Strongly Coordinating Ligands To Form Weakly Coordinating Yet Functional Organometallic Anions

Abstract

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.

1,3‐Bis(tricyanoborane)imidazoline‐2‐ylidenate Anion—A Ditopic Dianionic N‐Heterocyclic Carbene Ligand

“…In 2014, anionic carboranyl units were introduced as substituents at the imidazole nitrogen atoms, [10] for example in the dianion V (Figure 1). [10a] The concept of using anionic boron clusters as substituents at NHCs via C cluster −N bonds was extended to other boron cages such as { nido ‐7,8‐C 2 B 9 }, [11] and recently, halogenated { closo ‐1‐CB 11 } cages have been attached as well [12] . To the best of our knowledge, no other dianionic NHCs are known.…”

“… [10a] The concept of using anionic boron clusters as substituents at NHCs via C cluster −N bonds was extended to other boron cages such as { nido ‐7,8‐C 2 B 9 }, [11] and recently, halogenated { closo ‐1‐CB 11 } cages have been attached as well. [12] To the best of our knowledge, no other dianionic NHCs are known. In contrast, many carbenes with two tethered anionic groups have been studied in the past.…”

Das 1,3‐Bis(tricyanoboran)imidazolin‐2‐ylidenat‐Anion – Ein ditopischer dianionischer N‐heterocyclischer Carben‐Ligand

“…Anionische Carboranyl‐Einheiten wurden 2014 als Substituenten an den Imidazol‐Stickstoffatomen mit einer C Cluster ‐N‐Bindung eingeführt, [10] zum Beispiel im Dianion V (Abbildung 1). [10a] Das Konzept anionischer Borcluster als Substituenten an NHCs mit einer C Cluster ‐N‐Bindung wurde auf andere Borkäfige wie zum Beispiel { nido ‐7,8‐C 2 B 9 } [11] übertragen, und kürzlich wurden auch halogenierte { closo ‐1‐CB 11 }‐Käfige angebunden [12] . Weitere analoge dianionische NHCs sind uns nicht bekannt.…”

“…[10a] Das Konzept anionischer Borcluster als Substituenten an NHCs mit einer C Cluster -N-Bindung wurde auf andere Borkäfige wie zum Beispiel {nido-7,8-C 2 B 9 } [11] übertragen, und kürzlich wurden auch halogenierte {closo-1-CB 11 }-Käfige angebunden. [12] Weitere analoge dianionische NHCs sind uns nicht bekannt. Carbene mit zwei anionischen Gruppen, die über eine Brücke an das NHC-Grundgerüst angebunden sind, wurden dagegen intensiv untersucht.…”

Carborane Guests for Cucurbit[7]uril Facilitate Strong Binding and On-Demand Removal

“…This work further highlights how unique stimuli-responsive features of boron clusters can aid the development of new complex hybrid chemical systems. [56][57][58][59][60][61][62][63][64] (65) Unfortunately, in TFA or H2O no significant chemical shift changes were observed by IR, 11 B-NMR or 1 H-NMR spectroscopy precluding a Ka determination of unfunctionalized carboranes (including nido-carborane) with CB [7].…”