Hydride compounds hydrometallation

Addition reactions of three kinds of main group metal compounds, namely R—M X (carbometallation, when R are alkyl, alkenyl, aryl or allyl groups), H—M X (hydrometallation with metal hydrides) and R—M —M"—R (dimetallation with dimetal compounds) to alkenes and alkynes, are important synthetic routes to useful organometallic compounds. Some reactions proceed without a catalyst, but many are catalysed by transition metal complexes. 

Addition of hydride bonds of main group metals such as B—H, Mg—H, Al—H, Si—H and Sn—H to alkenes and alkynes to give 513 and 514 is called hydrometallation and is an important synthetic route to compounds of the main group metals. Further transformation of the addition product of alkenes 513 and alkynes 514 to 515,516 and 517 is possible. Addition of B—H, Mg—H, Al—H and Sn—H bonds proceeds without catalysis, but their hydrometallations are accelerated or proceed with higher stereoselectivity in the presence of transition metal catalysts. Hydrometallation with some hydrides proceeds only in the presence of transition metal catalysts. Hydrometallation starts by the oxidative addition of metal hydride to the transition metal to generate transition metal hydrides 510. Subsequent insertion of alkene or alkyne to the M—H bonds gives 511 or 512. The final step is reductive elimination. Only catalysed hydrometallations are treated in this section. 

The mixed coupling of two different alkenes allows the formation of new functional unsaturated products but requires high regioselectivity. A ruthenium hydride complex, generated in situ from the reaction of RuHCl(CO)(PCy3)2 with HBF4.OEt2, was found to be an effective catalyst for the hydrovinylation of alkenes [8]. The reaction of styrene with ethylene produced the hydrovinylation compound 10 in 93% yield (Eq. 5). Initial hydrometallation of the alkene and insertion of ethylene seemed to be a plausible mechanism. 

The synthesis of (7-alkylcobalts from the reaction of Co hydrides and alkenes is relevant to the use of Co hydrides in alkene hydroformylation and is of interest because of the biological significance of carbon-cobalt bonds in vitamin B12 chemistry. The reaction of HCo(CO)4 with simple alkenes involves hydrometalation as a key step in hydrogenation, isomerization or hydroformylation of alkenes . ff-Alkylcobalt compounds are detectable intermediates in reactions of HCo(CO)4 and alkenes by Ir, but... 

RS-M" L c-i)- The other is the oxidative addition of thiols to low-valent transition metals (M"L ) to give the corresponding transition metal complexes bearing both hydride and thiolate ligands (RS-M" L c 2-H). The reaction of the former complexes (RS-M" L c-i) with carbon-carbon unsaturated compounds such as alkynes may proceed via thiometallation, in which relatively more bulky is bonded at the terminal carbon of alkynes. On the other hand, in the reaction of the latter complexes (RS-M" L c-2 H) with alkynes both hydrometallation and thiometallation processes are possible. These processes proceed via sy -addition. Alternative pathway for the addition of thiols to alkynes involves coordination of alkynes to transition metals and then nucleophilic addition of thiols (or thiolate anions) to the alkynes. These processes take place via a f -addition. By controlling these pathways, regio- and stereoselective hydrothiolation of alkynes is expected to be attained successfully. 

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