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Issue 22, 2014
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Reductive functionalization of a rhodium(III)–methyl bond by electronic modification of the supporting ligand

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Abstract

Net reductive elimination (RE) of MeX (X = halide or pseudo-halide: Cl, CF3CO2, HSO4, OH) is an important step during Pt-catalyzed hydrocarbon functionalization. Developing Rh(I/III)-based catalysts for alkane functionalization is an attractive alternative to Pt-based systems, but very few examples of RE of alkyl halides and/or pseudo-halides from RhIII complexes have been reported. Here, we compare the influence of the ligand donor strength on the thermodynamic potentials for oxidative addition and reductive functionalization using [tBu3terpy]RhCl (1) {tBu3terpy = 4,4′,4′′-tri-tert-butylpyridine} and [(NO2)3terpy]RhCl (2) {(NO2)3terpy = 4,4′,4′′-trinitroterpyridine}. Complex 1 oxidatively adds MeX {X = I, Cl, CF3CO2 (TFA)} to afford [tBu3terpy]RhMe(Cl)(X) {X = I (3), Cl (4), TFA (5)}. By having three electron-withdrawing NO2 groups, complex 2 does not react with MeCl or MeTFA, but reacts with MeI to yield [(NO2)3terpy]RhMe(Cl)(I) (6). Heating 6 expels MeCl along with a small quantity of MeI. Repeating this experiment but with excess [Bu4N]Cl exclusively yields MeCl, while adding [Bu4N]TFA yields a mixture of MeTFA and MeCl. In contrast, 3 does not reductively eliminate MeX under similar conditions. DFT calculations successfully predict the reaction outcome by complexes 1 and 2. Calorimetric measurements of [tBu3terpy]RhI (7) and [tBu3terpy]RhMe(I)2 (8) were used to corroborate computational models. Finally, the mechanism of MeCl RE from 6 was investigated via DFT calculations, which supports a nucleophilic attack by either I or Cl on the Rh–CH3 bond of a five-coordinate Rh complex.

Graphical abstract: Reductive functionalization of a rhodium(iii)–methyl bond by electronic modification of the supporting ligand

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Publication details

The article was received on 22 Jan 2014, accepted on 25 Feb 2014 and first published on 09 Apr 2014


Article type: Paper
DOI: 10.1039/C4DT00234B
Citation: Dalton Trans., 2014,43, 8273-8281
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    Reductive functionalization of a rhodium(III)–methyl bond by electronic modification of the supporting ligand

    M. E. O'Reilly, D. R. Pahls, J. R. Webb, N. C. Boaz, S. Majumdar, C. D. Hoff, J. T. Groves, T. R. Cundari and T. B. Gunnoe, Dalton Trans., 2014, 43, 8273
    DOI: 10.1039/C4DT00234B

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