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Strongly Coordinating Ligands To Form Weakly Coordinating Yet Functional Organometallic Anions

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posted on 19.12.2019, 15:56 authored by Steven P. Fisher, Scott G. McArthur, Varun Tej, Sarah E. Lee, Allen L. Chan, Isaac Banda, Aaron Gregory, Kevin Berkley, Charlene Tsay, Arnold L. Rheingold, Gregorio Guisado-Barrios, Vincent Lavallo
Weakly coordinating anions (WCAs) are generally tailored to act as spectators with little or no function. Here we describe the implementation of strongly coordinating dianionic carboranyl N-heterocyclic carbenes (NHCs) to create organometallic -ate complexes of Au­(I) that serve both as WCAs and functional catalysts. These organometallic WCAs can be utilized to form both heterobimetallic (Au­(I)/Ag­(I)+; Au­(I)/Ir­(I)+) and organometallic/main group ion pairs (Au­(I)/(CPh3+ or SiEt3+). Because parent unfunctionalized dianionic carboranyl NHC complex 3 is unstable in most solvents when paired with CPh3+, novel synthesis methodology was devised to create polyhalogenated carboranyl NHCs, which show superior stability toward electrophilic substitution and cyclometalation chemistry. Additionally, the WCAs containing polyhalogenated carboranyl NHCs are among the most active catalysts reported for the hydroamination of alkynes. This investigation has also produced the first examples of a low-coordinate Au­(III) center with two cis accessible coordination sites and the first true dianionic carbene. These studies pave the way for the design of functional ion pairs that have the potential to participate in tandem or cooperative small-molecule activation and catalysis.