Radical-Mediated Anti-Markovnikov Hydrophosphonation of Olefins

The radical-mediated addition of triphenylphosphonium tetrafluoroborate to olefins (hydrophosphonation) is reported. Both standard radical initiators and photochemical conditions are effective, up to the gram scale. The phosphonium salts are shown to serve as Z-selective Wittig olefination reagents, even without purification

Bidentate N,O-prolinate ruthenium benzylidene catalyst highly active in RCM of disubstituted dienes

The synthesis of a bidentate N,O-prolinate ruthenium benzylidene from commercially available starting materials and its activity in ring-closing metathesis of functionalized disubstituted dienes at 30 °C is disclosed

Hope Is the Color Orange

This is a nonfiction short I wrote as part of a collection of shorts concerning my home. This piece specifically addresses how to fix something that doesn\u27t seem blatantly broken, but something is definitely wrong. I play with concepts of a the color orange as hope but come to realize orange can mean more than just hope, and life can be as complex as colors

Free Space Optical Link Utilizing a Modulated Retro-Reflector Intended for Planetary Duplex Communication Links Between an Orbiter and Surface Unit

Presented are simulation and experimental results that provide duplex optical-free space communication links with minimal power and pointing requirements by using a modulated retro-reflector (MRR) for planetary communications. The design is the MRR resides on the surface of a planet or moon, where energy is scarce, while the source of the communication laser resides on an orbiter to achieve satellite-to-ground communications. Also, a simulated scenario using the Mars Reconnaissance Orbiter (MRO) is provided for real world potential results. The information sent through this communication path can range from raw scientific data to multimedia files such as videos and pictures. Bidirectional communications is established with the MRR by using a nested pulse position modulation (PPM) structure. This modulation scheme is then evaluated for its validity in a proof-of-concept experiment. Initial results indicate a promising return-link performance of at least 300 kbps in the nested arrangement

Alkene Chemoselectivity in Ruthenium-Catalyzed Z-Selective Olefin Metathesis

Chelated ruthenium catalysts can facilitate highly chemoselective olefin metathesis. Terminal and internal Z olefins reacted selectively to form new Z olefins in the presence of internal E olefins. Chemoselectivity for terminal olefins was also observed over both sterically hindered and electronically deactivated alkenes

Fast-Initiating, Ruthenium-based Catalysts for Improved Activity in Highly E-Selective Cross Metathesis

Ruthenium-based olefin metathesis catalysts bearing dithiolate ligands have been recently employed to generate olefins with high E-selectivity (>99% E) but have been limited by low to moderate yields. In this report, ^1H NMR studies reveal that a major contributing factor to this low activity is the extremely low initiation rates of these catalysts with trans olefins. Introducing a 2-isopropoxy-3-phenylbenzylidene ligand in place of the conventional 2-isopropoxybenzylidene ligand resulted in catalysts that initiate rapidly under reaction conditions. As a result, reactions were completed in significantly less time and delivered higher yields than those in previous reports while maintaining high stereoselectivity (>99% E)

A Highly Efficient Synthesis of Z-Macrocycles using Stereoretentive, Ruthenium-Based Metathesis Catalysts

A highly efficient, Z-selective ring-closing metathesis system for the formation of macrocycles using a stereoretentive, ruthenium-based catalyst supported by a dithiolate ligand is reported. The catalyst is remarkably active as observed in initiation experiments showing complete catalyst initiation at −20 °C within 10 minutes. Macrocyclization reactions generated Z-products from easily accessible diene starting materials bearing a Z-olefin moiety. This approach provides a more efficient and selective route to Z-macrocycles relative to previously reported systems. Reactions were completed within shorter reaction times, and turnover numbers of up to 100 could be achieved. Macrocyclic lactones ranging in size from twelve- to seventeen-membered rings were synthesized in moderate to high yields (67–79 %) with excellent Z-selectivity (95–99 %)

New Insights into the Mechanism of Ruthenium-Catalyzed Olefin Metathesis Reactions

Over the past two decades, olefin metathesis has emerged as a mild and efficient method for the formation of carbon−carbon double bonds. In particular, (PCy_3)_2(Cl)_2RuCHPh (1)^2 has found extensive use in organic and polymer chemistry due to its high reactivity with olefins in the presence of a diverse array of functional groups. Recently, a new family of ruthenium-based olefin metathesis catalysts have been prepared by the substitution of a single PCy_3 ligand of 1 with an N-heterocyclic carbene. These new alkylidenes, particularly [Figure 1], exhibit dramatically increased activity over the parent system in ring-opening metathesis polymerization, ring-closing metathesis,4a and cross metathesis reactions. The mechanism of olefin metathesis reactions catalyzed by 1 has received intense investigation in our group and others and early studies established that phosphine dissociation is a crucial step along the reaction coordinate. As such, it has been suggested that the high activity of 2 and its analogues is due to their increased ability to promote this critical phosphine dissociation step. We report herein a detailed mechanistic study of phosphine exchange and initiation kinetics in alkylidenes 1 and 2. This study provides new and surprising evidence concerning the origin of the large activity differences between these two catalysts