A theoretical study of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with stannous(II) 2-ethylhexanoate (Sn(Oct)2) is presented. The B3LYP density functional method has been used for the quantum chemical calculations. Our results support a coordination-insertion mechanism initiated by a tin-alkoxide species formed prior to the ROP. The ratedetermining step in the ROP was the nucleophilic attack of the alkoxide on the carbonyl carbon of the monomer. The activation energy for the ROP of DXO with Sn(Oct′)2 has been determined to be 19.8 kcal/mol and for L-lactide 20.6 kcal/mol. At normal reaction temperatures, a ligand may dissociate as Oct′H during propagation. An excess of carboxylic acid hinders the coordination of monomer to the initiating/propagating complex.

The coordination of a range of substituted alkenes (C2H3X; X = H, CH3, t-Bu, CN, CO2CH3, CF3, OCH3, CHCH2, C6H5, F, Cl, Br) to a cationic methyl- or phenylpalladium(II)diimine complex and the subsequent migratory insertion into the methyl−palladium and phenyl−palladium bonds are studied using DFT calculations at the B3LYP level of theory. The focus of this investigation is on monitoring the insertion barrier and the regiochemical outcome as a function of alkene properties, with special attention to the functionalized alkene as a potential comonomer in polymerization. In general, electron-rich alkenes coordinate more strongly, whereas electron poor alkenes insert more readily. The barriers of insertion range from 4.7 to 26.5 kcal/mol, and mostly the 2,1-insertion is favored. In all cases the alkenes have a weaker coordination to the phenylpalladium(II)diimine compared to the methylpalladium(II)diimine complex and, as expected, a lower insertion barrier.

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Arylations of electron-rich heteroatom-substituted olefins were performed with arylboronic acids. This appears to constitute the first example of palladium(II)-catalyzed internal Heck arylations. The novel protocol exploits oxygen gas for environmentally benign reoxidation and a stable 1,10-phenanthroline bidentate ligand to promote the palladium(II) regeneration and to control the regioselectivity. Internal arylation is strongly favored with electron-rich arylboronic acids. DFT calculations support a charge-driven selectivity rationale, where phenyls substituted with electron-donating groups prefer the electron-poor alpha-carbon of the olefin. Experiments, verified by calculations, confirm the cationic nature of the catalytic route. This Heck methodology provides a facile and mild access to functionalized enamides. Controlled microwave heating and increased oxygen pressure were used to further reduce the reaction time to 1 h.