Synthesis and Structural Characterization of p-Carboranylamidine Derivatives

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 = Pr-i, Cy (= cyclohexyl)), in DME or THF afforded the new p-carboranylamidinate salts p-C2H10B10[C((NPr)-Pr-i)(2)Li(DME)](2) (2) and p-C2H10B10[C(NCy)(2)Li(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{(PrN)-Pr-i(SiMe3)}(=(NPr)-Pr-i)](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.