Ring Opening Polymerization

The goal of the research discussed in this paper is to demonstrate that N-heterocyclic carbenes can be bonded to a transition metal center resulting in a complex that is able to effectively catalyze the ring opening polymerization of caprolactone. While N-Heterocyclic carbene ligands have been documented as effective catalysts for the ring opening polymerization (ROP) of lactones and lactides, less is known about the catalytic abilities of these ligands when bound to a labile metal center. This article focuses on examining the synthesis and reactivity of different transition metal complexes containing tin, zinc, aluminium and titanium metal centers. In addition to comparing metal centers, the performance of a uni-functional alcohol initiator, benzyl alcohol, was compared to a bifunctional alcohol initiator 1,4-butanediol. The aluminium based complex combined with the uni-functional initiator resulted in some of the highest degrees of polymerization and increased control over the polymer chain length. Lastly, a series of studies were performed to better understand the kinetics of this optimized system. The findings detailed in this paper indicate that transition metal complexes containing N-Heterocyclic carbene ligands are capable of polymerizing caprolactone monomers resulting in good product yields and the ability to grow chains ranging from 10-30 units in length by varying feed ratios. One of the most pertinent uses of these short chained polyesters is their ability to be grafted into other polymers providing an efficient method of manufacturing specialty polyurethanes

Highly Regioselective Copper-Catalyzed Transfer Hydrodeuteration of Unactivated Terminal Alkenes

Catalytic transfer hydrodeuteration of unactivated alkenes is challenging because of the requirement that similar hydrogen and deuterium undergo selective insertion across a π-bond. We now report a highly regioselective catalytic transfer hydrodeuteration of unactivated terminal alkenes across a variety of heteroatom- or heterocycle-containing substrates. The base-metal-catalyzed reaction is also demonstrated on two complex natural products. Reaction studies indicate modular conditions that can also be extended to perform either an alkene transfer hydrogenation or transfer deuteration

Enantioselective Synthesis of Enantioisotopomers with Quantitative Chiral Analysis by Chiral Tag Rotational Spectroscopy

Fundamental to the synthesis of enantioenriched chiral molecules is the ability to assign absolute configuration at each stereogenic center, and to determine the enantiomeric excess for each compound. While determination of enantiomeric excess and absolute configuration is often considered routine in many facets of asymmetric synthesis, the same determinations for enantioisotopomers remains a formidable challenge. Here, we report the first highly enantioselective metal-catalyzed synthesis of enantioisotopomers that are chiral by virtue of deuterium substitution along with the first general spectroscopic technique for assignment of the absolute configuration and quantitative determination of the enantiomeric excess of isotopically chiral molecules. Chiral tag rotational spectroscopy uses noncovalent chiral derivatization, which eliminates the possibility of racemization during derivatization, to perform the chiral analysis without the need of reference samples oft he enantioisotopomer

Exploring New Techniques For Precision Deuteration of Alkenes and Alkynes

Deuterium labeled compounds are often utilized in chemical research as internal standards in mass spectrometry, to study reaction mechanisms and in the pharmaceutical industry to slow the rate of metabolism. With the increase interest for deuterium labeled molecules, there is a renewed interest in selective methods for the installation of deuterium atoms into small organic molecules. However, current methods to incorporate deuterium atoms into organic molecules can lead to isotopic mixtures such as isotopologues and isotopomers. These isotopic species are indistinguishable due to their similar physical properties, leading to inseparable products by common purification techniques. Furthermore, common spectroscopic techniques to specifically characterize and measure the precise location of the deuterium atom and sample composition of isotopic species are deficient.Catalytic transfer hydrodeuteration and deuteration reactions are emerging powerful techniques for site-selective and chemo-selective reactions to install deuterium atoms into small molecules. This method offers advantageous opportunities to improve selectivity and access precisely deuterated molecules as it offers tunable reaction conditions and tolerates a broad substrate scope. Additionally, this method uses inexpensive, readily available, easy to handle deuterium donors precluding the need of highly flammable deuterium gas. Herein, methods to precisely install deuterium atom(s) in a single step across alkene and alkyne functionalities under copper-catalyzed transfer deuteration and hydrodeuteration conditions are described. In this dissertation, reactivity, regioselectivity, and enantioselectivity is investigated. Molecular rotational resonance (MRR) spectroscopy is also employed for characterization of possible isotopic species present in the reaction mixture from Cu-catalyzed transfer hydrodeuteration reactions. Through MRR spectroscopy, confirmation of regioselectivity was acquired and any possible isotoplogues and isotopmers were quantified. Lastly, by using chiral tagging in MRR spectroscopy, we report the first general spectroscopic technique for enantiomeric excess and absolute configuration determination of chiral by virtue of deuterium substitution compounds synthesized by a novel metal-catalyzed enantioselective transfer hydrodeuteration method

Catalytic Transfer Deuteration and Hydrodeuteration: Emerging Techniques to Selectively Transform Alkenes and Alkynes to Deuterated Alkanes

Increasing demand for deuterium-labeled organic molecules has spurred a renewed interest in selective methods for deuterium installation. Catalytic transfer deuteration and transfer hydrodeuteration are emerging as powerful techniques for the selective incorporation of deuterium into small molecules. These reactions not only obviate the use of D2 gas and pressurized reaction setups but provide new opportunities for selectively installing deuterium into small molecules. Commercial or readily synthesized deuterium donors are typically employed as easy-to-handle reagents for transfer deuteration and hydrodeuteration reactions. In this minireview, recent advances in the catalytic transfer deuteration and hydrodeuteration of alkenes and alkynes for the selective synthesis of deuterated alkanes will be discussed

Copper-Catalyzed Formal Transfer Hydrogenation/Deuteration of Aryl Alkynes

A copper-catalyzed reduction of alkynes to alkanes and deuterated alkanes is described under transfer hydrogenation and transfer deuteration conditions. Commercially available alcohols and silanes are used interchangeably with their deuterated analogues as the hydrogen or deuterium sources. Transfer deuteration of terminal and internal aryl alkynes occurs with high levels of deuterium incorporation. Alkyne-containing complex natural product analogues undergo transfer hydrogenation and transfer deuteration selectively, in high yield. Mechanistic experiments support the reaction occurring through a cis-alkene intermediate and demonstrate the possibility for a regioselective alkyne transfer hydrodeuteration reaction