Platinum(II) phosphonate complexes derived from endo-8-camphanylphosphonic acid

The reactions of cis-[PtCl2L2] [L = PPh3, PMe2Ph or L2 = Ph2P(CH2)2PPh2 (dppe)] with endo-8-camphanylphosphonic acid (CamPO3H2) and Ag2O in refluxing dichloromethane gave platinum(II) phosphonate complexes [Pt(O3PCam)L2]. The X-ray crystal structure of [Pt(O3PCam)(PPh3)2]·2CHCl3 shows that the bulky camphanyl group, rather than being directed away from the platinum, is instead directed into a pocket formed by the Pt and the two PPh3 ligands. This allows the O3P–CH2 group to have a preferred staggered conformation. The complexes were studied in detail by NMR spectroscopy, which demonstrates non-fluxional behaviour for the sterically bulky PPh3 and dppe derivatives, which contain inequivalent phosphine ligands in their 31P NMR spectra. These findings are backed up by theoretical calculations on the PPh3 and PPhMe2 derivatives, which show, respectively, high and low energy barriers to rotation of the camphanyl group in the PPh3 and PPhMe2 complexes. The X-ray crystal structure of CamPO3H2 is also reported, and consists of hydrogen-bonded hexameric aggregates, which assemble to form a columnar structure containing hydrophilic phosphonic acid channels surrounded by a sheath of bulky, hydrophobic camphanyl groups.