Ruthenium anti-Markovnikov hydroamination

Ruthenium complexes also catalyze the anti-Markovnikov hydroamination of vinylarenes. In this case, the combination of l,5-bis(diphenylphosphino)pentane (DPPPent), triflic acid, and a ruthenium(II) precursor generates a catalyst for the additions of secondary amines to vinylarenes (Equation 16.72). This mixture of catalyst components has been shown to generate a cationic Ti -arene complex of a PCP pincer ligand generated from the DPPPent ligand. The mechanism of this reaction involves nucleophilic attack of the amine on an Ti -vinylarene complex, as described in more detail in the section on the mechanisms of hydroamination. 

Scheme 15.17 Ruthenium-catalyzed anti-Markovnikov hydroamination of styrene.

SCHEME 3.128 Z-selective anti-Markovnikov hydroamination using ruthenium catalysts [140]. 

The anti-Markovnikov addition of nitrogen nucleophiles to alkynes has been accomplished using ruthenium catalysts (Scheme 3.125) [137]. During the screening process, the authors discovered that when the reactions were carried out at 80 °C, moderate yields of the hydroamination products were obtained (50%) however, the stereocontrol was poor and a 4 1 ( ratio of the enamines was obtained. When the temperature was increased to 100°C, the Zi-isomer was obtained exclusively. At the higher temperatures, most substrates exclusively generated the E-isomer, although some substrate-specific reactivity was observed. 

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