In pursuit of natural occurring chiral dienes {(R/S)-carvone} as bidentate ligands for coordination to rhodium(I)

Bis-rhodium-<i>mu</i>-chlorido dinuclear complexes with natural occurring limonene-type enantiomeric diene nucleophiles, (S)- and (R)-carvone [<b>S</b>Car and <b>R</b>Car], are presented and their single crystal structures reported. Utilizing the diolefinic bonds of the carvones, <i>mu</i>-[Rh^I(<b>S</b>Car)Cl]₂ (<b>IA/B</b>) and <i>mu</i>-[Rh^I(<b>R</b>Car)Cl]₂ (<b>IIA/B</b>) were obtained in ca. 80% yields in clean reactions with reactant RhCl₃(H₂O)_x. The “structured” chiral nanomaterials (<b>IA/B</b> and <b>IIA/<i>B</i> </b>&gt;<b> </b>1.1 nm) crystallize as two independent, dinuclear chiral molecules <i>Syn-mu</i>-[Rh^I(<b>S</b>Car)Cl]₂ (<b>IA</b>), <i>Anti-mu</i>-[Rh^I(<b>S</b>Car)Cl]₂ (<b>IB</b>), and <i>Syn-mu</i>-[Rh^I(<b>R</b>Car)Cl]₂ (<b>IIA</b>, <i>Anti-mu</i>-[Rh^I(<b>R</b>Car)Cl]₂ (<b>IIB</b>), respectively (based on the relative orientation of the carvone ring, oxo and methyl groups). Principal differences between the <b>IA/IIA</b> <i>vs</i> <b>IB/IIB</b> complexes in the solid state include the relative orientation of the two carvones, inducing a significant distortion in the <i>µ</i>²-Rh₂Cl₂ core, with the dihedral angles of 49.7(1)°/49.73(6)° in <b>IA/IIA</b> (<i>Syn-mu</i> geometry), versus 23.8(1)°/24.00(6)° in <b>IB/IIB</b> (<i>Anti-mu</i> geometry), respectively. The presence of the two structurally independent complexes in the solid state is also inferred from ¹H NMR spectra. Exploiting the diolefinic bonds of (<b>R/S</b>)-carvone in the reaction with RhCl₃(H₂O)_x enabled the high-yield synthesis and SCXRD of the “structured” dinuclear enantiomeric nanomaterials <i>Syn-mu</i>-[Rh^I(<b>R</b>Car)Cl]₂ (<b>IIA</b>) and <i>Anti-mu</i>-[Rh^I(<b>R</b>Car)Cl]₂ (<b>IIB</b>).