Calix[4]arene-derived diphosphines, diphosphinites and diphosphites as chelating ligands for transition metal ions. Encapsulation of silver(I) in a calix-crown diphosphite

Article abstract of DOI:10.1039/b009005k

A series of lower rim-functionalised calix[4]arenes bearing 1,3-positioned phosphorus(III) ligands L¹-L⁹ have been synthesized and their coordinative properties examined. L¹ and L² {5,11,17,23-tetra-tert-butyl-25,27-bis[2-(diphenylphosphino) ethoxy]- and -25,27-bis(diphenylphosphinomethoxy)-26,28-bis(3-oxabutyloxy)calix[4]arene} react with [Rh(nbd)(THF)₂]BF₄ (nbd = 1,5-norbornadiene; THF = tetrahydrofuran) to afford in high yield the complexes [Rh(nbd)L ¹]BF₄ and [Rh(nbd)L²]BF₄, respectively, where the calixarene behaves as a P,P′ chelator. Both complexes catalyse hydroformylation of styrene at comparable rates, the linear:branched aldehyde ratio being 5:95. The presence of the ether side groups did not exert a noticeable effect on the selectivity nor the catalytic activity. Reaction of L¹-L⁸ with [Pd(η³- C₃H₄Me)(THF)₂]BF₄ gave the corresponding cationic chelate complexes [Pd(η³-C ₃H₄Me)Lⁱ]BF₄ that are active in the catalytic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate. Owing to the presence of a non-planar Pd-allyl fragment, the achiral calixarene subunits of some of these complexes are no longer C_2v-symmetrical, as evidenced by the ¹H and ¹³C NMR spectra that show non-equivalent side groups. Selective chelation via the two phosphorus atoms was also observed in the complexes [RuCl(p-MeC₆H₄Pr ⁱ)Lⁱ]BF₄ (Lⁱ = L³ or L⁴) obtained by reaction of the amide phosphines Li with [RuCl(p-MeC₆H₄Prⁱ)(THF)₂]BF ₄ [L³ = 5,11,17,23-tetratert-butyl-25,27- bis(diethylcarbamoylmethoxy)-26,28-bis(diphenylphosphinomethoxy)- and L ⁴ = 5,11,17,23-tetratert-butyl-25,27-bis(diphenylphosphinomethoxy)- 26,28-bis{(1-(R)-phenylethyl)carbamoylmethoxy}-calix[4]arene]. Reaction of L³ or L⁴ with neutral [RuCl₂(p-MeC ⁶H₄Pri)]₂ afforded the bimetallic complexes [{RuCl(p-MeC₆H₄Pri)}₂-Lⁱ] where the calixarene acts as a P,P′ bridging ligand. Reaction of AgBF₄ with calix-crown L⁹ {25,27-bis(diethoxyphosphinoxy)-26,28-(3,6,9- trioxaundecane-1,11-dioxy)calix[4]arene} resulted in quantitative formation of the complex [AgL⁹]BF₄ in which the silver(I) ion lies inside the cavity constituted by the crown ether fragment and the two phosphorus arms. As revealed by a single crystal X-ray diffraction study, the Ag ⁺ ion has a trigonal P₂O coordination environment with a P-Ag-P angle of 134.74(4)°. The Royal Society of Chemistry 2001.