Impact of Incorporating Substituents onto the P‐o‐Anisyl Groups of DiPAMP Ligand on the Rhodium(I)‐Catalyzed Asymmetric Hydrogenation of Olefins

Abstract

phosphino]ethane (DiPAMP) as a P-stereogenic ligand for rhodium(I)-catalyzed hydrogenation by Knowles et al. came after their evaluation of several diphosphines. However, no in-depth study was carried out on incorporating various substituents on its P-o-anisyl groups. In this work, we have prepared a large series of enantiopure and closely related DiPAMP analogues possessing various substituents (MeO, TMS, t-Bu, Ph, fused benzene ring) on the oanisyl rings. The new ligands were evaluated in rhodium-catalyzed hydrogenation of several model substrates: methyl a-acetamidoacrylate, methyl (Z)-aacetamidocinnamate, methyl (Z)-b-acetamidocrotonate, dimethyl itaconate, and atropic acid. They displayed enhanced activities and increased enantioselectivities, particularly the P-(2,3,4,5-tetra-MeO-C 6 H)-substituted ligand (4MeBigFUS). Interestingly enough, 88% ee was obtained in the hydrogenation of atropic acid using the Rh-(4MeBigFUS) catalyst under mild conditions (10 bar H 2 , room temperature) versus 7% ee using Rh-DiPAMP. Conversely, the ligand possessing P-(2,6-di-MeO-C 6 H 3 ) groups proved to slow down considerably the hydrogenation. X-Ray structures of their corresponding Rh complexes are presented and discussed.

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

“…The C 2 -symmetric P-stereogenic bisphosphorus ligands reported from 2001 to 2023 are shown in Figure , in the order of their publication years. ,− ,,,− A tetraphosphine ligand L41 and a C 3 -symmetric triphosphine ligand MT-Siliphos are also included in this figure as exceptions. All of these ligands possess unique structural and electronic properties, arising from the two different substituents on the phosphorus atoms and the ligand backbones, and exhibit their characteristic reactivities and stereoselectivities in various transition-metal-catalyzed asymmetric reactions.…”

Phosphines and related C–P bonded compounds

“…133 Among other new phosphines prepared as potential ligands for metal-catalysed reactions is the watersoluble triarylphosphine (95), 134 highly fluorous bidentate phosphines (96) 135 and (97), 136 tunable 2,2 0 -biphenylenediphosphines, e.g., (98) 137 and (99), 138 diphospholane-based chiral diphosphine mononoxide ligands, e.g., (100), 139 2,2 0 -bis(dialkylphosphinomethyl)biphenyls, 140 the chiral heterocyclic ligands (101), 141 and a series of chiral bis(diarylphosphino) ethanes bearing one phenyl and one substituted-o-anisyl group at each phosphorus. 142 Several groups have reported the synthesis of b-phosphinoethylboranes by hydroboration of diphenylvinylphosphine. [143][144][145] Heating a 3-(o-diphenylphosphinophenyl)pyrazole derivative with potassium borohydride to 220 1C resulted in the formation of the tris(phosphinoarylpyrazolyl)borate ligand (102), isolated in 64% yield.…”

“…In these systems, the normal interaction between donor and acceptor centres is inhibited and alternative reaction pathways are often followed, giving products in which the Lewis acid and Lewis base sites may still be available for further reactivity. 261 Of particular recent interest is the discovery that crowded phosphino-boranes of various types, e.g., (141), are able to take up molecular hydrogen, reversibly cleaving the molecule to form zwitterionic salts, e.g., (142), which then function as reducing agents for the hydrogenation of enamines, imines and conjugated phosphinoalkenylboranes. 262 The past year has also seen further publications concerned with the activation of molecular hydrogen in this way.…”

Asymmetric homogeneous hydrogenations at scale

“…A number of studies have been performed to elucidate the mechanism of Rh-catalysed reductions of didehydroamino acids derivatives with Dipamp (4) and other bidentate phosphorus ligands. [27][28][29]103 A number of studies have also been performed with Ru(BINAP), Ru-diamine, 104 and related systems for the reductions of carbonyl groups, [104][105][106][107][108][109][110] as well as Ir-based systems. 111 In many cases mechanistic insight has led to catalyst improvement, for example, the ligand system SegPhos (70) has been found to be superior in many applications where BINAP has traditionally been used.…”