A structural, electrochemical and kinetic investigation of fluorinated and metallocene-containing phosphines and their rhodium complexes

English: Metallocene-containing ligands, as well as their rhodium(I) complexes, were synthesized and their physical properties examined. Four known metallocene-containing β-diketones, FcCOCH2COR with R = CF3, Fc, Rc and Oc, were synthesized, as well as a range of metallocene-containing phosphine ligands, including the known PPh2Fc, and the new ligands PPh2Rc, PPh2Oc and the positively-charged (PPh2Cc+)(PF6 -). The new rhodium(I) dicarbonyl complexes [Rh(FcCOCHCOR)(CO)2], where R = CF3, Fc, Rc and Oc, were synthesized as starting materials for rhodium(I) phosphine complexes. Electron-rich phosphine complexes, containing metallocenyl-phosphines of the type [Rh(FcCOCHCOCF3)(CO)(PPh2Mc)], where Mc = Fc and Rc, as well as the known complex [Rh(FcCOCHCOCF3)(CO)(PPh3)], were synthesized. A series of electron-poor phosphine complexes containing pentafluorophenyl rings substituted on the phosphine ligand of the type [Rh(FcCOCHCOCF3)(CO){PPhn(C6F5)3-n}], with n = 0, 1 and 2, were also synthesized. Crystal structures of FcCOCH2COOc, PPh2Rc and [Rh(FcCOCHCOCF3)(CO)(PPh2Fc)] were solved. The oxidative addition (the first, rate determining step of the Monsanto process to form acetic acid) of methyl iodide to above mentioned rhodium(I) phosphine complexes were followed kinetically by UV, FT-IR, 1H NMR, 31P NMR and 19F NMR. Results showed that oxidative addition proceeded by up to three consecutive reaction steps, involving two Rh(III) alkyl and two Rh(III) acyl species. NMR results also showed the existence of at least two isomers of each Rh(III) alkyl and acyl species in the reaction mixture. Large variations in rate constant were observed. The rate of reaction for [Rh(FcCOCHCOCF3)(CO)(PPh2Rc)] {χR(Rc) =1.99, k1 = 0.015 dm3 mol-1 s-1} was found to be about double that of [Rh(FcCOCHCOCF3)(CO)(PPh2Fc)] {χR(Fc) = 1.87, k1 = 0.0075 dm3 mol-1 s-1}, with [Rh(FcCOCHCOCF3)(CO)(PPh3)] {χR(Ph) = 2.21, k1 = 0.006 dm3 mol-1 s-1} slightly slower. Rates of reaction for fluorinated compounds were dramatically slower, due to the highly electron-withdrawing pentafluorophenyl groups attached. [Rh(FcCOCHCOCF3)(CO){PPh2(C6F5)}] (k2 = 0.0003 dm3 mol-1 s-1) showed rates of reaction of up to 20x slower than that of [Rh(FcCOCHCOCF3)(CO)(PPh3)], with [Rh(FcCOCHCOCF3)(CO){PPh(C6F5)2}] (k2 = 0.000010 dm3 mol-1 s-1) showing rates of reaction 600x slower. [Rh(FcCOCHCOCF3)(CO){P(C6F5)3}] did not undergo oxidative addition at all. Acetylacetonato ligands substituted with a tetrathiafulvalene group in either the α- or the β-position of the β-diketone were complexed with rhodium(I) cyclooctadiene complexes to form [Rh(cod)(β-diketone)]. The substitution reaction of the TTF-containing β- diketonato ligand with 1,10-phenanthroline was investigated by stopped-flow methods due to the high rate of reaction for these compounds (k2 = 1 x 10 3 dm3 mol-1 s-1). A full electrochemical study was carried out on all synthesized complexes in CH2Cl2 / 0.1 mol dm-3 [NnBu4][B(C6F5)4] as solvent and supporting electrolyte. Where appropriate, spectro-electrochemical investigations were also performed. This study was also the first to develop techniques able to investigate slow kinetics electrochemically. The reaction used to develop these techniques was the isomerization from enol to keto form of the β- diketone RcCOCH2COFc. All newly synthesized compounds were tested for anti-tumor activity. It was found that the pentafluorophenyl group is a powerful anti-tumor fragment with significant synergism in [Rh(FcCOCHCOCF3)(CO){P(C6F5)3}]. Group electronegativity (χR) is the determining factor for cytotoxicity, in the absence of synergistic effects. An increase in group electronegativity leads to an increase in cytotoxicity. TTF-containing ligands also showed significant activity, but rhodium(I) complexes thereof had no effect.