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. 2023 Apr 30;28(9):3837.
doi: 10.3390/molecules28093837.

Synthesis and Structural Characterization of p-Carboranylamidine Derivatives

Nicole Harmgarth  1 , Phil Liebing  2 , Volker Lorenz  1 , Felix Engelhardt  1 , Liane Hilfert  1 , Sabine Busse  1 , Rüdiger Goldhahn  3 , Frank T Edelmann  3
Affiliations

Synthesis and Structural Characterization of p-Carboranylamidine Derivatives

Nicole Harmgarth et al. Molecules. .

Abstract

In this contribution, the first amidinate and amidine derivatives of p-carborane are described. Double lithiation of p-carborane (1) with n-butyllithium followed by treatment with 1,3-diorganocarbodiimides, R-N=C=N-R (R = iPr, Cy (= cyclohexyl)), in DME or THF afforded the new p-carboranylamidinate salts p-C2H10B10[C(NiPr)2Li(DME)]2 (2) and p-C2H10B10[C(NCy)2Li(THF)2]2 (3). Subsequent treatment of 2 and 3 with 2 equiv. of chlorotrimethylsilane (Me3SiCl) provided the silylated neutral bis(amidine) derivatives p-C2H10B10[C{iPrN(SiMe3)}(=NiPr)]2 (4) and p-C2H10B10[C{CyN(SiMe3)}(=NCy)]2 (5). The new compounds 3 and 4 have been structurally characterized by single-crystal X-ray diffraction. The lithium carboranylamidinate 3 comprises a rare trigonal planar coordination geometry around the lithium ions.

Keywords: boron; carborane; carboranylamidinate; lithiation; p-carborane.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Three isomers of the icosahedral closo-carborane cage C2B10H12.
Scheme 1
Scheme 1
Preparation of lithium carboranylamidinates derived from o-carborane.
Scheme 2
Scheme 2
Formation of polycylic diazadiborepines from m-carborane.
Scheme 3
Scheme 3
Synthetic route to the title compounds 2 and 3.
Scheme 4
Scheme 4
Preparation of the silylated bis(amidine) derivatives 4 and 5.
Figure 2
Figure 2
Molecular structure of 3 in the crystal. Displacement ellipsoids of the heavier atoms are drawn with 50% probability; H atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg.): C(1)-C(2) 1.551(2), N(1)-C(2) 1.305(2), N(2)-C(2) 1.340(2), N(2)-Li 1.953(3), O(1)-Li 1.949(3), O(2)-Li 1.933(3), N(1)-C(2)-N(2) 136.9(1), N(1)-C(2)-C(1) 109.7(1), N(2)-C(2)-C(1) 113.4(1), C(2)-N(2)-Li 134.9(1). Symmetry code to generate equivalent atoms: ‘2–x, 1–y, 1–z.
Figure 3
Figure 3
Molecular structure of 4 in the crystal. Displacement ellipsoids of the heavier atoms with 50% probability; H atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg.): C(1)-C(2) 1.539(2), C(2)-N(1) 1.265(2), C(2)-N(2) 1.423(2), Si(1)-N(2) 1.751(1), N(1)-C(2)-N(2) 128.9(1), N(1)-C(2)-C(1) 113.8(1), N(2)-C(2)-C(1) 117.3(1), C(2)-N(2)-Si(1) 121.00(9). Symmetry code to generate equivalent atoms: ‘1–x,1–y, 1–z.
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