Studies of Ruthenium and Osmium Silyl Complexes

by Maddock, Susan Marie

Abstract (Summary)
Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. Transition metal-silicon chemistry is an interesting and rewarding area of study. Many advances have been made in recent years which contribute to our understanding of the bonding in transition metal-silicon complexes and the role they play in various catalytic cycles. This thesis is concerned with the synthesis and reactivity of new silicon complexes of ruthenium and osmium. Chapter One presents a review of transition metal-silicon chemistry, covering the bonding, methods of synthesis and reactivity of transition metal-silyl complexes. Part of this thesis concerns the effects on the metal-silicon bond of varying the ancillary ligands on the metal. A number of the new compounds which are described in Chapter Two contain p-tolylisocyanide as an ancillary ligand, therefore, a brief summary of transition metal isocyanide chemistry is also covered in Chapter One. In Chapter Two new coordinatively unsaturated complexes of formula M(SiR3)Cl(CNptoyl)(PPh3)2 (M=Ru, Os) are described. These complexes were synthesized by reaction of a metal hydride (MH2(CNp-tolyl)(PPh3) or MHCl(CNp-tolyl)(PPh3)3) and a hydridohalosilane. The reactivity of these chlorosilyl complexes with nucleophiles such as water and ethanol are described. A trimethylsilyl complex Ru(SiMe3)Cl(CNp-tolyl)(PPh3)2, was synthesized from a vinylsilane and RuHC1(CNp-tolyl)(PPh3)3, X-ray crystal structures of Ru(SiMe3)Cl(CNp-tolyl)(PPh3)2, Ru(siCl3)Cl(CNp-tolyl)(PPh3)2 and Ru[Si(OEt)3]Cl(CNp-tolyl)(PPh3)2, were obtained. The five coordinate complexes react with small neutral donor ligands such as CO to form six coordinate complexes. Three isomers of Ru(SiCl3)Cl(CNp-tolyl)(CO)(PPh3), were obtained. The X-ray crystal structure of the most thermodynamically stable isomer is described. A preliminary investigation into the reactivity of the newly developed isocyanide complexes RuHCl(CNp-tolyl)(PPh3)3 and OsHCl(CNp-tolyl)(PPh3)3 is described in Chapter Three. These compounds react with diphenylmercury to form five coordinate complexes of formula MClPh(CNp-tolyl)(PPh3)2 which undergo a novel reaction with dioxygen. The crystal structure of the dioxygen adduct OsCl(?2-C[Ph]Np-tolyl)(?2-O2)(PPh3)2" resulting from the reaction of OsClPh(CNp-tolyl)(PPh3)2 with dioxygen is described. The five coordinate complexes, OsClPh(CNp-tolyl)(PPh3)2, react with both neutral ligands such as CO and anionic ligands such as acetate to form coordinatively saturated complexes of formula OsClPh(CNp-tolyl)(CO)(PPh3)2 and Os(ph)(?2-O2CCH3.)(CNp-tolyl)(PPh3)2 respectively. On reaction of RuClPh(CNp-tolyl)(PPh3)2 and CO, coordination of the sixth ligand is followed by a migratory insertion reaction to generate RuCl(?2-C[Ph]Np-tolyl)(CO)(PPh3)2. Reaction of RuClPh(CNp-tolyl)(PPh3)2 with CNp-tolyl, followed by addition of HCI affords a carbine complex, RuCl2(CNp-tolyl)(C[Ph]NHp-tolyl)(PPh3)2. RuClPh(CNp-tolyl) (PPh3)2, reacts with di-2-thienylmercury and DMF to form RuCl(C4H3S)(DMF)(CNp-tolyl) (PPh3)2. Reaction of this compound with HCl results in protonation of the ring and formation of RuCl2(C4H4S)(CNp-tolyl)(PPh3)2. The crystal structure of this has been determined. Both OsClPh(CO)(PPh3)2 and OsClPh(CNp-tolyl)(PPh3)2 react with dimethylacetylenedicarboxylate to form novel complexes in which the phenyl group has migrated onto the coordinated alkyne. The crystal structure of the carbonyl-containing compound is described. In addition to substitution by ethoxy and hydroxy groups at silicon, substitution reactions involving other oxygen nucleophiles are described in Chapter Four. A tosyl group can be placed on silicon by reaction of Os[SiMe2(OEt)Cl(CO)(PPh3)2, and toluenesulfonic acid. Phenoxy and catecholate groups can be substituted for chloride by reaction of a compound bearing a chlorosilyl group, with phenol or catechol in the presence of base. Fluorosilyl complexes of formula M(SiMenF3-n)Cl(CO)(PPh3)2, (M=Ru, Os; n=0, l, 2) can be made by the reaction of aqueous HF with ethoxysilyl complexes. The X-ray crystal structure of Os(SiF3)Cl(CO)(PPh3)2, has been determined. The strong M-Si bond in these fluorosilyl complexes enables ligand exchange to occur at the metal centre without disruption of the M-Si bond. Successful reactions have been carried out with sodium iodide and sodium formate. Decarboxylation of the formate derivative Os(SiF3)(?2-O2CH)(CO)(PPh3)2, leads to the silylhydrido complex Os(SiF3)H(CO)(PPh3)3. Chapter Five begins with a review of transition metal catalysed hydrosilylation, focusing on the hydrosilylation of alkynes in particular. Reaction of the five coordinate silyl complexes Ru(SiR3)Cl(CO)(PPh3)2 (SiR3=SiMe2(OEt), SiMe3, SiEt3, SiPh3) with acetylene gives products arising from insertion of the alkyne into the metal-silicon bond- The thermodynamically stable product having trans geometry at the double bond is isolated. These five coordinate complexes react with CO to form six coordinate complexes. The X-ray crystal structure of Ru[CH=CHSiMe2(OEt)]Cl(CO)2(PPh3)2 has been determined. However, reaction of Ru[siMe2(OH)Cl(CO)(PPh3)2 results in isolation of Ru[CH=CHSiMe2(OH)]Cl(CO)(PPh3)2, in which the hydroxysilyl oxygen is bound to the metal. This compound was characterised principally by the synthesis of derivatives. Reaction with AgClO4 removes the chloride ligand and forms the cationic product [Ru{CH=CHSiMe2(OH)}(NCMe)(CO)(PPh3)2]ClO4. The labile acetonitrile ligand can be substituted with CO or p-tolylisocyanide. These compounds can then be deprotonated to form Ru(CH=CHSiMe2O)(CO)(L)(PPh3)2 (L=CO, CNp-tolyl). Insertion of alkynes into M-Si bonds is believed to be a key step in some transition metal catalysed hydrosilylations and Ru(SiEt3)Cl(CO)(PPh3)2, is found to be a catalyst for the hydrosilylation of acetylene and phenylacetylene. The products arising from hydrosilylation were analysed by 1H-NMR and G.C./M.S. Based on the observation of the insertion reaction and the silyl group exchange reaction, a catalytic cycle for the hydrosilylation is proposed. Chapter Six briefly outlines some routes to the formation of bis(silyl) transition metal complexes. The reaction of RuCl2(PPh3)3 with HSiCl3, which is believed to result in formation of a bis(silyl) ruthenium complex, is reinvestigated. Reaction of this compound (formulated as [Ru(siCl3)2(PPh3)2]) with CO gives Ru(SiCl3)2(CO)2(PPh3)2. The X-ray crystal structure of this compound has been determined.
Bibliographical Information:


School:The University of Auckland / Te Whare Wananga o Tamaki Makaurau

School Location:New Zealand

Source Type:Master's Thesis



Date of Publication:01/01/1995

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