Transition metal catalysts alkyne hydration

The hydration of alkynes represents a prime example in which simple coordinative activation by transition metal complexation greatly facilitates an otherwise very slow chemical process (Equation (107)). This reaction has been a long-studied problem, but only recently have alternatives to the classical use of catalysts such as Hg(n) salts been sought. These new catalyst systems typically display much enhanced reactivity, and some can mediate an anti-Markovnikov hydration through a novel mechanism (Table 1). 

For the later transition metals rRhQfPEt ) .] catalysed addition of aniline to norbomene is very slow (25 TO in 12 days). Fragments, derived from BuONO, are added to alkenes leading to oximes and nitrosyis by iron or cobalt catalysts and these are alternative routes for nitrogen inclusion. A short summary of ruthmium catalysed incorporation of R2NCO2 into alkynes covers the latest developments in this area, while alkyne hydration by [RhCl4(H20)2] is proposed to involve a cis-hydroxide addition. ... 

Lanthanum is the first element of the sixth-period transition metals. Its properties are close to those of the other rare earth elements and, as a consequence, the catalytic behavior of the lanthanum triflate is also very close to that of the entire series. An important example concerning the stability of these compounds in water is that indicating the capability of metal triflates, such as Yb(OTf)3, Eu(OTf)3, Sc(OTf)3 or La(OTf)3, to catalyze the hydration of alkynes to the corresponding ketones [56]. However, the interest in water-compatible lanthanide triflate-based catalysts is much larger and mainly includes the carbon-carbon bond-forming reactions. To increase the utility of these catalysts understanding of their aqueous mechanism is very important. For such a purpose, dynamic measurements of the water... 

The first hydration of an alkyne was discovered in 1881 by Mikhail Kucherov, a Russian chemist from the Imperial Forestry Institute in St. Petersburg, using mercury(II) bromide as the catalyst [97] producing acetaldehyde. This reaction has been extensively applied in synthesis, although due to the toxicity of mercury compounds and the relatively low turnover numbers (<500), much effort has been done to find new catalysts. Thus, transition-metal-complexes containing Pd (II) [98], Pt(II) [99], Ru(ll) [100], Rh [101], and other metal centers [91] have been used, although in most cases the catalytic efficiency was only moderate. 

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