Tackling N-Alkyl Imines with 3d Metal Catalysis: Highly Enantioselective Iron-Catalyzed Synthesis of α-Chiral Amines

A readily activated iron alkyl precatalyst effectively catalyzes the highly enantioselective hydroboration of N-alkyl imines. Employing a chiral bis(oxazolinylmethylidene)isoindoline pincer ligand, the asymmetric reduction of various acyclic N-alkyl imines provided the corresponding α-chiral amines in excellent yields and with up to >99 % ee. The applicability of this base metal catalytic system was further demonstrated with the synthesis of the pharmaceuticals Fendiline and Tecalcet.

Asymmetric Transfer Hydrogenation of Imines in Water by Varying the Ratio of Formic Acid to Triethylamine

Asymmetric transfer hydrogenation (ATH) of imines has been performed with variation in formic acid (F) and triethylamine (T) molar ratios in water. The F/T ratio is shown to affect both the reduction rate and enantioselectivity, with the optimum ratio being 1.1 in the ATH of imines with the Rh-(1S,2S)-TsDPEN catalyst. Use of methanol as a cosolvent enhanced reduction activity. A variety of imine substrates have been reduced, affording high yields (94-98%) and good to excellent enantioselectivities (89-98%). In comparison with the common azeotropic F-T system, the reduction with 1.1/1 F/T is faster.

Asymmetric transfer hydrogenation of imines in water/methanol co-solvent system and mechanistic investigation by DFT study

Asymmetric transfer hydrogenation of various cyclic imines proceeded efficiently with H₂O/MeOH (1 : 1, v/v) co-solvent media in 20 min with excellent yields and enantioselectivities by using Rh–TsDPEN catalyst and HCOONa as a hydrogen donor.

High Structural Control in Metal-Mediated Synthesis of New Functionalized Diphosphines Using Diphosphinoketenimines as Precursors

The diphosphinoketenimine ligand in the neutral complexes fac-[MnI(CO)(3){(PPh(2))(2)C=C=NR}] (1 a: R = Ph; 1 b: R = p-tolyl) undergoes nucleophilic attack by MeLi and nBuMgCl yielding, after hydrolysis, the diphosphinoenamine-containing complexes fac-[MnI(CO)(3){(PPh(2))(2)C=C(R')NHR}] (3 a,b: R' = Me; 4 a,b: R' = nBu). Complex 1 a reacts under the same conditions with H(2)C=C=CHMgBr to afford fac-[MnI(CO)(3){(PPh(2))(2)C=C(CH(2)CC[triple chemical bond]CH)NHR}] (5 a), which contains a terminal alkyne group on the alpha-carbon atom of the diphosphinoenamine ligand. The cationic complexes fac-[Mn(CO)(4){(PPh(2))(2)C=C=NR}](+) (6) react with H(2)C=C=CHMgBr to afford diphosphinomethanide derivatives bearing three different types of functional groups, depending upon the substituent on the nitrogen atom of the ketenimine: cumulene in fac-[Mn(CO)(4){(PPh(2))(2)C--C(CH=C=CH(2))=N-xylyl}] (7 d), internal alkyne in fac-[Mn(CO)(4){(PPh(2))(2)C--C(C[triple chemical bond]CCH(3))=NtBu}] (8), and quinoline in 9 (R = Ph), whose formation implies an unusual cyclization process. Protonation of 7 d, 8, and 9 with HBF(4) occurs at the nitrogen atom to give the cationic derivatives 10 d, 11, and 12, respectively, which contain the corresponding functionalized diphosphine ligands. Irradiation of 3 a,b and 4 a,b with Vis/UV light makes it possible to isolate the free ligands (PPh(2))(2)C=C(R')NHR (13 a,b and 14 a,b), completing the metal-assisted synthesis of these novel functionalized diphosphines. Irradiation of 12 with Vis/UV light generates free phosphinoquinoline ligand 15, which readily affords a complex 16 containing 15 as a P,N-chelating ligand when treated with [PdCl(2)(NCMe)(2)], thus demonstrating its coordination capability.

Well-Defined Chiral Spiro Iridium/Phosphine−Oxazoline Cationic Complexes for Highly Enantioselective Hydrogenation of Imines at Ambient Pressure

New chiral phosphine-oxazoline ligands (7, SIPHOX) with a rigid and bulky spirobiindane scaffold were synthesized, starting with optically pure 7-diphenylphosphino-7'-trifluoromethanesulfonyloxyl-1,1'-spirobiindane, in four steps in 40-64% overall yield. Iridium complexes of 7, the chiral analogues of the Crabtree catalyst, were generated by coordination of ligands 7 and [Ir(COD)Cl](2) in the presence of sodium tetrakis-3,5-bis(trifluoromethyl)phenylborate. The complexes were characterized by NMR, ESI-MS, and X-ray diffraction analysis. The Ir-SIPHOX complexes can catalyze the hydrogenation of acyclic N-aryl ketimines under ambient pressure with excellent enantioselectivities (up to 97% ee) and full conversions. This result represents the highest enantioselectivity and the first example of the hydrogenation of imines catalyzed by chiral analogues of the Crabtree catalyst at ambient pressure. Studies on the stability of the catalysts revealed that the catalysts Ir-SIPHOX are very stable and resistant to the formation of inactive trimers under hydrogenation conditions. On the basis of the X-ray diffraction analysis of the structures of catalysts and amine products, a rational explanation for the enantiocontrol of the chiral catalysts in the hydrogenation of imines is proposed.

Hydride transfer reactivity of tetrakis(trimethylphosphine)(hydrido)(nitrosyl)molybdenum(0)

The tetrakis(trimethylphosphine) molybdenum nitrosyl hydrido complex trans-Mo(PMe(3))(4)(H)(NO) (2) and the related deuteride complex trans-Mo(PMe(3))(4)(D)(NO) (2a) were prepared from trans-Mo(PMe(3))(4)(Cl)(NO) (1). From (2)H T(1 min) measurements and solid-state (2)H NMR the bond ionicities of 2a could be determined and were found to be 80.0% and 75.3%, respectively, indicating a very polar Mo--D bond. The enhanced hydridicity of 2 is reflected in its very high propensity to undergo hydride transfer reactions. 2 was thus reacted with acetone, acetophenone, and benzophenone to afford the corresponding alkoxide complexes trans-Mo(NO)(PMe(3))(4)(OCHR'R'') (R' = R'' = Me (3); R' = Me, R'' = Ph (4); R' = R'' = Ph (5)). The reaction of 2 with CO(2) led to the formation of the formato-O-complex Mo(NO)(OCHO)(PMe(3))(4) (6). The reaction of with HOSO(2)CF(3) produced the anion coordinated complex Mo(NO)(PMe(3))(4)(OSO(2)CF(3)) (7), and the reaction with [H(Et(2)O)(2)][BAr(F)(4)] with an excess of PMe(3) produced the pentakis(trimethylphosphine) coordinated compound [Mo(NO)(PMe(3))(5)][BAr(F)(4)] (8). Imine insertions into the Mo-H bond of 2 were also accomplished. PhCH[double bond, length as m-dash]NPh (N-benzylideneaniline) and C(10)H(7)CH=NPh (N-1-naphthylideneaniline) afforded the amido compounds Mo(NO)(PMe(3))(4)[NR'(CH(2)R'')] (R' = R'' = Ph (9), R' = Ph, R'' = naphthyl (11)). 9 could not be obtained in pure form, however, its structure was assigned by spectroscopic means. At room temperature 11 reacted further to lose one PMe(3) forming 12 (Mo(NO)PMe(3))(3)[N(Ph)CH(2)C(10)H(6))]) with agostic stabilization. In a subsequent step oxidative addition of the agostic naphthyl C-H bond to the molybdenum centre occurred. Then hydrogen migration took place giving the chelate amine complex Mo(NO)(PMe(3))(3)[NH(Ph)(CH(2)C(10)H(6))] (15). The insertion reaction of 2 with C(10)H(7)N=CHPh led to formation of the agostic compound Mo(NO)(PMe(3))(3)[N(CH(2)Ph)(C(10)H(7))] (10). Based on the knowledge of facile formation of agostic compounds the catalytic hydrogenation of C(10)H(7)N=CHPh and PhN=CHC(10)H(7) with 2 (5 mol%) was tested. The best conversion rates were obtained in the presence of an excess of PMe(3), which were 18.4% and 100% for C(10)H(7)N=CHPh and PhN=CHC(10)H(7), respectively.

Asymmetric transfer hydrogenation of imines and iminiums catalyzed by a water-soluble catalyst in water

The first asymmetric transfer hydrogenation of cyclic imines and iminiums in water was successfully performed in high yields and enantioselectivities with sodium formate as the hydrogen source and CTAB as an additive catalyzed by a water-soluble and recyclable ruthenium(II) complex of the ligand (R,R)-2.

New approach to sulfonated diphosphine complexes: synthesis and amphoteric behaviour of zwitterionic [Mn+(CO4{(PPh2)2C(H)SO3–}]

Oxidation of the thioketone residue in the complex [Mn(CO)4{(PPh2)2C=S}]+ (2) with hydrogen peroxide affords the sulfonate derivative [Mn(CO)4{(PPh2)2C(H)SO3}] (3), which shows amphoteric behaviour in reversible acid-base processes, and is easily chlorinated to give [Mn(CO)4{(PPh2)2C(Cl)SO3}] (8).

Application of monodentate secondary phosphine oxides, a new class of chiral ligands, in Ir(i)-catalyzed asymmetric imine hydrogenation

Secondary phosphine oxides were prepared from R(1)PCl(2) and R(2)MgBr, followed by hydrolysis. They were obtained in an enantiopure form by preparative chiral HPLC. These new monodentate ligands were tested in the iridium-catalyzed hydrogenation of imines at 25 bar. Enantioselectivities up to 76% were obtained at L/Ir = 2. Addition of pyridine (Pyr/Ir = 1:2) raised the ee to 83%. Using pyridine as an additive allowed reduction of the L/Ir ratio to 1 without reduction of ee. [reaction: see text]

A novel amphiphilic chiral ligand derived from D-glucosamine. Application to palladium-catalyzed asymmetric allylic substitution reaction in an aqueous or an organic medium, allowing for catalyst recycling

A novel amphiphilic phosphinite-oxazoline chiral compound, 2-methyl-4,5-[4,6-O-benzylidene-3-O-bis[4-((diethylamino)methyl)phenyl]phosphino-1,2-dideoxy-alpha-D-glucopyranosyl]-[2,1-d]-2-oxazoline (1), has been prepared from natural D-glucosamine hydrochloride. The newly prepared complex, [Pd(2-methyl-4,5-[4,6-O-benzylidene-3-O-bis[(4-((diethylmethylammonium)methyl)phenyl)]phosphino-1,2-dideoxy-alpha-D-glucopyranosyl]-[2,1-d]-2-oxazoline)(eta3-C3H5)]3+ x 3BF4- (3), is soluble in water and an efficient catalyst for asymmetric allylic substitution reaction in water or an aqueous/organic biphasic medium (up to 85% ee). This catalytic system offers an easy separation of the aqueous catalyst phase from the product phase and allows recycling of the catalyst phase. In addition, compound 1 also works as an effective ligand for the palladium-catalyzed reaction under conventional homogeneous conditions in an organic medium, in which the catalyst (Pd-1 complex) can be recovered by simple acid/base extraction and reused in the second reaction.

Novel Water-Soluble Bisphosphinite Chiral Ligands Derived from alpha,alpha- and beta,beta-Trehalose. Application to Asymmetric Hydrogenation of Dehydroamino Acids and Their Esters in Water or an Aqueous/Organic Biphasic Medium

Novel 2,3:4,6-di-O-isopropylidene-alpha-D-glucopyranosyl-(1,1)-4,6-O-isopropylidene-2,3-di-O-diphenylphosphino-alpha-D-glucopyranoside (2), 2,3:4,6-di-O-cyclohexylidene-alpha-D-glucopyranosyl-(1,1)-4,6-O-cyclohexylidene-2,3-di-O-diphenylphosphino-alpha-D-glucopyranoside (4), and 2,3:4,6-di-O-cyclohexylidene-beta-D-glucopyranosyl-(1,1)-4,6-O-cyclohexylidene-2,3-di-O-diphenylphosphino-beta-D-glucopyranoside (11) were prepared from the corresponding alpha,alpha- or beta,beta-trehalose. The ligands were transformed into cationic Rh complexes, such as [Rh(alpha-D-glucopyranosyl-(1,1)-2,3-di-O-diphenylphosphino-alpha-D-glucopyranoside)(cod)]BF(4) (3) and [Rh(beta-D-glucopyranosyl-(1,1)-2,3-di-O-diphenylphosphino-beta-D-glucopyranoside)(cod)]BF(4) (12) bearing free hydroxy groups. These complexes were soluble in water and were efficient catalysts for the asymmetric hydrogenation of dehydroamino acids and their esters in water or an aqueous/organic biphasic medium with high enantioselectivity (up to 99.9% ee). Aqueous biphasic systems offer an easy separation of the aqueous catalyst phase from the product phase and allow recycling of the catalyst phase without the loss of enantioselectivity.