Title:

N-borane substituted N-heterocyclic carbenes for small-molecule activation

Since 2006, the new field of frustrated Lewis pair (FLP) chemistry has grown as an approach towards small-molecule activation and other possibly catalytic transformations. An FLP is created when a traditional Lewis acid-base adduct is prevented from forming due to steric constraints on either species, leaving them “frustrated”, or able to react with molecules such as dihydrogen in a concerted manner. Work has predominantly included the use of boron/aluminum-containing Lewis acids and nitrogen/phosphorus-containing Lewis bases. While less investigated, the use of N-heterocyclic carbenes as frustrated Lewis bases offers many advantages towards rational design of an FLP. N-heterocyclic carbenes (NHCs) have quickly surpassed phosphines as some of the most useful ligands for catalysis. Strong σ-donating and π-accepting abilities of the divalent carbon atom has led to prevalence of NHCs in traditional transition metal catalysis. Additionally, their modifiable backbone and substituents (and consequently easy steric and electronic tuning) makes them prime candidates for use in FLP chemistry. This work seeks to combine the carbene’s affinity for transition metals with the additional possibility for FLP-generated molecule activation by preparing a series of N-borane substituted NHCs. We propose that bulky, Lewis-acidic substituents at nitrogen will affect catalytic activity in the following ways: π-acceptance of the carbene can be tuned through addition of a Lewis-base (such as F-) to the borane centers; bulkiness of these substituents will make a kinetically stable (“persistent”) carbene and may increase catalytic turnover at a metal center; and presence of both Lewis-acidic and basic sites on the molecule will create the potential for intramolecular FLP chemistry

Name

Comment*

Comments are viewable only by submitter

Captcha*