Tungsten unsaturated organic substrates

Acetylene hydratase [74] is unique among the molybdenum and tungsten enzymes. This enzyme catalyzes the hydration of an unsaturated organic substrate, acetylene, a reaction that is neither an oxidation nor a reduction. Although tungsten may assume different oxidation states, the non-redox nature of the sub-... 

Transition-metal-based Lewis acids such as molybdenum and tungsten nitro-syl complexes have been found to be active catalysts [49]. The ruthenium-based catalyst 50 (Figure 3.6) is very effective for cycloadditions with aldehyde- and ketone-bearing dienophiles but is ineffective for a,)S-unsaturated esters [50]. It can be handled without special precautions since it is stable in air, does not require dry solvents and does not cause polymerization of the substrates. Nitromethane was the most convenient organic solvent the reaction can also be carried out in water. 

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