A structural, electrochemical and kinetic investigation of fluorinated and metallocene-containing phosphines and their rhodium complexes
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Date
2008-03
Authors
Fourie, Eleanor
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
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.
Afrikaans: Metalloseenbevattende ligande, sowel as hul rodium(I)-komplekse, is gesintetiseer en hul fisiese eienskappe bestudeer. Vier bekende metalloseenbevattende β-diketone, FcCOCH2COR met R = CF3, Fc, Rc en Oc, is gesintetiseer, sowel as die reeks PPh2Fc, PPh2Rc, PPh2Oc en die positief gelaaide (PPh2Cc+)(PF6 -) metalloseenbevattende fosfien ligande. Die voorheen onbekende rodium(I)-dikarbonielkomplekse [Rh(FcCOCHCOR) (CO)2], met R = CF3, Fc, Rc en Oc, is gesintetiseer as uitgangstof vir die sintese van rodium(I)-fosfienkomplekse. Nuwe elektronryk metalloseen-bevattende fosfienkomplekse, [Rh(FcCOCHCOCF3)(CO) (PPh2Mc)], met Mc = Fc en Rc, sowel as die bekende [Rh(FcCOCHCOCF3)(CO)(PPh3)], is gesintetiseer. ‘n Reeks elektronarm komplekse, wat pentafluoorfenielringe op die fosfienligande bevat, [Rh (FcCOCHCOCF3)(CO){PPhn(C6F5)3-n}] met n = 0, 1 en 2, is ook gesintetiseer. Die kristalstrukture van FcCOCH2COOc, PPh2Rc en [Rh(FcCOCHCOCF3)(CO)(PPh2Fc)] is opgelos. Die oksidatiewe addisiereaksie (die snelheidsbepalende eerste stap van die Monsantoproses vir die sintese van asynsuur) van metieljodied aan die bogenoemde rodium(I)- fosfienkomplekse is bestudeer met behulp van UV, FT-IR, 1H KMR, 31P KMR en 19F KMR. Resultate het gewys dat oksidatiewe addisie tot drie opeenvolgende stappe behels. Twee Rh(III)-alkiel- en twee Rh(III)-asielspesies is waargeneem. KMR-data het verder minstens twee isomere van elke Rh(I)-alkiel en -asielspesie geïdentifiseer. Groot verskille in die oksidatiewe addisiereaksiesnelhede is waargeneem. Die reaksietempo vir [Rh(FcCOCHCOCF3)(CO)(PPh2Rc)] {χR(Rc) = 1.99, k1 = 0.015 dm3 mol-1 s-1} is ongeveer dubbel die van [Rh(FcCOCHCOCF3)(CO)(PPh2Fc)] {χR(Fc) = 1.87, k1 = 0.0075 dm3 mol-1 s-1}, met [Rh(FcCOCHCOCF3)(CO)(PPh3)] {χR(Ph) = 2.21, k1 = 0.006 dm3 mol-1 s-1} se snelheid effens stadiger. Die reaksietempo’s vir fluoorbevattende komplekse was a.g.v. die sterk elektron-onttrekkende uitwerking van die pentafluoorfenielringe dramaties stadiger. Die tempo van [Rh(FcCOCHCOCF3) (CO){PPh2(C6F5)}] (k2 = 0.0003 dm3 mol-1 s-1) was ongeveer 20x stadiger as die van [Rh(FcCOCHCOCF3)(CO)(PPh3)], terwyl [Rh(FcCOCHCOCF3)(CO){PPh(C6F5)2}] (k2= 0.000010 dm3 mol-1 s-1) ongeveer 600x stadiger was. Die kompleks [Rh (FcCOCHCOCF3)(CO){P(C6F5)3}] het geen oksidatiewe addisie ondergaan nie. Asetielasetonatoligande wat in of die α- of die β-posisie gesubstitueer is met ‘n tetrathiafulvaleen-groep, is met rodium(I)-siklooktadieen gekomplekseer om [Rh(cod)(β- diketoon)] te gee. Die substitusiereaksies van die β-diketonato-ligande met 1,10- fenantrolien is bestudeer met behulp van stopvloeitegnologie, a.g.v. die hoë reaksietempos (k2 = 1 x 10 3 dm3 mol-1 s-1). ‘n Volledige elektrochemiese studie is uitgevoer op alle gesintetiseerde verbindings in CH2Cl2 / 0.1 mol dm-3 [NnBu4][B(C6F5)4] as oplosmiddel en hulpelektroliet. Waar van toepassing, is spektro-elektrochemiese studies ook uitgevoer. Hierdie studie was ook die eerste wat in staat was om tegnieke daar te stel waarmee kinetika van stadige reaksies elektrochemies bestudeer kan word. Die reaksie wat gekies is om die tegniek te ontwikkel was die isomerisasie van enol- na keto-vorms van die β-diketoon RcCOCH2COFc. Sitotoksiese toetse is op alle nuwe verbindings uitgevoer. Daar is gevind dat die pentafluoorfenielring ‘n kragtige antitumor-fragment is met beduidende sinergisme in [Rh(FcCOCHCOCF3)(CO){P(C6F5)3}]. Groepelektronegatiwiteite (χR) is die bepalende faktor vir die voorspelling van die sitotoksisiteit verbindinge. In die afwesigheid van sinergistiese effekte dui hoër groepelektronegatiwiteit op hoër sitotoksisiteit. Tatrathiafulvaleen-bevattende ligande het ook sitotoksiese aktiwiteit getoon, maar nie rodium(I)-komplekse daarvan nie.
Afrikaans: Metalloseenbevattende ligande, sowel as hul rodium(I)-komplekse, is gesintetiseer en hul fisiese eienskappe bestudeer. Vier bekende metalloseenbevattende β-diketone, FcCOCH2COR met R = CF3, Fc, Rc en Oc, is gesintetiseer, sowel as die reeks PPh2Fc, PPh2Rc, PPh2Oc en die positief gelaaide (PPh2Cc+)(PF6 -) metalloseenbevattende fosfien ligande. Die voorheen onbekende rodium(I)-dikarbonielkomplekse [Rh(FcCOCHCOR) (CO)2], met R = CF3, Fc, Rc en Oc, is gesintetiseer as uitgangstof vir die sintese van rodium(I)-fosfienkomplekse. Nuwe elektronryk metalloseen-bevattende fosfienkomplekse, [Rh(FcCOCHCOCF3)(CO) (PPh2Mc)], met Mc = Fc en Rc, sowel as die bekende [Rh(FcCOCHCOCF3)(CO)(PPh3)], is gesintetiseer. ‘n Reeks elektronarm komplekse, wat pentafluoorfenielringe op die fosfienligande bevat, [Rh (FcCOCHCOCF3)(CO){PPhn(C6F5)3-n}] met n = 0, 1 en 2, is ook gesintetiseer. Die kristalstrukture van FcCOCH2COOc, PPh2Rc en [Rh(FcCOCHCOCF3)(CO)(PPh2Fc)] is opgelos. Die oksidatiewe addisiereaksie (die snelheidsbepalende eerste stap van die Monsantoproses vir die sintese van asynsuur) van metieljodied aan die bogenoemde rodium(I)- fosfienkomplekse is bestudeer met behulp van UV, FT-IR, 1H KMR, 31P KMR en 19F KMR. Resultate het gewys dat oksidatiewe addisie tot drie opeenvolgende stappe behels. Twee Rh(III)-alkiel- en twee Rh(III)-asielspesies is waargeneem. KMR-data het verder minstens twee isomere van elke Rh(I)-alkiel en -asielspesie geïdentifiseer. Groot verskille in die oksidatiewe addisiereaksiesnelhede is waargeneem. Die reaksietempo vir [Rh(FcCOCHCOCF3)(CO)(PPh2Rc)] {χR(Rc) = 1.99, k1 = 0.015 dm3 mol-1 s-1} is ongeveer dubbel die van [Rh(FcCOCHCOCF3)(CO)(PPh2Fc)] {χR(Fc) = 1.87, k1 = 0.0075 dm3 mol-1 s-1}, met [Rh(FcCOCHCOCF3)(CO)(PPh3)] {χR(Ph) = 2.21, k1 = 0.006 dm3 mol-1 s-1} se snelheid effens stadiger. Die reaksietempo’s vir fluoorbevattende komplekse was a.g.v. die sterk elektron-onttrekkende uitwerking van die pentafluoorfenielringe dramaties stadiger. Die tempo van [Rh(FcCOCHCOCF3) (CO){PPh2(C6F5)}] (k2 = 0.0003 dm3 mol-1 s-1) was ongeveer 20x stadiger as die van [Rh(FcCOCHCOCF3)(CO)(PPh3)], terwyl [Rh(FcCOCHCOCF3)(CO){PPh(C6F5)2}] (k2= 0.000010 dm3 mol-1 s-1) ongeveer 600x stadiger was. Die kompleks [Rh (FcCOCHCOCF3)(CO){P(C6F5)3}] het geen oksidatiewe addisie ondergaan nie. Asetielasetonatoligande wat in of die α- of die β-posisie gesubstitueer is met ‘n tetrathiafulvaleen-groep, is met rodium(I)-siklooktadieen gekomplekseer om [Rh(cod)(β- diketoon)] te gee. Die substitusiereaksies van die β-diketonato-ligande met 1,10- fenantrolien is bestudeer met behulp van stopvloeitegnologie, a.g.v. die hoë reaksietempos (k2 = 1 x 10 3 dm3 mol-1 s-1). ‘n Volledige elektrochemiese studie is uitgevoer op alle gesintetiseerde verbindings in CH2Cl2 / 0.1 mol dm-3 [NnBu4][B(C6F5)4] as oplosmiddel en hulpelektroliet. Waar van toepassing, is spektro-elektrochemiese studies ook uitgevoer. Hierdie studie was ook die eerste wat in staat was om tegnieke daar te stel waarmee kinetika van stadige reaksies elektrochemies bestudeer kan word. Die reaksie wat gekies is om die tegniek te ontwikkel was die isomerisasie van enol- na keto-vorms van die β-diketoon RcCOCH2COFc. Sitotoksiese toetse is op alle nuwe verbindings uitgevoer. Daar is gevind dat die pentafluoorfenielring ‘n kragtige antitumor-fragment is met beduidende sinergisme in [Rh(FcCOCHCOCF3)(CO){P(C6F5)3}]. Groepelektronegatiwiteite (χR) is die bepalende faktor vir die voorspelling van die sitotoksisiteit verbindinge. In die afwesigheid van sinergistiese effekte dui hoër groepelektronegatiwiteit op hoër sitotoksisiteit. Tatrathiafulvaleen-bevattende ligande het ook sitotoksiese aktiwiteit getoon, maar nie rodium(I)-komplekse daarvan nie.
Description
Keywords
Rhodium(I), Ferrocene, Phosphine, β-diketone, Oxidative addition, Substitution kinetics, Electrochemistry, Group electronegativity, Phosphine -- Synthesis, Phosphorus compounds, Organorhodium compounds, Thesis (Ph.D. (Chemistry))--University of the Free State, 2008