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The Finze Group

Regioselective functionalization of boron clusters


The syntheses of functionalized boron clusters with easily modifiable substituents form the basis for the broad application of borate anions and boranes, for example as ligands in coordination chemistry. The focus of our investigation is on the selective mono- and poly functionalization of the carba-closo-dodecaborate anion and related boron clusters. Different synthetic strategies, such as cluster aufbau reactions, selective halogenations and (microwave-assisted) cross-coupling reactions are pursued.


The selective monofunctionalization of the {closo-1-CB11} cage on the upper B5 ring to {2-R-closo-1-CB11} clusters is achieved by inserting dihaloboranes into carba-nido-undecaborate trianions [7-R-nido-7-CB10H11]3–. Corresponding reactions with Cl2BN(SiMe3)2 allow a first, simple synthetic access to 2-mono- as well as 1,2-diaminocarba-closo-dodecaborate anions.

 

The synthetic strategy we developed for carba-closo-dodecaborate anions with one or two alkynyl groups in the 12- and 7-position of the cluster via palladium-catalyzed cross-coupling reaction of alkynyl Grignard reagents with the corresponding mono- and diiodinated {closo-1-CB11} derivatives is the first access to carba-closo-dodecaborate anions with easily modifiable functional groups on the lower B5 ring and on the antipodal boron atom of the {closo-1-CB11} cluster.