Syntheses and characterization of alpha- and beta-cyclodextrin rotaxanes with dinuclear platinum(II) and pentacyanoferrate(II) stoppers.

摘要

A series of the linear 4′-pyridiimine ligands, 4 ′-pyrCHN(CH₂)_nNCH-4′-pyr, (pyr = pyridine, n = 2, 4 and 6) have been synthesized and characterized by 1H and 13C NMR electrospray mass spectrometry, and elemental analyses. These ligands form [2]pseudorotaxanes with α- and β-cyclodextrins (CD), {lcub}4′-pyrCHN(CH₂)_nNCH-4 ′-pyr·CD{rcub}, in basic aqueous solution and the stability constants have been determined at 25°C by means of 1H NMR chemical titrations. The kinetics and mechanisms of the ligand substitution reaction pathways in the self-assembly of the [(NC)₅Fe{lcub}4 ′-pyrCHN(CH₂)_nNCH-4′-pyr·CD{rcub}Fe(CN) ₅]6− rotaxanes from the corresponding dimer have been investigated using visible stopped-flow and 1H NMR spectroscopic techniques.; Two novel series of dinuclear platinum complexes, [Pt(dien)NH₂(CH ₂)_nNH₂Pt(dien)]Cl₄ (dien = diethylenetriamine, n = 8, 9, 10 and 12) and [Pt(en)(py)NH₂(CH₂)_nNH ₂Pt(en)(py)]Cl₂(NO₃)₂ (en = ethylenediamine, n = 8, 9, 10, 12) and their corresponding [2]rotaxanes with α-CD have been synthesized and characterized by 1H, 13C and 195Pt NMR, electrospray mass spectrometry, and elemental analyses. The rotaxanes were prepared by reacting the {lcub}NH₂(CH ₂)_nNH₂·α-CD{rcub} pseudorotaxanes with [Pt(dien)]+ and [Pt(en)pyCl]Cl, respectively, to stopper the linear diaminoalkane chains with inert platinum(II) stoppers. Attempts to stopper a series of α-cyclodextrin [2]pseudorotaxanes, prepared with novel [CH₃NH(CH₂)₂NCH₃(CH ₂)_nNCH₃(CH₂)₂NHCH₃ ] (n = 9, 10, 11 and 12) threads with platinum(II) ion complexes, were unsuccessful. The stability constants for the α-CD [2]pseudorotaxanes were determined by means of 1H NMR spectroscopic titrations.; Proton NMR kinetic investigation of the self-assembly and dissociation of [2]pseudorotaxanes of β-cyclodextrin with tetracationic platinum(II) dimer, [Pt(dien)NH₂(CH₂)₁₀NH₂Pt(dien)] 4+ and α-cyclodextrin with neutral guest, [CH₃NH(CH ₂)₂NCH₃(CH₂)₁₂NCH₃ (CH₂)₂NHCH₃], are consistent with the slippage mechanism due to the comparable size of the cavity of β-CD and α-CD with the (diethylenetriamine)platinum(II) and N,N′-dimethylethylenediamine end groups, respectively. A relatively weak inclusion of the end groups in CD cavity precedes a thermally promoted passage of the CD over the end group onto hydrophobic polymethylene chain of the thread.