A comprehensive investigation was undertaken in order to determine the effect of different reaction parameters on the molecular weights of polymers formed in a Suzuki polycondensation. In particular, we studied how the choice of solvent, base, ligand cocatalyst, palladium source, and monomers could affect the molecular weights. For these particular polymerizations, the best solvent and base were found to be CH2Cl2 and aqueous 3 M K3PO4, respectively. More interestingly, we determined that tri(o-tolyl)phosphine far surpassed not only the traditional triphenylphospine ligand cocatalyst, but also the more-recently developed hindered, electron-rich ligands that have yielded impressive results in small-molecule Suzuki coupling reactions. Molecular weights were also found to depend upon the source of palladium, with bis[tri(o-tolyl)phosphine]palladium(0) providing the best overall catalyst system. Finally, contrary to earlier reports, we found no advantage to replacing the more readily accessible bromide monomers with the corresponding iodides, and that pinacol boronic esters were inferior to the more traditional 1,3-propanediol boronic ester monomers. In sum, the work performed here shows that under optimized conditions, molecular weights on the order of 105 g/mol can be readily achieved with a Suzuki polycondensation.

Arylnaphthalene lignan lactones are valuable natural products with promising anticancer and antiviral properties. In an effort to simplify their synthesis, we investigated a one-pot multicomponent coupling reaction between phenylacetylene, carbon dioxide, and 3-bromo-1-phenyl-1-propyne. After the corresponding 1,6-diyne was generated in situ, cyclization afforded the desired product. The level of regioselectivity was enhanced through the tuning of electronic properties. The use of cinnamyl bromide which led to the formation of a 1,6-enyne intermediate was also studied.

The selective 4e–/4H+ reduction of dioxygen to water is an important reaction that takes place at the cathode of fuel cells. Monomeric aromatic tetrapyrroles (such as porphyrins, phthalocyanines, and corroles) coordinated to Co­(II) or Co­(III) have been considered as oxygen reduction catalysts due to their low cost and relative ease of synthesis. However, these systems have been repeatedly shown to be selective for O2 reduction by the less desired 2e–/2H+ pathway to yield hydrogen peroxide. Herein, we report the initial synthesis and study of a Co­(II) tetrapyrrole complex based on a nonaromatic isocorrole scaffold that is competent for 4e–/4H+ oxygen reduction reaction (ORR). This Co­(II) 10,10-dimethyl isocorrole (Co­[10-DMIC]) is obtained in just four simple steps and has excellent yield from a known dipyrromethane synthon. Evaluation of the steady state spectroscopic and redox properties of Co­[10-DMIC] against those of Co porphyrin (cobalt 5,10,15,20-tetrakis­(pentafluorophenyl)­porphyrin, [Co­(TPFPP)]) and corrole (cobalt 5,10,15-tris­(pentafluorophenyl)­corrole triphenylphosphine, Co­[TPFPC]­(PPh 3 )) homologues demonstrated that the spectroscopic and electrochemical properties of the isocorrole are distinct from those displayed by more traditional aromatic tetrapyrroles. Further, the investigation of the ORR activity of Co­[10-DMIC] using a combination of electrochemical and chemical reduction studies revealed that this simple, unadorned monomeric Co­(II) tetrapyrrole is ∼85% selective for the 4e–/4H+ reduction of O2 to H2O over the more kinetically facile 2e–/2H+ process that delivers H2O2. In contrast, the same ORR evaluations conducted for the Co porphyrin and corrole homologues demonstrated that these traditional aromatic systems catalyze the 2e–/2H+ conversion of O2 to H2O2 with near complete selectivity. Despite being a simple, easily prepared, monomeric tetrapyrrole platform, Co­[10-DMIC] supports an ORR catalysis that has historically only been achieved using elaborate porphyrinoid-based architectures that incorporate pendant proton-transfer groups or ditopic molecular clefts or that impose cofacially oriented O2 binding sites. Accordingly, Co­[10-DMIC] represents the first simple, unadorned, monomeric metalloisocorrole complex that can be easily prepared and shows a privileged performance for the 4e–/4H+ peractivation of O2 to water as compared to other simple cobalt containing tetrapyrroles.

The selective 4e–/4H+ reduction of dioxygen to water is an important reaction that takes place at the cathode of fuel cells. Monomeric aromatic tetrapyrroles (such as porphyrins, phthalocyanines, and corroles) coordinated to Co(II) have been considered as oxygen reduction catalysts due to their low cost and relative ease of synthesis. How- ever, these systems have been repeatedly shown to be selective for O2 reduction by the less desired 2e –/2H+ pathway to yield hydrogen peroxide. Herein, we report the initial synthesis and study of a Co(II) tetrapyrrole complex based upon a non-aromatic isocorrole scaffold that is competent for 4e–/4H+ ORR. This Co(II) 10,10-dimethyl isocorrole (Co[10- DMIC]) is obtained in a just four simple steps and excellent yield from a known dipyrromethane synthon. Evaluation of the steady state spectroscopic and redox properties of Co[10-DMIC] against those of Co(II) porphyrin ([Co(TPFPP)]) and corrole ([Co(TPFPC)(PPh3)]) homologs demonstrated that the light harvesting and electrochemical properties of the isocorrole are distinct from those displayed by more traditional aromatic tetrapyrroles. Further, investigation of the ORR activity of Co[10-DMIC] using a combination of electrochemical and chemical reduction studies revealed that this simple, unadorned monomeric Co(II) tetrapyrrole is ~85% selective for the 4e–/4H+ reduction of O2 to H2O over the more kinetically facile 2e–/2H+ process that delivers H2O2. By contrast, the same ORR evaluations conducted for the Co(II) porphyrin and corrole homologs demonstrated that these traditional aromatic systems catalyze the 2e–/2H+ conversion of O2 to H2O2 with near complete selectivity. Despite being a simple, easily prepared, monomeric tetrapyrrole platform, Co[10-DMIC] supports an ORR catalysis that has historically only been achieved using elaborate porphyrinoid-based architectures that incorporate pendant proton-transfer groups, ditopic molecular clefts, or which impose cofacially ori- ented O2 binding sites. Accordingly, Co[10-DMIC] represents the first simple, unadorned, monomeric metalloisocorrole complex that can be easily prepared and which shows a privileged performance for the 4e–/4H+ peractivation of O2 to water as compared to other simple Co(II) tetrapyrroles.

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