Preparation and properties of inclusion compounds of transition-metal complexes of cycloocta-1,5-diene and norbornadiene with cyclodextrins

Article abstract of DOI:10.1021/om00113a007

Inclusion compounds of rhodium and platinum complexes of cycloocta-1,5-diene (COD) and norbornadiene (NBD) with cyclodextrins were prepared. Two-to-one (cyclodextrin to guest) inclusion compounds were obtained in high yields in a crystalline state by the treatment of β-cyclodextrin (β-CD) with bis(μ-halo)bis(η⁴-cycloocta-1,5-diene)dirhodium, [Rh(μ-X)(COD)]₂ (X = Cl, Br, I), and bis(μ-chloro)bis(η⁴-norbornadiene)dirhodium, [Rh(μ-Cl)(NBD)]₂. The formation of inclusion compounds is selective. One-to-one inclusion compounds were obtained by the reaction of β-CD with (cycloocta-1,5-diene)platinum dihalides, Pt(COD)X₂ (X = Cl, Br, I), in high yields, while γ-CD formed 1:1 inclusion compounds with Pt(COD)I₂ but not with Pt(COD)Cl₂. α-Cyclodextrin did not form inclusion compounds with any transition-metal complexes of cyclooctadiene and norbornadiene. The inclusion compounds are thermally stable and do not liberate the guest when heated to 200°C in vacuo at which temperature the nonincluded guest [Rh(μ-Cl)(COD)]₂ already decomposed. The inclusion compounds were characterized by ¹H NMR, IR, UV, and circular dichroism spectra. A large induced Cotton effect was observed with β-CD-[Rh(μ-Cl)(COD)]₂. The ¹H NMR spectrum of [Rh(μ-Cl)(COD)]₂ in the presence of β-CD shows two sets of resonances for two different CD species that are assigned to free β-CD and the complexed β-CD, respectively. The binding mode will be discussed.