Cyclodextrin-Based Supramolecular P,N Bidentate Ligands and their Platinum and Rhodium Complexes

We report the elaboration of supramolecular P, N bidentate ligands starting from mono- N, N -dialkylamino-β-cyclodextrins (CD) and an appropriate phosphane, namely the sodium salt of the bis(3-sodiosulfonatophenyl)(4- tert -butylphenyl)phosphane ( 2 ). The inclusion complexes stemmed from inclusion of 2 in the cavity of mono- N, N -diethylamino-β-CD ( 3 ) or monopyrrolidino-β-CD ( 4 ) have been characterized by NMR and isothermal titration calorimetry (ITC) measurements. A 1/1 stoichiometry was established for each complex, the phosphane entering the CD cavity by the primary face. High association constants of 65.000 ± 3.000 and 70.350 ± 7.000 M −1 were measured for supramolecular complexes 2⊂3 and 2⊂4, respectively. The coordination ability of these supramolecular P, N bidentate ligands with K 2 PtCl 4 as a platinum precursor in water was demonstrated by NMR measurements. While phosphorus coordination on the platinum occurred rapidly at room temperature, heating the solution at 60 °C was required in order to access a κ 2 -P, N coordination mode. Complexes [κ 2 -P, N -Pt( 2⊂3 )Cl 2 ] ( 5 ) and [κ 2 -P, N -Pt( 2⊂4 )Cl 2 ] ( 6 ) were obtained quantitatively. Similarly, complexes [κ 2 -P, N -Rh( 2⊂3 )(acac)(CO)] ( 7 ) and [κ 2 -P, N -Rh( 2⊂4 )(acac)(CO)] ( 8 ) were synthesized by addition of an aqueous solution of 2⊂3 and 2⊂4 respectively on the Rh(CO) 2 (acac) rhodium precursor (acac = acetylacetonate). No variation in their 1 H NMR spectra could be detected from 20 to 80 °C, suggesting that these supramolecular P, N chelate complexes are structure invariant over the temperature range.