The decarbonylation of aldehydes using ruthenium porphyrins

• Main Author: Tarpey, Bláithín
• Language: English
• Published: 2010
• Subjects: Carbonyl compounds
• Online Access: http://hdl.handle.net/2429/23215

The topic of this thesis is the catalytic and stoichiometric decarbonylation of aldehydes. A carbonylation reaction, the reaction of RuTPP(n-Bu₃P)₂ with CO gas was also studied. A catalytic decarbonylation system, using RuTPP(PPh₃)₂ as catalyst plus added excess tri-n-butylphosphine in acetonitrile-dichloromethane, was employed to decarbonylate several organic aldehydes. This system proved to be an effective decarbonylation agent, which also exhibited some selectivity. Some mechanistic studies were carried out in an attempt to elucidate the details of the reaction mechanism. From these and other findings in this laboratory, a tentative mechanism was proposed for the decarbonylation reaction. A radical mechanism, involving Ru(III) intermediates was favoured on the basis of e.s.r. data, spectral evidence and cyclic voltammetry studies. However, no intermediates were isolated. The full details of the mechanism, such as the precise nature of the postulated intermediates, have not been fully determined, although there are indications that solvated species, like RuTPP(CO)(CH₃CN), may be important. The stoichiometric reaction between RuTPP(n-Bu₃P)₂ and phenylacetaldehyde was also studied. The kinetic analysis indicated that the reaction, equation i, RuTPP(n-Bu₃P)₂ + C₆H₅CH₂CH0 --> RuTPP(CO)(n-Bu₃P) + n-Bu₃P + C₆H₅CH₃ equation i followed a pseudo-first-order rate law in the absence of excess phosphine, however, the actual k obsd values were found to be irreproducible. Some features of this reaction, such as the failure of the reaction to go to completion, and also the effect of trace oxygen on the reaction were investigated. The carbonylation of RuTPP(n-Bu₃P)₂ by CO gas was of interest, with respect to the catalytic reaction, which seems to involve pretreatment with CO (or aldehyde) to form a phosphine monocarbonyl. The reaction was found to follow a simple dissociative mechanism, which is similar to that observed for analogous M(porp)L₂, where M = Ru or Fe. A K value of 0.054 at 26°C was obtained and individual rate constants were calculated also. The temperature dependence of K was used to find the thermodynamic parameters ΔS° and ΔH° for the reaction. Some electrochemical studies were performed on RuTPP(n-Bu₃P)₂ and the corresponding monocarbonyl, RuTPP(CO)(n-Bu₃P). Electrochemical oxidation of RuTPP(CO)(n-Bu₃P) yielded a ir-cation radical, whereas bromine oxidation appeared to effect oxidation of the metal. === Science, Faculty of === Chemistry, Department of === Graduate