Towards understanding monomer coordination in atom transfer radical polymerization: synthesis of [Cu I(PMDETA)(π-M)][BPh 4] (M = methyl acrylate, styrene, 1-octene, and methyl methacrylate) and structural studies by FT-IR and 1H NMR spectroscopy and X-ray crystallography

Abstract

Cu I complexes of the form [Cu I(PMDETA)(π-M)][BPh 4] (where PMDETA = N, N, N′, N″, N″-pentamethyldiethylenetriamine, and M = vinyl monomer) were synthesized and isolated from solution as crystals with methyl acrylate (MA), styrene (Sty), and 1-octene (Oct). The interaction of the C C double bond of the vinyl monomer with Cu I was characterized via FT-IR and 1H NMR spectroscopy and single crystal X-ray crystallography. A fourth complex with methyl methacrylate (MMA) was synthesized and characterized spectroscopically, but no crystals suitable for X-ray structure analysis could be obtained. In all complexes, PMDETA acts as a tridentate ligand, while the pseudotetrahedral coordination geometry around Cu I is completed by a π-interaction with the C C double bond of M in the presence of a non-coordinating counter-ion. A decrease in C C IR stretching frequencies of Δ ν(C C) = −110, −80, −109, and −127 cm −1 for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coordination. No significant change in C C bond length was seen in the crystal structure for complexes with MA and Oct while a slight lengthening was observed for the Sty complex. The upfield shift of the vinyl proton resonances indicated the presence of significant π-back-bonding.