Synthesis of Chiral Bis(phosphinite) Ligands with a Tetrahydrothiophene Backbone:  Use in Asymmetric Hydrogenation

Abstract

A series of novel chiral nonracemic bis(phosphinites) derived from (R,R)-trans-2,5-tetrahydrothiophenedimethanol has been prepared. Reaction of these ligands, 6, with Rh(COD)2X (COD = cyclooctadiene, X = OS(O)2CF3, SbF6) yields rhodium complexes which have been tested in the asymmetric hydrogenation of methyl α-acetamidocinnamate, providing enantioselectivities of up to 55%. The racemic bis(diphenylphosphinite) ligand 6c binds in an unusual tridentate mode, forming the thioether-bridged species ((6c)Rh)2(OTf)2 (7). This was characterized by conventional spectroscopic methods and by single-crystal X-ray analysis.

Chiral Complexes of RhI Containing Binaphthalene‐Core P,S‐Heterobidentate Ligands − Synthesis, Characterization, and Catalytic Activity in Asymmetric Hydrogenation of α,β‐Unsaturated Acids and Esters

“…[11] The preparation of the enantiopure complexes 3a and 3b was accomplished as reported in Scheme 1 by treating the rhodium complex [Rh(NBD)(THF) 2 ] ϩ BF 4 Ϫ (2) (NBD ϭ 1,4-norbornadiene) with a stoichiometric amount of (S)-1a and (S)-1b, respectively. The required intermediate adduct 2 was prepared in situ from the corresponding chloro-bridged dimer [Rh(NBD)Cl] 2 and AgBF 4 . [12] The isolated yields of the complexes 3a and 3b were in the range of 60Ϫ70%.…”

“…A tridentate coordination of the ligand, forming thioether-bridged dinuclear species, has been proposed. [4] Novel P,S-bidentate ligands possessing an oxathiane ring condensed onto pulegone [5] or norbornane [6] moieties led to quite good enantioselectivity in the Co-catalysed asymmetric intramolecular PausonϪKhand reaction and in the Pdcatalysed asymmetric allylic substitution reaction, respectively.…”

Bidentate Ligands Containing a Heteroatom–Phosphorus Bond

“…Reetz Rh-catalyzed asymmetric hydrogenation of itaconic acid and its derivatives, dehydroamino acid derivatives and enamides led to extremely poor to moderate enantioselectivities (Table 27.7). Although NMR spectroscopic studies of the iridium(I) cyclooctadiene complexes of 169 and 172 suggested that they possessed well-defined C 2 -symmetry, implying that both sulfur atoms have the same configuration, their corresponding cis-dihydridoiridium(III) adducts appeared in the NMR spectrum as either a mixture of diastereomers or C 1 -symmetric complexes, suggestive of the configurational lability of the ligated sulfur atom under remote chiral control in the octahedral complex, thus explaining the observed [135,136]. Slight improvements resulted when neighboring stereocenters were introduced, as in (-)-DegusR 2 170 [133] and 171 [134] with S-substituents larger than a methyl group (Table 27.7, entries 29 and 30).…”

“…To date, only a few ligands of this type have been tested. The tridentate tetrahydrothiophene 175 flanked by two trans-O-methylene phosphinites was among the first P/S-ligands examined by Hauptman and co-workers, but only mediocre enantioselectivity was recorded in the hydrogenation of methyl a-acetamidoacrylate (Table 27.7, entry 12) [136]. Whilst the mode of coordination of 175 in the actual operating Rh-catalyst was unknown, the bidentate phosphine-thioethers 176, prepared by the same team, also showed unsatisfactory results [137].…”

Asymmetric transfer hydrogenation of aromatic ketones with the ruthenium(II) catalyst derived from C2 symmetric N,N′-bis[(1S)-1-benzyl-2-O-(diphenylphosphinite)ethyl]ethanediamide

“…Already more than a thousand of chiral nonracemic bis(phosphines), striking examples include L-DOPA [11], L-menthol [12,13], and dissymmetric phosphine ligand BINAP [14], have been synthesized. Recently, phosphine [15][16][17], phosphite [18], bis(phosphinites) [19][20][21], and aminophosphinephosphinite [22][23][24] (abbreviated as AMPP) compounds have been of great interest and widely used in asymmetric transfer hydrogenation reactions.…”