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Issue 40, 2011
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Probing the influence of steric bulk on anion binding by triarylboranes: comparative studies of FcB(o-Tol)2, FcB(o-Xyl)2 and FcBMes2

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Abstract

Steric crowding brought about on pyramidalization at boron has been predicted computationally to be of central importance to the strength and selectivity of anion binding by triarylboranes. The role of steric factors in systems containing a ferrocenyl reporter unit has been systematically probed in the current study by comparison of the F/CN binding properties of FcB(o-Tol)2 (1, o-Tol = C6H4Me-2), FcB(o-Xyl)2 (2, o-Xyl = C6H3Me2-2,6) and FcBMes2 (3, Mes = C6H2Me3-2,4,6)), both in solution and in the solid state. Somewhat surprisingly, the inclusion of an extra ortho-methyl aryl substituent (e.g. for 2/3vs.1) is found to have a relatively small effect on the binding affinities of these boranes (e.g. log10KCN = 5.94(0.02), 4.73(0.01), 5.56(0.02), for 1, 2 and 3 respectively). Consistent with this observation, the degree of pyramidalization at boron determined for the cyanide adducts [1·CN], [2·CN] and [3·CN] in the solid state is also found to be essentially invariant (∠Caryl–B–Caryl = 338, 337, 337°, respectively), as are the B–CN and mean B–Caryl distances. In the solid state at least, it is apparent that the adverse steric effects potentially brought about by increasing ortho substitution are mitigated by a greater degree of synchronous rotation of the aryl substituents about the B–Caryl bonds. Thus a mean inter-plane angle of 71° is observed for [1·CN] while the corresponding values for [2·CN] and [3·CN] are 78° and 79°.

Graphical abstract: Probing the influence of steric bulk on anion binding by triarylboranes: comparative studies of FcB(o-Tol)2, FcB(o-Xyl)2 and FcBMes2

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Supplementary files

Article information


Submitted
02 Feb 2011
Accepted
18 Feb 2011
First published
15 Mar 2011

Dalton Trans., 2011,40, 10345-10350
Article type
Paper

Probing the influence of steric bulk on anion binding by triarylboranes: comparative studies of FcB(o-Tol)2, FcB(o-Xyl)2 and FcBMes2

I. Siewert, P. Fitzpatrick, A. E. J. Broomsgrove, M. Kelly, D. Vidovic and S. Aldridge, Dalton Trans., 2011, 40, 10345
DOI: 10.1039/C1DT10185D

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