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The solution behavior and reactivity of some triarylphosphine complexes of ruthenium

University of British Columbia

This thesis describes the results of re-investigations into the solution behavior and interaction with molecular hydrogen of several triarylphosphine and -arsine complexes of ruthenium(ll) and ruthenium(III) The complex RuCl₂(PPh₃)₃ was found to exist in N,N-dimethyl-acetamide (DMA) solutions in equilibrium with, a triply chloro-bridged bis(phosphine) dimer, I (L = DMA). Addition of chloride ion caused [Figure 1] substitution of the solvent to form an anionic dimer, I (L = CI ), and this is discussed, with respect to the stability of this bridging arrangement. In the presence of added base, Proton Sponge® (1,8-bis(dimethyl- amino)naphthalene) , the complexes RuX₂YL₂ (X = Y = CI, Br, or X = CI, Br, Y = 0₂CR; L = PPh₃, Ptol₃, or AsPB₃), [RuCl₂ (PPh₃)₂]₂, [RuCl(DMA)(PPh₃)₂(0₂CCH₂)]₂, and HRuCl(nbd)(PPh₃)₂ were found to react with H₂ in DMA or toluene to give complexes of the form [H₂RuXL₂]₂ (X = CI, Br). The ruthenium(III) product. [H₂RuCl(Ptol₃)₂]₂ has been characterized by analytical, molecular weight, ¹H- and ³¹P-n.m.r. methods and chemical reactions, and the data indicate an asymmetric dichloro-bridged dimer, II. The reaction of II with Ptol₃ in DMA to form HRuCl(Ptol₃)₃ has been studied kinetically; the results suggest that II is in equilibrium with the ruthenium(ll) dimer, [HRuClCPtol₃)₂]₂. The reaction between RuCl₂(PPh₃)₃ and H₂ in DMA to form HRuCl(PPh₃)₃ has also been re-investigated. In the presence of a large excess of PPh₃, the reaction is believed to proceed by way of a bis(phosphine) monomer species, consistent with previous findings. However, in the presence of excess chloride, where the precursor exists as I (L = CI⁻), spectrophotometry evidence indicates the presence of a long-lived intermediate. Investigations .of the v corresponding bis (phosphine) complex, [RuCl₂(PPh₃)₂]₂, have made it possible to formulate the nature of the intermediate. Based mainly on ³¹P-n.m.r. and hydrogen uptake data, the intermediate is believed to be H₃Ru₂Cl₃(PPh₃)₄, a cogener of II. This allows for an overall scheme for the tris(phosphine) system under the conditions of excess chloride: [Figure 2] A similar scheme can be invoked to explain the reactivity of the bis-(phosphine) system. Investigations of the corresponding reactivity toward H₂ of other bis(phosphine) systems for comparison led to the discovery of a new method of preparing carboxylato complexes. Based on a presumed, but not detected, alkyl intermediate, it was possible to prepare the dimer [RuCl(DMA)(PPh₃)₂(O₂CCH₂]₂, containing a bridging succinic acid linkage, and a series of RuCl(0₂CR)(PPh₃)₃ complexes. These have been characterized and their reactivity towards in toluene investigated. At concentrations sufficiently high for n.m.r. studies, the tris(phosphine) species react with to form HRuCl(PPh₃)₃ by a pathway involving initial formation of HRu(₂CR) (PPh₃)₃. The bis (phosphine) system, [RuCl(DMA)(PPh₃)₂(O₂CCH₂)]₂, forms the tetrahydride dimer, II, but the mechanism of formation could not be elucidated. The nature of HRuCl(nbd)(PPh₃)₂ has be en examined; the species possesses the coplanar arrangement of metal, hydride, and olefin deemed requisite for olefin insertion reactions. Indeed, reaction with CO gives an acyl-dicarbonyl derivative, III, which results from consecutive olefin and CO insertion reactions. The HRuCl(nbd)(PPh₃)₂ complex reacts [Figure 3] cleanly with hydrogen in the absence of added base in toluene to form [H₂RuCl(PPh₃)₂]₂. Studies show that the reaction proceeds by a disproportionate reaction to form HRuCl(PPh₃)₃ and subsequent conproportionation with an unobserved phosphine deficient species to form the final product.

Text

2010-05-02

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http://hdl.handle.net/2429/24282

Chemistry

University of British Columbia

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