Polymorphs, enantiomorphs, chirality and helicity in [Rh{N,O}(η4-cod)] complexes with {N,O} = salicylaldiminato Schiff base or aminocarboxylato ligands

Abstract

The dimeric complex acetato(eta4-cycloocta-1,5-diene)rhodium(I), [Rh(O2CMe)(eta4-cod)]2 (cod = cycloocta-1,5-diene) reacts with N,O-chelating Schiff-base ligands or with N-phenylglycine to afford the diminato- or aminocarboxylato(4-cycloocta-1,5-diene)rhodium(I) complexes [{Rh(eta4-cod)}2(salen)] (1), [{Rh(eta4-cod)}2(salophen)] (2), [Rh((S)-N-phenylglycinato)(eta4-cod)] (3S), [Rh(rac-N-phenylglycinato)(eta4-cod)] (3rac), [Rh((R)-N-(4-methoxphenyl)ethyl-2-oxo-1-naphthaldiminato)(eta4-cod)] (4) and [Rh(N-(o-tolyl)-2-oxo-1-naphthaldiminato)(eta4-cod)] (5) [salen2- = N,N-ethylene-bis(salicylaldiminato), salophen2- = N,N-(1,2-phenylene)-bis(salicylaldiminato)]. The complexes are characterized by IR-, UV/Vis-, 1H/13C-NMR- and mass-spectroscopy. Complexes 1, 2, 4 and 5 contain six-membered metallaaromatic Rh-(N-CCC-O)-chelate rings which accept C-H...pi contacts. The crystal structure of 2 presents a polymorph (dimorph) (2a) to a previously reported structure (2b, CSD refcode SCLIRB10). Polymorphic forms 2a and 2b are traced to a different interlocking of adjacent dinuclear molecules with their corrugated van der Waals surface. The achiral N-phenylglycine ligand gives a chiral N-phenylglycinato complex [Rh(O2C-CH2-NHPh)(eta4-cod)] (3) with the nitrogen atom becoming the stereogenic center upon metal coordination. Complex 3 can crystallize as the enantiomorph 3S in the tetragonal, chiral space group P41 in a spontaneous resolution of the racemic mixture into homo-chiral helix-enantiomers due to inter-molecular N-H...O hydrogen bonding which connects only molecules of the same (S-) configuration into (right-handed or P-) 41-helical chains. Variation of the crystallization conditions gives 3 as a racemic polymorphic 3rac. R- and S-complexes 3 assemble in the polymorph 3rac in parallel chains along the 21-axes through N-HO hydrogen bonding. Again, only molecules of the same configuration are combined into a chain, albeit neighboring chains have complexes of opposite configuration. The chiral enantiomeric naphthaldiminato complex 4 displays a herring-bone arrangement. Achiral compound 5 crystallizes in the non-centrosymmetric polar space group Cc where all molecules show the same orientation.

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.…”

Synthesis, characterisation and reactivity of water-soluble ferrocenylimine-Rh(I) complexes as aqueous-biphasic hydroformylation catalyst precursors

“…Outline of the preparation of the t-butyl-substituted sulfonated mononuclear (5) and heteronuclear (7) complexes. related compounds [22]. The exo-and endo-methylene protons of the COD (d ¼ 2.4 and 1.9 ppm) are observed further upfield as two multiplets.…”

{2‐[1‐(2,6‐Diisopropylphenylimino)ethyl]pyridyl}palladium Dibromide Polymorphs Originating from Different Br···π and C–H···Br Contacts

“…It has been suggested that an active electron delocalization within a metal-Nheterocyclic chelate ring could exhibit some degree of "metalloaromaticity" [25,19,20] so that a Br···π contact could be invoked. [21] The dimorphs are the result of two different ways of crystal packing of these dimeric building blocks. In 1-red they form a herringbone array, in 1-yellow they are parallel (Figure 3).…”