This thesis describes new catalytic reactions, new activation methods and new ligand derivatives based on chromium lV,N-bis(diarylphosphino)amine (PNP) olefin trimerisation catalysts. Chapter 1 presents an introduction to this area. The main differences between non-selective olefin olig.omerisation and selective trimerisation are discussed, as well as the commercial uses of LAOs. The mechanism of trimerisation and a survey of successful catalyst systems is given, with particular emphasis on PNP ligands. More recent advances such as selective tetramerisation are discussed. Chapter 2 describes the use of chromium PNP catalysts for the cotrimerisation of ethene and other alkene monomers, particularly styrene. The effect of temperature, reaction time, comonomer concentration and ligand structure are investigated and a mechanism scheme is proposed. The cotrimerisation .of ethene and styrene was found to form phenylhexene, with the ligand 1 system giving predominantly I-phenylhexene isomers 50 and 51, with a TOF of 2468 h-I. Other PNP ligands tested gave 3-phenylhexene isomers 55 and 56. The trimerisation of isoprene using the same chromium PNP systems is explored in Chapter 3. Using the ligand 1 system, the trimerisation of isoprene produced isomers of 2,6,11-trimethyldodecatetraene, 1,5,1 O-trimethyl-l ,5,9cyclododecatriene and higher isoprene oligomers, with a productivity of 826 g (g Cr hrl . Other PNP ligands tested produced the same products as ligand 1 with differing productivities. Some of the results from these two chapters have been published.93.130 Chapter 4 describes the use of chromium(I) PNP carbonyl complexes for the oligomerisation of ethene. The syntheses and structures of [Cr(CO)4(1)], [Cr(CO)4(19)], [Cr(CO)4(5)] and [Cr(CO)4(NO)(1)] are reported. These compounds were then tested for ethene trimerisation by activation with an oxidising agent with a weakly coordinating anion, [N(p-BrC6fu)3][B(C6Fs)4] and a CO scavenger, AlEt3. The results from this chapter have been published.16o A series of novel PNP and dppe based ligands with ortho oxygen donors on the phenyl rings were also synthesised and tested for ethene trimerisation, as described in Chapter 5. Finally Chapter 6 gives experimental details for the preceding chapters.
|Date of Award||2008|