Organometallic chemistry is concerned with the study of metal-carbon bonded species. A wide variety of bonding modes have been discovered ranging from simple σ- through to more complex π- and μ-interactions. This thesis deals with the synthesis and chemistry of just three classes of compound, those containing formal TM-C single, double and triple bonds. These species are normally referred to as transition metal alkyl (σ-aryl), carbene and carbyne complexes respectively. The material is divided into five chapters and each is introduced by a relevant review. In chapter 1 the syntheses of σ-alkyl and -aryl complexes of ruthenium and osmium are described. These species are produced from organomercury reagents either by oxidative addition to the zerovalent complex Ru(CO)₂(PPh₃) ₃ or by reaction with the hydrido complexes MClH(CO)(PPh₃) ₃ (M = Ru, Os). This latter reaction provides a new route to organotransition metal complexes and some possible mechanisms are discussed. The organo-complexes formed by this latter method are coordinatively unsaturated and the structure of RuCl(p-tolyl)(CO)(PPh₃)₂ has been obtained by X-ray crystallography. The migratory insertion and reductive elimination reactions of these new compounds are discussed in chapters 2 and 3. Predictably, the Lewis base CO rapidly adds to these 16 electron species and the expected octahedral derivatives are formed. In some cases these are in equilibrium in solution with the corresponding dihapto-acyl complexes. The positions of the equilibria, the rates of interconversion and the relative solubilities of the two forms are such that in each case either essentially pure dicarbonyl or essentially pure dihapto-acyl can be isolated from solution. The dihapto-mode of bonding has been confirmed by X-ray crystallography for two of the derivatives. CNp-tolyl also adds to the 16 electron organo-compounds in an analogous fashion and equilibrium with the corresponding dihapto-iminoacyl compounds is attained in some cases. The dihapto-iminoacyl formulation has been confirmed by X-ray crystallography. Factors affecting the positions of all these equilibria are discussed and the possible relevance of these dihapto-acyl and -iminoacyl complexes as models for the proposed intermediates in the CO and CNR insertion reactions is noted. Compounds containing cis-H,R ligands are rarely stable since reductive elimination of R-H usually occurs very readily. Species of this type, therefore, appear to be ideal precursors for reactive, low valent complexes which are unobtainable by other means. A synthetic route has been developed by which an hydrido ligand can be incorporated into the coordination sphere of the new organo-derivatives described in chapter 1. The key step involves the thermal decarboxylation of a dihapto-formate ligand. In this way remarkably stable cis-H, tolyl complexes of osmium have been prepared. Toluene is eliminated from these derivatives only under forcing conditions. In contrast, reductive elimination from the analogous ruthenium complexes proceeds much more rapidly and in only one case has a stable hydrido, aryl complex been isolated. Other compounds that have been formed by this route are the zerovalent complex Ru(CO)(dppe)₂ and the ortho-metallated complex Ru(C6H₄PPh₂)H(CO)(PPh₃)₂. Factors affecting the rates of all these reactions are discussed. Some reactions of Ru(C₆H₄PPh₂)H(CO)(PPh₃)₂ have been investigated, and most notably a methyl, formate complex is produced with formaldehyde and a small amount of a dichlorocarbene complex with CCl₄. The reactions of this ortho-metallated compound may proceed via the intermediate "Ru(CO)(PPh₃)₃". Extension of the synthetic procedure described in chapter 1 has led to the production of the dichlorocarbene complex OsCl₂ (CO)(CCl₂)(PPh₃)₂, the structure of which has been determined by X-ray crystallography. This compound, which formally contains an Os-Ccarbene double bond, provides the subject matter for chapter 4. The carbene carbon atom is attacked by nucleophiles and the chloride substituents are easily displaced. This species therefore behaves as a remarkably versatile synthetic intermediate. Reaction with the chalcogen hydrides HX⁻ (or H₂X) leads to the corresponding chalcocarbonyl derivatives and OsCl₂ (CO)(CTe)(PPh₃)₂ is the first tellurocarbonyl complex to be isolated. Characterization of this complex includes an X-ray crystallographic analysis. Primary mines react with OsCl₂ (CO)(CCl₂)(PPh₃)₂ to form the corresponding coordinated isocyanides and reactions with other nucleophiles are also discussed. The most important of these, however, is the reaction with Li(p-tolyl). This produces the monomeric carbyne complex, Os(Cp-tolyl)Cl(CO)(PPh₃)₂, the structure of which has been determined by X-ray crystallography. This compound has an extremely short Os-Ccarbyne bond length and this is consistent with a triple bond formulation. The synthesis and chemistry of this compound is discussed in chapter 5. Although other carbyne complexes have been isolated previously this is a relatively new area of organometallic chemistry and reports of the chemistry of these species are restricted mainly to compounds of the GpVIa and VIIa metals. Os(Cp-tolyl)Cl(CO)(PPh₃)₂ displays a rather different chemistry from these compounds and some new reactions have been observed. Electrophiles such as H₊ and Cl₂ readily attack Ccarbyne and the corresponding carbene complexes are formed. This suggests that Ccarbyne is nucleophilic. The elements S, Se and Te add to the Os-Ccarbyne triple bond under ambient conditions to give the corresponding dihapto-chalcoacyl complexes. Adducts of the Os-Ccarbyne triple bond are also formed with the GpIb metals and the structure of Os(C{p-tolyl}AgCl)Cl(CO)(PPh₃)₂ has been determined by X-ray crystallography. Analogues of all these reactions are to be found in acetylene chemistry. In contrast to the cationic carbyne complexes of the GpVIa and VIIa metals, Ccarbyne in [Os(Cp-tolyl)(CO)₂ (PPh₃)₂]ClO₄ is not attacked by nucleophiles. Instead LiBHEt₃ preferentially attacks the para-carbon atom of the Ccarbyne p-tolyl substituent and an Os(O) vinylidene complex is formed. The structure of this compound has been confirmed by X-ray crystallography. Although the aromatic ring is destroyed in this reaction it is replaced by an extensively conjugated system which reaches through to the osmium atom. Further reactions of this species and the cationic carbyne complex [Os(Cp-tolyl)(CO)(CNp-tolyl)(PPh₃)₂]ClO₄ are also discussed. / Note: Whole document restricted due to copyright restrictions, but available by individual request use the feedback form to request access.
| Identifer | oai:union.ndltd.org:ADTP/276113 |
| Date | January 1980 |
| Creators | Wright, Leonard James |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Whole document restricted but available by request. Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
Page generated in 0.0022 seconds