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Abstract
This thesis describes investigations into the catalysed syntheses of amines and imines using organoiridium and organorhodium complexes with N-donor ligands as the catalysts. These catalysed syntheses were achieved via hydroamination, hydrosilylation, and hydrogenation reactions, as well as tandem hydroamination/imine reduction reactions.
An in situ catalysis study found that the most active catalysts for the hydroamination of 4-pentyn-1-amine (1) to give 2-methyl-1-pyrroline (4) were formed from a combination of catalyst components that resulted in an electron deficient metal centre, indicating that an alkyne binding mechanism was most likely. The kinetics of the hydroamination of 4-pentyn-1-amine (1), catalysed by the complexes [Rh(bim)(CO)2][BPh4] (7), [Ir(bim)(CO)2][BPh4] (8), [Rh(bpm)(CO)2][BPh4] (9), and [Ir(bpm)(CO)2][BPh4] (10) (bpm = bis(1-pyrazolyl)methane and bim = bis(Nmethylimidazol-2-yl)methane) were modelled and compared. The nature of the metal centre was found to have the most influence on the rate of the product release step, while the nature of the N-donor ligand was found to have the most influence on the rate
of the substrate binding step. The investigation of the catalysed hydroamination of the phenyl substituted alkynylamines 5-phenyl-4-pentyn-1-amine (2), 4-phenyl-3-butyn-1-amine (13) and 2-phenyl-4-pentyn-1-amine (34) revealed a difference in catalytic activity between the rhodium and iridium complexes depending on the alkyne substituent. A series of novel rhodium(I) complexes were synthesised: [RhClCO(Mes-DAD(Me))] (38), [RhClCO(Mes-BIAN)] (22), [Rh(COD)(Mes-BIAN)][BF4] (39), [Rh2(COD)2(bmimen)](BPh4)2 (40) and [Rh2(CO)4(bmimen)](BPh4)2 (41), where Mes-DAD(Me) = biacetylbis(2,4,6-trimethylphenylimine), Mes-BIAN = bis(2,4,6-trimethylphenylimino)acenapthene and bmimen = 1,2-bis[(1-methyl-2-imidazolyl)methylene-amino]ethane. The cationic complex 40 was found to be an active hydroamination catalyst, while the neutral complexes 38 and 22 were only active in the presence of the tetraphenylborate counterion.
A range of imines was found to be efficiently reduced to their respective amines via hydrosilylation or hydrogenation using the iridium(I) complex [Ir(bpm)(CO)2][BPh4](10) as catalyst. The hydrosilylation reaction was found to be significantly faster in a protic solvent (methanol), giving the desilylated amines without the need for a desilylation step. The mechanism of this reaction was proposed to involve a monohydride iridium(I) complex as a key intermediate. The tandem hydroamination/hydrosilylation of a series of alkynylamine substrates was achieved using the iridium complexes 8 and 10, in which the iridium complex catalyses the two mechanistically distinct reactions in the one-pot. Catalysed tandem hydroamination/hydrogenation reactions were also achieved, but were less facile.