acetylene black) and pressed onto a Ni-foam current collector. The impedance of the particle surface is determined by the charge transfer resistance of hydrogen reduction, double layer capacitance, and the impedance of subsequent solid-state diffusion into the bulk of the particle. To take into account electronic resistance between the particles and ionic resistance of electrolyte in pores, as well as the impedance of the particle surface, we can use the transmission line model of Figure 4.5.9. Because particle shape is best approximated as a sphere, diffusion with spherical boundary conditions, as in Eq. (30) can be used for Za. 

Vinylaluminiums, prepared from addition of di-isobutylaluminium hydride to acetylenes, are converted by addition of methyl-lithium into the corresponding... 

That conjugate additions are a very general phenomenon for a wide range of acceptor groups is demonstrated with the hydride additions to acetylenic sulfone 7[1]. 

The effects of variations in ligands and the coordination geometry of the metal on the facility of platinum hydride addition to acetylenes have been investigated. Both neutral and cationic complexes react at 25° with alkynes via n-complexed intermediates to produce vinyl complexes resulting from cis M—H addition (Clark et aU 1975). The orientation of addition is that... 

Methylsulfinyl carbanion (dimsyl ion) is prepared from 0.10 mole of sodium hydride in 50 ml of dimethyl sulfoxide under a nitrogen atmosphere as described in Chapter 10, Section III. The solution is diluted by the addition of 50 ml of dry THF and a small amount (1-10 mg) of triphenylmethane is added to act as an indicator. (The red color produced by triphenylmethyl carbanion is discharged when the dimsylsodium is consumed.) Acetylene (purified as described in Chapter 14, Section I) is introduced into the system with stirring through a gas inlet tube until the formation of sodium acetylide is complete, as indicated by disappearance of the red color. The gas inlet tube is replaced by a dropping funnel and a solution of 0.10 mole of the substrate in 20 ml of dry THF is added with stirring at room temperature over a period of about 1 hour. In the case of ethynylation of carbonyl compounds (given below), the solution is then cautiously treated with 6 g (0.11 mole) of ammonium chloride. The reaction mixture is then diluted with 500 ml of water, and the aqueous solution is extracted three times with 150-ml portions of ether. The ether solution is dried (sodium sulfate), the ether is removed (rotary evaporator), and the residue is fractionally distilled under reduced pressure to yield the ethynyl alcohol. 

In a manner similar to OsH(OH)(CO)(P Pr3)2, the hydride-metallothiol complex OsH(SH)(CO)(P Pr3)2 adds Lewis bases that are not bulky such as CO and P(OMe)3 to give the corresponding six-coordinate hydride-metallothiol derivatives OsH(SH)(CO)L(P Pr3)2 (L = CO, P(OMe)3). OsH(OH)(CO)(PiPr3)2 and OsH(SH)(CO)(P Pr3 also show a similar behavior toward dimethyl acetylenedi-carboxylate. Treatment of OsH(SH)(CO)(P Pr3)2 with this alkyne affords 6sH SC(C02Me)CHC(OMe)6 (CO)P Pr3)2, which is the result of the tram addition of the S—H bond to the carbon-carbon triple bond of the alkyne. Phenyl-acetylene, in contrast to dimethyl acetylenedicarboxylate, reacts with OsH(SH) (CO)(P Pr3)2 by insertion of the carbon-carbon triple bond into the Os—H bond to give the unsaturated alkenyl-metallothiol derivative Os ( )-CH=CHPh (SH) (CO)(P Pr3 )2, the inorganic counterpart of the organic a, (3-unsaturated mercaptans (Scheme 46).92... 

In the general context of donor/acceptor formulation, the carbonyl derivatives (especially ketones) are utilized as electron acceptors in a wide variety of reactions such as additions with Grignard reagents, alkyl metals, enolates (aldol condensation), hydroxide (Cannizzaro reaction), alkoxides (Meerwein-Pondorff-Verley reduction), thiolates, phenolates, etc. reduction to alcohols with lithium aluminum hydride, sodium borohydride, trialkyltin hydrides, etc. and cyloadditions with electron-rich olefins (Paterno-Buchi reaction), acetylenes, and dienes.46... 

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