Syntheses, Structures, and Bonding Analyses of Carbene-Stabilized Stibinidenes

Reactions of two equivalents of LGa {L = HC[C(Me)NAr]₂; Ar = 2,6-iPr₂-C₆H₃} with SbX₃ (X = Cl, Br) yield double-inserted products (LGaX)₂SbX (X = Cl 1, Br 2), which were isolated at –40 °C. Warming solutions of 1 and 2 to ambient temperature results in intramolecular elimination of LGaX₂ and formation of Ga-substituted stibinidenes L(X)GaSb as reaction intermediates, which were stabilized by coordination of strong σ-donating carbenes. Four carbene-stabilized stibinidenes ^MeCAAC-SbGa(X)L {^MeCAAC = [H₂C(CMe₂)₂NAr]C, Ar = 2,6-iPr₂-C₆H₃, X = Cl 3, Br 4} and IDipp-SbGa(X)L {IDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene, X = Cl 5, Br 6} were characterized by single-crystal X-ray diffraction and the nature of the bonding in 3–6 was further investigated by quantum chemical methods. The studies reveal substantial Sb–C_carbene π-backbonding contributions in 3 and 4, whereas the IDipp-stabilized derivatives 5 and 6 exhibit Sb–C_carbene single bonds. DFT computations with and without dispersion corrections reveal that dispersion interactions mainly from the bulky aryl groups decisively contribute to the stability of 3–6.