The development of novel aqueous cross-coupling strategies has emerged as a rapidly expanding area of research within organic synthesis. However, many of these cross-coupling reactions require the pre-formation of an organohalide substrate, which often involves toxic halogenating reagents and harsh reaction conditions. This work details the development of a tandem halogenation/cross-coupling procedure in which an electron-rich arene or heteroarene is brominated through an enzymatic halogenation reaction catalyzed by a vanadium dependent haloperoxidase (VHPO) and then used without workup in a subsequent aqueous Suzuki cross-coupling reaction. This sequential process allows the arylated product to be accessed in a single pot from the unfunctionalized substrate via the brominated intermediate. Optimization of the enzymatic halogenation step was performed for three different substrates, resulting in the discovery of conditions for the bromination of 2,3-dihydrobenzofuran, chromane, and anisole in high yield (>95%). The scope of the reaction was then investigated for a range of electron-rich arene and heteroarene substrates. Next, Suzuki cross-coupling conditions were developed in a reaction mixture of pH 5 citrate buffer and acetonitrile and applied to the arylation of 2,3-dihydrobenzofuran utilizing an array of arylboronic acid coupling partners. Finally, the two procedures were combined to perform a tandem enzymatic halogenation/aqueous Suzuki cross-coupling of 2,3-dihydrobenzofuran to give the arylated product in 74% yield.

Post-consumer plastic and polymer waste accumulation in recent years continues to become more of a problem. One of the common polymers that has become ubiquitous to modern life is polyethylene terephthalate, a polymer that makes up 6.2% of all polymers produced and only 39% of which is recycled in the US annually.1,5 In this study a new catalyst was for the methanolysis of PET and compared to a common organic base, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), that has been used in academia and industry for the depolymerization of PET. In this study it was concluded that yttrium (III) acetylacetonate hydrate was a more active catalyst for the methanolysis of PET at 120 °C in comparison to TBD. It was also determined that there is no co-catalytic effect between yttrium (III) acetylacetonate hydrate and TBD when used in combination. The use of manganese (II) acetate tetrahydrate was also explored as a potential catalyst and was found to shown significant reactivity. However, it was concluded that the optimal conditions for PET methanolysis had not been reached and that further research into reaction times as well as co-solvents needs to be conducted. The synthesis of a novel o-phenylenediamine ligand functionalized with a labile phosphine substituent was also explored with the end goal of metalation and implementation in the methanolysis of PET. It has been assumed through nuclear magnetic resonance spectroscopy (NMR) characterization that the N,N’-(1,2-phenylenediamine)bis[3-(diphenylphosphanyl)-propanamide]-borane precursor was successfully synthesized and isolated. The subsequent deprotection of the N,N’-(1,2-phenylenediamine)bis[3-(diphenylphosphanyl)-propanamide]-borane complex was performed but has not been fully characterized. The 31P NMR does indicate a fully deprotected tertiary organophosphine. Through this work a detailed procedure for the ligand precursor has been laid out and developed so that the synthesis may now be scaled up, further characterized, metalated, and used to support catalysis.

Amidinates and guanidinates are promising supporting ligands in organometallic and coordination chemistry, highly valued for their accessibility, tunability, and comparability with other popular anionic N-chelating hard donor ligands like β-diketiminates. By far the most powerful way to access these ligands involves direct metal-nucleophile insertion into N,N’- substituted carbodiimides. However, the majority of reported examples require the use of commercially accessible carbodiimide peptide coupling reagents with simple alkyl substituents leading to low variation in potential substituents. Presented here is the design, synthesis, and isolation of a novel N,N’-bis[3-(diphenylphosphino)propyl]carbodiimide via an Aza-Wittig reaction between two previously described air stable substrates. At room temperature, 3-(diphenylphosphanyl-borane)-propylisocyanate was added to N-(3-(diphenylphospino)propyl)-triphenylphosphinimine, leading to product formation in minutes. One-pot phosphine-borane deprotection, followed by simple filtration of the crude mixture through a small, basic silica plug using pentane and diethyl ether granted the corresponding carbodiimide in high purity and yield (over 70%), confirmed by 1H, 13C, and 31P NMR spectroscopy. In addition to accessing different central carbon substituents, modification of phosphine substituents should be easily accessible through minor variations in the synthesis. With these precursors, anionic amidinates and guanidinates capable of κ4 -N,N,P,P-coordination may be accessed. The ability of the labile phosphine arms to associate and dissociate may facilitate catalysis. Thus, this carbodiimide provides a tunable, reliable one step precursor to novel substituted amidinates and guanidinates for homogeneous transition metal catalysis.