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Reactivity of rhodium-heteroatom bonds: from catalytic bond activation to new strategies for olefin functionalization van Rooy, Sara Emily

Abstract

Rhodium complexes bearing multidentate nitrogen donor ligands were investigated for their ability to promote alkyne and olefin functionalization reactions. This thesis work is comprised of two projects in which rhodium-heteroatom reactivity is investigated: P-H bond activation reactions and olefin functionalizations via rhodaoxetane intermediates. [Tp*Rh(PPh3)2] [Tp* = hydrotris(3,5-dimethylpyrazolyl)borate] and [Tp*Rh(cod)]2 (cod = cyclooctadiene) were evaluated for their activity in alkyne hydrophosphinylation in comparison to known catalysts for this reaction. [Tp*Rh(PPh3)2]and [Tp*Rh(cod)]2 were both shown to effect hydrophosphinylation of 1-octyne with diphenylphosphine oxide with high regioselectivity but moderate yields in comparison with Wilkinson's catalyst [C1Rh(PPh3)3]. [Tp*Rh(PPh3)2] was further shown to effect hydrophosphinylation of a range of aromatic and aliphatic alkynes with diphenylphosphine oxide, in each case exclusively providing the E-linear vinylphosphineoxide product. 1H and 31P NMR spectroscopy provided evidence that alkyne hydrophosphinylation in the presence of pyrazolylborate rhodium complexes follows an analogous mechanism to that proposed for this reaction catalyzed by [C1Rh(PPh3)3] or[C1Rh(cod)]2. The 2-rhodaoxetane [(TPA)Rhmec2_,-4u, 0-2-oxyethypr BPh4- (TPA = tris[(2-pyridal)methyl]amine) was investigated for its potential as an intermediate in proposed functionalization reactions of olefins. RTPA)Rh111(K2-C,0-2-oxyethyl)]+ BPh4- was prepared by two published methods with limited success. A third method involved the use of nitrous oxide to oxygenate [(12-ethene)(K4-TPA)Rh1]+ to RTPA)Rh1110(-2-C,0-2-oxyethyDr. Only a trace amount of [(TPA)Rhmoc2 -C,0-2-oxyethypr was observed in the 1I-1 NMR spectrum of this reaction mixture. Initial test reactions of [(TPA)Rhilioc2_C,0-2-oxyethypr combined with substrates (aniline, toluenesulfonamide, phenylboronic acid, or benzaldehyde) were inconclusive since the results were obscured by the impurity of the samples.

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