Nicholas A. Isley

On the Way Towards Greener Transition-Metal-Catalyzed Processes as Quantified by E Factors

Transition-metal-catalyzed carbon-carbon and carbon-heteroatom bond formations are among the most heavily used types of reactions in both academic and industrial settings. As important as these are to the synthetic community, such cross-couplings come with a heavy price to our environment, and sustainability. E Factors are one measure of waste created, and organic solvents, by far, are the main contributors to the high values associated, in particular, with the pharmaceutical and fine-chemical companies which utilize these reactions. An alternative to organic solvents in which cross-couplings are run can be found in the form of micellar catalysis, wherein nanoparticles composed of newly introduced designer surfactants enable the same cross-couplings, albeit in water, with most taking place at room temperature. In the absence of an organic solvent as the reaction medium, organic waste and hence, E Factors, drop dramatically.

Transforming Suzuki–Miyaura Cross-Couplings of MIDA Boronates into a Green Technology: No Organic Solvents

New technology has been developed that enables Suzuki-Miyaura couplings involving widely utilized MIDA boronates to be run in water as the only medium, mainly at room temperature. The protocol is such that no organic solvent is involved at any stage; from the reaction through to product isolation. Hence, using the E factor scale as a measure of greenness, the values for these cross-couplings approach zero.

Leveraging the Micellar Effect: Gold-Catalyzed Dehydrative Cyclizations … in Water at Room Temperature

The first examples of gold-catalyzed cyclizations of diols and triols to the corresponding hetero- or spirocycles in an aqueous medium are presented. These reactions take place within nanomicelles, where the hydrophobic effect is operating, thereby driving the dehydrations, notwithstanding the surrounding water. By the addition of simple salts such as sodium chloride, reaction times and catalyst loadings can be significantly decreased.

C–C bond formation via copper-catalyzed conjugate addition reactions to enones in water at room temperature

Conjugate addition reactions to enones can now be done in water at room temperature with in situ generated organocopper reagents. Mixing an enone, zinc powder, TMEDA, and an alkyl halide in a micellar environemnt containing catalytic amounts of Cu(I), Ag(I), and Au(III) leads to 1,4-adducts in good isolated yields: no organometallic precursor need be formed.

Dehalogenation of functionalized alkyl halides in water at room temperature

Alkyl bromides and chlorides can be reduced to the corresponding hydrocarbons utilizing zinc in the presence of an amine additive. The process takes place in water at ambient temperatures, enabled by a commercially available designer surfactant. The reaction medium can be readily recycled, and the amount of organic solvent invested for product isolation is minimal, leading to very low E Factors.