The synthesis of aminomethylphosphines, their metal complexes and their use in homogeneous catalysis.

Chapter 1 reviews the literature concerning synthetic routes to amino- methylphosphines and studies of their reactivity together with a brief review of related aminoethylphosphines and isostructural tertiary phosphine analogues to aminomethylphosphines. The preparation and characterisation of the phosphonium salts [R2P(CH2 OH)2]+X- (R = Ph, Cy, C8H14; X- = C1-, HSO4-) and the preparation and characterisation of aminomethylphosphines are presented in Chapter 2. Treatment of the mixed isomers of the salt [C8H14P(CH2OH)2]+X- in boiling sulphuric acid gives the 3,3,1 isomer by decomposition of the 4,2,1 isomer. The X-ray crystal structure of [PH2P(CH2OH)2]+C1- shows hydrogen bonding between the hydroxyl groups and chlorine anion. Treatment of the reported phosphonium salts with triethylamine and a primary or secondary amine gave aminomethylphosphines in good yields. The 1H, 13C and 31P n.m.r. spectra are reported for all important aminomethylphosphines. The novel nature of the 1H n.m.r. signals for the methylene protons, in the PCH2N link of these phosphines have been investigated using two-dimensional (31P-1H) (HSC) n.m.r. and variable temperature n.m.r. spectra. The X-ray crystal structure of (Cy2PCH2) 2NCHMePh reveals the bulky nature of the phosphine and the relationship between the methylene protons and phosphorus in the solid state. In Chapter 3 a variety of transition metal complexes have been prepared using aminomethylphosphines of the type (R2PCH2) 2NR' reported in Chapter 2. The preparation and characterisation of cis platinum(II), palladium(II) and nickel (II) dichloride complexes is described together with the X-ray crystal structure of cis-[PdC12 (Ph2PCH2) 2NCH2CH2OH] which shows the phosphine in a six-membered chelate chair conformation. Cobalt(II) dichloride, and molybdenum(0) and tungsten(0) tetracarbonyl complexes of the bis-amino- methylphosphines are also prepared and characterised. Treatment of [Rh (COD)Cl]2 with a phosphine in the presence of KPF6 gave hydrogenation catalyst precursors of the type [Rh(COD) (R2PCH2)2NR'] PF6 in good yields. Treatment of the cis-Pt(II) aminomethylphosphine complexes with SnC12 gave [PtC1(SnCl3)(R2PCH2)2NR'] complexes which displayed poor solubility. Reactions of the phosphine (Cy2PCH2) 2NCHMePh with various metal complexes have been investigated, as have some reactions of Pt(II) dichloride, diphosphine complexes. The last Chapter investigates the use of Rh(I) and Pt(II) aminomethylphosphine complexes in catalytic hydrogenation and hydroformylation. The catalytic hydrogenation of ?-acetamidocinnamic acid using [Rh(COD)- (R2PCH2) 2NR'] +PF6-catalyst precursors at 1.1 atmospheres of H2, gave N-acetylphenylalanine in good yields but only as racemic mixtures. The hydroformylation of styrene at 100 atmospheres of CO/H2 and at 60°C using a [PtCl2(R2PCH2)2NR'] + SnCl2 catalyst system gave low yields of 2-phenylpro-panal with optical inductions of up to 31% and high branched to chain product ratios, up to 36:1. Phosphines with R = Cy showed no reaction and phosphines with R = C6H14 gave better yields but higher ratios of 3-phenyl-propanal (chain product).