Towards understanding monomer coordination in atom transfer radical polymerization:: synthesis of [CuI(PMDETA)(μ-M)][BPh4] (M = methyl acrylate, styrene, 1-octene, and methyl methacrylate) and structural studies by FT-IR and 1H NMR spectroscopy and X-ray crystallography

Cu-1 complexes of the form [Cu-1(PMDETA)(pi-M)][BPh4] (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-1 was characterized via FT-IR and H-1 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-1 is completed by a pi-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 Deltav(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 pi-back-bonding. (C) 2004 Elsevier B.V. All rights reserved.