Events & Seminars > Event Details

Where:

4:00 pm
Room 304, Chemistry Building

Trianionic pincer ligands and their role in creating highly active transition metal catalysts.

Speaker:

Professor Adam Veige
University of Florida

Hosted by: Professor Brent Gunnoe

To catalyze alkyne polymerization one approach is to create a coordinatively unsaturated metal complex using an OCO3- ligand. Our recent discovery of the highly active (8,000 kg/molCat/h) precatalyst [tBuOCO]W≡CtBu (1) supports this contention. However, the high activity is not derived from the presence of a trianionic pincer ligand, but rather the in situ formation of a complex featuring a novel tetraanionic pincer-alkylidene ligand [O2C(R)C=]4-, where R = Ph, and tBu (Figure 1). The consequence of forming a tetraanionic pincer ligand is discussed. In addition to the discovery of this new form of a pincer-type ligand, we present evidence for a fundamentally new reaction involving the overall formal reductive alkylidyne migratory insertion into a metal-arene bond. In contrast to proposed acetylene polymerization chain growth steps, the mechanistic data to be presented provides a compelling case for initial acetylene addition to form a metallacyclopropene and subsequent insertion to form a metallacyclopentadiene, and so forth, more similar to proposed mechanisms for acetylene cyclotrimerization.
Recent advances in alkyne metathesis catalysts development have spurred renewed focus on creating a highly active catalyst, more akin to their alkene metathesis counterparts. Appending an amine to a C=C double bond drastically increases the nucelophilicity of the β-carbon atom of the alkene and are known as enamines. In an attempt to create highly nucleophilic M≡C multiple bonds for alkyne metathesis and polymerization, we developed a new CF3-ONO3- trianionic pincer-type ligand that is rationally designed to mimic enamines within a metal coordination sphere. Presented is a synthetic strategy to create enhanced nucleophilic tungsten-alkylidene and -alkylidyne complexes and features a new bonding concept termed “inorganic enamine”.

 

 

 

 

 

 

 

 

Figure 1. New tetraanionic pincer-type ligand [O2C(R)C=]4-, R = Ph, tBu.