The mechanisms for Ni(dppe)Cl(2)-catalyzed chain-growth polymerization of 4-bromo-2,5-bis(hexyloxy)phenylmagnesium chloride and 5-bromo-4-hexylthiophen-2-ylmagnesium chloride were investigated. Rate studies utilizing IR spectroscopy and gas chromatography revealed that both polymerizations exhibit a first-order dependence on the catalyst concentration but a zeroth-order dependence on the monomer concentration. (31)P NMR spectroscopic studies of the reactive organometallic intermediates suggest that the resting states are unsymmetrical Ni(II)-biaryl and Ni(II)-bithiophene complexes. In combination, the data implicate reductive elimination as the rate-determining step for both monomers. Additionally, LiCl was found to have no effect on the rate-determining step or molecular weight distribution in the arene polymerization.

Although Staudinger realized makromoleküles had enormous potential, he likely did not anticipate the consequences of their universal adoption. With 6.3 billion metric tons of plastic waste now contaminating our land, water, and air, we are facing an environmental and public health crisis. Synthetic polymer chemists can help create a more sustainable future, but are we on the right path to do so? Herein, a comprehensive literature survey reveals that there has been an increased focus on “sustainable polymers” in recent years, but most papers focus on biomass-derived feedstocks. In contrast, there is less focus on polymer end-of-life fates. Moving forward, we suggest an increased emphasis on chemical recycling, which sees value in plastic waste and promotes a closed-loop plastic economy. To help keep us on the path to sustainability, the synthetic polymer community should routinely seek the systems perspective offered by life cycle assessment.

Lithium diisopropylamide (LDA) is a prominent reagent used in organic synthesis. In this Review, rate studies of LDA-mediated reactions are placed in the broader context of organic synthesis in three distinct segments. The first section provides a tutorial on solution kinetics, emphasizing the characteristic rate behavior caused by dominant solvation and aggregation effects. The second section summarizes substrate- and solvent-dependent mechanisms that reveal basic principles of solvation and aggregation. The final section suggests how an understanding of mechanism might be combined with empirical methods to optimize yields, rates, and selectivities of organolithium reactions and applied to organic synthesis.

The recent discovery of a living, controlled chain-growth method for synthesizing π-conjugated polymers has ignited the field and led to the development of many new materials. This Perspective focuses on the mechanistic underpinnings of the synthetic transformation, highlighting the controversial hypotheses and supporting data. A critical analysis of the literature revealed that the monomer scope remains largely limited to electron-rich monomers at this time. Last, a brief overview of some exciting new materials accessed via this method is provided.

Stereoselective Diels-Alder cycloadditions that probe substituent effects in aryl-aryl sandwich complexes were studied experimentally and theoretically. Computations on model systems demonstrate that the stereoselectivity in these reactions is mediated by differential π-stacking interactions in competing transition states. This allows relative stacking free energies of substituted and unsubstituted sandwich complexes to be derived from measured product distributions. In contrast to gas-phase computations, dispersion effects do not appear to play a significant role in the substituent effects, in accord with previous experiments. The experimental π-stacking free energies are shown to correlate well with Hammett σm constants (r = 0.96). These substituent constants primarily provide a measure of the inductive electron-donating and withdrawing character of the substituents, not donation into or out of the benzene π-system. The present experimental results are most readily explained using a recently proposed model of substituent effects in the benzene sandwich dimer in which the π-system of the substituted benzene is relatively unimportant and substituent effects arise from direct through-space interactions. Specifically, these results are the first experiments to clearly show that OMe enhances these π-stacking interactions, despite being a π-electron donor. This is in conflict with popular models in which substituent effects in aryl-aryl interactions are modulated by polarization of the aryl π-system.