Mechanistic Insights into Polar Monomer Insertion Polymerization from Acrylamides

N-Isopropyl acrylamide (NIPAM), N,N-dimethyl acrylamide (DMAA), and 2-acetamidoethyl acrylate (AcAMEA) were copolymerized with ethylene employing [(P boolean AND O)PdMe(DMSO)] (1-DMSO; P boolean AND O = kappa(2)-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) as a catalyst precursor. Inhibition studies with nonpolymerizable polar additives show that reversible kappa-O-coordination of free amide retards polymerization significantly. Retardation of polymerization increases in the order ethyl acetate << methyl ethyl sulfone < acetonitrile < N,N-dimethylacetamide approximate to N-methylacetamide approximate to propionic acid < dimethylsulfoxide. Pseudo-first-order rate constants for the insertion into 1-DMSO were determined to increase in the order DMAA < AcAMEA < NIPAM < methyl acrylate. Exposure of 1-DMSO to NIPAM resulted in the formation of consecutive insertion products [(P boolean AND O)Pd(C6H11NO2)(n)Me] (n <= 3), as determined by electrospray ionization mass spectrometry. The solid-state structure of the methanol adduct of the 2,1-insertion product of NIPAM into 1-DMSO, [(P boolean AND O)Pd{eta(1)-CH(CONHiPr)CH2CH3}(kappa(1)-O-MeOD)] (2-MeOD), was determined by single crystal X-ray diffraction. Both 2,1- and 1,2-insertions of DMAA into the Pd-Me bond of a [(P boolean AND O)PdMe] fragment occur to afford a ca. 4:1 mixture of chelates [(P boolean AND O)Pd{kappa(2)-C,O-C(CH2CH3)C(O)NMe2}] (3) and [(P boolean AND O)Pd(kappa(2)-C,O-CH2C(CH3)C(O)NMe2}] (4). The four-membered chelate of 3 is opened by coordination of 2,6-lutidine (3 + 2,6-lutidine reversible arrow 3-LUT) with Delta H degrees = -41.8(10.5) kJ and Delta S degrees = -115(37) J mol(-1) K-1.