Resorcin[4]arene based N-heterocyclic carbenes as catalysts for carbon-carbon formation

Ngodwana, Lonwabo (2016-12)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Resorcin[4]arenes are 3-dimensional cyclic tetramers belonging to a class of compounds called cyclophanes. Because of their properties, including several sites of functionalization and possession of a cavity, these compounds found their way into several applications. These include cation extraction, ion exchange mimics, molecular switches and catalysis. The latter is still at its infancy. This work was aimed at developing the first examples of resorcin[4]arene based Nheterocyclic carbene (NHC) complexes of palladium and evaluating their potential for catalysis of carbon-carbon bond formatting reactions. Using an ortholithiation technology that was developed in our group, a distally functionalized resorcin[4]arene di-ester was prepared. The reduction of the ester and bromination of the resulting di-ol led to a distal bromomethylresorcin[4]arene. The reactions of this new resorcin[4]arene with a variety of N-alkylimidazoles gave a small library of resorcin[4]arene imidazolium NHC precursor salts. Initially, the preparation of a bidentate palladium complex from the salts was attempted. The metal complex was isolated in 35% yield from an N-mesityl imidazolium salt. When the preparation of a dinuclear metal complex series, i.e. PEPPSI, was attempted, the compounds in this class could be isolated in yields over 90%. Although these compounds show the expected coordination modes (square-planer Pd center), they showed some variations in solid state conformations. Resorcin[4]arene NHC compounds, both pre-formed and prepared in situ, were evaluated for catalytic ability in the Suzuki-Miyauri and Tsuji-Trost reactions. These compounds could facilitate moderate to complete conversion of starting materials to products.

AFRIKAANSE OPSOMMING: Resorsin[4]arene is 3-demensionele sikliese tertramere wat behoort aan ‘n klas verbindings genaamd siklofage. As gevolg van hulle eienskappe, onder andere ‘n menigte hoeveelheid funksionele groepe as ook ‘n molekulêre holte, het hierdie klas verbindings verskeie toepassings. Van hierdie toepassings sluit in katioon ekstraksie, ioonuitruiling nabootsing, molekulêre aanskakelaars en kataliese. Die laasgenoemde punt is nogsteeds in die vroeë stadium van navorsing. Die werk beoog om die eerste voorbeelde van resorsin[4]areen gebaseerde Nheterosikliese karbeen (NHK) komplekse met palladium te ontwikkel, gevolg deur die komplekse se potensiaal vir koolstof-koolstof bindingsvorming reaksies te evalueer. Deur die gebruik van orto-litiëring tegnologie wat ontwikkel is in ons groep is ‘n distaal gefunksioniseerde resorsin[4]areen di-ester gesintetiseer. Na die reduksie van die ester en gevolglike bromering van die diol was n distaal bromometielresorsin[4]arene geskep. Reaksies met hierdie nuwe resorsin[4]areen met ‘n verskeidenheid N-alkielimidasole het ‘n klein versameling van resorsin[4]areen imidasolium NHK voorloper soute gelewer. Aanvanklik was die poging om ‘n bidentate palladium kompleks van hierdie soute te sintetiseer. Die gebruik van ‘n sekere N-mesitiel imidasolium sout het gelei na ‘n metaal kompleks was geïsoleer is met ‘n opbrengs van 35%. Voorbereiding van ‘n dinukliêre metal kompleks soos PEPPSI het gelei tot die isolering van hierdie klas verbindings met n opbrengs van 90% en meer. Alhoewel hierdie verbindings die regte koördinasie toon (vierkantig-planêr Pd sentrale atoom) is daar variasies gevind in die soliede staat konformasies. Resorsin[4]areen NHK verbindings wat óf vooraf gesintetiseer is óf direk in situ berei is was geëvalueer vir katalietiese eienskappe in die Suzuki-Miyauri en Tsuji-Trost reaksies. Hierdie verbindings het matig tot volledige omskakeling van begin produk na eind produk getoon.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100377
This item appears in the following collections: