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Issue 13, 2014
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Novel inorganic heterocycles from dimetalated carboranylamidinates

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Mono- and dianionic carboranylamidinates are readily available in one-pot reactions directly from o-carborane (1). In situ-monolithiation of 1 followed by treatment with N,N′-diisopropylcarbodiimide, iPrN[double bond, length as m-dash]C[double bond, length as m-dash]NiPr, or N,N′-dicyclohexylcarbodiimide, CyN[double bond, length as m-dash]C[double bond, length as m-dash]NCy, provided the lithium carboranylamidinates (o-C2B10H10C(NHiPr)([double bond, length as m-dash]NiPr)-κ2C,N)Li(DME) (2a) and (o-C2B10H10C(NHiCy)([double bond, length as m-dash]NiCy)-κ2C,N)Li(THF)2 (2b). Controlled hydrolysis of 2a,b afforded the free carboranylamidines o-C2B10H11C(NHiR)([double bond, length as m-dash]NiR) (3a: R = iPr, 3b: R = Cy). The first dimetalated carboranylamidinates, o-C2B10H10C(NiPr)([double bond, length as m-dash]NiPr)Li2(DME)2 (4a) (DME = 1,2-dimethoxyethane) and o-C2B10H10C(NiPr)([double bond, length as m-dash]NiPr)Li2(THF)4 (4b), were prepared in high yield (83% yield) directly from 1 using a simple one-pot synthetic protocol. Treatment of 4b with 2 equiv. of Me3SiCl afforded the disilylated derivative o-C2B10H102C,N-[C(NiPrSiMe3)([double bond, length as m-dash]NiPr)]SiMe3 (5). Dianionic 4b also served as an excellent precursor for novel inorganic heterocycles incorporating the closo-1,2-C2B10H10 cage, including the unsymmetrical distannene [o-C2B10H10C(NiPr)([double bond, length as m-dash]NiPr)-κ2C,N]Sn[double bond, length as m-dash]Sn[(iPrN)2CnBu]2 (6) and the azaphosphole derivative [o-C2B10H10C(NiPr)([double bond, length as m-dash]NiPr)-κ2C,N]PPh (7). Surprisingly, it was found that the synthesis of new inorganic ring systems from dianionic carboranylamidinates can also be achieved by employing only 1 equiv. of n-butyllithium in the generation of the anionic carboranylamidinate intermediates. Using this straightforward one-pot synthetic protocol, the Group 14 metallacycles [o-C2B10H10C(NCy)([double bond, length as m-dash]NCy)-κ2C,N]SiR2 (R = Cl (8), Me (9), Ph (10)) and [o-C2B10H10C(NCy)([double bond, length as m-dash]NCy)-κ2C,N]GeCl2 (11) have become accessible. The same synthetic strategy could be successfully adapted to prepare the corresponding Group 4 metallocene derivatives Cp2Ti[o-C2B10H10C(NCy)([double bond, length as m-dash]NCy)-κ2C,N] (12) and Cp2Zr[o-C2B10H10C(NCy)([double bond, length as m-dash]NCy)-κ2C,N] (13). The molecular structures of 2b, 3b, 4b, 5, 6, 7, 10, 12, and 13 were confirmed by single-crystal X-ray diffraction.

Graphical abstract: Novel inorganic heterocycles from dimetalated carboranylamidinates

  • This article is part of the themed collection: Carboranes
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Publication details

The article was received on 02 Oct 2013, accepted on 29 Oct 2013 and first published on 29 Oct 2013

Article type: Paper
DOI: 10.1039/C3DT52751D
Citation: Dalton Trans., 2014,43, 5001-5013
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    Novel inorganic heterocycles from dimetalated carboranylamidinates

    N. Harmgarth, D. Gräsing, P. Dröse, C. G. Hrib, P. G. Jones, V. Lorenz, L. Hilfert, S. Busse and F. T. Edelmann, Dalton Trans., 2014, 43, 5001
    DOI: 10.1039/C3DT52751D

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