A novel hemilabile calix[4],quinoline-based P,N-ligand: coordination chemistry and complex characterisation

Abstract

The synthesis of the calix[4]arene-based P,N-ligand 3 (5,11,17,23-tetra-tert-butyl-25-[(2-quinolylmethyl)oxy]-26,27,28-(μ₃-phosphorustrioxy)calix[4]arene), in which the nitrogen atom-containing moiety has been introduced at the lower rim of the cavity prior to P-functionalisation, is described and its coordination properties investigated. In the crystal structure, the calix[4]-cavity adopts a cone conformation with an exo orientation of the phosphorus lone pair enabling P-N chelation. ¹H, ¹³C, ³¹P and ¹H{¹⁵N} HMQC NMR spectra indicated that, in complexes [PdCl(CH₃)(3)] (4) and [Rh(CO)Cl(3)] (5), ligand 3 coordinates in a chelating fashion, while in cis-[PtCl₂(3)₂] (6) and [Rh(acac)(CO)(3)] (7) it behaves as a monodentate ligand, coordinating via the phosphorus atom only. X-Ray crystal structure determinations were performed for [PdCl(CH₃)(3)] (4) and cis-[PtCl₂(3)₂] (6). The cationic Pd complex [Pd(CH₃)(CH₃CN)(3)][PF₆] (8) was found to be active in a CO/ethylene copolymerisation reaction. Good selectivities were observed for the Pd-catalysed allylic alkylation of cinnamyl acetate with in situ prepared catalysts. [Rh(acac)(CO)₂] modified with ligand 3 catalyses the hydroformylation of 1-octene with low selectivities towards linear aldehydes. High-pressure NMR experiments on the hydrido carbonyl rhodium(3) were inconclusive, different species were formed.