Syntheses, Spectroscopic Studies, and Crystal Structures of Chiral [Rh(aminocarboxylato)(η⁴‐cod)] and Chiral [Rh(amino alcohol)(η⁴‐cod)](acetate) Complexes with an Example of a Spontaneous Resolution of a Racemic Mixture into Homochiral Helix‐Enantiomers

Abstract

The dimeric complex acetato(η4‐cycloocta‐1,5‐diene)rhodium(I), [Rh(O2CMe)(η4‐cod)]2 (cod = cycloocta‐1,5‐diene), reacts with amino acids [HAA = L‐alanine, (S)‐2‐amino‐2‐phenylacetic acid (L‐phenylglycine), N‐methylglycine, and N‐phenylglycine] and with the amino alcohol (S)‐2‐amino‐2‐phenylethanol to afford the aminocarboxylato(η4‐cycloocta‐1,5‐diene)rhodium(I) complexes [Rh(AA)(η4‐cod)] (AA = deprotonated amino acid = aminocarboxylato ligand) and [(S)‐2‐amino‐2‐phenylethanol](η4‐cycloocta‐1,5‐diene)rhodium(I) acetate, [Rh{(S)‐HOCH2–CH(Ph)‐NH2}(η4‐cod)](O2CMe) (V). The complexes are characterized by IR, UV/Vis, 1H/13C NMR and mass spectroscopy. The achiral N‐phenylglycine ligand gives a chiral N‐phenylglycinato complex [Rh(O2C–CH2–NHPh)(η4‐cod)] (IV) with the amine nitrogen atom becoming the stereogenic center upon metal coordination. Complex IV crystallizes in the tetragonal, chiral space group P43 and the crystal structure reveals twofold spontaneous resolution of a racemic mixture into homochiral helix‐enantiomers. The investigated crystal contained only one type of helix, namely (left‐handed or M‐) 43‐helical chains. This is traced first to an intermolecular N–H···O hydrogen bonding from the stereogenic amino group to a neighboring unligated carboxyl oxygen atom that connects only molecules of the same (R)‐configuration into (left‐handed or M‐) 43‐helical chains. This intrachain homochirality is supplemented, secondly, by the interlocking of adjacent chains with their corrugated van der Waals surface to allow for an interchain transmission of the sense of helicity, building the single crystal from the same homochiral helix‐enantiomer. The enantiomeric amino alcohol complex V crystallizes in the monoclinic, noncentrosymmetric (Sohncke) space group P21. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, X-ray, and Spectroscopic Study of Dissymmetric Tetrahedral Zinc(II) Complexes from Chiral Schiff Base Naphthaldiminate Ligands with Apparent Exception to the ECD Exciton Chirality

“…The phenolic proton, which shows a broad signal at ca. δ 14.70−14.85 ppm in the free ligand due to strong intermolecular hydrogen bonding, 15,17,28 is obviously absent in the complex. If the dynamic equilibrium between two diastereomers (Δ vs Λ) is sufficiently slow, it can be followed in solution using time dependent 1 H NMR techniques.…”

Syntheses, spectroscopy, X-ray and DFT/TDDFT investigations of Rh(η4-cod)-enantiopure aminocarboxylate complexes

“…The RheNH(prolinate) bond length is little shorter (2.113 Å) than that in RheNH(N-phenylglycinate) (2.145 Å [10] or 2.151 Å [11]) due to the lower rigidity of the nitrogen atom in the later case. Similarly, the O1eRheN angle is slightly larger by 1 in Rh(I)-prolinate (81.9 ) compare to that in Rh(I)-N-phenylglycinate (80.8 ) [10,11].…”

“…Applied Pressure Chemical Ionization (APCI, positive mode) mass spectra were taken on Thermo-Finnigan TSQ 700. Dinuclear [Rh(h 4 -cod) (ac)] 2 was synthesized from [Rh(h 4 -cod)Cl] 2 according to our previous literature [9,10]. The enantiopure aminocarboxylic acids, L-proline and D-4-hydroxy-phenylglycine were used as received from the Merck.…”

“…The most significant observations in our studies are that the achiral N-phenylglycinate ligand gives a racemic chiral Rh(I)eN-phenylglycinate, [Rh(h 4 -cod) (N-phenylglycinate)] with the nitrogen atom becoming the stereogenic center upon metal coordination. The crystal structures reveal a case of two-fold spontaneous resolution of a racemic mixture into two homochiral helix-enantiomers, namely the (left-handed) P4 3 -and (right-handed) P4 1 -helical chain with the R-and S-N-phenylglycinate, respectively [10,11]. The cod ligand in these complexes can easily be replaced with the phosphine ligands (dppe/dppp/triphos) to give the cationic [Rh(dppe) 2 ](chiral-aminocarboxylate) or neutral [Rh(dppp/triphos) (chiral-aminocarboxylate)] complexes [12].…”

Amino Acid Ligand Chirality for Enantioselective Syntheses

“…The fact that non-polymeric products could be obtained and identified hints at broad applicative possibilities. The coordination chemistry of amino acids with Rh was intensively studied later [11], even some single-crystal X-ray diffraction structure determinations were reported recently [12]. Recently, Beck and co-workers reported on the reaction of amino acidate anions with an aminoferrocenyl/palladium heterobinuclear complex [13].…”