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

CuI complexes of the form [CuI(PMDETA)(π-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 Cdouble bond; length as m-dashC double bond of the vinyl monomer with CuI 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 CuI is completed by a π-interaction with the Cdouble bond; length as m-dashC double bond of M in the presence of a non-coordinating counter-ion. A decrease in Cdouble bond; length as m-dashC IR stretching frequencies of Δν(Cdouble bond; length as m-dashC) = −110, −80, −109, and −127 cm−1 for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coordination. No significant change in Cdouble bond; length as m-dashC 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.