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Issue 14, 2016
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Variable coordination modes and catalytic dehydrogenation of B-phenyl amine–boranes

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Abstract

The chemistry of N-substituted amine–boranes and their reactivity towards transition metal centres is well established but the chemistry of B-substituted amine–boranes is not. Here we present the coordination chemistry of H2PhB·NMe3 towards a range of Rh(I) fragments with different P–Rh–P ligand bite angles, {Rh(PiPr3)2}+, {Rh(PiBu3)2}+, {Rh(iPr2P(CH2)3PiPr2)}+, {Rh(Ph2P(CH2)nPPh2)}+ (n = 3, 5), as characterised by NMR spectroscopy and single-crystal X-ray diffraction. This reveals a difference in the coordination mode of the amine–borane, with large bite angle fragments favouring η2-coordination through a sigma-interaction with BH2, whereas fragments with small bite angles favour η6-coordination through the aryl group of the amine–borane. The catalytic dehydrocoupling of H2PhB·NMe2H is also explored, with the aminoborane HPhB[double bond, length as m-dash]NMe2 found to be the sole dehydrogenation product. Stoichiometric reactivity with H2PhB·NMe2H again showed small bite angle fragments to prefer η6-aryl coordination, while the larger bite angle {Rh(PiPr3)2}+ gave rapid dehydrogenation to form a mixture of the Rh(III) dihydride [Rh(PiPr3)2(H)22-H2PhB·NMe2H)][BArF4] and the low coordinate aminoboryl complex [Rh(PiPr3)2(H)(BPhNMe2)][BArF4]. These results suggest that precatalysts which η6-bind arenes strongly should be avoided for the dehydrocoupling of amine–boranes bearing aryl substituents.

Graphical abstract: Variable coordination modes and catalytic dehydrogenation of B-phenyl amine–boranes

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Publication details

The article was received on 15 Jan 2016, accepted on 23 Feb 2016 and first published on 24 Feb 2016


Article type: Paper
DOI: 10.1039/C6DT00197A
Citation: Dalton Trans., 2016,45, 6183-6195
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    Variable coordination modes and catalytic dehydrogenation of B-phenyl amine–boranes

    A. Kumar, I. K. Priest, T. N. Hooper and A. S. Weller, Dalton Trans., 2016, 45, 6183
    DOI: 10.1039/C6DT00197A

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