This thesis deals with thiocarbonyl complexes of ruthenium and osmium [LnM-CS]. In chapter 1 a comprehensive review of all transition metal thiocarbonyl complexes is presented. Unlike carbon monoxide, carbon monosulphide is a highly reactive molecule which does not exist under normal laboratory conditions. However, transition metal complexes of this reactive intermediate are typically stable compounds of which there are now approximately two hundred reported examples. This small number has made a complete review possible. Slow spasmodic growth has accompanied transition metal thiocarbonyl chemistry since the prototype complex was discovered in 1966 and chapter 1 discusses the synthetic reasons for this, describes critically the current bonding models, and presents the reactions of thiocarbonyl complexes. The very new field of the chemistry of selenocarbonyl complexes [LnM-CSe] is included and comparison with this and with the well-documented chemistry of carbonyl complexes allows for an analysis of periodic changes. The review indicates that CS ligand reactions had received little attention at the outset of this project. Interligand reactions involving CS were unknown primarily because thiocarbonyl complexes containing ligands suitable for investigating reactions of this type had not been synthesised. In particular, transfer of hydrido or aryl ligand to CS had not been observed. Such reactions are the subjects of chapters 3 and 6. The investigation of these transfer reactions necessitated the prior preparation of complexes containing hydrido or aryl ligands cis to the thiocarbonyl ligand. Suitable complexes were synthesised from the very versatile synthetic intermediate OsCl2 (CS) (PPh3)3 [Chapter 3], which was discovered after considerable effort had been devoted to finding high yield routes for introducing the CS ligand into the coordination sphere of ruthenium and osmium [Chapter 2]. Chapter 3 is concerned with hydride transfer to the CS ligand. The thioformyl ligand [OS-C-H-S] results from the transfer of one hydrido ligand to CS and subsequent reactions, which are also probably hydride transfers, produce the thioformaldehyde [Os-S-C-H-H] and methylthiolato [Os-SCH3] ligands. The possible relevance of these ligands as models for postulated intermediates in the Fischer-Tropsch synthesis is noted. The thioformyl and thioformaldehyde ligands were hitherto unknown and the formulations have been additionally verified by investigating the reactivity of these novel ligands and characterising the derivatives obtained. A synthetic route to secondary carbine complexes and to nitrogen and oxygen equivalents of the thioformyl ligand [Os-C-H—NMe and Os-C-H—O] is demonstrated. The review in chapter 1 also recounts how observation has shown that strong σ-donor and strong π-acceptor properties of the CS ligand exert a profound effect upon the reactivity of CS complexes. In particular, strong π-acceptor properties mark the CS ligand as an ideal candidate for stabilising very electron-rich metal centres such as d8 ruthenium(O) or osmium(O). In chapter 4 high yield routes to zerovalent osmium thiocarbonyl complexes are detailed and the reactivity of these complexes is exploited to afford the first high yield syntheses of dithiocarbonyl complexes. The thiocarbonyl ligand is also viewed, from the collected information in chapter 1, as being more responsive to the coordinative environment than the better-known carbonyl ligand. Thus, while CS can remove more electron-density from basic metal centres than CO, CS can also donate more electron-density than CO when coordinated to very electron-poor metal centres. Consequently, it is not surprising that reactions which have been regarded in a classical sense as electrophilic or nucleophilic attack at CO are also found for CS. In chapter 5 several novel reactions which can be described as nucleophilic attack at the CS carbon atom are reported for both neutral and cationic complexes. One such reaction is an interligand reaction of cis thiocarboxamido and thiocarbonyl ligands which affords a four-membered osmium metallocycle. Chapter 6 describes how coordinatively unsaturated aryl-thiocarbonyl-containing complexes react with potentially bidentate anionic ligands to produce coordinatively saturated complexes. coordinative saturation also occurs with carbon monoxide or isocyanide and these latter compounds undergo a rearrangement reaction which involves the thiocarbonyl ligand. Available evidence, which includes the results of an incomplete X-ray crystal structure determination, suggests that a bidentate thioacyl ligand [Os-S-C-R] is produced by transfer of the aryl ligand to CS with ring-closure. Some further reactions of this novel ligand are also discussed. In conclusion, the work reported here extends this research group’s interest in the chemistry of low valent transition metal compounds and the ligands which stabilise such compounds to thiocarbonyl complexes of ruthenium and osmium. The present status of the chemistry of transition metal thiocarbonyl complexes has been examined and the work presented in the experimental chapters contributes to this small area of chemistry by examining, for the first time, interligand reactions which involve CS, by providing synthetic routes to CS complexes of osmium(O), and by beginning to examine the synthetic potential of the novel compounds and ligands obtained.
| Identifer | oai:union.ndltd.org:ADTP/276082 |
| Date | January 1977 |
| Creators | Collins, Terence James |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | 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 |
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