Enantiopure Complexes Research Articles

Construction of Enantiopure Taxoid and Natural Product-like Scaffolds Using a C-C Bond Cleavage/Arylation Reaction.

An approach to construct enantiopure complex natural product-like frameworks, including the first reported synthesis of a C17 oxygenated taxoid scaffold, is presented. A palladium-catalyzed C-C activation/cross-coupling is utilized to access these structures in a short sequence from (+)-carvone; the scope of this reaction is explored.

New Racemic and Single Enantiopure Hybrid Scorpionate/Cyclopentadienyl Magnesium and Zinc Initiators for the Stereoselective ROP of Lactides

The preparation of the first racemic bis(pyrazol-1-yl)methane-based NNCp-donor hybrid scorpionate/cyclopentadienyl magnesium and zinc complexes [Mg(R)(κ2-η5-NNCp)] (1–6) [NNCp = bpztcp, R = Me (1), Et (2), CH2SiMe3 (3); bpzpcp, R = Me (4), Et (5), CH2SiMe3 (6)] and [Zn(R)(κ2-η1-NNCp)] (7–12) [NNCp = bpztcp, R = Me (7), Et (8), CH2SiMe3 (9); bpzpcp, R = Me (10), Et (11), CH2SiMe3 (12)] has been carried out by the reaction of the corresponding racemic NNCp-H-donor scorpionate pro-ligands with Grignard reagents RMgCl, after deprotonation with nBuLi, or directly with ZnR2. The resulting alkyl magnesium complexes (1–6) have been employed in a protonolysis reaction with 2,6-dimethylphenol to yield the aryloxide magnesium complexes [Mg(OAr)(κ2-η5-NNCp)] (13 and 14) [NNCp = bpztcp (13), bpzpcp (14)]. Subsequently, the enantiopure scorpionate pro-ligand (R,R)-bpmycpH (16a) {bpmycpH = 1-{2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-(2R)-2-[(1R)-6,6-[3.1.1]-2-hepten-2-yl]ethyl}cyclopentadiene} and (R,R)-bpmycp′H (16b) {bpmycp′H = 2-{2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-(2R)-2-[(1R)-6,6-[3.1.1]-2-hepten-2-yl]ethyl}cyclopentadiene} reacted with RMgCl (after addition of nBuLi) or with ZnR2 to give the single enantiopure complexes [Mg(R)(κ2-η5-R,S-bpmycp)] (17–19) (R = Me (17), Et (18), CH2SiMe3 (19)) {R,S-bpmycp = 2-{2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-(2S)-2-[(1R)-6,6-[3.1.1]-2-hepten-2-yl]ethyl}cyclopentadienyl} and [Zn(R)(κ2-η1-R,S-bpmycp)] (20–22) (R = Me (20), Et (21), CH2SiMe3 (22)). The structures of these complexes were elucidated by 1H and 13C{1H} NMR spectroscopy, and the X-ray crystal structures of 2, 3, 7 and 21 were also established. These racemic and single enantiopure complexes 1–3, 5–9, 11–14, 19, and 21 can act as single-component initiators for the ring-opening polymerization of rac-lactide under mild conditions. Microstructural analysis of poly(rac-lactide)s revealed that, whereas the myrtenal substituent on the single enantiomerically pure initiator 21 exerts an appreciable influence on the degree of stereoselectivity to produce isotactic-enriched poly(lactide)s with a Pi value up to 0.77, the racemic mixtures of initiators impart more discrete levels of heteroselectivity in the production of PLAs, with a Ps value of 0.72.

Molecular tectonics: heterometallic (Ir,Cu) grid-type coordination networks based on cyclometallated Ir(III) chiral metallatectons.

A chiral-at-metal Ir(III) organometallic metallatecton was synthesised as a racemic mixture and as enantiopure complexes and combined with Cu(II) to afford a heterobimetallic (Ir,Cu) grid-type 2D coordination network.

Chiral Group 4 Cyclopentadienyl Complexes and Their Use in Polymerization of Lactide Monomers

A family of group 4 alkoxide and aryloxide complexes of a chiral cyclopentadienyl-derived (hydro)permethylpentalenyl ligand (C8Me6H; Pn*(H)) have been prepared and fully characterized. Both racemic and enantiopure complexes of all group 4 congeners were prepared with a wide variety of alkoxide and aryloxide ligands. The complexes Pn*(H)Ti(OtBu)3 (1), Pn*(H)Ti(O-2,6-Me-C6H3)3 (2), Pn*(H)Zr(OtBu)3 (3), Pn*(H)Zr(OCH2Ph)3 (4), Pn*(H)Zr(S-OCH{CH3}C6H5)3 (5), Pn*(H)Zr(rac-OCH{CH3}C6H5)3 (6), Pn*(H)Zr(O-2,6-Me-C6H3)3 (7), Pn*(H)Zr(O-2,6-iPr-C6H3)3 (8), Pn*(H)ZrCl2(O-2,6-tBu-C6H3) (9), Pn*(H)Hf(O-2,6-Me-C6H3)3 (10), Pn*(H)HfCl(O-2,6-iPr-C6H3)2, (11), and Pn*(H)HfCl2(O-2,6-tBu-C6H3) (12) were prepared by the reaction of Pn*(H)MCl3 complexes with the corresponding potassium alkoxides and aryloxides. Single-crystal X-ray diffraction studies implied that, despite multiple diastereomers being possible for each complex, the diastereomers isolated are limited to configurations in which the methyl group at the chiral cen...

Iron(II) Complexes Containing Unsymmetrical P–N–P′ Pincer Ligands for the Catalytic Asymmetric Hydrogenation of Ketones and Imines

After their treatment with LiAlH4 and then alcohol, new iron dicarbonyl complexes mer-trans-[Fe(Br)(CO)2(P-CH═N-P')][BF4] (where P-CH═N-P' = R2PCH2CH═NCH2CH2PPh2 and R = Cy or iPr or P-CH═N-P' = (S,S)- Cy2PCH2CH═NCH(Me)CH(Ph)PPh2) are catalysts for the hydrogenation of ketones in THF solvent with added KOtBu at 50 °C and 5 atm H2. Complexes with R = Ph are not active. With the enantiopure complex, alcohols are produced with an enantiomeric excess of up to 85% (S) at TOF up to 2000 h(-1), TON of up to 5000, for a range of ketones. An activated imine is hydrogenated to the amine in 90% ee at a TOF 20 h(-1)and TON 99. This is a significant advance in asymmetric pressure hydrogenation using iron. The complexes are prepared in two steps: (1) a one-pot reaction of phosphonium dimers ([cyclo-(PR2CH2CH(OH)(-))2][Br]2), KOtBu, FeBr2, and Ph2PCH2CH2NH2 (or (S,S)-Ph2PCH(Ph)CH(Me)NH2 for the enantiopure complex) in THF under a CO atmosphere to produce the complexes cis- and trans-[Fe(Br)2(CO)(P-CH═N-P')]; (2) the reaction of these with AgBF4 under CO(g) to afford the dicarbonyl complexes in high yield (50-90%). NMR and DFT studies of the process of precatalyst activation show that the dicarbonyl complexes are converted first to hydride-aluminum hydride complexes where the imine of the P-CH═N-P' ligand is reduced to an amide [P-CH2N-P'](-) with aluminum hydrides still bound to the nitrogen. These hydride species react with alcohol to give monohydride amine iron compounds FeH(OR')(CO)(P-CH2NH-P'), R' = Me, CMe2Et as well as the iron(0) complex Fe(CO)2(P-CH2NH-P') under certain conditions.

A Racemic and Enantiopure Unsymmetric Diiron(III) Complex with a Chiral o‐Carborane‐Based Pyridylalcohol Ligand: Combined Chiroptical, Magnetic, and Nonlinear Optical Properties

The design of molecule-based systems combining magnetic, chiroptical and second-order optical nonlinear properties is still very rare. We report an unusually unsymmetric diiron(III) complex 1, in which three bulky chiral carboranylpyridinealkoxide ligands (oCBhmp(-)) bridge both metal ions and the complex shows the above-mentioned properties. The introduction of o-carborane into the 2-(hydroxymethyl)pyridine (hmpH) architecture significantly alters the coordination of the simple or aryl-substituted 2-hmpH. The unusual architecture observed in 1 seems to be triggered by the poor nucleophilicity of our alkoxide ligand (oCBhmp(-)). A very rare case of spontaneous resolution takes place on precipitation or exposure to solvent vapor for the bulk compound, as confirmed by a combination of single-crystal and powder X-ray diffraction, second-harmonic generation, and circular dichroism. The corresponding enantiopure complexes (+)1 and (-)1 have also been synthesized and fully characterized. This research provides a new building block with unique geometry and electronics to construct coordination complexes with multifunctional properties.

Stereoselective aggregation of chiral complexes with threefold-symmetric pendant carboxyl groups: an example of “perfect” self-assembly not seen in the crystalline state?

The self-assembly of tris(bidentate) chiral complexes, [M(4-carboxyphenyldipyrrinato)3] (M = Co(III), Rh(III)), with a threefold-symmetric array of peripheral carboxyl groups is detailed. Thin sheet-like aggregates are observed in methanol/water mixtures of the racemic complex but not the enantiopure complex. Significant changes occur in the UV/vis spectrum upon aggregation and the intensity of fluorescence emission is enhanced. A model for the structure of the aggregate is proposed on the basis of the observed stereoselectivity of the aggregation process and the spectral changes. This model invokes the ‘perfect’ self-assembly of the building blocks which involves all three carboxyl groups in hydrogen bonding with neighbouring molecules. This differs from their crystal structures in which only two carboxyl groups participate in intermolecular hydrogen bonds.

A highly active and site selective indium catalyst for lactide polymerization

Chiral indium salen complexes are highly active, isoselective catalysts for the ring opening polymerization of racemic lactide. The polymerizations are well controlled and polymers with high molecular weights and low molecular weight distributions are obtained. Preliminary kinetic investigations with the enantiopure complex confirm enantiomorphic site control as the dominant contributor to selectivity and formation of block copolymers.

Crystallographic evidence of side-arm lariat effect in the series of chiral ortho- and para-methoxyphenoxymethyl-15-crown-5 complexes with sodium perchlorate

The single crystals of the NaClO4 complexes with two potential lariat 15-crowns-5 having ortho- or para-methoxyphenoxymethyl side arms were investigated by X-ray analysis in racemic and enantiopure form. Only ortho-derivative demonstrates lariat effect, i.e. the assistance of lateral fragment in cation complexation. No one oxygen atom of para-substituted side arm takes part in guest encapsulation in the solid phase. Whereas the crystals of racemic and enantiopure ortho-substituted crown complexes differ substantially from one another in packing characteristics, racemic and enantiopure complexes of para-derivatives are almost isostructural. This fact indicates that the last chiral complex belong to the rare class of continuous solid solutions of enantiomers.

Enantiopure Zn(II) and Cu(II) complexes of hexaazatetracyclomacrocycles based on cyclohexane moiety

The template condensation of (1R,2R)- or (1S,2S)-1,2-diaminocyclohexane, N,N′-bis(3-aminopropyl)ethylenediamine and paraformaldehyde in the presence of zinc(II) chloride or copper(II) chloride, followed by the metathesis with hexafluorophosphate or tetraphenylborate, afforded chiral, enantiopure Zn(II) complexes (R,R)-[ZnL1Cl](PF6), (S,S)-[ZnL1Cl](PF6), (R,R)-[ZnL1Cl](BPh4) (R,R)-[CuL1Cl](BPh4) and (S,S)-[CuL1Cl](BPh4) of the chiral macrocyle L1 (1,3,10,12,16,19-hexaazatetracyclo[17,3,1,112,16,04,9]tetracosane). Similar condensation of (1R,2R)-1,2-diaminocyclohexane, N,N′-bis(2-aminoethyl)ethylenediamine and paraformaldehyde in the presence of zinc(II) chloride afforded the enantiopure complex (R,R)-[ZnL2Cl](BPh4) of the chiral macrocyle L2 (1,3,10,12,15,18-hexaazatetracyclo[16,2,1,112,15,04,9]docosane). The complexes have been characterised on the basis of NMR, CD and ESI MS spectra and elemental analyses. In these complexes the chirality at the carbon atoms of the cyclohexyl fragment determines the chirality at the coordinated nitrogen atoms. The X-ray crystal structures of the (R,R)-[ZnL1Cl](PF6), (R,R)-[ZnL1Cl](BPh4) and (R,R)-[CuL1Cl](BPh4) complexes indicate the untypical for this class of complexes (R,S,R,S) configuration at the coordinated nitrogen atoms. The 1,3-diazacyclohexane rings fused to the two six-membered chelate rings are both bend towards the apical chloride anion. The 2D NMR spectra confirm the presence of single conformation of the complex present in acetone solution, in particular the ROESY spectrum confirms the characteristic bending of the 1,3-diazacyclohexane rings towards the same side of the macrocyle, observed in the crystal structure. On the other hand the crystal structure of the (R,R)-[ZnL2Cl](BPh4) complex indicate more common (R,R,S,S) configuration at the coordinated nitrogen atoms, accompanied by bending of the two fused 1,3-diazacyclopentane rings towards the opposite sides of the macrocycle.

Direct Synthesis of NNN-Donor Enantiopure Scorpionate Ligands by an Efficient Diastereoselective Nucleophilic Addition to Imines

New enantiopure imines (1-9) with a chiral substrate to control the stereochemistry of a newly created stereogenic center have been synthesized by reaction of the commercially available (1R)-(-)-myrtenal and different primary amines. The diastereomerically enriched lithium-scorpionate compounds [Li(κ(3)-mobpza)(THF)] (10) (mobpza = N-p-methylphenyl-(1R and 1S)-1-[(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl]-2,2-bis(3,5-dimethylpyrazol-1-yl)ethylamide), [Li(κ(3)-mobpza)(THF)] (11) (mobpza = N-p-methoxyphenyl-(1R and 1S)-1-[(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl]-2,2-bis(3,5-dimethylpyrazol-1-yl)ethylamide), [Li(κ(3)-fbpza)(THF)] (12) (fbpza = N-p-fluorophenyl-(1R and 1S)-1-[(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl]-2,2-bis(3,5-dimethylpyrazol-1-yl)ethylamide), and [Li(κ(3)-clbpza)(THF)] (13) (clbpza = N-p-chlorophenyl-(1R and 1S)-1-[(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl]-2,2-bis(3,5-dimethylpyrazol-1-yl)ethylamide) were obtained by a diastereoselective 1,2-addition of an organolithium reagent to imines in good yield and with good diastereomeric excess (ca. 80%). The complexes [LiCl(κ(2)-R,R-fbpzaH)(THF)] (14) and [LiCl(κ(2)-R,R-clbpzaH)(THF)] (15) were obtained in enantiomerically pure form by the treatment of THF solutions of 12 or 13 with NH(4)Cl. The enantiomerically pure amines (R,R-mbpzaH) (16), (R,R-mobpzaH) (17), (R,R-fbpzaH) (18), and (R,R-clbpzaH) (19) were obtained by hydrolysis of the lithium-scorpionate compounds 10-13 with H(2)O. The lithium compound 12 was reacted with [TiCl(4)(THF)(2)] or [ZrCl(4)] to give the enantiopure complexes [MCl(3)(κ(3)-R,R-fbpza)] [M = Ti (20), Zr (21)]. The amine compound 18 reacted with [MX(4)] (M = Ti, X = O(i)Pr, OEt; M = Zr; X = NMe(2)) to give the complexes [MX(3)(κ(3)-R,R-fbpza)] (22-24). The reaction of Me(3)SiCl with [Zr(NMe(2))(3)(κ(3)-R,R-fbpza)] (24) in different molar ratios led to the halide-amide-containing complexes [ZrCl(NMe(2))(2)(κ(3)-R,R-fbpza)] (25) and [ZrCl(2)(NMe(2))(κ(3)-R,R-fbpza)] (26) and the halide complex 21. The isolation of only one of the three possible diastereoisomers of complexes 25 and 26 revealed that chiral induction from the ligand to the zirconium center took place. The structures of these compounds were elucidated by (1)H and (13)C{(1)H} NMR spectroscopy, and the X-ray crystal structures of 5, 12, 14, 15, and 24 were also established.

Heteroscorpionate rare-earth initiators for the controlled ring-opening polymerization of cyclic esters

A series of neutral rare-earth metal amides containing different achiral and chiral heteroscorpionate ligands was synthesized and characterized and these compounds were employed in the polymerization of cyclic esters. Thus, treatment of [Ln{N(SiHMe(2))(2)}(3)(thf)(2)] (Ln = Nd, Sm) with acetamide or thioacetamide heteroscorpionate ligands for 2 h at 0 °C afforded the α-agostic silylamido dimeric rare-earth compounds [Ln{N(SiHMe(2))(2)}(NNE)](2) (Ln = Nd and Sm; NNE = heteroscorpionate ligands, E = O, S) (1-8), some as enantiopure complexes. Complexes 1-8 contain dianionic heteroscorpionate pseudoallyl ligands resulting from C-H activation of the bridging methine group of the bis(pyrazol-1-yl)methane moiety and subsequent coordination to the metal center. However, when the reaction was carried out for 1 h at lower temperature new bis(silylamido) dimeric lanthanide compounds [Ln{N(SiHMe(2))(2)}(2)(NNE)](2) (Ln = Nd and Sm; E = O) (9 and 10) were obtained. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 1, and 4 were also established. Neodymium complexes are active initiators for the ring-opening polymerization (ROP) of lactide (LA) and lactones, giving rise to medium-high molar mass polymers under mild conditions and with narrow polydispersities. These complexes were well suited for achieving well-controlled polymerization through an insertion-coordination mechanism. Achiral and racemic complexes did not affect stereocontrol in the polymerizarion of rac-LA but the enantiomerically pure complex 1 was found to exhibit a homosteric preference for one of the two enantiomers of rac-LA at low conversions.

Chelated Ruthenium Complexes of Functionalized Pentaarylcyclopentadienes

The Pd-catalyzed arylation of tetraphenylcyclopentadiene (7) and the classical “tetracyclone route” are tested as preparative entries to a variety of pentaarylcyclopentadienes 4 monofunctionalized in the ortho-position. The corresponding chelated ruthenium complexes 6 can be formed either thermally induced or by photochemical irradiation. These complexes contain stereogenic ruthenium centers. Enantiopure complexes 6f and 6g, with chiral oxazoline moieties, were tested for the asymmetric transfer hydrogenation of phenyl ketones 9.

Color difference caused by chirality

Synthesis, crystal structure and spectra properties of enantiopure and corresponding racemic Cu(II)-dipyridine amido complexes are reported. The different coordination styles result in the unexpected chiral-unrelated color changes between chiral and racemic complexes. Molecular packing in the crystal of the racemic - 1 . ( R,R ) and ( S,S ) molecules pack alternately with intermolecular Cu–O bond length of 2.451 Å. ► Chiral-unrelated optical properties could be affected by molecular chirality. ► A racemic and corresponding Enantiopure complex showed different color in crystal. ► The color difference came from the different coordination style of Cu.

Chiral diphosphines and diphosphinites derived from 2,2-biphosphole: Stereodynamic ligands for asymmetric catalysis

Abstract In this account, the recent advances on chiral stereochemically dynamic 2,2’-biphosphole ligands for applications in asymmetric catalysis are reported. In the first part, the synthesis of stereodynamic diphosphines and diphosphinites derived from 2,2’-biphosphole is presented. The second part describes the kinetic dynamic resolution to give diastereo- and enantiopure complexes. Applications in asymmetric allylic substitution, hydroformylation and hydrogenation are presented in the last part.

Preparation of Cp-Functionalized N-Heterocyclic Carbene Complexes of Ruthenium. Resolution of Chiral Complexes and Catalytic Studies

A series of piano-stool ruthenium(II) complexes bearing bidentate cyclopentadienyl-functionalized N-heterocyclic carbene ligands Ru(CpX-NHC)(CO)I [Cp = tetramethylcyclopentadienyl (Cp*) and tetrabenzylcyclopentadienyl (CpBz)] have been prepared by the diastereoselective reaction of the imidazolium CpX-NHC proligands with [Ru3(CO)12]. The new complexes have been characterized by spectroscopic techniques and X-ray diffraction methods. The enantiopure complexes have been separated by preparative thin-layer chromatography of the diastereomeric mixtures resulting from the reaction of the Ru(CpX-NHC)(CO)I compounds with an auxiliary chiral amine. Ru(Cp*-NHC)(CO)I is an efficient catalyst for the isomerization of allylic alcohols both in water and in THF.

Chiral, Neutral, and Paramagnetic Gold Dithiolene Complexes Derived from Camphorquinone

AbstractReaction of racemic (dl)‐ or enantiopure (D)‐camphorquinone with P4S10in dimethylimidazolidinone followed by addition of NiCl2·6H2O or KAuCl4affords the corresponding bornylenedithiolato metal complexes [(dl‐bordt)2Ni], [(D‐bordt)2Ni], [(dl‐bordt)2Au], and [(D‐bordt)2Au] in their neutral form. Cyclic voltammetry and UV/Vis/NIR spectrometry show that the bornylenedithiolato ligand acts as a highly electron‐rich dithiolene ligand. Complete assignment of the1H and13C NMR signals of the diamagnetic enantiopure [(D‐bordt)2Ni] is reported thanks to a combination of 2D NMR spectroscopy experiments. X‐ray crystal structure determinations were performed for the four complexes, showing that the two diastereomeric mixtures, [(dl‐bordt)2Ni] and [(dl‐bordt)2Au], are isomorphous (space groupP21/c), as are also the two enantiopure complexes, [(D‐bordt)2Ni] and [(D‐bordt)2Au] (space groupP21). Positional disorder of the two (D)‐ and (L)‐bornylenedithiolate enantiomers on the same position is observed in the structure of the diastereomeric mixtures, with the complex located on the inversion center. The temperature dependence of the magnetic susceptibility of the paramagnetic gold complexes [(dl‐bordt)2Au] and [(D‐bordt)2Au] demonstrates the presence of antiferromagnetic interactions, to a larger extent in the diastereoisomeric mixture [(dl‐bordt)2Au] than in the enantiopure complex [(D‐bordt)2Au], as a consequence of stronger lateral S···S intermolecular interactions in the former. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis, characterization and antiproliferative studies of the enantiomers of cis-[(1,2-camphordiamine)dichloro]platinum(II) complexes

The platinum(II) complex cis-[(1 S,2 R,3 S)-1,7,7-trimethylbicyclo[2.2.1]heptane-2,3-diamine]dichloroplatinum(II) ( 1) and its enantiomer ( 2) have been synthesized and physically and spectroscopically characterized. To obtain the enantiopure complexes the chiral pool approach was applied. The synthetic pathway has four steps, starting from (±)-diphenylethylenediamine (DPEDA) ( 3) and the natural products (1 S)-camphorquinone or (1 R)-camphorquinone to obtain enantiomers 1 and 2, respectively. The interaction of the Pt(II) complexes with DNA was studied by several techniques: circular dichroism, electrophoresis on agarose gel and atomic force microscopy (AFM). These studies showed differences in the degree of interaction between both enantiomers and DNA (calf thymus DNA and plasmid pBR322 DNA). The cytotoxicity of enantiomers 1 and 2 against the HL-60 cell line was studied by in vitro tests of antiproliferative activity, incubating during both 24 h and 72 h. An important difference of activity was found between both enantiomers regarding the IC 50 data at 24 h of incubation. Thus, complex 1 showed to be much more active than its enantiomer 2.

Water-soluble arene ruthenium catalysts containing sulfonated diamine ligands for asymmetric transfer hydrogenation of α-aryl ketones and imines in aqueous solution

A new family of nine cationic organometallic aqua complexes of the type [(arene)Ru(RSO2N∩NH2)(OH2)]+ (1–9), containing chiral N,N-chelating ligands, has been synthesised and isolated as the tetrafluoroborate salts, which are water-soluble and stable to hydrolysis. The enantiopure complexes 1–9 catalyse the transfer hydrogenation of prochiral aryl ketones and imines in aqueous solution to give the corresponding alcohols and amines with good conversion and enantioselectivity. This method gives an environmentally friendly access, for instance, to isoquinoline alkaloids by asymmetric catalysis in water.

Stereoselective dimerization of racemic C3-symmetric Ti(iv) amine triphenolate complexes

A novel, mononuclear Ti(IV) amine triphenolate complex obtained by reaction of Ti(OiPr)(4) with tris(2-hydroxy-3-phenylbenzyl)amine bearing phenyl ortho-substituents affords quantitatively and spontaneously the corresponding heterochiral micro-oxo dinuclear compound whereas an analogous chiral, enantiopure complex maintains its mononuclear structure even in the presence of an excess of water.