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

Abstract

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 K2PtCl4 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 κ2 -P,N coordination mode. Complexes [κ2 -P,N-Pt(2⊂3)Cl2] (5) and [κ2 -P,N-Pt(2⊂4)Cl2] (6) were obtained quantitatively. Similarly, complexes [κ2 -P,N-Rh(2⊂3)(acac)(CO)] (7) and [κ2 -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 1H 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.

Supramolecular catalysis. Part 1: non-covalent interactions as a tool for building and modifying homogeneous catalysts

“…Analogues of the b-cyclodextrin derivative 61, bearing more basic amino groups, favour the formation of neutral Pt and Rh complexes featuring the supramolecular P,N ligand in a chelate coordination mode. 199 The related rhodium P, N-complexes are selective catalysts for the hydroformylation of styrene in water (b : l ratio = 10.1 in the best case). 200 Gennari and co-workers have used p-p interactions between electron-rich and electron-poor arenes as the driving force to generate chiral hetero-complexes containing a combination of two different monodentate phosphane ligands.…”

Hydroformylation in Aqueous Biphasic Media Assisted by Molecular Receptors

“…The art of synthesizing efficient molecular receptors and phosphines has been of tremendous help in the understanding of the catalytic process and now opens fascinating opportunities in the area of biphasic aqueous catalysis. For example, the formation of inclusion complexes between modified CDs and appropriate water soluble phosphines can be advantageously used to design new water soluble self-assembled supramolecular bidentates ligands for aqueous organometallic catalysis [95,96]. …”

Cyclodextrin-based PNN supramolecular assemblies: a new class of pincer-type ligands for aqueous organometallic catalysis

“…14 Concurrently to the strategies developed in organic media, we demonstrated that the supramolecular approach was applicable to water-soluble bidentate ligands through hydrophobic effects using an appropriate cyclodextrin (CD)/phosphane combination. 15,16,17,18 More precisely, we showed that CDs functionalized on their primary face by nitrogen donor groups could partially include within their cavity a water-soluble sulfonated phosphane to form supramolecular PN ligands. The resulting self-assembled entities were capable of coordinating platinum and rhodium complexes in a κ 2 -P,N coordination mode, the CD simultaneously acting as a first-and secondsphere ligand (Scheme 1).…”