Synthesis of new N-heterocyclic carbene metal complexes

This thesis describes the synthesis of new N-heterocyclic carbene complexes through the synthesis of 1,4-bis-substituted imidazolium salts or tricyclic saturated imidazolium salts. The introduction highlights some of the most successful methods for preparing N-heterocyclic carbenes and corresponding metal complexes. Examples of the use of these complexes in transition metal-catalysed processes are provided towards the end of this chapter. The second chapter is dedicated to our efforts to synthesize 1,4-bis-substituted imidazolium salts as precursors for the synthesis of N-heterocyclic carbene complexes. The first part of this chapter describes the synthesis of 1,4-bis-substituted imidazolium salts using 1,4-bis-substituted diazabutadienes. Following this, attempts to deprotonate imidazolium salts to afford the desired N-heterocyclic carbenes are discussed. On the basis of the results obtained for the synthesis of 1,4-bis-substituted imidazol-2-ylidenes, the synthesis of N-heterocyclic carbene complexes, where the carbene is generated in situ are explored at the end of this chapter. The synthesis of enantiomerically pure tricyclic saturated imidazolium salts via enantiomerically pure diamines is discussed in the third chapter. Firstly, different methods were tested for the preparation of diamines from 6,6'-dimethyl-2,2'-bipyridine, 2,2'-biquinoline and (S,S)-6,6-bis-(1-methoxy-2,2'-dimethylpropyl)-2,2'-bipyridine. Following this, is reported the synthesis of tricyclic saturated imidazolium salts. Suzuki cross coupling of 4-chlorotoluene with phenylboronic acid was investigated in the presence of different imidazolium salts. This chapter concludes with a few suggestions for the synthesis of enantiomerically pure 2,6-bipiperidines. The fourth chapter is the experimental section and is dedicated to the methods of synthesis and characterization of the compounds mentioned in the previous chapters. X-ray reports regarding the crystallographic representation of the structures presented in chapter two and three are provided in chapter five.