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Issue 17, 2017
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Structure and dynamic NMR behavior of rhodium complexes supported by Lewis acidic group 13 metallatranes

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Abstract

Monovalent Rh was installed into the group 13 metallatranes, M[N(o-(NCH2P(iPr)2)C6H4)3] (where M = Al and Ga, abbreviated as ML) to generate Rh → M bonds in the parent complexes, Cl–RhAlL (1-Cl) and Cl–RhGaL (2-Cl). The electron-withdrawing nature of the group 13 metalloids was probed by cyclic voltammetry, and Rh–Ga was found to be more electron-deficient than Rh–Al (Epc = −2.07 and −1.95 V vs. Fc+/Fc for 1-Cl and 2-Cl, respectively). Both 1-Cl and 2-Cl were further functionalized through metathesis reactions using MeLi to generate 1-CH3 and 2-CH3, respectively, or using LiHBEt3 to form 1-H and 2-H, respectively. The solid-state structures of all Rh–M bimetallics feature Rh–M bond lengths that are less than the sum of the covalent radii of Rh and M (Rh–M: 2.50–2.54 Å for 1-X and 2.49–2.46 Å for 2-X, where X = Cl, CH3, and H). In the Rh–M structures, the Rh center is distorted from square pyramidal geometry due to steric interactions between X and the isopropyl substituents of L. Finally, all the Rh–M bimetallics exhibit fluxionality that involves phosphine exchange. Of note, the two phosphines cis to the X ligand become inequivalent at low temperature. The activation barrier to exchange these two phosphine donors is: 14.9, 14.2, 10.9, and 11.5 kcal mol−1 for 1-Cl, 2-Cl, 1-H, and 2-H, respectively. The activation barriers for 1-CH3 and 2-CH3 are both >15.2 kcal mol−1. At high temperature, 2-Cl was also found to exchange all three phosphine donors. Mechanisms for the different types of phosphine exchange are proposed.

Graphical abstract: Structure and dynamic NMR behavior of rhodium complexes supported by Lewis acidic group 13 metallatranes

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Publication details

The article was received on 18 Dec 2016, accepted on 14 Feb 2017 and first published on 15 Feb 2017


Article type: Paper
DOI: 10.1039/C6DT04769F
Citation: Dalton Trans., 2017,46, 5689-5701
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    Structure and dynamic NMR behavior of rhodium complexes supported by Lewis acidic group 13 metallatranes

    J. T. Moore, N. E. Smith and C. C. Lu, Dalton Trans., 2017, 46, 5689
    DOI: 10.1039/C6DT04769F

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