Furthering the reactivity of low-nuclearity N-heterocyclic carbene supported copper(I) complexes

Abstract

This thesis focuses on the synthesis of N-heterocyclic carbene (NHC) supported copper(I) complexes and their bond-breaking and bond-forming reactivity. The body of this work discusses new (NHC)copper(I) hydride dimers, the electrophilic fluorination of (NHC)copper(I) vinyls, and the nitrosylation of (NHC)copper(I) sulfide complexes. First, the expanded-ring N-heterocyclic carbenes 6Dipp and 7Dipp (6Dipp = 1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetra-hydropyrimidin-2-ylidene and 7Dipp = 1,3-bis(2,6-diisopropyl-phenyl)-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene) are shown to support isolable neutral copper hydride dimers. [(6Dipp)CuH]2 reacts with 1-hexene to give (6Dipp)copper(I) hexyl by 1,2-insertion, and with benzyl isonitrile to afford an η1-formimidoyl by 1,1-insertion. Next, we show that the electrophilic fluorination of (NHC)copper(I) vinyls results in fluoroalkene formation. Alkynes can be converted to cis-(β-fluorovinyl)boronates by reaction with an (NHC)copper(I) boryl generated in situ, followed by N-fluorobenzenesulfonimide (NFSI). This sequence gives rise to anti-Markovnikov fluorination products from terminal alkynes. Oxidation of a cis-(β-fluorovinyl)trifluoroboronate yields an α-fluoroketone, whereas a palladium-catalyzed Suzuki-Miyuara coupling yields a tetrasubstituted monofluoroalkene. Lastly, the reactivity of a series of copper(I) sulfide complexes stabilized by the expanded-ring N-heterocyclic carbene 7Dipp, towards nitrosonium (NO+) is shown. 7Dipp is shown to support neutral sulfide- and disulfide-bridged dicopper(I) complexes, in addition to a mononuclear copper(I) hydrosulfide. Addition of NO+ to each of these results in the formation of NHC-supported copper(I) cations and elemental sulfur. Concomitant decomposition of copper(I) to Cu0 upon reaction of NO+ with the dicopper(I) sulfide or disulfide is observed, whereas ammonium ion formation is observed upon reaction of the copper(I) hydrosulfide with NO+. Ammonium ion formation is likewise observed upon reaction of NO+ with (7Dipp)copper(I) hydride.