Emil Albin Broger

New efficient methods for the synthesis and in-situ preparation of ruthenium(II) complexes of atropisomeric diphosphines and their application in asymmetric catalytic hydrogenations

Abstract A new synthetically useful method for the synthesis of the diphosphine ruthenium dicarboxylato complexes (PP)Ru(O2CR)2 (R = CF3 and CH3) is presented, which uses the easily accessible complex (COD)2Ru2(μ-O2CCF3)4 as starting material. This complex as well as (COD)Ru(η2-O2CCH3)2 and (COD)2Ru2Cl4(NCCH3) have been shown to be suitable precursor complexes for the in-situ preparation of ruthenium(II) dicarboxylato and dichloro complexes of atropisomeric diphosphines, respectively. The high efficacy of the preformed and in-situ generated ruthenium complexes as precatalysts is demonstrated in asymmetric hydrogenations of allylic alcohols, enamides, and a β-keto ester.

New amidophosphine-phosphinites (tLANOPs) as chiral ligands for asymmetric hydrogenation reactions

Abstract The new amidophosphine-phosphinite (AMPP) ligands 4a–g (called tLANOP ligands) derived from the chiral hydroxy amide (R)- or (S)-2-hydroxy-3,3,N-trimethylbutyramide have been prepared in 48–83% yield. The crystal structures of the square planar complexes [(SP-4-3)-Pd((R)-dmphea)((S)-4a)]BF4 and [Rh((R)-4a)(COD)]BF4 have allowed the absolute configurations of the ligands to be assigned. In both complexes the 7-membered chelating ring of 4a has virtually the same twist-boat conformation. With this class of ligands the rhodium catalyzed asymmetric hydrogenation of 4-oxoisophorone enol acetate gave (S)-phorenol acetate in up to 71% ee. The iridium catalyzed asymmetric hydrogenation of the cyclic iminium salts 16a and 16b afforded after work-up the corresponding cyclic secondary amine (S)-17 in up to 86% ee, when bulky groups were present on the phenyl substituents on the two phosphorus atoms.

(R)- and (S)-6,6′-dimethyl- and 6,6′-dimethoxy-2,2′-diiodo-1,1′-biphenyls: Versatile intermediates for the synthesis of atropisomeric diphosphine ligands

Abstract Starting from enantiomerically pure 6,6′-dimethyl- or 6,6′-dimethoxy-2,2′-diiodo-1,1′-biphenyls (1a or 1b) a variety of atropisomeric diphosphine ligands of defined axial chirality are directly accessible in good yields: asymmetric diphosphines of type B and the corresponding diphosphines with one (type C) or two (type D) stereogenic phosphorus atoms. Pitfalls of the lithiation/phosphination reaction are discussed. The number of P-chiral diastereomers can be reduced by thermal epimerization.

Synthesis and evaluation in asymmetric hydrogenation of carbohydrate-derived 1,3-bisphosphines

Abstract 1,3-Bisphosphines and 1,3-phosphine sulfides have been prepared from 1,6-anhydro-β- d -glucopyranose in view of their application as bidentate ligands in transition-metal-catalyzed asymmetric hydrogenation. Reaction of 1,6:3,4-dianhydro-2- O -( p -toluenesulfonyl)-β- d -galactopyranose ( 1 ) with Ph 2 PH in the presence of AlMe 3 gave 1,6:2,3-dianhydro-4-deoxy-4-(diphenylphosphino)-β- d -mannopyranose ( 6 ) which, upon treatment with LiPPh 2 , led to 1,6-anhydro-2,4-dideoxy-2,4-bis(diphenylphosphino)-β- d -glucopyranose ( 9 ). Esterification of 9 with 1-naphthoyl chloride yielded the naphthoate 11 . Upon exposure to air, 9 and 11 were oxidized to the corresponding bisphosphine dioxides 10 and 12 . Treatment of 6 with PhSH and DBU led to 1,6-anhydro-2,4-dideoxy-4-(diphenylphosphino)-2-phenylthio-β- d -glucopyranose ( 13 ) and, after oxidation with air, to the corresponding phosphine oxide 14 . Similarly, 1 was transformed into 1,6-anhydro-2,4-dideoxy-2-(diphenylphosphino)-4-phenylthio-β- d -glucopyranose ( 16 ) and its oxide 17 . Attempted ring opening of 1 by Ph 2 PH/KOH or by Ph 2 PH/AlMe 3 and oxidative work-up gave 1,6-anhydro-3,4-dideoxy-4-(diphenylphosphoryl)-β- d - threo -hex-3-enopyranose ( 3 ). In the presence of HCl, both 3 and 7 (obtained by air oxidation of 6 ) were transformed into 1,6-anhydro-2-chloro-2,4-dideoxy-4-(diphenylphosphoryl)-β- d -glucopyranose ( 8 ). The structure of 8 was established by an X-ray analysis. 1 H-, 13 C-, and 31 P-n.m.r. spectroscopy showed that the phosphines ( 9, 11, 13 , and 16 ) prefer a 1 C 4 and the phosphine oxides ( 8, 10, 12, 14 and 17 ) a B 3,O conformation. The results of the rhodium- or ruthenium-catalyzed asymmetric hydrogenation with the phosphines 9, 11, 13, and 16 ligands are presented. In the hydrogenation of olefins (geraniol or the α-acetamidoacrylic acid 19 ), low enantioselectively is observed. Better enantiomeric excesses were obtained in the hydrogenation of α- and β-ketoesters (ketopantolactone, e.e.