published_or_final_version / Chemistry / Master / Master of Science

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This thesis will explore and study rhodium, a group VIII element that has rarely been studied.

The work reported in this thesis is concerned with two separated but related studies. The first involved examination of hydrogenation reactions of alkenes, dienes and alkynes using (Rh[sub]2C1(CO)[sub]2(dppm)[sub]2JBPh[sub]4 as a catalyst. Kinetic studies have been performed on the reaction of hexene. The system only well-behaved in the presence of a base, R[sub]3N, where a rst order dependance on both catalyst and hydrogen concentations observed. The order with respect to alkene is of the Michaelis-Menton type. This behaviour suggests that the active catalyst is a neutral monohydride generated by deprotonation of a ionic dihydride. It is proposed that the active catalyst is a dinuclear species, since none of the likely mononuclear breakdown oducts shows any catalytic activity. A catalytic cycle for the reaction is proposed. The second study was an investigation into the use of fast atom bombardment (FAB) mass spectrometry as a means of anaylsis organometallic compounds which have proved difficult to identify using other ionisation modes. The technique was shown to informative spectra for a series of dinuclear rhodium-dppm mplexes and some dinuclear manganese carbonyl derivatives. FAB ionisation also proved effective for identification of phosphine and phosphite derivatives of [RCC0[sub]3(CO)[sub]9.] (R=CH[sub]3, C1). The technique was also combined with thin layer chromatography (TLC) in examining a reaction of [Mo(CO)[sub]6.] with Ph[sub]2P(CH[sub]2)[sub]2P(O)Ph[sub]2 (dppeO) which yields a mixture of seven products. It was found that good spectra of pure materials could be obtained TLC separation, followed by removal of the appropriate section silica support from the plate. This was subjected directly to FAB mass spectrometry without prior extraction of the product from silica. Using this technique, it proved possible to identify three new dppeO derivatives of [Mo(CO)[sub]4 (dppeO) derivatives of [Mo(CO)[sub]6. These are [Mo(CO)[sub]5 (dppeO)] cis-[Mo(CO)[sub]4 (dppeO)[sub]2] and [Mo[sub]2(CO)[sub] 4 (dppeO)[sub]2].

A highly enantioselective and diastereoselective rhodium-catalysed addition of potassium allyltrifluoroborates to cyclic imines is described within. By utilising rhodium-chiral diene complexes, a wide range of cyclic imines were successfully allylated in high yields and enantioselectivities. Using a variety of more highly substituted allyl reagents, additional stereocentres and further molecular complexity was achieved with good yields, enantioselectivities and diastereoselectivities. Investigations involving isomeric allyl species and deuterated allyl species provided results that gave mechanistic insight, leading to the proposal of a plausible mechanistic pathway and suggested the formation of interconverting allylrhodium intermediates. Furthermore, during these investigations, a highly interesting isomerisation of the allylrhodium intermediate was discovered. Such isomerisation led to the in situ formation of the more complex allylrhodium intermediates which led to complex products upon allylation with cyclic imines that would be difficult to synthesis via other methods. This isomerisation was found to occur for a range of cyclic imines and disubstituted allyltrifluoroborates, proceeding in good yields and diastereomeric ratios. Deuterium studies indicate it is probable that this isomerisation proceeds via a 1,4 rhodium migration and a plausible mechanism is proposed explaining both the connectivity of the products and the relative stereochemistry.

Luminescent organotransition metal complexes are of much current interest. As the large spin-orbit coupling of 2nd and 3rd row transition metals usually leads to rapid intersystem crossing from S1 to T1, which enables phosphorescence, there is a special interest in using triplet-emitting materials in organic or organometallic light emitting diodes (OLEDs). Marder et al. have found that, reductive coupling of both para-R-substituted diarylbutadiynes and diaryldodecatetraynes on Rh(PMe3)4X leads to quantitative yields of bis(arylethynyl)-rhodacyclopentadienes with complete regiospecificity (R = BMes2, H, Me, OMe, SMe, CF3, CN, CO2Me, NMe2, NO2, C≡C-TMS and X = -C≡C-TMS, -C≡C-C6H4-4-NMe2, -C≡C-C≡C-C6H4-4-NPh2, Me, Cl).47,49 Unexpectedly, these compounds show intense fluorescence rather than phosphorescence (ɸf = 0.33-0.69, t = 1.2 3.0 ns). The substituent R has a significant influence on the photophysical properties, as absorption and emission are both bathochromically shifted compared to R = H, especially for R = π-acceptor. To clarify the mechanism of the formation of the rhodacyclopentadienes, and to investigate further their unique photophysical properties, a series of novel, luminescent rhodacyclopentadienes with dithiocarbamate as a bidentate ligand at the rhodium centre has been synthesised and characterised (R = NO2, CO2Me, Me, NMe2, SMe, Ar = C6F4-4-OMe). The rhodacyclopentadienes have been formed via reductive coupling of diaryl undecatetraynes with [Rh(k2-S,S`-S2CNEt2)(PMe3)2]. The structures of a series of such compounds were solved by single crystal X-ray diffraction and are discussed in this work. The compounds were fully characterised via NMR, UV/Vis and photoluminescence spectroscopy as well as by elemental analysis, high-resolution mass spectrometry (HRMS) and X-ray diffraction. When heating the reactions, another isomer is formed to a certain extent. The so-called dibenzorhodacyclopentadienes already appeared during earlier studies of Marder et al., when acetylacetonate (acac) was employed as the bidentate ligand at the Rh-centre. They are probably formed via a [4+2] cycloaddition reaction and C-H activation, followed by a β-H shift. Use of the perfluorinated phenyl moiety Ar = C6F4-4-OMe provided a total new insight into the mechanism of formation of the rhodacyclopentadiene isomers and other reactions. Besides the formation of the expected rhodacyclopentadiene, a bimetallic compound was generated, isolated and characterised via X-ray crystallography and NMR spectroscopy, elemental analysis and high resolution mass spectrometry. For further comparison, analogous reactions with [Rh(k2 S,S` S2CNEt2)(PPh3)2] and a variety of diaryl undecatetraynes (R = NO2 CO2Me, Me, NMe2, SMe, Ar = C6F4-4-OMe) were carried out. They also yield the expected rhodacyclopentadienes, but quickly react with a second or even third equivalent of the tetraynes to form, catalytically, alkyne cyclotrimerisation products, namely substituted benzene derivatives (dimers and trimers), which are highly luminescent. The rhodacyclopentadienes (R = NO2, CO2Me, Me, SMe, Ar = C6F4-4-OMe) are stable and were isolated. The structures of a series of these compounds were obtained via single crystal X-ray crystallography and the compounds were fully characterised via NMR, UV/Vis and photoluminescence spectroscopy as well as by elemental analysis and HRMS. Another attempt to clarify the mechanism of formation of the rhodacyclopentadienes involved reacting a variety of diaryl 1,3-butadiynes (R = CO2Me, Me, NMe2, naphthyl) with [Rh(k2 S,S` S2CNEt2)(PMe3)2]. The reactions stop at an intermediate step, yielding a 1:1 trans π-complex, confirmed by single crystal X-ray diffraction and NMR spectroscopy. Only after several weeks, or under forcing conditions (µw / 80 °C, 75 h), the formation of another major product occurs, having bound a second diaryl 1,3-butadiyne. Based on earlier results of Murata, the product is identified as an unusual [3+2] cycloaddition product, ϭ-bound to the rhodium centre. / Lumineszierende Übergangsmetallkomplexe sind aktuell sehr gefragt. Da die starke Spin-Bahn-Kopplung von Übergangsmetallen der zweiten und dritten Reihe zu einem schnellen Inter-System-Crossing führt, und damit zu Phosphoreszenz, gilt der Verwendung Triplett-emittierender Materialien in organischen und organometallischen Licht emittierenden Dioden (OLEDs) besonders großes Interesse. Marder et al. fanden heraus, dass die reduktive Kupplung von para R-substituierten Diarylbutadiinen und Diaryldodecatetraynen an Rh(PMe3)4X zu quantitativen Ausbeuten von Bis(Arylethinyl)-Rhodacyclopentadienen führt (R = BMes2, H, Me, OMe, SMe, CF3, CN, CO2Me, NMe2, NO2, C≡C-TMS and X = -C≡C-TMS, -C≡C-C6H4-4-NMe2, -C≡C-C≡C-C6H4-4-NPh2, Me, Cl), wobei sich nur ein Regioisomer bildet. Überaschenderweise zeigen diese Verbindungen intensive Fluoreszenz an Stelle von Phosphoreszenz (ɸf = 0.33-0.69, t = 1.2 3.0 ns). Der Substituent R hat großen Einfluss auf die Lumineszenz Eigenschaften. Die Absorption sowie Emission sind im Vergleich zu R = H jeweils bathochrom verschoben, wobei der Effekt im Fall von R = π-Akzeptor stärker ausgeprägt ist. Um den Bildungsmechanismus der Rhodacyclopentadiene aufzuklären und ihre einzigartigen Lumineszenz Eigenschaften intensiver zu untersuchen, wurde eine Reihe von neuen, lumineszierenden Rhodacyclopentadienen mit dem bidentaten Liganden Dithiocarbamat am Rhodium-Zentrum dargestellt und charakterisiert (R = NO2, CO2Me, Me, NMe2, SMe, Ar = C6F4-4-OMe). Die Rhodacyclopentadiene entstanden durch reduktive Kupplung von Diarylundecatetrainen mit [Rh(k2-S,S`-S2CNEt2)(PMe3)2]. Die Strukturen einiger solcher Verbindungen wurden mit Hilfe von Röntgenstrukturanalyse gelöst und werden in der vorliegenden Arbeit diskutiert. Die Verbindungen wurden mit Hilfe von NMR, optischer Spektroskopie, sowie Elementaranalyse, hochauflösender Massenspektrometrie (HRMS) und Röntgenstrukturanalyse vollcharakterisiert. Wurden die Reaktionen erhitzt, bildete sich zu einem gewissen Anteil ein anderes Isomer. Das sogenannte Dibenzorhodacyclopentadien tauchte bereits während früherer Untersuchungen von Marder et al. auf, wobei Acetylacetonat (acac) als bidentater Ligand am Rh-Zentrum eingesetzt wurde. Diese werden möglicherweise durch eine [4+2] Zykloaddition und eine C-H Aktivierung, gefolgt von einem β-H Shift gebildet. Reaktionen die mit dem perfluorierten Phenylrest Ar = C6F4-4-OMe durchgeführt wurden, ermöglichten völlig neue Einblicke in den Bildungsmechanismus der Isomere der Rhodacyclopentadiene und anderer Reaktionen. Neben der Bildung des erwarteten Rhodacyclopentadiens, entstand eine bimetallische Verbindung, welche isoliert und mittels Röntgenstrukturanalyse, NMR-Spektroskopie, Elementaranalyse und HRMS charakterisiert wurde. Um weitere Vergleiche anzustellen, wurde analoge Reaktionen mit einer Reihe von Diarylundecatetrainen (R = NO2 CO2Me, Me, NMe2, SMe, Ar = C6F4-4-OMe) und [Rh(k2 S,S` S2CNEt2)(PPh3)2] durchgeführt. Diese führen ebenfalls zu den erwarteten Rhodacyclopentadienen, jedoch erfolgt schnelle Reaktion mit einem zweiten oder sogar dritten Äquivalent Tetrain um katalytisch Alkin-Trimerisierungsprodukte zu bilden, bei denen es sich um substituierte Benzolderivate (Dimere und Trimere) handelt. Diese sind stark lumineszierend. Die Rhodacyclopentadiene sind stabil und konnten isoliert werden. Von einigen Verbindungen konnten Röntgenstrukturanalysen durchgeführt werden. Alle isolierten Verbindungen wurden mittels NMR und optischer Spektroskopie, sowie Elementaranalyse und HRMS charakterisiert. Ein weiterer Ansatz um den Bildungsmechanismus der Rhodacyclopentadiene aufzuklären beinhaltete die Reaktion einer Reihe von Diarylbutadiinen (R = CO2Me, Me, NMe2, naphthyl) mit [Rh(k2 S,S` S2CNEt2)(PMe3)2]. Die Reaktionen stoppen an der Stelle eines Zwischenproduktes, bei dem es sich um einen 1:1 trans π-Komplex handelt, der mittels Röntgenstrukturanalyse und NMR Spektroskopie bestätigt werden konnte. Erst nach einigen Wochen oder unter harschen Reaktionsbedingungen (µw / 80 °C, 75 h), konnte die Bildung eines weiteren Produktes beobachten werden, an welches ein zweites Diarylbutadiin gebunden ist. Ausgehend von früheren Ergebnissen von Murata, wurde das Produkt als ein [3+2]-Zykloadditionsprodukt identifiziert.

This thesis describes a broad range of coordination and organometallic chemistry on a series of ruthenium and rhodium complexes towards the aim of activating unsaturated N Ξ N, C=O, and C=C bonds. The dinitrogen complex [RuTp(pzP)(N2)]BPh4 (5) (where Tp= tris(pyrazolyl)borate, and PzP= 1-(2-diphenylphosphinoethyl)pyrazole) was synthesized via displacement of the chloride ligand from the complex [RuTp(pzP)Cl] (1). It was found that N2 coordination proceeded through an unusual oxidation/reduction cycle with the Ru(III) intermediate, [RuTp(pzP)CI]BF4 (6), isolated upon reaction of 1 with AgBF4 in THF. Investigations of the coordination chemistry of the related Tp complex [RuTp(Bp)PPh3] (4) (where Bp= bis(pyrazolyl)borate), resulted in several unusual reactions occurring on the Bp chelate. Reaction of 4 with AgBF4 gave the unusual product [RuTp(BpF')PPh3] (6), which had the Bp B-hydride substituents replaced by fluoride substituents from the BF4 anion, (i.e. BpF,). Alternatively, reaction of 4 with AgOTf, or SOCb, led to the synthesis of the products [RuTp(BpoH)PPh3]OTf (34), and [RuTp(BpoH)PPh3]Cl (35), respectively, which have a single hydroxyl substituent substituted in place of the two B-hydrides to yield a highly unusual neutral borane chelate (BpOH). A series of ruthenium tris(pyrazolyl)methane (Tpm) complexes [RuTpm(PPh3)2Cl]BPh4 (44.BPh4) RuTpm(PPh3CI2] (46), [RuTpm(PPh3)2CI]BPh4 (44.BPh4) [RuTpm(PPh3)(MeCN)Cl]BPh4 (50), [RuTpm(PPh3HMeCN)](BF4)2 (51), [RuTpm(PPh3)(MeCNh](BF4)2 (52), and [RuTpm(MeCNhCI]BPh4 (54.BPh4) were synthesized. These complexes varied in the number of labile acetonitrile ligands they contained, the net charge of the complex, and the presence or absence of strongly coordinating phosphine coligands on the complex. The influence of these properties on the catalytic activity of the complexes for the transfer hydrogenation of acetophenone was investigated. It was shown that the net charge and number of labile MeCN donors on the complex had little influence on the activity of the catalyst. It was also observed that the catalyst [RuTpm(MeCN)2CI]BPh4 (54.BPh4), which does not contain a strongly coordinating PPh3 ligand, would rapidly decompose during catalysis. A series of bis(tert-butylthiomethyl)pyridyl (SNS tBU ) pincer complexes [Ru(SNStBU)(PPh3)Cb] (65), [Ru(SN StBU)(PPh3)(MeCN)CI]BPh4 (66), [Ru(SNStBU)(PPh3)(MeCN)2](BF4h (67), and [Ru(SNStBU)(MeCN)Cb] (68) were synthesized and their as catalysts for the transfer hydrogenation of acetophenone was investigated. The activity of these complexes for as transfer hydrogenation catalysts was shown to increase as the number of labile coligands on the complex increased, with an extremely high transfer hydrogenation activity obtained using 68. The catalytic activity of 68 is one of the fastest to be reported in the literature, achieving a superlative TOF (turnover frequency) of 87360 h- I. The coordination of SNStBu in 66 and the related complexes [Ru(SNS (MeCN)2CI]BPh4 (70), and [Ru(SNS)(MeCN)2CI]2[??-Ag(MeCN)2]2(BF4)4(71) was observed to yield a range of different conformational isomers. These isomers were studied in detail using low temperature NMR and 20 NOESY and COSY IH_1H correlation experiments. The complex 71 was also characterized crystallographically and was shown to have an unusual tetrametallic macrocyclic structure with two [Ru(SNS)(MeCN)2C1r moieties bridged by two [Ag(MeCN)2r ions through a chloro and thioether donor group. The hydrogenation of unsaturated olefinic bonds was achieved using a series of Rh N-heterocyclic carbene (NHC) complexes of the type [Rh(L)(COD)]BPh4 (where L= and NHC-pyrazolyl chelate). A series of NHC-pyrazoly ligands (L) were synthesized that contained varying degrees of steric bulk on the pyrazolyl and NHC donor group. The influence of these steric parameters on the rhodium complex structure and activity of the complexes as catalysts for the hydrogenation of styrene was investigated. It was found that increasing the steric bulk around Rh decreased the activity of the catalyst.

This thesis describes a broad range of coordination and organometallic chemistry on a series of ruthenium and rhodium complexes towards the aim of activating unsaturated N Ξ N, C=O, and C=C bonds. The dinitrogen complex [RuTp(pzP)(N2)]BPh4 (5) (where Tp= tris(pyrazolyl)borate, and PzP= 1-(2-diphenylphosphinoethyl)pyrazole) was synthesized via displacement of the chloride ligand from the complex [RuTp(pzP)Cl] (1). It was found that N2 coordination proceeded through an unusual oxidation/reduction cycle with the Ru(III) intermediate, [RuTp(pzP)CI]BF4 (6), isolated upon reaction of 1 with AgBF4 in THF. Investigations of the coordination chemistry of the related Tp complex [RuTp(Bp)PPh3] (4) (where Bp= bis(pyrazolyl)borate), resulted in several unusual reactions occurring on the Bp chelate. Reaction of 4 with AgBF4 gave the unusual product [RuTp(BpF')PPh3] (6), which had the Bp B-hydride substituents replaced by fluoride substituents from the BF4 anion, (i.e. BpF,). Alternatively, reaction of 4 with AgOTf, or SOCb, led to the synthesis of the products [RuTp(BpoH)PPh3]OTf (34), and [RuTp(BpoH)PPh3]Cl (35), respectively, which have a single hydroxyl substituent substituted in place of the two B-hydrides to yield a highly unusual neutral borane chelate (BpOH). A series of ruthenium tris(pyrazolyl)methane (Tpm) complexes [RuTpm(PPh3)2Cl]BPh4 (44.BPh4) RuTpm(PPh3CI2] (46), [RuTpm(PPh3)2CI]BPh4 (44.BPh4) [RuTpm(PPh3)(MeCN)Cl]BPh4 (50), [RuTpm(PPh3HMeCN)](BF4)2 (51), [RuTpm(PPh3)(MeCNh](BF4)2 (52), and [RuTpm(MeCNhCI]BPh4 (54.BPh4) were synthesized. These complexes varied in the number of labile acetonitrile ligands they contained, the net charge of the complex, and the presence or absence of strongly coordinating phosphine coligands on the complex. The influence of these properties on the catalytic activity of the complexes for the transfer hydrogenation of acetophenone was investigated. It was shown that the net charge and number of labile MeCN donors on the complex had little influence on the activity of the catalyst. It was also observed that the catalyst [RuTpm(MeCN)2CI]BPh4 (54.BPh4), which does not contain a strongly coordinating PPh3 ligand, would rapidly decompose during catalysis. A series of bis(tert-butylthiomethyl)pyridyl (SNS tBU ) pincer complexes [Ru(SNStBU)(PPh3)Cb] (65), [Ru(SN StBU)(PPh3)(MeCN)CI]BPh4 (66), [Ru(SNStBU)(PPh3)(MeCN)2](BF4h (67), and [Ru(SNStBU)(MeCN)Cb] (68) were synthesized and their as catalysts for the transfer hydrogenation of acetophenone was investigated. The activity of these complexes for as transfer hydrogenation catalysts was shown to increase as the number of labile coligands on the complex increased, with an extremely high transfer hydrogenation activity obtained using 68. The catalytic activity of 68 is one of the fastest to be reported in the literature, achieving a superlative TOF (turnover frequency) of 87360 h- I. The coordination of SNStBu in 66 and the related complexes [Ru(SNS (MeCN)2CI]BPh4 (70), and [Ru(SNS)(MeCN)2CI]2[??-Ag(MeCN)2]2(BF4)4(71) was observed to yield a range of different conformational isomers. These isomers were studied in detail using low temperature NMR and 20 NOESY and COSY IH_1H correlation experiments. The complex 71 was also characterized crystallographically and was shown to have an unusual tetrametallic macrocyclic structure with two [Ru(SNS)(MeCN)2C1r moieties bridged by two [Ag(MeCN)2r ions through a chloro and thioether donor group. The hydrogenation of unsaturated olefinic bonds was achieved using a series of Rh N-heterocyclic carbene (NHC) complexes of the type [Rh(L)(COD)]BPh4 (where L= and NHC-pyrazolyl chelate). A series of NHC-pyrazoly ligands (L) were synthesized that contained varying degrees of steric bulk on the pyrazolyl and NHC donor group. The influence of these steric parameters on the rhodium complex structure and activity of the complexes as catalysts for the hydrogenation of styrene was investigated. It was found that increasing the steric bulk around Rh decreased the activity of the catalyst.

Thesis (M. Sc.)--University of Hong Kong, 1972. / Includes a reprint of a paper entitled Crystal structure of Trichlorobis (tri-n-butylphosphine) trimethylphosphiterhodium (III), by F.H. Allen and others, from Chemical communications, 1970. Offset from typescript.