Alkynes, carbonylative coupling

Scheme 10 Plausible catalytic mechanism for alkyne-carbonyl coupling as supported by the effect of chiral Bronsted acid catalyst and deuterium-labeling...

Huoboric acid is employed as a chemical reagent and catalyst in different organic syntheses like alkyne-carbonyl coupling [59], Biginelli reactions [60] and Balz-Schiemann reactions. 

Under the conditions of iridium-catalyzed hydrogenation, alkyne-carbonyl and alkyne-imine reductive coupling occurs in the absence of stoichiometric byproducts. For example, iridium-catalyzed hydrogenation of nonconjugated alkynes in the presence of ot-ketoesters delivers the corresponding a-hydroxy esters in... 

By contrast, in 2000 Shibata reported the Ir-catalyzed enantioselective Pauson-Khand-type reaction of enynes [30aj. The chiral Ir catalyst was readily prepared in situ from [lrCl(cod)]2 and tolBINAP (2,2 -bis(di-p-tolylphosphino)-l,T-binaphthyl), both of which are commercially available and air-stable, and the reaction proceeded under an atmospheric pressure of carbon monoxide. The Ir-catalyzed carbonylative coupling had a wide generality in enynes with various tethers (Z), substituents on the alkyne terminus (R ) and the olefinic moiety (R ). In the case of less-reactive enynes, a lower partial pressure of carbon monoxide achieved a higher yield and ee-value (Table 11.1) [30b]. 

Iridium-phosphine complexes were found to be efficient carbonylative alkyne-alkene coupling catalysts [62]. Although frequently applied in other transformations, the dimeric complex [ Ir( x-Cl)(cod) 2] appeared to be a very active catalyst in the coupling of silylated diynes with CO [63], giving bicyclic products with a carbonyl moiety (Scheme 14.12). 

Alkyne-alkene carbonylative coupling. Intramolecular carbonylative coupling of dialkynes catalyzed by Fe(CO)3 provides a route to cyclopentadienones (equation I). The more difficult carbonylative alkyne-alkene coupling to provide cyclopen-tenones (Pauson-Khand reaction) can also be effected with Fe(CO)s, but in modest yield. In an improved coupling, acetone is treated with Fe2(CO)9 to form Fe-... 

While platinum and rhodium are predominantly used as efficient catalysts in the hydrosilylation and cobalt group complexes are used in the reactions of silicon compounds with carbon monooxide, in the last couple of years the chemistry of ruthenium complexes has progressed significantly and plays a crucial role in catalysis of these types of processes (e.g., dehydrogenative silylation, hydrosilylation and silylformylation of alkynes, carbonylation and carbocyclisation of silicon substrates). 

An X-ray crystallographic investigation 116) of Co4(CO)io(EtC2Et) has revealed the structure shown in (VI). The structure is derived from that of the parent carbonyl, Co4(CO)i2> by substitution of two bridging carbonyl groups with an alkyne unit coupled with a substantial modification of the C04 skeleton. The structure is different from that first postulated for Co4(CO)io(RC2R ) complexes, where it was assumed that the basic tetrahedron of cobalt atoms remained intact 48, 117). 

Templeton and co-workers used the alkylidyne-carbonyl coupling reaction shown in Eq. (156) for the synthesis of the asymmetric alkyne com-... 

With alkynes hydrocarbonylative coupling leads to unsaturated ketones with exclusive cis addition of hydrogen and the acyl group. Thus, rhodium carbonyl catalyzed carbonylation of acetylenes and ethene with carbon monoxide and hydrogen stereospecifically leads to a./l-un-saturated ethyl ketones by cross hydrocarbonylation4- 5, e.g., diphenylacetylene with ethene in the presence of Rh4(CO)l3 gives ( )-1.2-diphenyl-l-penten-3-one in 91 % yield5. 

The reactions between alkynes and multinuclear metal carbonyls give various product types, with alkyne coupling and alkyne-CO coupling often being observed, e.g. reaction 23.80, in which the organic ligand in the product is a 6-electron donor (two a- and two w-interactions). Predicting the outcome of such reactions is difficult. 

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