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A pair of enantiopure [6]‐azairidahelicenes incorporating chirality at the metal center and on the helicenic ligand were synthesized by dynamic kinetic resolution (dkr) of a configurationally labile [4]‐helicenic ligand (4‐(2‐pyridyl)‐benzo[g]phenanthrene, L1H) using bis‐cyclometalated chiral‐at‐metal only iridium(III) precursors as chiral inductors. The origin of the observed dkr is attributed to the different conformation and stability of diastereomeric reaction intermediates formed during the cyclometalation process. The isolated enantiomers exhibited circularly polarized phosphorescence (CPP), with |gphos| values of 1.8×10−3. [ABSTRACT FROM AUTHOR]

A transformation of fluxional into configurationally stable axially chiral N-arylpyrroles was achieved with a highly atroposelective electrophilic aromatic substitution catalyzed by a chiral-at-metal rhodium Lewis acid. Specifically, N-arylpyrroles were alkylated with N-acryloyl-1H-pyrazole electrophiles in up to 93 % yield and with up to >99.5 % ee, and follow-up conversions reveal the synthetic utility of this new method. DFT calculations elucidate the origins of the observed excellent atroposelectivity.

A transformation of fluxional into configurationally stable axially chiral N-arylpyrroles was achieved with a highly atroposelective electrophilic aromatic substitution catalyzed by a chiral-at-metal rhodium Lewis acid. Specifically, N-arylpyrroles were alkylated with N-acryloyl-1H-pyrazole electrophiles in up to 93 % yield and with up to >99.5 % ee, and follow-up conversions reveal the synthetic utility of this new method. DFT calculations elucidate the origins of the observed excellent atroposelectivity.

Main observation and conclusion: Chiral‐at‐metal strategy was developed to resolve the essential sulfoxide pharmaceutical intermediates R‐modafinil acid and its analogues with high yields and ee values. The efficient resolution process was achieved based on the diastereoselective discrimination caused by hydrogen bond and intramolecular π‐π interaction between chiral‐at‐metal center and the coordinated chiral sulfoxide ligands. Moreover, the chiral Ir(III) receptor can be reused with complete retention of their configurations and without the loss of reaction activity and enantioselectivity. This work provides a new access to synthesize R‐modafinil acid as well as its analogues and develops the application of chiral‐at‐metal strategy in chiral resolution. [ABSTRACT FROM AUTHOR]

An enantioselective ring‐closing C(sp3)−H amination of 2‐azidoacetamides is catalyzed by a chiral‐at‐metal ruthenium complex and provides chiral imidazolidin‐4‐ones in 31–95 % yield, with enantioselectivities of up to 95 % ee, and at catalyst loadings down to 0.1 mol % (turnover number (TON)=740). To our knowledge, this is the first example of a highly enantioselective C(sp3)−H amination with aliphatic azides. Mechanistic experiments reveal the importance of the amide group, which presumably enables initial bidentate coordination of the 2‐azidoacetamides to the catalyst. DFT calculations show that the transition state leading to the major enantiomer features a better steric fit and favorable π–π stacking between the substrate and the catalyst framework. Achiral ligands, chiral catalyst: By utilizing a newly prepared chiral‐at‐metal ruthenium catalyst for chelate activation of 2‐azidoacetamides, the challenging catalytic enantioselective ring‐closing C(sp3)−H amination of these substrates was achieved in high yields and enantioselectivities. [ABSTRACT FROM AUTHOR]

Treatment of NiCl2 with the tripod ligand (LMent,SC)-1H led to (LMent,SC)-[Cp(PNMent)NiCl] in which the potentially tridentate ligand coordinated to the metal center in a bidentate way via the cyclopentadienyl system and the phosphorus atom. In the presence of NH4PF6 [(LMent,SC)-[Cp(PNMent)NiCl] readily underwent Cl/PPh3 exchange to give (LMent,SC)-[Cp(PNMent)NiPPh3]PF6. Reaction of (LMent,SC)-[Cp(PNMent)NiCl] with 0.5 eq. of dppe afforded [{(LMent,SC)-[Cp(PNMent)Ni]}2dppe](PF6)2. (LMent,SC)-[Cp(PNMent)NiPPh3]PF6 and [{(LMent,SC)-[Cp(PNMent)Ni]}2dppe](PF6)2 were characterized by NMR and MS spectroscopy, and also by single crystal X-ray diffraction. The cyclopentadienyl ligand of (LMent,SC)-[Cp(PNMent)NiPPh3]PF6 shows a distortion intermediate between the ene-allyl and diene types, while the two cyclopentadienyl ligands of [{(LMent,SC)-[Cp(PNMent)Ni]}2dppe](PF6)2 have intermediate and diene distortions, respectively. According to the temperature dependent NMR spectra of (LMent,SC)-[Cp(PNMent)NiPPh3]PF6 and [{(LMent,SC)-[Cp(PNMent)Ni]}2dppe](PF6)2 two different conformations of the tether in the Cp(PNMent)Ni system could be frozen out at low temperatures. [ABSTRACT FROM AUTHOR]

Chiral-at-metal RhIII complexes catalyze the efficient enantioselective Mannich reaction of 2-acyl imidazoles with 1,3,5-triazinanes, affording the corresponding adducts in 81-99 % yield with up to >99 % enantioselectivity. This protocol performs with 0.1 mol-% of RhIII complex on gram scale without any loss in enantioselectivity. [ABSTRACT FROM AUTHOR]

Chiral fullerene-metal hybrids with complete control over the four stereogenic centers, including the absolute configuration of the metal atom, have been synthesized for the first time. The stereochemistry of the four chiral centers formed during [60]fullerene functionalization is the result of both the chiral catalysts employed and the diastereoselective addition of the metal complexes used (iridium, rhodium, or ruthenium). DFT calculations underpin the observed configurational stability at the metal center, which does not undergo an epimerization process. [ABSTRACT FROM AUTHOR]

Abstract: The monoalkylation of mixed-ring complex η 5-cyclopentadienyl-η 5-(1-neomenthyl-4,5,6,7-tetrahydroindenyl)zirconium dichloride (CpCp′ZrCl2) by lithium, magnesium and aluminum alkyls has been studied by the means of NMR spectroscopy. It is shown the reaction of CpCp′ZrCl2 with 1 eq. of RLi (R = Et, nBu) at −78 °C in toluene gives the chiral-at-zirconium complexes CpCp′ZrRCl with epimer ratio 12:1. The use of Grignard reagent (EtMgBr) reduces the epimer ratio to 3:1. The reaction of CpCp′ZrCl2 with AlEt3 in the same conditions yields two diastereomers of complex [CpCp′ZrEt(μ-Cl)·AlEt3] in a ratio 1.6:1, followed by five-membered bimetallic hydride complex [CpCp′Zr(μ-H)(CH2CH2AlEt2] with diastereomeric ratio 10:1. Cyclohexyl isocyanide (CyNC) insertion into the Zr-R bond of CpCp′ZrRCl provides the corresponding η 2-iminoacyl complexes CpCp′ZrC(R) = N(Cy)(Cl) (R = Et, nBu), which were characterized by NMR, IR spectroscopy and mass-spectrometry (MALDI/TOF). [Copyright &y& Elsevier]

The complexes Cp*Rh(beapy)Cl (5) and Cp*Ir(beapy)Cl (6) were synthesized by reaction of [Cp*MCl2]2 (M=Rh, Ir) and the deprotonated ligand Hbeapy, the condensation product of benzylamine and 2-pyrrolcarbaldehyde. In each case two enantiomers (SM) and (RM) arise, differing only in the metal chirality. The CH2 group of the benzyl substituent in the ligand forms an AB spectrum which was used for 1H NMR coalescence measurements (Tc=115.1 °C). The half-life for the racemization of Cp*Rh(beapy)Cl (5) was 46 ms at 115.1 °C. Substitution of the chloride ligand in Cp*Rh(pepy)Cl (3), pepy anion of Schiff base (+)-2-N-[(S)-1-phenylethyl]pyrrolcarbaldimine, afforded the complexes Cp*Rh(pepy)Br (7) and Cp*Rh(pepy)I (8). Single crystals of the two compounds contained only one of the two diastereomers. In solution the compounds epimerized via a change of the metal configuration, the half-life for (RRh,SC)-Cp*Rh(NN*)I (8) being 40.8 min at −40 °C in CD2Cl2 solution (obtained by time dependent integration of suitable 1H NMR signals). Reaction of [CpRhCl2]2 with (+)-N-[(S)-1-phenylethyl]salicylaldimine gave CpRh(pesa)Cl (9). Surprisingly, single crystals of 9 contained both diastereomers (RRh,SC) and (SRh,SC) in a 1:1 ratio following the molecular recognition motif of the inverted pianostools. The half-lifes for the epimerization of 9 with respect to the metal center, derived from 1H NMR coalescence experiments, were 31 and 9.2 ms at 11.3 °C (CD2Cl2) for the forward and back reactions, respectively. [Copyright &y& Elsevier]

Ortho-metalated derivatives of the optically active ligand (S)-(−)-N,N-dimethyl(1-phenylethyl)amine (LL*-H) react with [(η6-p-cymene)MCl2]2 (M=Ru, Os) to give the half-sandwich complexes [(η6-p-cymene)Ru(LL*)Cl] (1a,b) and [(η6-p-cymene)Os(LL*)Cl] (2a,b). In both cases two diastereomers (RM,SC) and (SM,SC) arise differing only in the metal configuration. On crystallization the (RM,SC)-isomers of both complexes 1 and 2 were obtained diastereomerically pure. The absolute configurations were established by X-ray structure analyses. Epimerization studies clearly showed that the metal configuration in both complexes is labile in solution. [Copyright &y& Elsevier]