Selective Ruthenium‐Catalyzed Hydroaminomethylation of Unsaturated Oleochemicals

Abstract

Rhodium-catalyzed hydroaminomethylation (HAM) is recently described as an innovative way to functionalize triglycerides. In the search to reduce production costs, rhodium is sought to be replaced by ruthenium whose price is currently more than 20 times lower. In this study, HAM of unsaturated oleochemicals using ruthenium precursors is proceeded under phosphine-free conditions. The experimental conditions are optimized by changing the nature of the solvent, the reaction temperature, and the CO/H 2 pressure. While rhodium leads to good catalytic activity and low chemoselectivity (mixture of hydroxyl and amino groups), ruthenium proves to be less active but more chemoselective as amino-substituted products are mainly formed. Of interest, HAM of methyl 10-undecenoate (MU) occurs in a highly chemo-and regioselective fashion using acetonitrile as solvent. Practical Applications: Selective Ru-catalyzed hydroaminomethylation can be implemented on an industrial scale for the conversion of unsaturated oleochemicals into amines. This finding is of importance as the obtained amino-products can be used in many industrial areas such as surfactants, polymers, or lubricants.

The Hydrogenation Problem in Cobalt‐based Catalytic Hydroaminomethylation

“…Addition of 2 or 5 eq of pyrrolidine resulted in a lower catalytic activity than for 1 eq of pyrrolidine (17 % conversion at 5 eq of pyrrolidine). The lower catalytic activity is probably due to coordination of pyrrolidine to the cobalt center, as reported before for the use of ammonia in combination with Co 2 (CO) 8 and P(n-Bu) 3 in the HAM of 1-hexene. [20] The rather basic pyrrolidine could also deprotonate the hydride species, [49] forming an inactive complex […”

“…[1] Since then, the HAM reaction has been studied extensively using rhodium- [2][3][4][5][6][7] and ruthenium-based homogeneous catalysts. [2,[8][9][10][11][12][13][14][15] In general, rhodium and ruthenium form poor isomerization catalysts, and in most cases a terminal alkene is used as substrate to form the linear N-alkylated amine. [6][7][8][9][10][11][12][13][14][15] A secondary amine is used in these HAM reactions to prevent overalkylation of the amine.…”

“…[2,[8][9][10][11][12][13][14][15] In general, rhodium and ruthenium form poor isomerization catalysts, and in most cases a terminal alkene is used as substrate to form the linear N-alkylated amine. [6][7][8][9][10][11][12][13][14][15] A secondary amine is used in these HAM reactions to prevent overalkylation of the amine. However, some rhodium-based catalytic systems have been reported which can be used to convert internal alkenes to the desired linear N-alkylated amine with 80-90 % selectivity.…”