Abstract

Recyclable Polyolefins as Solvents and Tools in more Sustainable Homogeneous Catalysis

Recycling ligands, catalysts, and solvents remains a challenge for homogeneous catalysis. This talk will describe how polyolefins can be used to molecularly engineer more sustainable homogeneous catalysis systems. The studies we will discuss show that terminally functionalized polyisobutylene (PIB) oligomer ligands and catalysts can be readily prepared and that such species have chemistry that is identical to that of conventional ligands and catalysts.

Our studies have also shown that these PIB oligomers are readily recycled and separated as oligomers. However, we also show that if necessary we can some functionalized PIB oligomers to substituted arenes under very mild conditions (i.e. in minutes at 25 ᵒC). In a typical of PIB-bound catalysts, these catalysts are dissolved and used in miscible alkane/cosolvent mixtures. After a reaction, a physical or chemical perturbation forms biphasic mixtures where the catalyst and product phases are separated by density. This chemistry typically uses heptane as an alkane solvent. However, we have also shown that heptane can be replaced by more sustainable poly(-olefin) (PAO)g solvents. Those studies show that nonvolatile and nontoxic PAOs are more recyclable and sustainable than heptane and that PAOs are more efficient in recovering PIB-bound catalysts or catalyst surrogates. Ongoing studies also suggest that alkane-solubilized polymers can even serve as alternative recyclable cosolvents, partly or fully replacing conventional solvents used in these solvent mixtures leading to even more sustainable solvent systems for catalysis chemistry.

Biography

He has published over 260 papers and made over 640 presentations in my independent career. These research accomplishments are the product of my collaboration with >150 undergraduate, graduate, and postdoctoral students.

The results we've reported have included seminal contributions to understanding regio- and stereoselectivity in azaallyl anion formation, the invention of new synthetic methodology, the development of new methods and strategies for syntheses of functional surfaces, and work that elucidated the basis of and that later used the Hofmeister effect in studies of polymeric materials that exhibit stimuli-responsive solubility. His group has been especially successful and we are leaders in studies of phase separable catalysts that control reaction rates (e.g. ‘smart’ catalysts) or that facilitate the reuse and/or separation of homogeneous catalysts from products. This work has emphasized pioneering studies that have explored new ways to use soluble polymers to recover and reuse homogeneous catalysts. This included the first description of thermomorphic liquid/liquid solvent systems for catalyst systems and ongoing work that is elucidating the principles that make such systems efficient and workable. His varied contributions in research have been recognized with a local university-level research award in 2008, receipt of the 2008 ACS Southwest Regional award, recognition as a fellow of the AAAS in 2006, and recognition as an ACS Fellow in 2011.

He has taught over 30 different courses in my career at Texas A&M University including freshman, sophomore, senior, and graduate lecture classes, laboratory courses at all levels, as well as seminar-style classes for entering undergraduates, freshmen students, honors students, chemistry majors and graduate students. He also has extensively mentored undergraduates in research with 25 of these 60 students being coauthors on peer-reviewed publications or patents. He has also been recognized with every award for teaching at Texas A&M given by faculty/student committees.

His involvement in research and education has been matched by service to both ACS and to the profession of chemistry more broadly. Within ACS, he has served locally as Chair of the local section and he has been the local section councilor for nearly 20 years. He has served on several ACS committees including the Minority Affairs Committee. He is currently a member of the Joint Board Council Committee on Publications. He served as Secretary General of the Catalysis and Surface and Science Secretariat in 2000, a Secretariat which is now a Division. He has organized or participated in symposia in over 100 ACS National, regional or Divisional meetings.