The new 16-electron ruthenium compounds (v5-C5Me5)Ru(L)CI [(l), L = PPri,; (2), L = PCy3) (Cy = cyclohexyl) were prepared from [ ( ~p -C ~M e ~) R u C l l ~ and PPri3 or PCy3, respectively, and the X-ray crystal structure of (1) has been determined; reactions of the title compounds with CO, C2H4, pyridine, and PhSiH3 are described.A plethora of mechanistic and synthetic information has been reported regarding compounds of the type (qS-CSHS)FeL2X, and related Ru and 0 s systems. 1 In many instances reactive 16-electron intermediates formed via thermal or photoinduced dissociation of L play an important role in the chemistry of these species.2 Here we report the preparation, characterization, and initial reactivity studies of stable, co-ordinatively unsaturated 'half sandwich' compounds (qs-CsMeS) Ru( PR3)Cl.Combination of methylene chloride solutions of PR3 [4 equiv.; R = Pri or Cy, (Cy = cyclohexyl)] and [(qs-CSMeS)-RuC1I43 (1 equiv.) at room temperature produced an immediate colour change from dark orange to deep blue. The highly crystalline 16-electron complexes (q~-CSMeS)Ru(L)C1 [(1), L = PPri,; (2), L = PCy3] were isolated as blue crystals from pentane in 92 and 82% yields, respectively (equation 1).Both reactions are quantitative in [zH,]benzene by IH n.m.r. spectroscopy. Compounds (1) and (2) were charac-and R u C ~] ~.
The Au(III) complex Au(OAc(F))2(tpy) (1, OAc(F) = OCOCF3; tpy = 2-p-tolylpyridine) undergoes reversible dissociation of the OAc(F) ligand trans to C, as seen by (19)F NMR. In dichloromethane or trifluoroacetic acid (TFA), the reaction between 1 and ethylene produces Au(OAc(F))(CH2CH2OAc(F))(tpy) (2). The reaction is a formal insertion of the olefin into the Au-O bond trans to N. In TFA this reaction occurs in less than 5 min at ambient temperature, while 1 day is required in dichloromethane. In trifluoroethanol (TFE), Au(OAc(F))(CH2CH2OCH2CF3)(tpy) (3) is formed as the major product. Both 2 and 3 have been characterized by X-ray crystallography. In TFA/TFE mixtures, 2 and 3 are in equilibrium with a slight thermodynamic preference for 2 over 3. Exposure of 2 to ethylene-d4 in TFA caused exchange of ethylene-d4 for ethylene at room temperature. The reaction of 1 with cis-1,2-dideuterioethylene furnished Au(OAc(F))(threo-CHDCHDOAc(F))(tpy), consistent with an overall anti addition to ethylene. DFT(PBE0-D3) calculations indicate that the first step of the formal insertion is an associative substitution of the OAc(F) trans to N by ethylene. Addition of free (-)OAc(F) to coordinated ethylene furnishes 2. While substitution of OAc(F) by ethylene trans to C has a lower barrier, the kinetic and thermodynamic preference of 2 over the isomer with CH2CH2OAc(F) trans to C accounts for the selective formation of 2. The DFT calculations suggest that the higher reaction rates observed in TFA and TFE compared with CH2Cl2 arise from stabilization of the (-)OAc(F) anion lost during the first reaction step.
The interest in organogold compounds continues to grow. Gold(III) complexes are being investigated as catalysts for organic transformations as well as tested as potential anti-cancer drugs. Despite this wide-ranging interest in the properties of such complexes, the synthetic methods for preparing them are underdeveloped. Thus, Chapter 2 discusses the synthesis of cyclometalated gold(III) complexes bearing the C-N chelating ligand 2-(p-tolyl)pyridine (tpy). Monoalkylation andarylation were possible by use of Grignard reagents, whereas alkyl and aryl lithium reagents gave the dialkylated and diarylated gold(III) complexes. By a combination of the two alkylation procedures, mixed alkyl/aryl complexes of the type AuMePh(tpy) were obtained and both isomers were available. Chapter 3 discusses the reactivity of the cyclometalated gold(III) complexes towards different gases such as carbon monoxide and oxygen. Most of the cyclometalated gold(III) complexes prepared react with acids. The monoalkylated and-arylated complexes of the type AuBrR(tpy) (R = Me, Et, CHCH 2 , CCH, Ph) react with silver(I) salts to give a potential open coordination site at gold(III). Ethylene formally inserts into the Au-O bond trans to nitrogen in the chelating C-N ligand of the complex Au(OCOCF 3) 2 (tpy) (62) in trifluoroacetic acid or dichloromethane, to yield Au(CH 2 CH 2 OCOCF 3)(OCOCF 3)(tpy) (94). In trifluoroethanol, a slightly different complex resulted due to nucleophilic attack by trifluoroethanol rather than trifluoroacetate, Au(CH 2 CH 2 OCH 2 CF 3)(OCOCF 3)(tpy) (95). The mechanism of the insertion was investigated experimentally as well as computationally and the results are discussed in Chapter 4. The formal insertion takes place with alkenes other than ethylene, and alkynes react too. A key step in the catalytic reactions involving gold(III) is assumed to be the coordination of a CC multiple bond to the gold centre. Various catalytic cycles involving a gold(III) π-complex have been proposed. However, gold(III) alkene, alkyne, allene, or arene complexes have until recently not been conclusively detected and characterised. Chapter 5 discusses the first, and thus far only, crystallographically characterised gold(III) alkene complex, Au(cod)Me 2 BArF (133-BArF, BArF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, cod = 1,5-cyclooctadiene).
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