Phosphaalkene-oxazoline copolymers with styrene as chiral ligands for rhodium(i)

Abstract

The radical-initiated copolymerization of phosphaalkene-oxazoline, MesPC(Ph)CMe₂Ox [1, Ox = CNOCH(iPr)CH₂] with different loadings of styrene affords poly(methylenephosphine-co-styrene)s [2a (1 : S = 1 : 2): M_w = 7400 g mol⁻¹, PDI = 1.1; 2b (1 : S = 1 : 5): M_w = 18 000 g mol⁻¹, PDI = 1.2; 2c (1 : S = 1 : 10): M_w = 16 000 g mol⁻¹, PDI = 1.3]. Copolymers 2a–2c are demonstrated as viable macromolecular ligands for rhodium(I). By comparison with the crystallographically characterized model P,N-bidentate complex, [Mes(Me)P–CH(Ph)CMe₂Ox·Rh(cod)]BF₄, the polymer complexes [2·Rh(cod)]BF₄ were prepared. The macromolecular metal complexes were characterized by GPC {for [2a·Rh(cod)]BF₄: M_w = 14 000 g mol⁻¹, PDI = 1.2}, UV/Vis spectroscopy, ¹H, ¹³C and ³¹P NMR spectroscopy. Integration of the ³¹P NMR spectra of mixtures of 2 and [Rh(cod)₂]BF₄ permitted the determination of the mol% of incorporation of monomer 1 in copolymer 2 (2a: 17%; 2b: 5%; 2c: 4%). These results compared favorably with those determined by elemental analysis (2a: 17%; 2b: 6%).