Ruthenium-arene complex bearing a pta ligand. Evaluation of its catalytic activity in the synthesis of enol esters

Ruthenium-arene complexes are widely used as efficient catalysts in various chemical reactions such as olefin metathesis, atom transfer radical reactions, isomerization of allylic alcohols and the addition of carboxylic acids to terminal alkynes.
Ruthenium-arene complexes bearing a PTA ligand (PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane), are known as water soluble complexes and extensively studied for anticancer activity due to their high selectivity towards cancer cells. As part of our research program directed toward the synthesis of vinyl esters, we decided to investigate the catalytic activity of [RuCl2(η6-p-cymene)(PTA)]. To the best of our knowledge, the catalytic activity of this complex has never been reported for the synthesis of vinyl esters.
Compared to [RuCl2(η6-arene)(PR3)] complexes, [RuCl2(η6-p-cymene)(PTA)] was much less efficient for the synthesis of vinyl esters through the addition of carboxylic acids to terminal alkynes. The selectivity for the Markovnikov isomer was quite good at 60°C, but decreased with the temperature. A maximum TON of around 1500 was obtained as for corresponding [RuCl2(η6-arene)(PR3)] catalytic systems.