Alkyne complexes nitrogen donor ligands

Tetramethyl- or tetraphenyl- (cyclobutadiene)nickel dihalides undergo reductive ligand substitution with nitrogen donor ligands such as 2,2 -bipyridine or 1,4-diaza-1,3-dienes with the addition of sodium metal237. The 2,2/-bipyridyl ligand is readily displaced and reaction of this complex with a variety of olefins and alkynes leads to cycloaddition reactions with the cyclobutadiene ligand. 

Examples of palladium- and rhodium-catalyzed hydroaminations of alkynes are shown in Equations 16.90-16.92 and Table 16.9. The reaction in Equation 16.90 is one of many examples of intramolecular hydroaminations to form indoles that are catalyzed by palladium complexes. The reaction in Equation 16.91 shows earlier versions of this transformation to form pyrroles by the intramolecular hydroamination of amino-substituted propargyl alcohols. More recently, intramolecular hydroaminations of alkynes catalyzed by complexes of rhodium and iridium containing nitrogen donor ligands have been reported, and intermolecular hydroaminations of terminal alkynes at room temperature catalyzed by the combination of a cationic rhodium precursor and tricyclohexylphosphine are known. The latter reaction forms the Markovnikov addition product, as shown in Equation 16.92 and Table 16.9. These reactions catalyzed by rhodium and iridium complexes are presumed to occur by nucleophilic attack on a coordinated alkyne. 

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