Pinwheel-like tridentate phosphines for controlling divergent regioselectivity in Pd-catalyzed alkoxycarbonylation of alkenes

The elaborate control of regioselectivity regulated by the involved ligands with specific structural skeleton and compositions is always demanded in alkoxycarbonylation of alkenes. Herein, a series of pinwheel-like tridentate phosphine ligands with rotatable flexibility ( L3 ) or hard rigidity ( L5–L7 ) were synthesized and characterized for the first time, in which the incorporated three PPh 2 -fragments are located at meta-positions of phenyl groups. It was proved that the tridentate phosphine of L3 with the flexible configuration favorably corresponded to the linear regioselectivity with l/b ratio of 98/2, whereas L7 with the rigid configuration absolutely did favor to the branched regioselectivity with l/b ratio of 1/99. The presence of the three PPh 2 -frgaments in L3 did contribute to the remarkable performance of L3 -Pd(TFA) 2 system in terms of activity, linear regioselectivity and stability, subjected to 10-run recycling uses in anti -Markovnikov’s methoxycarbonylation of styrene without activity loss and Pd-black precipitation. In comparison, although the optimal L7 -Pd(MeCN) 2 Cl 2 system could catalyze Markovnikov’s alkoxycarbonylation of alkenes to afford the branched esters with excellent regioselectivity in the fresh use, its stability was too poor to support the recycling experiments. L3 -Pd(TFA) 2 and L7 -Pd(MeCN) 2 Cl 2 catalytic systems were both applicable to a wide range of substrates in alkoxycarbonylation of alkenes to afford the target esters in the isolated yields of 41–91 %, with the well maintained divergent regioselectivity.